Author Topic: SURGE TECTONICS  (Read 24 times)

Admin

  • Administrator
  • Full Member
  • *****
  • Posts: 174
    • View Profile
SURGE TECTONICS
« on: March 22, 2017, 09:24:31 am »
Surge Tectonics
CONTENTS
Chapter 1 Why a New Hypothesis?
1.2 Former & Current Concepts of Earth Dynamics
1.2.3 Mantle Convection
1.2.4 Earth Expansion
1.2.5 Vertical Tectonics
1.2.6 Zonal Rotation
1.2.7 Continental Drift, Polar Wandering
1.2.8 Seafloor Spreading and Plate Tectonics
1.2.9 Tectonostratigraphic Terraces
1.2.10 Wedge Tectonics
1.2.11 Plate Tectonics with Fixed Continents
1.2.12 Zipper Tectonics (Spiral Tectonics)
1.2.13 Viscous Flow Model
Chapter 2 Unraveling Earth History: Tectonic Dating Sets
2.1 Data Availability
2.2 New Data Acquisition
2.2.1 Submersibles and Deep-Sea Drilling
2.2.2 Sonography
2.2.3 Accurate Bathymetry
2.2.4 Seismotomography
2.2.5 Space Geology
2.2.6 Satellite Photography
2.2.7 Satellite Radar Altimetry
2.2.8 Radar Mapping of Venus
2.2.9 Other Techniques
2.3 Data Sets Unexplained in Current Tectonic Models: Foundation for a New Hypothesis
Chapter 3 Surge Tectonics
=3.2 Velocity Structure of the Earth's Outer Shells
3.2.1 Basic Framework
3.2.2 Continents Have Deep Roots
3.3 Contraction
3.3.2 Contraction Skepticism
3.3.3 Evidence For a Differentiated, Cooled Earth
3.4 Contraction as an Explanation of Earth Dynamics
3.5 Review of Surge and Related Concepts in Earth-Dynamics Theory
3.6 Geotectonic Cycle of Surge Tectonics
3.7 Pascal's Law---the Core of Tectogenesis
3.8 Evidence for the Existence of Surge Channels
3.8.1 Seismic-Reflection Data
3.8.3 Seismotomographic Data
3.8.4 Surface-Geological Data
3.8.5 Other Data
3.9 Geometry of Surge Channels
3.9.1 Surge-Channel Cross Section
3.9.2 Surge-Channel Surface Expression
3.9.3 Role of the Moho
3.9.4 Formation of Multitiered Surge Channels
3.10 Demonstration of Tangential Flow in Surge Channels
3.11 Mechanism for Eastward Surge
3.12 Classification of Surge Channels
3.12.2 Ocean-Basin Surge Channels
3.12.3 Continental-Margin Surge Channels
3.12.4 Continental Surge Channels
3.13 K Structures
3.14 Criteria for the Identification of Surge Channels
Chapter 4 Examples of Surge Channels
=4.1 Ocean-Basin Surge Channels
=4.2 Surge Channels of Continental Margins
4.3 Continental Surge Channels
4.4 Surge Channels in Zones of Transtension-Transpression
Chapter 5 The Tectonic Evolution of Southeast Asia - A Regional Application of the Surge-Tectonics Hypothesis
5.1 Surge Tectonic Framework
5.2 Surge-Tectonic History
Chapter 6 Magma Floods, Flood Basalts, and Surge Tectonics
6.2 Descriptions of Selected Continental Flood Basalt Provinces
6.3 The Use of Geochemistry in Identifying Flood Basalts
6.4 Geochemical Comparisons among Basalts Erupted in Different Tectonic Settings
6.5 Duration of Individual Basalt Floods
6.6 Flood-Basalt Provinces and Frequency in Geologic Time
6.7 Non-Basalt Flood Volcanism in Flood-Basalt Provinces
6.8 Flood Basalts or Magma Floods?
6.9 Surge-Tectonics Origin of Magma Floods
Chapter 7 Conclusions
APPENDIX

Chapter 3
SURGE TECTONICS
3.1 Introduction
Surge tectonics is a new hypothesis quite unlike previously proposed hypotheses, although many of its component parts are based on ideas long known. We believe the hypothesis provides a comprehensive and internally consistent explanation of all tectonic phenomena without the necessity of making unsupported assumptions or ad hoc explanations. We have found nothing that surge tectonics cannot explain in a simpler way than other tectonic hypotheses. Surge tectonics draws on well-known physical laws, especially those related to Newton's laws of motion and gravity. Fluid dynamics plays an important role in surge tectonics. (For more information on the laws we utilize, those mentioned in the text are defined in the Appendix; those withing more detail are referred to two standard physics textbooks by Sears et al. [1974] and Blatt [1983]. An excellent state-of-the-art fluid-dynamics text is that by Tritton [1998]).
 Surge tectonics is based on the concept that the lithosphere contains a worldwide network of deformable magma chambers (surge channels) in which partial magma melt is in motion (active surge channels) or was in motion at some time in the past (inactive surge channels). These surge channels play the role of the holes in the "hole-in-the-plate" problem ("elliptical hole problem") of civil and construction engineering, industrial engineering, and rock mechanics (..., 1913-1991). The presence of surge channels means that all of the compressive stress in the lithosphere is oriented at right angles to their walls. As this compressive stress increases during a given geotectonic cycle, it eventually ruptures the channels that are deformed bilaterally into kobergens (Fig. 2.15). Kobergens were named by Meyerhoff et al. (1992b) in honor of Austrian geologist, Leopold Kober (1921-1928). Kober observed that Alpide foldbelts have been bilaterally deformed with the northern ranges vergent toward Europe and the southern toward Africa (see Fig. 12 in M-b, 1992b). Thus, bilaterally deformed foldbelts in surge-tectonics terminology are called kobergens.
 Surge tectonics involves three separate but interdependent and interacting processes. The first process is the contraction or cooling of the Earth. The second is the lateral flow of fluid, or semifluid, magma through a network of interconnected magma channels in the lithosphere. We call these surge channels for reasons that will become apparent. The third process is the Earth's rotation. This process involves differential lag between the lithosphere and the strictosphere (the hard mantle beneath the asthenosphere and lower crust), and its effects--- eastward shifts---already discussed (Table 2.3). Because lithosphere compression caused by cooling is the mechanism that propels the lateral flow of fluid, or semifluid, magma through surge channels, we discuss first the velocity structure of the Earth's lithosphere and underlying layers, then the contraction hypothesis (Earth cooling), and then the effects of contraction on the Earth's outer shells.

3.2 Velocity Structure of the Earth's Outer Shells
3.2.1 BASIC FRAMEWORK
The Earth's outer shells (Fig. 3.1) consist of a "hard" lithosphere above a "soft" asthenosphere (..., 1896-1940). The interpreted seismic structure of these two shells is given in Table 3.1, which is based on Press (1966) and Iyer and Hitchcock (1989). The asthenosphere overlies another hard shell that Bucher (1956, ...) named the strictosphere. Its seismic characteristics (at least near the upper surface of the strictosphere) also are given on Table 3.1. Of these shells, the lithosphere is especially important because visible tectonic effects provide the principal clues to the origin of tectogenesis. It has not been too long, since the seismic structure of the crust and upper mantle became sufficiently well imaged to permit more than just educated guesses about it.
 Before 1958, when Revelle (1958) discovered a layer of material with a velocity of 7.3 km/s on the southern part of the East Pacific Rise, the lithosphere was perceived as consisting of 6.6-km/s crust overlying directly the 8.1-km/s mantle. What Revelle (1958) discovered was a lens or high-velocity crust, or low-velocity mantle, with a P-wave velocity of 7.0-7.8 km/s separating the "normal" crust above from the "normal" crust below. Similar lenses were found almost everywhere beneath the midocean ridge system (..., 1959-1965). By 1982, a similar lens of 7.0-7.8-km/s material was found beneath most of the Earth's rifts (Figs. 2.9, 3.2-3.8). Mooney et al. (1983) suggested that such lenses are a characteristic of extensional tectonic belts.
 During the 1970s, refraction shooting in the northern Appalachians discovered a similar 7.0-km/s lens under the Acadian (Devonian) foldbelt (..., 1980-1989; and Fig. 3.13). It was not long before identical lenses beneath foldbelts were identified in many parts of the world (Figs. 2.13, 2.18, 2.21, 3.9-3.14). Good images of these lenses were recorded on reflection -seismic lines used for deep continental and oceanic tectonic studies (Figs. 2.10, 2.11, 2.14, 3.15; ..., 1988). Figures 2.10 and 2.11, from the English Channel and southwestern Queensland respectively, are particularly good images of two of these lenses near the base of the continental crust.
 Mooney and Braile (1989), summarizing the present state of knowledge of the structure of the Earth's crust, inserted a 7.0-7.9-km/s lower crustal layer between the 6.6-km/s sialic crust above, and the 8.1-km/s mantle below. They showed the layer to be absent in places. In general, it is present beneath cratons, platforms, foldbelts, rift systems, and wrench-fault zones. Under cratonic areas the layer is 7-15 km thick; under tectonic belts it is thicker, ranging from 10-25 km. In many places the 7.0-7.9-km/s velocity is gradational with mantle velocities (>7.9 km/s). In these places, the Moho- is not a true discontinuity but a transition zone several kilometers thick (..., 1989). Areas were found also beneath ancient platforms and shields where the 7.0-7.8-km/s layer is up to 30 km thick. Examples include the Baltic Shield (3.5; ..., 1989) and parts of the Canadian Shield (..., 1989).
 The preceding suggests that the 7.0-7.8-km/s layer is distributed rather randomly, and that its thickness in a given area is a result of random processes. These conclusions are almost unavoidable if one tries to explain the distribution and thickness with any of the Earth-dynamics hypotheses published during the last century. In surge tectonics this apparent randomness of distribution and thickness is in part predictable.
 The origin of the 7.0-7.8-km/s layer almost certainly is closely related to the high reflectivities of the lower crust as described and illustrated by Klemperer et al. (1986), Klemperer (1987), Goodwin and Thompson (1988), Thompson and McCarthy (1990), and others (see Figs. 2.10, 2.11, 2.14, 3.15). We emphasize the fact that a lens (or lenses) or 7.0-7.8-km/s material underlies all of the microearthquake bands that we studied, and therefore, all of the high heat-flow bands shown on Figure 2.26.

3.2.2 CONTINENTS HAVE DEEP ROOTS   
An important aspect of upper mantle and crustal structure is that continental cratons have deep crustal roots (..., 1963-1996). Contrary to general belief (..., 1987a), continental roots are fixed to the strictosphere (..., 1985-1986). This conclusion is supported by large and increasing volumes of data, including neodymium and strontium studies of crustal rocks (..., 1979). The absence, or near-absence, of a low-velocity asthenosphere beneath ancient cratons led Lowman (1985, 1986) to propose an Earth-dynamics hypothesis of sea-floor spreading between fixed continents. In this hypothesis, if sea-floor spreading takes place, it is restricted to suboceanic regions. Thus, the deep roots of continents are a major obstacle to any hypothesis requiring continental movements (..., 1985-1990).
 An example of deep continental roots is presented in Figure 1.1, a seismotomographic cross section of North America. The dark shading beneath the Canadian Shield shows a root extending to 400-450 km (..., 1987). Similar deep roots are seen beneath part of all of the Earth's ancient cratons. In places, however, lenses of 7.0-7.8-km/s material containing low-velocity zones (Fig. 3.5) are present (..., 1989). Such lenses containing low-velocity layers postdate the establishment of the deep cratonic roots, as we show in subsequent sections.

3.3 Contraction
3.3.1 GENERAL
A discussion of the history and concept of contraction have been presented in Chapter 1 of this book. It will not be repeated here, but the interested reader is encouraged to review that discussion.

3.3.2 Contraction Skepticism
Many workers today either doubt that contraction is taking place or fail to see why the possibility should even be considered. Bott (1971, p. 270), expressing a common opinion, wrote that because of the success of plate tectonics in producing foldbelts, contraction now "...is irrelevant to tectonic problems." Two reviewers of the paper by Meyerhoff et al. (1992b) also expressed doubts that contraction can be taking place. However, one of them, K.B. Krauskopf (pers. comm., 1990), conceded that "...too little is known about what goes on in the [Earth's] interior for any definite statement to be made." He noted that MacDonald's (1959-1965a) models could easily be as sound today as they were in 1965 because "...not much more is known today..." about the concentration of radioactive elements in the Earth's interior.

3.3.3 Evidence For a Differentiated, Cooled Earth
The evidence is straightforward. The most salient facts follow.
 1. The Earth includes several concentric shells, which are explicable only if the Earth differentiated efficiently and at a much higher temperature than today.
 2. The outermost of these shells may be the oceanic crust whose thickness ranges from about 4-7 km. This crust is characterized by relatively constant thickness and fairly uniform seismic properties. Both Worzel (1965) and Vogt et al. (1969) observed that if the plate-tectonic explanation of ocean-crust generation is correct, it is a truly remarkable process that produces such a uniform layer in all ocean basins regardless of the spreading rate---1.2 dm/yr or 60 cm/yr. This uniformity is explained, however, if the oceanic crust is the outermost of the Earth's concentric shells. There are other explanations, one of which is discussed later.
 3. Mehnert (1969), among several, noted that the further back one looks into the geological record, the greater is the abundance of mafic rocks. This is explained if the lithosphere has been thickening through time by cooling, as Mehnert (1969) suggested.
 4. Miyashiro et al. (1982), reporting on studies of the Earth's metamorphic rocks, noted that Precambrian rocks show the highest geothermal gradients and that geothermal gradients of younger rocks generally decrease to the present time.
 5. A convincing evidence that huge segments of the lithosphere have been and are being engulfed by tangential compression is the existence of the previously discussed Verschluckungszonen (swallowing or engulfment zones) of Ampferer (1906) and Ampferer and Hammer (1911). In places along such zones, whole metamorphic and igneous belts that are characteristic of parts of a given foldbelt simply disappear for hundreds of kilometers along strike (e.g., Alps: ..., 1983; K...-S... foldbelt ..., 1973; New Zealand Alps ..., 1974: ...; southern California Transverse Ranges: ..., 1984). Figures 2.23-2.24 and 3.16-3.17 illustrate the characteristics of typical Verschluckungszonen. Although Mueller (1983), Humphreys et al. (1984), and other workers considered these features to be former subduction zones, this interpretation is difficult to defend because all of these zones, regardless of age, are near-vertical bodies (1) reach only the top or middle of the asthenosphere (150 to 250 km deep) and (2) do not deviate more than 10 to 25 from the vertical (..., 1983-1984).
 6. The antipodal positions of the continents and ocean basins mean that Earth passed through a molten or near-molten phase (..., 1907-1968). Such antipodal relations are unlikely to be a matter of chance or coincidence (..., 1968).
 7. Theory (..., 1970) and laboratory experiment (..., 1956) showed that heated spheres cool by rupture along great circles. Remnants of two such great circles (as defined by hypocenters at the base of the asthenosphere) are active today: the Circum-Pacific and Tethys-Mediterranean fold systems. The importance of Bucher's (1956) experiment to contraction theory, in which he reproduced the great circles, is little appreciated.
 8. As Earth cooled, it solidified from the surface downward. Because stress states in cooled and uncooled parts are necessarily opposite one another, compression above and tension below, the two parts must be separated by a surface or zone that Davison (1887) called the level of no strain (Fig. 3.2). We, as did Wilson (1954), equate the cooled layer with the lithosphere (Fig. 3.1). The uncooled part below is what Bucher (1956) called the strictosphere. Thus, as originally proposed by Scheidegger and Wilson (1950), Davison's (1887) level of no strain must be the asthenosphere, or a zone of no strain across which the change in stress states is gradual (Fig. 3.1). Only in a cooling Earth, which approximates a closed thermal system, can an asthenosphere form.
 9. Continued cooling deepens the asthenosphere and the upper surface of the strictosphere. The stresses accumulated through cooling are relieved episodically by rupture along the great-circle fractures that are the Earth's cooling cracks or the Benioff zones of current literature. Because the lithosphere is being compressed and the strictosphere subjected to tension, the mechanics of rupture should follow the Navier-Coulomb maxiumum shear-stress theory (..., 1962). Accordingly, the lithosphere Benioff zone must dip less than 45 to a tangent to the Earth's surface (in actual fact, it dips 22 to 44, Figs. 2.36, 3.1). In contrast, the strictosphere Benioff zone must dip more than 45 to a tangent to the Earth's surface (50 to 75, Figs. 2.36, 3.1). Benioff (1949, 1954) discovered the change in Benioff-zone dip from lithosphere to strictosphere, but Scheidegger and Wilson (1950) recognized these dips as an expression of the Navier-Coulomb maximum shear-stress theory (Figs. 2.36, 3.1). The dip values of the lithosphere and strictosphere Benioff zones confirm that the Earth is a cooling body. (Ritsema [1957, 1960], working independently, also discovered the abrupt dip changes in the dip of the Benioff zone with increasing depth.)
 An important fact concerning the Benioff zone is that the two segments, one in the lithosphere and the other in the strictosphere, do not necessarily form a single, continuous zone as depicted in diagrams and cross sections (e.g., Figs. 2.36, 3.1). Benioff (1949, 1954) found that the two segments of the Benioff zone, instead of joining near the base of the asthenosphere, may be offset for distances of 100 to 200 km (Fig. 3.18). In some places such as the Lesser Antilles arc, a strictosphere Benioff zone may not even be present below the lithosphere Benioff zone (e.g., Lesser Antilles and Scotia volcanic arcs). These facts are explained in our surge- tectonics hypothesis but not by other hypotheses. In fact, all detailed modern studies of hypocenter distribution in Benioff zones show the same clear division into a shallow, gently dipping lithosphere benioff zone and a deeper, steeply dipping strictosphere Benioff zone (Fig. 2.36; ..., 1973; ..., 1977).
 Ritsema's (1957, 1960) focal-mechanism studies of shallow, intermediate, and deep earthquakes showed that the Benioff-zone dip in the lithosphere is only half of its dip in the strictosphere. An even more significant discovery made by Ritsema (1957, 1960), although he attached little importance to it, was the revelation that earthquake foci above 0.03R (approximately 180 km depth) show mainly compression, whereas those below 0.03R show mainly tension. Most earthquakes above and below 0.03R, as Scheidegger (1963) also noted, have a strike-slip component. Thus Ritsema's findings lend support to Scheidegger and Wilson's (1950) interpretation of the Benioff zone as a manifestation of the Navier-Coulomb maximum shear-stress theory.
 10. Computer simulations of possible Earth thermal histories (...,1959, 1963; ..., 1961; Reynolds et al., 1966), using a broad spectrum of assumed initial temperatures and chemical compositions, show that the Earth is cooling (..., 1959-1966). The fact that Earth's Benioff zones still are active earthquake-generating zones provides strong support for this conclusion. Perhaps the strongest support comes from the Basalt Volcanism Study Project (1981) report by 101 petrologists, mineralogists, and petrographers, who wrote that the repeated extrusion of basalt to the Earth's surface through its history is proof of the Earth's long history of cooling.
 11. Finally, the existence of Verschluckungszonen in the lithosphere and upper mantle also constitutes evidence that the Earth is actively cooling. Verschluckungszonen are interpreted by us to be large masses of lithosphere and upper mantle that were downbuckled into the upper mantle during tectogenesis as the lithosphere readjusted its shape to fit the underlying, cooling strictosphere (Figs. 2.24, 3.16-3.17). If this interpretation is correct, the existence of Verschluckungszonen may constitute proof that the Earth has been cooling to the present day. We discuss Verschluckungszonen in a subsequent section.

3.4 Contraction as an Explanation of Earth Dynamics
3.4.1 CONTRACTION ACTING ALONE
Despite the attraction of a cooling Earth, both Scheidegger (1963) and Bott (1971) concluded that contraction acting alone is inadequate to produce the crustal shortening measured in Earth's many tectonic belts. For both geological and seismological reasons, this conclusion appears to be well-founded. They gave several reasons; three of which and one of our own are crucial.
 1. The total amount of shortening measured across the Earth's foldbelts far exceeds what can be inferred on theoretical grounds, whether one uses the contraction model of MacDonald (1963) or of Jeffreys (1970). Even if one accepts Bucher's (1955...; 1956...) outstanding demonstration that apparent (measured) shortening can be and generally is four to five times true shortening, the contraction hypothesis cannot explain all true shortening in foldbelts. (Lyttelton's [1982] theoretical estimate of 2,000 km of shortening adequately explained the measured shortening, but his hypothesis requires cataclysmic geological events that need to be sought in the field.)
 2. Contraction alone is unable to explain the origins of all types of tectonic belts---compressional foldbelts, tensional rift zones (including midocean ridges), and strike-slip zones.
 3. Ritsema (1957, 1960) and Scheidegger (1963) observed that earthquake first- motion studies show that strike-slip motions are most common in Benioff zones, not just in strike-slip and rift zones. Contraction alone cannot explain the ubiquitous strike-slip component.
 4. Contraction theory requires that foldbelts are concentrated in and adjacent to oceanic trenches. This is not observed. More than 50% of the Earth's foldbelts lie at great distances from the surface trace of a Benioff zone, and all Jurassic- Cenozoic foldbelts lie within the high heat-flow bands illustrated on Figure 2.26. This cannot be explained by any Earth-dynamics hypothesis yet proposed. However, if contraction could lead to tectogenesis of large parts of the lithosphere far removed from Benioff zones, the preceding objections to the contraction hypothesis would be irrelevant.

3.4.2 CONTRACTION ACTING AS THE TRIGGER FOR TECTOGENESIS
Figure 2.26, as we have discussed, portrays the bands of high heat flow that crisscross the Earth's surface. We believe that this reticulate network of high heat-flow bands is underlain by a network of interconnected magma chambers. In our surge-tectonics hypothesis, these magma chambers are the mantle diapirs discussed in preceding sections and summarized in part in Table 2.1. Figure 2.26 indicates that these mantle diapirs, or magma chambers, are interconnected. The interconnected channels comprise the surge channels of surge tectonics. If the hot material in these channels is sufficiently mobile, lateral flow through them should be possible provided a pressure gradient is present. The compression already present in the lithosphere would provide the force needed to initiate and maintain flow. We emphasize that such flow would be temporally discontinuous (.i.e., episodic) and, when it did occur, would be extremely slow. Flow velocities are discussed later.
 We have pointed out that in a cooling Earth, the lithosphere by definition is everywhere and at all times in a state of compression (Fig. 3.1; ..., 1887-1982). The compression is concentrated in planes tangent to the Earth's surface, and is equal in all directions. James C. Meyerhoff (pers. comm., 1988) called this equiplanar tangential compression, and this compression in the lithosphere is what Bucher (1956) referred to (incorrectly) as all-sided compression.
 The only elements in the lithosphere that disturb this approximately equiplanar tangential stress state are the surge channels. Flow can take place in these channels wherever a pressure gradient develops. For example, the escape of lava from a channel lowers the pressure at that point, and equiplanar compression, acting at right angles to the surge-channel walls, mobilizes the fluid elements inside the channel until pressure equilibrium is restored. The presence above active channels of channel-parallel fault, fracture, and fissure systems indicates that (1) flow takes place along the full length of each tectonic belt and (2) the channels are in communication with the Earth's surface through the fault-fracture- fissure system.
 Surge channels and their fault-fracture-fissure systems constitute zones of weakness in the lithosphere. Because (1) the channels are the only bodies in the lithosphere that, owing to their potential to contain mobile fluids, they have the capacity to upset the state of equiplanar tangential compression, and because (2) they are constantly losing their contents to the surface lithosphere compression ultimately destroys them. Their deformation and ultimate destruction are the essence of tectogenesis. Thus the cooling process in the Earth's strictosphere effectively guarantees the presence within the lithosphere of a powerful mechanism for tectogenesis.

3.5 Review of Surge and Related Concepts in Earth-Dynamics Theory
Several workers proposed, on both theoretical and geological-geophysical grounds, the presence of bodies similar to surge channels in the lithosphere. Others developed concepts much like those that are the basis for surge tectonics.

3.5.1 SURGE CHANNELS
Our study of this topic was by no means exhaustive, we may have missed important references that deal with the concept of surge-channel-like edifices in the lithosphere and uppermost mantle. A particularly good example of a surge-channel- like feature was proposed by Vogt (1974) for the Iceland region, including the Kolbeindey, Reykjanes, and Faeroe-Greenland ridges. He wrote (...), "In the model I assume there is a pipe-like region below the spreading axis, extending subhorizontally away from a plume such as Iceland.... This mid-oceanic pipe extends from the base of the axial lithosphere, about 5 or 10 km deep, down to maximum depths (30 to 50 km?) from which basalt melts segregate and rise. Tholeiitic fluids would be released from the entire pipe; origin depths of 23 km for the Mid-Atlantic Ridge and 16 km for the East Pacific Rise ... Would approximate depth to the center ot the pipe. The ultrabasic mush in this pipe is assumed to be flowing away from the hot spot at a rate determined by pipe diameter, viscosity, and horizontal pressure gradient...." Vogt (1974) estimated that flow ranged laterally outward from Iceland from 500 to 600 km. A similar study by Gorshkov and Lukashevich (1989) suggested that channels are present beneath the full length of the midocean ridge system. According to them, flow beneath the Mid-Atlantic Ridge would be from hot spots located beneath Antarctica in the south and Iceland in the north, with the two flows converging near the equator.
 Other midocean ridges where some type of axis-parallel flow and/or rift propagation have been postulated include the Juan de Fuca Ridge (..., 1975) and the Galapagos Rift (..., 1977). After the discovery of systematic segmentation along the midocean ridges beginning with the East Pacific Rise (..., 1982), Lonsdale, MacDonald, Fos, and others commenced a series of investigations that led to a general postulate of ridge-parallel flow in the midocean ridges (..., 1988-1989). Macdonald et al. (1988) proposed that mantle diapirs rise beneath the centers of each ridge segment, thereby accounting for the greater elevations of the central parts of such segments. From the crest, ridge-parallel lateral flow commences. Such flow halts in the depressed areas between adjacent segments because of mutual impingement.
 Sonographs of the midocean ridges show that the Macdonald et al. (1988) hypothesis is not tenable. Where the diapirs rise in the centers of the ridge segments, radial and/or annular structures should be present. Where the flows from adjacent segments impinge, compressional structures should be present. Neither structural form is observed. Instead, linear fractures and faults extend for hundreds of kilometers along strike, with interruptions only at transform faults, we traced individual fault traces through the fault zone from one ridge segment to the next, which negates the Macdonald et al. (1988) hypothesis.
 Surge-channel, or interconnected mantle-diapir systems have been reported from small oceanic basins and continental areas. A well-known example of the former is the Tyrrhenian Sea west of Italy, where geophysical techniques and very high heat flow show the presence of a very large diapir-like body at shallow depths (..., 1988).
 Among continental examples, the Fergana Valley in Soviet Central Asia is the best documented Kuchay and Yeryemin (1990) discovered a very large pipelike body, or channel, below this large east-west-striking late Cenozoic structural depression nestled among the western ranges of the Tian Shan. In their summary (p. 45), Kuchay and Yeryemin concluded: "Interpretation and interpolation of geophysical data from the [Fergana Valley] lead to the conclusion that the base of the 'granitic' layer undergoes partial melting, as a consequence of which there forms a layer of lowered viscosity that has been identified seismically as a zone of reduced velocity above the Conrad discontinuity. It is possible to consider this zone as a 'granitic' asthenochannel, a subhorizontal layer that has a high strain rate and in which relative lateral displacement takes place between the contents of the asthenochannel and the surrounding rock layers. The absence of a gravity anomaly, which is an indication of variations in thickness and other properties within the zone of reduced velocity, suggests that the 'granitic' layer and the 'granitic' asthenochannel have the same density."

3.5.2 USE OF THE SURGE CONCEPT IN TECTONICS
We have found three parallel and presumably independent derivations of the surge- tectonics concept. The most recent of these originated with Hollister and Crawford (1986) who used "tectonic surge" to describe rapid vertical uplift in the structural core of a bilaterally deformed foldbelt (i.e., in the center of what we call a kobergen). Hollister and Crawford (1986, ...) opined that "Weakening of the crust [by] anatexis and accompanying development of melt-lubricated shear zones..." is essential to rapid vertical uplift. Paterson et al. (1989, ...) referred to this type of tectonics as surge tectonics. Tobisch and Paterson (1990) used this term in two or three areas of southeastern Australia. Their usage is close to our own.
 The third and, as far as we can determine, oldest use of the term in tectonics in recent literature was by Meyerhoff and Meyerhoff (1977). They proposed that asthenosphere surges (1) from beneath the Asian continent, (2) between North and South America, and (3) between South America and Antarctica produced the eastward- facing island arcs in the three regions. The idea was used subsequently to explain the complexities of Caribbean tectonics (..., 1990). Morris et al. (1990) used the term surge tectonics (coined by Bruce D. Martin). The paper was written during 1987-1988 and was submitted to and accepted by the Geological Society of America in 1988. Regardless, the Paterson et al. (1989) use of the term in print precedes by five months that by Meyerhoff et al. (1989). The term surge tectgonics is used in this book in the same sense that it was employed by Taner and Meyerhoff (1990).

3.6 Geotectonic Cycle of Surge Tectonics
The asthenosphere alternately expands (during times of tectonic quiescence) and contracts (during tectogenesis). Thus, when the asthenosphere is expanding, the surge channels above it, which are supplied from the asthenosphere, also are expanding; and when tectogenesis takes place, the magma in the surge channels is expelled. Tectogenesis is triggered by collapse of the lithosphere into the asthenosphere along the 30 -dipping lithosphere Benioff zones. The following is Meyerhoff et al.'s (1992b) interpretation of the approximate sequence of events during a geotectonic cycle (Fig. 3.19).
 1. The strictosphere is always contracting, presumably at a steady rate, because the Earth is cooling.
 2. The overlying lithosphere, because it is already cool, does not contract, but adjusts its basal circumference to the upper surface of the shrinking strictosphere by (1) large-scale thrusting along the lightosphere Benioff zones, and (2) normal- type faulting along the strictosphere Benioff zones. These two types of deformation, one compressive and the other tensile, are complementary and together constitute an example of the Navier-Coulomb maximum shear stress theory (..., 1962 -1979).
 3. The large-scale thrusting of the lithosphere is not a continuous process, but occurs only when the lithosphere's underlying dynamic support fails. That support is provided mainly by the softer asthenosphere and frictional resistance along the Benioff fractures. When the weight of the lithosphere overcomes the combined resistance offered by the asthenosphere and Benioff-zone friction, lithosphere collapse ensues. Because this process cannot be perfectly cyclic, it must be episodic; hence tectogenesis is episodic.
 4. During the anorogenic intervals between lithosphere collapses, the asthenosphere volume increases slowly as the strictosphere radius decreases (Fig. 3.19). The increase in asthenosphere volume is accompanied by decompression in the asthenosphere.
 5. Decompression is accompanied by rising temperature, increased magma generation, and lowered viscosity in the asthenosphere, which gradually weakens during the time intervals between collapses.
 6. Flow in the asthenosphere is predominantly eastward as a consequence of the Earth's rotation (Newton's Third Law of Motion; ..., 1977). Magma flow in the surge channels above the asthenosphere also tends to be eastward, although local barriers may divert flow in other directions for short distances. Coriolis force also must exert an important influence on asthenosphere and surge-channel flow, which by its nature is Poiseuille flow. Therefore, the flow at the channel walls is laminar and is accompanied by viscous, or backward drag. The viscous drag produces the swaths of faults, fractures, and fissures (streamlines) that are visible at the surface above all active tectonic belts. These bands or swaths are examples of Stoke's Law (one expression of Newton's Second Law of Motion).
 7. During lithosphere collapse into the asthenosphere, the continentward (hanging wall) sides of the lithosphere Benioff zones override (obduct) the ocean floor (..., 1906-1911). The entire lithosphere buckles, fractures, and founders. Enormous compressive stresses are created in the lithosphere.
 8. Both the lithosphere and the strictosphere fracture along great circles at the depth of the strictosphere's upper surface, as predicted by theory (..., 1959-1976) and demonstrated in the laboratory (..., 1956). Only two partial great circle fracture zones survive on the Earth today. These include the fairly extensive, highly active Circum-Pacific great circle and the almost defunct Tethys- Mediterranean great circle.
 9. When the lithosphere collapses into the asthenosphere, the asthenosphere- derived magma in the surge channels begins to surge intensely. Wherever the volume of the magma in the channels exceeds their volumetric capacity, and then compression in the lithosphere exceeds the strength of the lithosphere that directly overlies the surge channels, the surge-channel roofs rupture along the cracks that comprise the fault-fracture-fissure system generated in the channel by Poiseuille flow before the rupture. Rupture is bivergent, whether it forms continental rifts, foldbelts, strike-slip zones, or midocean rifts. The foldbelts develop into kobergens, some of them alpinotype and some them germanotype. The tectonic style of a tectonic belt depends mainly on the thickness and strength of the lithosphere overlying it (Fig. 3.19).
 10. Tectogenesis generally affects an entire tectonic belt and, in fact, may be worldwide; the worldwide early to late Eocene tectogenesis is an example (M-b, 1992b) This indicates that the lithosphere collapse that generates tectogenesis transmits stresses everywhere in a give belt at the same time. Thus Pascal's Law is at the core of tectogenesis. Sudden rupture and deformation of surge channels may therefore be likened to what happens when someone stamps a foot on a full tube of toothpaste. The speed or rapidity of tectogenesis, then, is related to the number of fractures participating in the event, as well as to the thickness of lithosphere involved, the size of the surge channel or surge-channel system, the volume and types of magma involved, and related factors.
 11. Once tectogenesis is completed, another geotectonic cycle or subcycle sets in, commonly within the same tectogenic belt.

3.7 Pascal's Law---the Core of Tectogenesis
Pascal's Law (or theorem) states that pressure applied to a confined liquid at any point is transmitted undiminished through the fluid in all directions and acts upon every part of the confining vessel at right angles to its interior surfaces and equally upon equal areas. This law applies in part to all fluids, but wholly to Newtonian fluids; it is the principle behind every hydraulic machine, notably the hydraulic press. A most important condition of Pascal's Law is that the pressure (force per unit area) acts equally upon equal areas. This condition lies at the very core of tectogenesis.

The Earth, according to our surge-tectonics hypothesis, is a very large hydraulic press. Such a press consists of three essential parts: a closed vessel, the liquid in the vessel, and a ram or piston. The collapse of the lithosphere into the asthenosphere is the activating ram or piston of tectogenesis. The asthenosphere and its overlying lithospheric surge channels---which are everywhere connected with the asthenosphere by vertical conduits---are the vessels that enclose the fluid. The fluid is magma generated in the asthenosphere. The magma fills the lithosphere channels. When the piston (lithosphere collapse) suddenly compresses the channels and the underlying asthenosphere, the pressure is transmitted rapidly and essentially simultaneously through the worldwide interconnected surge-channel network; the surge channels burst and the tectogenesis is in full swing. The compression everywhere of the asthenosphere compensates for the fact that the basaltic magma of the surge channels is non-Newtonian.

A possible objection to this simple picture of tectogenesis is that the sudden application of pressure against the surge channels would consolidate the magma in the channels, and thereby prevent the bursting of the channel roof. This would be true if the channels had no communication with the surface at the onset of tectogenesis, but this is not the case. As Meyerhoff et al. (1992b) noted, the channels are connected to the surface by swaths of belt-parallel faults, fractures, and fissures.

A second possible ofjection is that the magma in surge channels is non-Newtonian; i.e., it is too viscous to transmit the added stress to all of the interconnected parts of the surge-channel system. This objection would be valid for a tectonic model in which the added stress is applied only at a single point in the system. In a contracting Earth, however, compression in the lithosphere is omnipresent. Hence, the added stress is applied everywhere along the interconnected lithosphere channels so that the viscosity argument is invalid; the added stress is being applied at an infinite number of points in the system. As shown in Figure 3.19, the thickness of the lithosphere overlying each channel is extremely important, because the thickness determines the resulting tectonic style of the channel during tectogenesis---rift valley, germanotype foldbelt, alpinotype foldbelt, midocean rift, and so forth.

Although Pascal's Law applies to all tectonic settings, it is especially important in midocean ridge systems. The law states that pressure applied to a confined liquid acts equally on equal areas of the walls of the confining vessel. The surge channels beneath midocean ridges can be thousands of kilometers wide. Hence, they are much larger than their continental-margin and continental counterparts. Morevoer, the lithosphere above midocean ridges is only 10 to 15 km thick, less than half of the thickness found in a continent-margin/continental setting. This means that the total force acting on the walls of a midocean-ridge surge channel is vastly greater than in any other setting. Thus, during tectogenesis, midocean ridges presumably rupture throughout their lengths and across widths far greater than those of continental surge channels, thereby producing veritable magma floods on the ocean floors. If one keeps in mind the fact that the most massive Phanerozoic continental flood volcanism took place from Late Permian through Middle Jurassic time (...), such magma flooding in the oceans during the same time interval would account for the fact that the oldest basalts thus far penetrated by deep sea dirlling beneath the abyssal plains are Middle Jurassic. On the midocean ridges themselves, however, basalts older than Middle Jurassic are common (Meyerhoff et al., 1992a).

3.8 Evidence for the Existence of Surge Channels
3.8.1 SEISMIC-REFLECTION DATA   
As noted above, reflection-seismic techniques (...) have shown that the continental crust of the upper lithosphere is divisible in a very general way into an upper moderately reflective zone and a lower highly reflective zone (...). Closer scrutiny of the newly-acquired data soon revealed the presence in the lower crust of numerous cross-cutting and dipping events. When many of these cross-cutting events were preceived to be parts of lens-like bodies, various names sprang up: .... Strictly nongenetic names include lenses, lenticles, lozenges, and pods (...). Finlayson et al. (1989) found that the lenses have P-wave velocities of 7.0-7.8 km/s, commonly with a low-velocity zone in their middle. Thus we equate the lenses with the pods of "anomalous lower crust" and "anomalous upper mantle" that we discussed in a preceding section. Klemperer (1987) noted that many of the lenses are belts of high heat flow. Hyndman and Klemperer (1989) observed that the lenses generally have very high electrical conductivity.

Meyerhoff et al. (1992b) discovered that there are two types of undeformed reflective lenses, and that many of these lenses have been severely tectonized. The first type of lens is transparent in the middle (Fig. 3.29); the second type is reflective throughout (Fig. 2.11). Tectonized lenses also may have transparent interiors, or parts of interiors; many, however, are reflective throughout (Fig. 3.21). Where transparent zones are present (Fig. 3.20), bands of high heat flow, bands of microearthquakes, belts of high conductivity, and bands of faults, fractures, and fissures are present. Where a transparent layer is not present, high heat flow and conductivity, however, are commonly still present. Meyerhoff et al. (1992b) also found that lenses with transparent interiors are younger than those without transparent interiors; moreover, there is a complete spectrum of lenses from those with wholly transparent interiors to those without.

The best explanations of thes observations are that (1) the lenses with transparent interiors are active surge channels with a low-velocity zone sandwiched between two levels of 7.0 to 7.8 km/s material; (2) the lenses with reflective interiors are former surge channels now cooled and consisting wholly of 7.0 to 7.8 km/s material; and (3) the tectonized lenses are either active or former surge channels since converted into kobergens by tectogenesis.

3.8.2 SEISMIC-REFRACTION DATA
After Revelle (1958) discovered the presence of a body of 7.0-7.8 km/s material on midocean ridges (the East Pacific Rise), a similar body was discovered on the Mid- Atlantic Ridge, and the general lens shape was reported for the first time (...). Subsequently Talwani et al. (1965) combined gravity and seismic data, and detailed the lens shape of the surge channel across the entire Mid-Atlantic Ridge (Fig. 2.27). Fuchs and Landismann (1966) found a similar but much smaller lens beneath the Upper Rhine graben with a P-wave velocity of 7.6 km/s. Now such a 7.0-7.8-km/s lens is known to underlie every well-sutdied tectonic belt, regardless of tectonic origin. Figure 3.6 shows a 7.0-7.8-km/s lens under the northern Appalachians (...). Meyerhoff et al. (1992a, 1992b) summarized the worldwide evidence for the presence of such lenses under every type of tectonic belt. These same authors showed that the lenses under older tectonic belts contain no low-velocity zone, but that lenses in younger tectonic belts contain low-velocity zones.

3.8.3 SEISMOTOMOGRAPHIC DATA
Seismotomographic data, wherever detialed studies have been made, indicate that the lenses seen in seismic-refraction and seismic-reflection studies form an interconnected, reticulate network in the lithosphere. Although only one highly detailed seismotomographic study has been made on a continental scale---this in China, it leaves no room for doubt that the 7.0-7.8-km/s lenses with transparent interiors and the seismotomographically detected low-velocity channels in the lithosphere are one and the same (...). Figure 2.31 shows the active surge channels at a depth of about 50 km in southwestern China. Figure 3.9 is a seismotomographic cross section to a depth of 300 km across the Yunnan surge channel shown in Figure 2.31. Figure 3.14 is a more detailed cross section (above a depth of 65 km) of the central part of Figure 3.9. Velocity data from refraction surveys have been added. The 7.6-7.9 km/s layer below 50 km is the Yunnan surge channel shown in Figure 2.31; the low-velocity layer between 22 and 44 km (5.4-6.0 km/s) is a part of the Yunnan surge-channel complex (...). Using seismotomographic techniques, it will be possible to map active surge channels over the world with comparative ease. The reader should note that Figure 3.22 shows a seismotomographic image of the active kobergen of the Hengduqn Shan-Shaluli Shan that overlies the Yunnan surge channel, a further demonstration of the validity of our tectonic interpretation.

3.8.4 SURFACE-GEOLOGICAL DATA
Direct evidence for the existence of surge channels comes from tectonic belts themselves, and from one type of magma flood province. The latter include rift igneous rocks that crop out nearly continuously for their full lengths. Examples include the rhyodactic Sierra Madre Occidental-Sierra Madre del Sur extrusive and intrusive belt of Mexico and Guatemala, some 2,400 km long; the 1,600-km-long Sierra Nevada-Baja California batholith belt; the 4,000-km+ batholith and andesite belt of the Andes south of the equator; the 4,000-km-long Okhotsk-Chukotka silicic volcanic belt; the 5,800-km-long Wrangellia linear basaltic province extending from eastern Alaska to Oregon, which erupted in less than 5 Ma; and many other similar continental magma belts. The ocean basins are equally replete with them, ranging from the 60,000-km-long midocean ridge system through the 5,800-km-long Hawaiian- Emperor island and seamount chain to many similar belts of shorter lengths. Geochemical studies also show that most of these belts are interconnected. Another linear flood-basalt belt, which has been studied only relatively recently, is the subsurface Mid-Continent province that extends 2,400 km from Kansas through the Great Lakes to Ohio (Figs. 3.23, 3.24).

3.8.5 OTHER DATA
Other data mentioned in the preceding sections corroborate the interconnection of active surge channels. One of these is the coincidence of the 7.0-7.8-km/s lenses of the active surge channels (Figs. 2.9, 2.31, 3.6, 3.9, 3.14, 3.20) with the belts of high heat flow (Fig. 2.26) and with belts of microseismicity. Both the presence of high heat flow and microseismicity indicate that magma is moving within active surge channels.

However, an even more dramatic example is the June 28, 1992, Landers, California, earthquake-related activity shown on Figure 3.25. This figure shows that the 7.5- magnitude earthquake was strong enough to affect areas up to 1,250 km from the epicenter (...) and provides an exampole of Pascal's Law in action. Given the importance of Pascal's Law in surge-channel systems, the fact should be noted that the viscosity of the magma in the surge channels affected by the Landers event is sufficiently low that, when the stress was applied at a single hypocentral point (Landers), the effects could still be transmitted for 1,250 km!

3.9 Geometry of Surge Channels
3.9.1 SURGE-CHANNEL CROSS SECTION
In cross sections, surge channels have a variety of shapes, and are of many sizes and depths within the lithosphere (M-a). Two models proposed for sill-and-laccolith complexes may be ideal representation of surge-channel complexes because, despite the differences in scale, the same physical principles apply. Corry (1988) published the "Christmas Tree" model shown in Figure 2.8; Bridgwater et al. (1974) published the more complex model shown in Figure 3.26. Either of these could be cross sections of surge channels. Both are multitiered with one or more magma chambers above the main chamber. Both are formed on the basis of Newton's Law of Gravity or, more specifically, the Peach-Kohler climb force (...).

Seismotomographic images are available from hundreds of surge channels in different parts of the world. They are complex structures as Figures 3.9 and 3.27 demonstrate. Figure 3.27 is a tracing of a seismotomographic image of the multitiered Yunnan surge channel (Fig. 2.31 ...). It is also quite large for a continental channel.

Figure 3.23 shows a partly deformed ("kobergenized") inactive Proterozoic surge channel that underlies the Midcontinent Rift of central North America (...). A surge-tectonic structural interpretation is shown on Figure 3.24. The figures show that the channel before deformation consisted of a large lower chamber at the Moho-, and a smaller, higher chamber at about 20 km. Kobergenic structure developed during tectogenesis (Fig. 3.24). The P-wave velocity in the channel is 7.0 to 7.2 km/s, and the top of the channel extends to within 10 km of the surface. The Midcontinent Rift was a major flood-basalt province of 1,100 Ma.

3.9.2 SURGE-CHANNEL SURFACE EXPRESSION
Study of Figures 2.8, 2.9, 2.11, 2.31, 3.6, 3.9, 3.13, 3.14, 3.20, 3.23 and 3.24 might lead one to believe that surge channels are everywhere fairly simple structures expressed at the surface by a single belt of earthquake foci, high heat flow, bands of faults-fractures-fissures (streamlines), and related phenomena which, during tectogenesis, deform into a single kobergen. Although this simple picture is true of many kobergens, it is not true of all. Study of Figures 3.26 and 3.27 suggests that, during tectogenesis of the surge-channel complexes shown on these figures, two or more parallel kobergens may exist at the surface. Such a complex surface expression is in fact quite common. Well-documented examples are found in the Western Cordillera of North America, the Mediterranean-Tethys orogenic belt (including the Qinghai-Tibet Plateau), and the Andes, inter alia. Within the Western Cordillera, the Qinghai-Tibet Plateau, and the Andes, we have found four or more parallel kobergens side by side at the surface as documented and illustrated by Meyerhoff et al. (1992b).

3.9.3 ROLE OF THE MOHOROVIC DISCONTINUITY
The principal forces acting on the lithosphere are compression, rotation, and gravity. We have discussed the first two briefly and now endeavor to describe gravity's role in lithosphere development.

Gravity controls the depths of all magma chambers which, because the Earth cools at the asthenosphere level, have to be in the upper asthenosphere and lithosphere. The mantle above the asthenosphere is believed to be peridotite from which basalt has already been extracted (Ringwood, 1979). It has a P-wave velocity just below the Moho- greater than 7.9-8.0 km/s. The oceaenic crust above the Moho- has been assumed until very recently to have a P-wave velocity of 6.8 km/s and less; the continental crust above the discontinuity has been assumed to have a P-wave velocity of about 6.5 km/s and less.

The liquid generated by the removal of basalt from the mantle cannot be ordinary basalt, but may be akin to tholeiitic picrite (Green et al, 1979). In any case, it is less dense than the peridotite above the asthenosphere and more dense than the basalt found in deep-sea drillholes. Therefore, while in the asthenosphere, it is gravitationally unstable. Consequently Newton's Law of Gravity works to bring the magma upward to a level where it is gravitationally stable. The mechanism for this is the Peach-Kohler climb force (Weertman and Weertman, 1964; Weertman, 1971). This force compels the magma to rise through available conduits to its level of neutral buoyancy, i.e., the level where the lithosphere density and the magma density are the same (...). At this level the magma can only move horizontally.

As we have stated repeatedly, the P-wave velocity of the walls of active surge channels is in the 7.0-7.8-km/s range; that of inactive channels is 7.0-7.8 km/s throughout. In the crustal models generally accepted until the late 1980s, there was no layer having a velocity in the 7.0-7.8-km/s range. In recent years, however, a lower crustal layer has been reported in large areas of North America and elsewhere with velocities in the 7.0-7.8-km/s range (...). Mooney and Meissner (1992) in fact state that the layer is omnipresent, is ca. 3.5 km thick, and is a transition zone between the mantle and the crust.

Thus, when the postulated tholeiitic picrite magma reachs the Moho- (i.e., the zone between 8.0-km/s mantle below and 6.6-km/s above), it has reached its level of neutral buoyancy and spreads laterally. Under the proper conditions---abundant magma supply and favorable crustal structure---a surge channel can form. We suggest the possibility that the entire 7.0-7.8-km/s layer may have formed in this way. In support of this suggestion, we note that the main channel of every surge channel studied, from the Archean to the Cenozoic, is located precisely at the surface of the Moho-. This indicates that the discontinuity is very ancient, perhaps as old as the Earth itself. This fact and the great difference in P-wave velicities above and below the Moho- surface suggest in turn that the discontinuity originated during the initial cooling of the Earth. Hence, Mooney and Meissner's (1992) "transition zone" was the level of neutral buoyancy at the time the 7.0-7.8-km/s material was emplaced.

The suboceanic Moho- is some 10-15 km below sea level; its subcontinental counterpart is deeper, at about 40 km below sea level. Hence the neutral buoyancy levels of the two regimes are separated vertically by 25 to 30 km. This fact probably is closely related to the fact that surge channels underlie all continental shelf-slope breaks. Thus these breaks are transition zones between continental and oceanic regimes. MacDonald (1963, 1964) long ago stated that this transition zone must be the site of vertical faulting. Writing of the differences in the vertical distribution of radioactive heat sources under continents and ocean basins, MacDonald (1963, p.589) stated that these differences ensure "...that the boundaries between them [continents and ocean basine] become discontinuities in subsurface vertical motion. The boundary regions are thus narrow regions where faults are formed and volcanic activity is concentrated." In summary, the ocean- continent boundary is a weakness zone due to differing crustal thicknesses and compositions on either side of that boundary, and the accompanying changes in temperature regimes, specific gravities, and velocities. This weakness zone is therefore a focus for faulting and ascending magma.

It is a fact that volcanism does take place along continental mragins, not just in the "active" margins, but in the "passive" ones as well, as for example along the eastern seaboard of North America (...) and the Atlantic margin of Africa (...). In fact, a recent study of North America's eastern seaboard by Hollbrook and Kelemen (1993) shows the presence beneath the outer shelf of a linear pod of volcanic material at the Moho-. The pod has a P-wave velocity of 7.2-7.5 km/s and is at least 3,300 km long. It should be added that the above explanation does not mean that all surge channels form at ocean-continent boundaries, rather, surge channels are found in every tectonic setting, one of which is the ocean-continent boundary.

The formation of the Christmas-tree-like structures (Figs. 2.8, 3.26) at the Moho- is simply an extension of the larger scale process of magma transfer from the asthenosphere to the discontinuity. Once surge channels are established at the discontinuity, the same processes take over that brought the magma to the discontinuity in the first place, specifically, magma differentiation in the channels and the Peach-Kohler climb force (...). After lighter magmas have formed by differentiation and related processes, they rise to their own neutral buoyancy levels, forming channels above the main surge channel (Figs. 3.23, 3.27).
« Last Edit: March 28, 2017, 07:54:33 pm by Admin »

Social Buttons


Admin

  • Administrator
  • Full Member
  • *****
  • Posts: 174
    • View Profile
Re: SURGE TECTONICS
« Reply #1 on: March 22, 2017, 05:17:23 pm »
SURGE TECTONICS
Chapter 6 Magma Floods, Flood Basalts, and Surge Tectonics
6.1 Introduction
... The old term, "plateau basalt", had functioned with comparative efficiency and illustration, but Tyrrell's "flood basalts" gave an immediate and striking image of basalts poured out in broad areal effusion. "Plateau basalt" has continued in the literature to a considerable degree, but "flood basalts" has become by far the preferred term in mafic volcanology.
 The origin of flood basalts has sparked controversy since they were first identified in the last century [the 1800s]. The purpose of this chapter is to re- examine the critical data, including descriptions of many flood-basalt provinces, to introduce the new term "magma floods" for flood basalts--a term that we consider more appropriate and encompassing--and to propose an explanation of our own in terms of surge tectonics.

6.1.1 SIGNIFICANCE OF FLOOD BASALTS
Some 63% of the ocean basins are covered flood basalts. At least 5% of the continents are likewise covered with flood basalts. Thus 68%---a minimum figure--- of the Earth's surface is covered with these basaltic rocks. Flood basalts, then, are not the oddities that many suppose them to be. In spite of this, they receive little attention among the scientific community. We examined nearly twenty geologic textbooks and reference works published since 1969, and found only two with more than three paragraphs on flood basalts. ... Such treatment---or lack of treatment---seems unusual, out of place, if one considers that flood basalts are the most important rock exposed at the Earth's surface (..., 1986...).
 Engel et al. (1965) long ago demonstrated that deep ocean-floor tholeiitic basalts are the oceanic equivalent of the continental flood basalts. The Basalt Volcanism Study Project (1981) differentiated between the continental flood basalts and "ocean-floor basalts," while recognizing that the principal differences were the abundance of minor and rare-earth elements. Press and Siever (1974...) recognized the fact that the ocean-floor basalts and continental flood basalts are nearly the same, and that their differences are explained readily by contamination in the continental crustal setting. Yoder (1988), one of the world's authorities on basaltic magmas, stated essentially the same thing.
 In fact, as increasing numbers of basalts are analyzed, the difference between the oceanic and continental floods blurs even further. For example, ... (1991) found groups of samples from the Siberian Traps that are essentially indistinguishable from midocean ridge basalts. Fitton et al. (1991) found numerous Great Basin basalts that are chemically indistinguishable from midocean ridge basalts, and Sawlan (1991) observed a complete chemical continuum from midocean ridge basalts to the flood basalts in the Baja California, Gulf of California, and Mexican basin- and-range province.
 These extremely close--in places identical--genetic relationships are well established. In a subsequent section of this chapter, we shall present geochemical data to support this statement.

6.1.2 CLASSIFICATION
Continental flood-basalt provinces are geometrically of two types. The first is broadly ovate, or even round, with the maximum diameter ranging from about 500 km (Columbia River Basalt) to more than 2,500 km (Siberian Traps). The second is distinctly linear, with a width of 100 to 200 km and lengths up to and even exceeding 3,000 km.
 Oceanic flood-basalt provinces at first appearance are difficult to classify. However, as more ... data ... become available, it is possible to distinguish the same two types of geometries there as well. Ovate to semi-ovate shapes characterize many oceanic submarine plateaus. The maximum diameters of these plateaus, excluding the Kerguelen Plateau, are in the order of 1,200 to 1,600 km.
 Linear ridges are of two types. The larger is the midocean-ridge system with widths between 1,200 and 3,600 km; the smaller is exemplified by the various linear island and seamount chains with widths of 100-200 km and lengths of thousands of kilometers.
 Ovate flood-basalt provinces include [over 13 places]....
 Linear flood-basalt provinces include [over 14 places]....
 Tectonism and metamorphism can severely disrupt any flood-basalt province after its formation. For example, ... the Antrim Plateau Volcanics of northern Australia ... parts ... have been removed by erosion. ... Similarly, only very scattered, strongly flooded, and metamorphosed remains of the Willouran Mafic rocks are preserved in ... South Australia, but their distribution shows that [it] is a linear flood-basalt province.

6.1.3 THE PETROGRAPHIC CHARACTER OF FLOOD-BASALT PROVINCES
To judge from the geological literature, many earth scientists assume that flood- basalt provinces are composed mainly of basalt and little else. This characterization is justified for some provinces but it is incorrect for many more. For example, the Columbia River flood-basalt province consists nearly 100% of tholeiitic basalt with small volumes of basaltic andesite and minuscule amounts of dacite and rhyolite (..., 1979-1988). In contrast the Snake River flood-basalt province on the southeastern side of the Columbia River province consists more than 50% of rhyolite and siliceous (rhyolitic) ignimbrites (..., 1989). A second example is the Lebombo monocline region of the Karroo flood-basalt province in southern Africa. Here are thick sequences of rhyolite (and perhaps ignimbrite) which, for most of the length of the monocline--at least 600 km--comprise 30 to 55% of the volcanic section (..., 1983). Yet another example is the Keweenawan (Midcontinent) flood-basalt province where every region has large volumes of rhyolite associated with the basalt. Our first point is that many flood-basalt provinces are bimodal, and the volume of associated silicic extrusive (or intrusive) rocks can be substantial.
 A second common assumption is that tholeiitic basalt and related tholeiitic rocks constitute the principal mafic rock types. Here again, the field evidence proves the assumption is incorrect. It is true that the Columbia River flood-basalt province consists 99% of tholeiitic mafic rocks. Yet the huge, 3,000-km-long Arabian flood-basalt province consists mainly of alkalic basalt. In fact, Camp and Roobol (1981) and Camp et al. (1991) refer to this example as the "Arabian continental alkalic basalt province." Thus our second point is that many types of basalts may be present in flood-basalt provinces. Tholeiitic basalt is just one of those types.

6.2 Descriptions of Selected Continental Flood Basalt Provinces
We present here some brief geological descriptions of representative ovate and linear continental flood-basalt provinces in order of decreasing age. Many additional continental provinces could have been added to this list, but we believe that those selected adequately illustrate the points we wish to make. Undoubtedly, some earth scientists will not agree that all of our examples are, in fact, flood- basalt provinces. Therefore, we include data on areal extent, volume, thickness, composition, and age which led us to conclude that we were dealing with flood- basalt provinces. Data concerning the ages, areal extent and volume of these provinces and others are summarized on Table 6.1.

6.3 The Use of Geochemistry in Identifying Flood Basalts
6.3.1 INTRODUCTION
Geochemical/petrochemical studies of igneous rocks for many decades were restricted to (1) studies of the bulk chemistry (major compounds only) of each rock type, and (2) deviations from the "norm" determined for each rock type. High- pressure ... and high-temperature studies were conducted in the search for the chemical phases and eutectics of rock melts. Such studies were invaluable in determining the origins of various rock types, and led to many classical papers, especially the Yoder and Tilley (1962) and Yoder (1976) treatises on the origin and generation of basalt.
 With the advent of plate tectonics, petrochemistry was used increasingly as a supplement to traditional methods of identifying tectonic environments. The assumption was made that each tectonic environment had its own petrochemical "signature." When major-element studies failed to bear out this assumption, however, increasing attention was given to minor (trace) and rare earth elements. Regrettably, nearly all large-scale petrochemical research concentrated on the basalts (e.g., the NASA-sponsored Basaltic Volcanism Study Project published in 1981), and other rock types have failed to receive anything like the attention that the basalts received. As an inevitable consequence, many conclusions were made on the basis of basalt geochemistries alone. Our points are: (1) that a great deal of research---many decades, in fact---will be necessary before sound conclusions regarding the chemical "signature" of tectonic environments will or can be soundly based; and (1) even though the more silicic magma types are in very large part aggregates of crustal compounds and processes, they too have important scientific "messages" to impart. It is too early to reach final conclusions based only on basalt data.
 The results of minor and rare-earth element studies, however, have been helpful, for they document in part the history of each sample with the use of spidergrams (Fig. 6.16). They also discriminate easily between midocean-ridge basalts and other basalts, although this already was possible from major element data alone. However, as we document below, the ability of spidergrams to discriminate among most tectonic settings is doubtful without much additional information, partly from isotope data and, in the long run, with the aid of actual field data.
 An important step that must be taken now is to standardize the order in which the trace and rare-earth elements appear on a spidergram (Fig. 6.16). Second, there is no consistency about which elements are included or excluded (Fig. 6.16), and this problem also must be resolved. Too often elements important to an interpretation are omitted on spidergrams. Finally, there is no consistency about which material is used for "normalizing" element plots. Currently some are chondrite-normalized; some are normalized against an idealized midocean-ridge basalt composition; and many are normalized against the composition of an hypothetical primordial mantle, a practice which, as Thompson et al. (1983) have noted, introduced unnecessary subjectivity into interpretations.

6.3.2 BASALT MAGMAS
... [Skipping 3 paragraphs]
It is important to be aware that the concentration of incompatible trace elements* [those most likely to be transported by melts and other fluids passing through the mantle and therefore most likely to preserve evidence of mantle enrichment and depletion processes in their relative abundances] changes greatly in this basaltic liquid, depending on their relative partition coefficients, initial concentrations, and dilution rates. In the midocean-ridge basalts, the volume of incompatible minor elements is very small, a fact that suggests that the parental material has already undergone some partial melting and loss of liquid, but still retains parts of all major melt phases (..., 1988).
 Several processes involved in the emplacement of magmas in the crust complicate the above picture. The composition of surface samples from rocks that were molten and under high pressure is not necessarily that of the parental liquid at depth. This is true because (1), as the liquid rises, internal reaction relations take place that successively eliminate olivine and orthopyroxene (..., 1967-1988). Hence the composition of the basalt may be altered considerably during its rise from ca. 130 km; (2) of heat loss; (3) the change in pressure further changes the liquid composition; and (4) the rise of the melt produces a change in the stable phases within the liquid.
 The reasons for the differences between continental flood basalts and midocean-ridge basalts are related in part to the above factors, but differences in the thickness of the lithosphere clearly must exert an important influence as well (..., 1988). The penetration of an old, thicker, continental massif by basalt melt is clearly more difficult than that of the much thinner oceanic lithosphere, although the rising magma rises in the same way under both lithospheres, following the Peach-Kohler climb force (Newton's Law of Gravity; ..., 1964-1989) and stops when the level of neutral buoyancy has been reached (..., 1989). The longer---or slower---the rise beneath the continental crust, the greater the fractionation, as reflected in the more iron-rich character of the continental lavas (..., 1981- 1988). Deep-seated magma segregation beneath the continents provides for more alkalic parental magmas, a greater range of enrichments, and a greater variation that depends on repose time, interactions with the continental crust, and the rates of ascent. The bimodal character of so many continental flood basalts implies the presence for periods of time of multiple magma chambers.

6.3.3 STUDIES OF MINOR AND RARE EARTH ELEMENTS
When studies of major elements and compounds revealed difficulties in discerning chemical signatures peculiar to each tectonic environment, research began to focus on studies of minor (trace) elements, rare-earth elements, and chemical isotopes. Although a high degree of success has been claimed for such studies, the facts tell quite a different story. Indeed, it is a poor reflection on the state of current geoscientific resaerch that the eagerness of some researchers to satisfy preconceived hypotheses and models has led some into publishing material that is scientifically sound [unsound?]. Minor (trace) element, rare-earth element and chemical isotopes studies are summarized for the following environments.
 Midocean-Ridge Basalts (Ocean-Floor Volcanism) ...
 Ocean-Island Basalts (Oceanic Intraplate Volcanism) ...
 Continental Flood Basalts (Continental Intraplate Volcanism) ...
 Volcanic Arc Basalts ("Subduction" Basalts) ...
 Island Arc Basalts ...
 Continental Margin Volcanic Arcs ...

6.4 Geochemical Comparisons among Basalts Erupted in Different Tectonic Settings
... 6.4.7 CONCLUSION
Our examination of the literature on basalt rocks has led us to conclude that geochemistry is useful in distinguishing between midocean-ridge basalts and other basalts. This is true of bulk geochemistry, major-element geochemistry, and minor (trace) element and rare-earth element tectonic settings other than that of the midocean ridge. Exceptions to this statement do exist, but only in areas where the investigator has exceptional knowledge of the field relations among the various igneous units that he/she is investigating. Geochemical techniques are useful, however, in deciphering the chemical histories of the various igneous units, subject once again to the proviso that field relations among the various units being studied are well understood.

6.5 Duration of Individual Basalt Floods
6.5.1 INTRODUCTION
The length of time during which a particular basalt flooding episode lasts differs greatly among the various flood-basalt provinces. Some, such as the Siberian flood-basalt province, have been active more than 200 Ma. Others---the Wrangellian province, for example---probably completed their flood activity in 5 Ma or less. Even in flood-basalt provinces of long duration, the largest volume of basalts may have been extruded in one, or perhaps two or three relatively short bursts. A close relationship seems to exist between times of tectogenesis and times of major basalt flooding.

6.5.2 FLOOD-BASALT PROVINCES OF LONG DURATION
Radiometric and/or paleontologic constraints are available for only a few flood- basalt provinces. Therefore, we mention only places where good dating is available. The radiometric data are summarized on Table 6.1.
[2.5-283 Ma are indicated.]

6.5.4 CONCLUSION
We have discussed several flood-basalt provinces which were active during periods that ranged from more than 210 Ma (long duration) to less than 12 Ma (short duration). We have found no evidence to suggest that there are any time controls or any rules of thumb that guide the length of time during which a flood-basalt province may remain active. Nor is there a relationship between type of flood- basalt province may remain active. Nor is there a relationship between type of flood-basalt province and the duration of its extrusion. For example, the Columbia River province is ovate while the Wrangellian province is linear; yet the two endured for approximately the same lengths of time. Reports that the Deccan and Siberian flood-basalt provinces were in fact of very short duration are based on a lack of information. In fact, information adequate to determine the "lifespans" of most flood-basalt provinces, including Siberian province, is not yet available.

6.6 Flood-Basalt Provinces and Frequency in Geologic Time
As we observed near the beginning of this chapter, the commonly used textbooks of physical geology, structural geology, and geotectonics rarely list more than 10 to 20 flood-basalt provinces. However, the magnificent review of basalts by the participants in the Basalt Volcanism Study Project (1981) mentions or figures not less than 56 flood-basalt provinces and 45 additional provinces of dike swarms which the project participants thought might have fed flood-basalt provinces that have since been removed by erosion.
 The participants in the Basalt Volcanism Study Project (1981) concurred on a large number of phenomena that characterize flood-type volcanism. However, they showed considerable confusion, ambivalence, and lack of agreement on which, and what type of, provinces should or should not be described as flood-basalt volcanism. This confusion and ambivalence manifest themselves with respect to the differences between flood-basalt provinces and continental rift-related provinces. Additionally, they used interchangeably the terms "flood basalt," "plateau basalt," "continental rift volcanism," and "hot-spot volcanism."
 We summarize here briefly their overall remarks on the ages of flood-basalt activity. They wrote that (1) most flood provinces are less than 200 Ma; (10 no major flood-basalt activity took place in the interval 1,100-200 Ma (yet ... they list eight provinces within this time span, two of which are huge---the Siberian Flood-Basalt Province and the Emeishan Flood-Basalt Province); (3) reasonably well-preserved remnants of flood provinces are known from the time interval 2,150- 1,100 Ma, and (4) a few poorly preserved remnants are present in the geological record to 3,760 Ma (..., 1981, ...). Yet, on page 41, the same authors state that flood-basalt provinces older than 1,200 Ma are unknown.
 The participants ... have for the first time, to the best of our knowledge, provided solid evidence that flood-basalt volcanism is a phenomenon that has persisted since the beginning of--or since very early in---the Earth's history. However, we have not seen any convincing evidence to support the claim by Rampino and Stothers (1988), and a similar claim by White and McKenzie (1989), that flood- basalt volcanism is periodic, with large outpourings every 32 to 30 Ma. We suspect, but cannot prove, that flood volcanism is triggered by tectogenic (orogenic) pulses that are episodic. In our opinion, the available evidence all but demonstrates an endogenic origin. Which of the various possible endogenic causes is the correct one must await the careful sampling and dating of thousands of more carefully located igneous-rock samples in every major flood-basalt province.
 Yoder (1988, ...) wrote that "Great basaltic 'floods' have appeared on the continents throughout geologic time (Table 1)," but showed on his Table 1 none older than 1,200+/- 50 Ma. He also ... made it clear that he regards midocean-ridge and other oceanic basalts as flood basalts, as have a number of earlier workers (..., 1974). We concur absolutely with their interpretation. We also concur with the participants of the Basalt Volcanism Study Project (1981) that evidence of the existence of flood provinces extends back in time to at least 3,760 Ma, and very likely to the Earth's earliest (but nowhere preserved) history. Interestingly, most of what Press and Siever (1974), Yoder (1988), and we concur in what was anticipated by the pioneer work of Engel et al. (1965).

6.7 Non-Basalt Flood Volcanism in Flood-Basalt Provinces
The bimodal nature of many flood-basalt provinces has been known and stressed for many years (..., 1981). Time seems not to be a major factor (the idea being that, the longer an underlying magma chamber is present, the more the magma will interact with the continental crust above it). The most important factor may be the crustal stress state.
 Estimates of the volume of non-basaltic rocks in a given flood-basalt province are difficult to find. Accordingly in Table 6.2 we have left many blank spaces and the percentages that we have supplied are poorly documented except in local areas.
 ... [Skipping 6 paragraphs]
 We believe that the evidence from these examples demonstrates convincingly that there is a complete gradation from all-basalt and basaltic andesite flood provinces to bimodal provinces containing mainly rhyolite and ignimbrite. Hence, there are basalt floods and rhyolite floods.
 ... [Skipping most of 1 paragraph] The volumetric predominance of these ash-flow tuffs has led to recognition of the [Sierra Madre Occidental] as the world's largest rhyolite-dominated volcanic province" (Fig. 6.28).
 ... [Skipping one paragraph]
 Thus, from 38 Ma until 17 Ma, a truly bimodal column of extrusive rocks accumulated in northern Mexico and adjoining parts of the United States, with rhyolite at one end, basaltic andesite at the other, and very little rock of intermediate compositions. ... [Skipping remainder of paragraph]
 We believe that these basalts of the "southern cordilleran basaltic andesite" suite are flood basalts. And if they are flood basalts, then we have demonstrated that the same mechanism that leads to continental and oceanic basalt outpourings also produces the "orogenic andesite suite".
 The Okhotsk-Chukotka Volcanic Belt, a linear belt of Cretaceous volcanics, is similar to the Sierra Madre Occidental. It extends 3,000 km from the mouth of Uda Bay (northwestern Sea of Okhotsk) to the Bering Sea almost at St. Lawrence Island. It seems to have every type of volcanic from andesitic through rhyolite. Basalts are scarce. Soviet geologists either ignore it or say that it is the remnant of a volcanic arc.
 
6.8 Flood Basalts or Magma Floods?
Although we advocate the continued use of the term "flood basalt," it is clear that another term is needed to describe floods of andesite, dacite, and rhyolite. For future studies, we suggest the all-encompassing term magma floods. In this way, we can include all of the various lava types, dikes, necks, and sills. It is a term that even embraces situations such as the Ferrar Dolerite of Antarctica and the network of sills and dikes of the Amazon basin.

6.9 Surge-Tectonics Origin of Magma Floods
In the preceding pages we have referred to the presence of several flood-basalt provinces around the world, and have shown that some flood provinces include large volumes of silicic rocks, usually rhyolite and/or dacite. We have also shown by the northern Mexican example that flood basalts can interfinger with the andesite orogenic suite. In addition, we have presented evidence that spidergrams are not more effective at identifying the tectonic setting than bulk chemistry. The available evidence has led us to the conclusion that the same mechanism causes volcanism in the midocean ridges, linear island and seamount chains, oceanic plateaus, island arcs, and continental interiors. We next attempt an explanation of our conclusion.
 Many attempts have been made to explain flood volcanism in the framework of the plate-tectonics hypothesis. The two principal explanations involve (1) hot spots, or mantle plumes and (2) an extraterrestrial cause (e.g., an asteroid impact).
 Extraterrestrial causes have been proposed by Alt et al. (1988), who applied this hypothesis to the Columbia River flood-basalt province. A major problem with this concept is that it does not explain linear flood-basalt provinces such as the Keweenawan (Mid-Continent) rift and Wrangellia. Furthermore, Mitchell and Widdowson (1991) pointed out that impact and shock phenomena should be present in the area surrounding the Columbia River province if it resulted from extraterrestrial action, but they are entirley absent.
 Mantle diapirism or asthenosphere upwelling constitutes the hot-spot or mantle- plume hypothesis (..., 1971) used widely in tectonic models today. Recent literature on mantle plumes include works by ... (1988-1991). Hot spots are often portrayed as diapiric bodies that are essentially cylindrical, mushrooming plumes. While this might account for isolated volcanoes, it does not account for the massive ovate and linear flood basalt provinces found in many parts of the world.
 Mantle upwelling also has been invoked by many writers to explain the presence of long, linear continental rifts (..., 1983), which are, for the most part, similar to one another. ... [Skipping remainder of paragraph listing widths and lengths of numerous linear rifts etc]
 As we noted in Chapters 3 and 4, Mooney et al. (1983) observed that all active rifts studied by them have an anomalous lower crust with P-wave velocities in the 7.0 to 7.7 km/s range (Fig. 6.36). [Others] obtained the identical result.... Fuchs (1974) believed that this pod of anomalous lower crustal material houses the mechanism that causes rifting. It is interesting to note that all midocean ridges have a pod of 7.0-7.7 km/s as well (..., 1959-1965). (Furthermore, each island arc and foldbelt also has a pod of 7.0-7.7 km/s material that pinches out from the center of the arc or foldbelt (..., 1987-1989 ... for the Japan arc ... [and] for the Appalachians.)
 Figure 3.6 is a cross section across the Baykal rift, from Krylov et al. (1979) and Sychev (1985). Years of refraction work have shown the Lake Baykal is underlain at about 32 km by a pod that is connected to the deeper asthenosphere. The shallow pod contains a low-velocity zone that presumably is a partial melt. The pod extends the full length of the rift. It is, in short, a channel containing partly molten magma and an excellent example of one of our surge channels. Were it to burst, we believe that it would produce another linear flood-basalt province.
 According to our surge tectonic hypothesis, magma in surge channels moves both vertically and horizontally. When two surge channels come in contact, their magmas join together. If they are oriented at an appreciable angle to one another, we believe that the result is a "collision". These5 "collisions" are responsible for the eruption of round or ovate flood-basalt provinces worldwide.

CHAPTER 7
CONCLUSIONS
We have proposed a new hypothesis of global tectonics in this book, one that is different and will be considered unorthodox by many scientists and non-scientists alike. However, we believe that current tectonic hypotheses cannot adequately explain the increasing volume of data being collected by both old and new technologies. We believe that the hypothesis of surge tectonics does explain these data sets, in a way that is simple and more accurate.
 The major points of the surge-tectonics hypothesis can be summarized as follows:
 1. All linear to curvilinear mesoscopic and megascopic structures and landforms observed on Earth (and similar features seen on Mars, Venus, and the moons of Jupiter, Saturn and Uranus), and all magmatic phenomena are generated, directly or indirectly, by surge channels. The surge channel is the common denominator of geology, geophysics, and geochemistry.
 2. Surge channels formed and continue to form an interconnected worldwide network in the lithosphere. They contain fluid to semifluid magma, or mush, differentiated from the Earth's asthenosphere by the cooling of the Earth. All newly differentiated magma in the asthenosphere must rise into the lithosphere. The newly formed magma has a lower density and therefore, is gravitationally unstable in the asthenosphere. It rises in response to the Peach-Kohler climb force to its level of neutral buoyancy (that is, to form a surge channel).
 3. Lateral movements in the Earth's upper layers are a response to the Earth's rotation. Differential lag between the more rigid lithosphere above and the (more) fluid asthenosphere below causes the fluid, or mushy, materials to move relatively eastward.
 4. Surge channels are alternately filled and emptied. A complete cycle of filling and emptying is a geotectonic cycle. The geotectonic cycle takes place along this sequence of events:
 a. Contraction of the strictosphere is always underway, because the Earth is cooling;
 b. The overlying lithosphere, which is already cool, does not contract, but adjusts its basal circumference to the upper surface of the shrinking strictosphere by large-scale thrusting along lithosphere Benioff zones and normal-type faulting along the strictosphere Benioff zones.
 c. Thrusting of the lithosphere is not a continuous process, but occurs when the lithosphere's underlying dynamic support fails. When the weight of the lithosphere overcomes combined resistance of the asthenosphere and Benioff zone friction, lithosphere collapse begins in a episodic fashion. Hence, tectogenesis is episodic.
 d. During anorogenic intervals between lithosphere collapses, the asthenosphere volume increases slowly as the strictosphere radius decreases and decompression of the asthenosphere begins.
 e. Decompression is accompanied by rising temperature, increased magma generation, and lowered viscosity in the asthenosphere, which gradually weakens during the time intervals between collapses.
 f. During lithosphere collapse into the asthenosphere, the continentward (hanging wall) sides of the lithosphere Benioff zones override (obduct) the ocean floor. The entire lithosphere buckles, fractures, and founders. Enormous compressive stresses are created in the lithosphere.
 g. When the lithosphere collapses into the asthenosphere, the asthenosphere- derived magma in the surge channels begins to surge intensely. Where volume of magma in the channels exceeds volumetric capacity, and when compression in the lithosphere exceeds the strength of the lithosphere that directly overlies the surge channels, the surge-channel roofs rupture along the cracks that comprise the fault-fracture-fissure system generated before the rupture. Rupture is bivergent and forms continental rifts, foldbelts, strike-slip zones, and midocean rifts. We call such bilaterally deformed belts kobergens.
 h. Once tectogenesis is completed, another geotectonic cycle or subcycle sets in, commonly within the same belt.
 5. Movement in the surge channel during the taphrogenic phase of the geotectonic cycle is parallel with the channel. It is also very slow, not exceeding a few centimeters per year. Flow at the surge-channel walls is laminar as evidenced by the channel-parallel faults, fractures, and fissures observed at the Earth's surface (Stoke's Law). Such flow also produced the more or less regular segmentation observed in tectonic belts.
 6. Tectogenesis has many styles. Each reflects the rigidity and thickness of the overlying lithosphere. In opcean basins where the lithosphere is thinnest, massive basalt flooding occurs. At ocean-continent transitions, eugeosynclines with alpinotype tectogenesis form. In continental interiors where the lithosphere is thicker, either germanotype foldbelts or continental rifts are created.
 7. During the geotectonic cycle, and within the eugeosynclinal regime, the central core (crest of the surge channel) evolves from a rift basin to a tightly compressed alpinotyhpe foldbelt. Thus a rift basin up to several hundred kilometers wide narrows through time until it is a zone no more than a few kilometers wide that is occupied by a streamline (strike-slip) fault zone (e.g. the San Andreas fault). Then as compression takes over and dominates the full width of the surge-channel crest, the streamline fault zone is distorted, until it and the adjacent rocks are severely metamorphosed. If the underlying, and now severely deformed surge channel still contains any void space, the overlying rocks may collapse into it, and through this process of Verschluckung (engulgment) become a Verschluckungzone.
 8. The Earth above the strictosphere resembles a giant hydraulic press that behaves according to Pascal's Law. A hydraulic press consists of a containment vessel, fluid in that vessel, and a switch or trigger mechanism. In the case of the Earth, the containment vessel is the interconnected surge-channel system; the fluid is the magma in the channels; and the trigger mechanism is worldwide lithosphere collapse into the asthenosphere when that body becomes too weak to sustain the lithosphere dynamically. Thus tectogenesis may be regarded as surge-channel response to Pascal's Law.
 9. Surge channels, active or inactive, underlie nearly every major feature of the Earth's surface, including all rifts, foldbelts, metamorphic belts, and strike-slip zones. These belts are roughly bisymmetrical, have linear surface swaths of faults, fractures, and fissures, and belt-parallel stretching lineations. Aligned plutons, ophiolites, melange belts, volcanic centers, kimberlite dikes, diatremes, ring structures and mineral belts are characteristic. Zoned metamorphic belts are also characteristic. In some areas, linear river valleys, flood basalts, and/or vortex structures may be present. A lens of 7.8-7.0 km/s material always underlies the belt.
 10. Active surge channels are most easily recognized by the presence of high heat flow (Fig. 2.26), microseismicity, lines of thermal springs, small negative Bouguer gravity anomalies, and a 7.8-7.0 km/s lens of material that is transparent in the center or throughout.
 11. Inactive surge channels possess a linear positive magnetic anomaly, a linear Bouguer positive gravity anomaly, and a linear, lens-shaped pod of 7.8-7.0 km/s material that is reflective throughout.
 12. A surge-tectonics approach to geodynamics provides a new means for determining the origin of the Earth's features and their evolution through time, for analyzing regions prone to earthquakes and volcanism, and for predicting the location and formation of mineral deposits throughout the globe.
« Last Edit: March 29, 2017, 07:45:29 pm by Admin »

Admin

  • Administrator
  • Full Member
  • *****
  • Posts: 174
    • View Profile
Re: SURGE TECTONICS
« Reply #2 on: March 23, 2017, 10:51:44 am »
CHAPTER 1
WHY A NEW HYPOTHESIS?
1.1 Introduction
Before 1962, the year in which H.H. Hess revived and revised Arthur Holmes's (1931) concept of seafloor spreading (which also was proposed by Ampferer [1941]), the geology and geophysical departments of the world taught several geodynamics hypotheses. These hypotheses stimulated lively discussions and resulted in the publication of a highly diversified spectrum of ideas. After Hess's version of seafloor spreading was published, diversity in geodynamics thinking began to wane, and outside of Asia and Eastern Europe, had all but vanished by the end of 1963. ... it is the belief of these authors that as intensive geotectonic research has vastly increased the database for Earth-dynamic studies, plate tectonics has not adequately and completely explained the geology of many regions of the world.
 The purpose of this book is to present a comprehensive and internally consistent hypothesis of global tectonics, an hypothesis that we call surge tectonics. [Skipping most of 2 paragraphs] ...
 ... a huge body of evidence has accumulated to show that this lithosphere mosaic is in a state of equiplanar tangential stress (..., 1979). That is, compressive stress is ubiquitous in the lithosphere; moreover it is tangential and directed approximately equally in all directions of the compass, in accord with Newton's Third Law of Motion. This fact alone means that, for one part of the mosaicwork to move laterally (and tangentially), all parts must shift in order to accommodate the movement of the one part (..., 1966). One of several convincing proofs of this involves the classical hole-in-the-plate-problem or architecture and architectural engineering (..., 1913-1991). Within any body (or plate) subjected to equiplanar tangential stress (e.g., compression), stresses in all directions are approximately equal and opposite, in accord with Newton's Third Law, unless there is a flaw (hole) in the body. Wherever a flaw, or 'hole', is present, the compressive stresses must of fault zone in California, where the axis of maximum compressive stress is everywhere at right angles to the fault trend (..., 1987; ...).
 We also know from geological field mapping that objects within the lithosphere mosaic are moved substantial distances, both vertically and laterally. However, the argument that large lithosphere plates, each 50 to 200 km thick, each extending for thousands of kilometers in all directions, and each weighing incalculable tons, can be moved freely and systematically about the Earth's surface defies all physical laws and common sense. Strictly lateral tangential movements are out of the question to explain the observed lateral and vertical motions that have been mapped in the field. To accommodate these visible, measurable, large lateral movements, rock bodies within the lithosphere mosaic must be able to move. To do this requires (1) upward (vertical) motion of rock bodies to positions of least resistance, followed by (2) lateral outward motions of the newly freed bodies on the upper lithosphere surface where the stresses required for lateral movements are far less than those required within the lithosphere. To accomplish the observed motions---which are not confined to relatively narrow mobile belts but occur everywhere within the lithospheric plates---a geodynamic explanation other than conventional plate tectonics and any other existing geodynamic hypothesis is required.
 Surge tectonics is a new hypothesis which proposes that the Earth acts like a hydraulic press. The containment vessel for this press is an interconnected network of magma chambers and channels in the lithosphere; the fluid in the chambers is magma from the asthenosphere; and the trigger mechanism, or press, is episodic collapse of the lithosphere into the asthenosphere along points of weakness. Three interdependent and interacting processes are involved: (1) lateral flow of fluid, or semifluid magma through the interconnected channels; (2) cooling of the Earth causing contraction, which contributes to tectogenesis; and (3) the Earth's rotation. Surge tectonics draws on well-known physical laws, especially those related to the laws of motion, gravity, and fluid dynamics. [Skipping last paragraph]

1.2 Former and Current Concepts of Earth Dynamics
1.2.1 GENERAL
1.2.2 CONTRACTION
[Skipping 5 paragraphs]
 Even though MacDonald (1963) answered many of the growing objections to the contraction hypothesis, the hypothesis fell from grace. ... A third reason was the observation that the amount of measured foreshortening in foldbelts is far greater than the amount that contraction can account for ... [which] in our judgment, is valid. If contraction does take place, another mechanism must produce the foldbelts. Regardless, many geophysicists (..., 1981-1982) still regard contraction as an ongoing process within the Earth.
 A contracting Earth is an extremely attractive model for tectonic processes, because---in theory at least---it can provide directly for tangential compression at the Earth's surface. However, contraction as the sole cause of tectogenesis is highly unlikely for many reasons, most of which were discussed by Scheidegger (1963) and Bott (1971). Not the least of these is the fact that in neither the contraction envisioned by Jeffreys (1970) nor that described by MacDonald (1963) can all of the true shortening in mobile belts be accounted for. However, if weak zones---surge channels---containing magma are present in the lithosphere, contraction can play a role much different than that usually attributed to it.

1.2.3 MANTLE CONVECTION
[Skipping almost all of the section]
 ... However, now that data are available---especially seismotomographic data---that suggest that convection cells are not present in the upper mantle, it may soon be unnecessary to discuss the pros and cons of convection on such a theoretical level.

1.2.4 EARTH EXPANSION
... Finally, MacDonald (1963) has shown that, whereas expansion probably was important during the first three eons of Earth history, it was rather minor and almost certainly is not taking place today.

CHAPTER 2
...
2.3 Data Sets Unexplained in Current Tectonic Models: Foundation for a New Hypothesis
2.3.1 LINEAR STRUCTURES
Sonographs of the midocean ridges reveal the presence everywhere of long, linear, ridge-parallel faults, fractures, and fissures. The ridge-parallel sets of faults, fractures, and fissures are not restricted to the crestal regions of the ridges, but extend down the ridge flanks to levels where the sediments of the adjacent abyssal-plain basins lap onto the ridges (..., 1979). Because several of the midocean ridges extend into adjacent continents (..., 1960-1992b), we extended our study of the ridge-parallel faults, fractures, and fissure systems to embrace all tectonic belts within the continental regions.
 So that there will be no misunderstanding, it is necessary to define here our use of the therm tectonic belt. In general, a tectonic belt is any structural megafeature developed at the Earth's surface above what we call a surge channel. Thus a tectonic belt includes the full spectrum of linear tectonic features known on Earth. In continental regions, these include continental rifts, strike-slip fault zones, germanotype and alpinotype foldbelts, and continental volcanic arcs. They also include such linear cross-strike features as the Colorado Mineral Belt and the Lower Yangzi Valley plutonic-volcanic belt. In oceanic regions, tectonic belts include midocean ridges, "aseismic ridges," linear island and seamount chains, and oceanic island arcs.
 Tectonic belt-parallel systems of faults, fractures, and fissures were found in every tectonic belt examined, whether a continental rift, a strike-slip fault zone, or a foldbelt. Examples include the Western Cordillera of the United States (Fig. 2.1; ..., 1978) and, at a smaller scale within the same tectonic province, the California Coast Ranges-San Andreas fault zone (Fig. 2.2; ..., 1976). Other examples are the East African Rift system (Fig. 2.3; ..., 1976-1987), the Rhine Graben (Fig. 2.4; ..., 1979), the Front Range of New Mexico, Colorado, and Wyoming (Fig. 2.5; ..., 1986), and the Reelfoot Graben beneath the Mississippi Embayment (Figs. 2.6, 2.7; ..., 1978-1982). Together, these systems involve a huge body of data that are not well explained in plate tectonics, and with rare exceptions, have not been addressed. The fact that faults, fractures, and fissures parallel the strike of each tectonic belt indicates, as a simple consequence of Stoke's Law (see Appendix), that each of these belts has been, or is underlain by a mobile body that moves parallel with the tectonic belt. Thus the primary motions producing these systems of faults, fractures, and fissures are not at right angles to the tectonic belts (..., 1986).
 Linear evaporite trends and many types of linear basins originate in half-gravens, grabens, and compression-produced topographic (synclinal) lows, and generally are explained as a consequence of tension or compression. However, all linear basins and all oval basins (e.g., Paris basin, Williston basin, Illinois basin, Moscow basin, Sichuan basin), both on cratons/platforms and in less stable regions such as rifts and foldbelts, are underlain by lenses of 7.0-7.8 km/s material.
 Linear valleys and mountain systems commonly can be explained as inherited from the strike of underlying older structures. Mountains that are transverse to regional structure, however, pose bigger problems (e.g., the California Transverse Ranges, the Uinta Mountains of the Rocky Mountains, the Wichita and Arbuckle Mountain of the United States Great Plains). Similarly, long, straight river courses across regional strike do not always have an obvious explanation. Examples include the lower courses of the Mississippi River (Mississippi  Embayment), the St. Lawrence River, and the Yangzi River. These linear to curvilinear valleys are underlain by lenses of 7.0-7.8 km/s material at the Moho-.

2.3.2 LITHOSPHERE DIAPIRS AND LITHOSPHERE MAGMA CHAMBERS
Ever since the publication of Wegmann's (1930, 1935) pioneer papers on the topic, mantle diapirism has been invoked increasingly as a mechanism for generating or promoting tectogenesis. Van Bemmelen (1933) and Glangeaud (1957, 1959), for example, favored mantle diapirism and subsequent lateral sliding and/or compression for creating the structures of the Mediterranean Sea region. Mantle-diapirism hypotheses have found favor at different times with many geologists (..., 1968) for explaining the structural evolution of the Mediterranean belt, and indeed still do (..., 1988).
 The evidence adduced for extensive lithosphere diapirism is now formidable (..., 1980-1992). Shallow magma chambers are ubiquitous beneath active tectonic belts, whether they be rift zones, streamline (strike-slip) fault zones, or foldbelts. Some rift-valley examples of shallow magma chambers or diapirs include the East African Rift system (..., 1992), the Red Sea Graven (..., 1988), the Rhine Graben (..., 1984), the Baykal Rift (..., 1979-1985),  the Rio Grande Rift (..., 1982), Iceland (..., 1982), the Hetao-Yinchuan Graben (..., 1989), the Fen Wei (Wei He) Graben (..., 1989), and many, many more. Streamline (strike-slip) fault zone examples include the San Andreas Fault zone (..., 1980), the Dead Sea Fault zone (..., 1989), the Alpine Fault (..., 1991), the Queen Charlotte Fault zone (..., 1988), and many more. One problem with finding examples of magma chambers at shallow depths along streamline (strike-slip) fault zones is that these zones have not been studied in the same way as rifts and foldbelts. Hence the discovery of shallow melt, or potential melt, zones beneath streamline fault zones has been largely serendipitous. Examples of shallow diapirs beneath foldbelts are also abundant. A few examples include the California Coast Ranges (..., 1983-1985), the Alps (..., 1983), the Dinaric Alps (..., 1974), the Himalaya and Qinghai-Xizang (Tibet) Plateau (..., 1991), the Yunnan Himalaya (..., 1989), the Japan Arc (..., 1987), and the Pyrenees (..., 1989).
 Almost since the beginning of the plate tectonics era, geophysicists such as Lliboutry (1971), Bonini et al. (1973), and many others have pointed out the important role that diapirism must play in any scheme of Earth dynamics. Despite this, mantle diapirism and related upwelling processes received little consideration as intrinsic parts of plate tectonics until Dewey (1988a) recognized their possible importance throughout the Alpide-Mediterranean and parts of the Circum-Pacific tectonic belts. Dewey's (1988a) explanations, however, do not account for coexisting states of compression and tension, as the field data from many areas required (e.g., Alboran Sea; ..., 1989). In contrast, surge tectonics requires the simultaneous formation of side-by-side compressional and tensil regimes during tectogenesis. Table 2.1, based on random sampling of some recent literature, shows how widespread the idea of mantle diapirism and upwelling has become. More than 50% of the examples listed are alpinotype or germanotype foldbelts; the remainder are tensile belts. Our point is that, whereas mantle diapirism may have a place in the tensile regimes of plate tectonics, it cannot be accommodated in the compressional regimes.

2.3.3 MAGMA CHAMBER-RELATED PHENOMENA
 Lithosphere magma chambers and related asthenosphere upwellings form zones of reduced seismic velocity, the low-velocity zones of the literature. Commonly a large magma chamber forms close to the mantle-crust boundary, followed by the formation at still higher levels in the middle to upper crust of smaller magma chambers whose sizes decrease upward, thereby forming a "Christmas Tree" structure as described by Corry (1988) for sill complexes in the upper crust (see Fig. 2.8). The large magma chamber close to the mantle-crust boundary is pod-shaped (see Fig. 2.9), and is referred to in the literature by various names--lenses, lenticles, lozenges, pillows, rift pillows, pods, shear pods, anastomosing networks of shear zones, and so forth---terms that show the lack of knowledge of their origin(s). These lenses, for many years, have been termed layers of "anomalous upper mantle" or, conversely, "anomalous lower crust." Although they have been observed most commonly at the mantle-crust boundary, such lenses do occur in some tectonic belts in the middle to upper crust (..., 1989-1990; Figs. 2.10, 2.11).
 The lens at the mantle-crust boundary typically has a P-wave velocity in the 7.0-7.8 km/s range (..., 1959-1983). Many of them contain a low-velocity zone (5.4-6.6 km/s) near their centers (..., 1970-1979). Beneath continents and many parts of the ocean basins, these lenses are typically between 100 and 500 km wide, most commonly in the 150-250-km range (..., 1980-1983). Where not present at the mantle-crust boundary, they pinch out laterally into a thin but nearly omnipresent zone with a velocity range of 6.9 to 7.9 km/s (..., 1987-1989).
 An identical but much larger lens occupies the crust-mantle boundary zone beneath midocean ridges (..., 1959-1965), where they were first discovered by Revelle (1958). Here beneath the midocean ridges, the lenses are typically 1,000 to 3,000 km across and they occupy the full 65,000-km length of the midocean ridge system
 Because these lenses pinch out laterally from the centers of the midocean ridges, they were at first perceived as an obstacle to the newly formulated hypothesis of sea-floor spreading (..., 1961), but were soon provided with an explanation conforming to plate tectonic models. _____The problem, as it was perceived, was that, if the "anomalous mantle" lens formed at the midocean ridge crests (as it had to do, in sea-floor spreading), then some process had to remove the 7.0-7.8-km/s material as the oceanic crust moved away from the midocean ridge crest toward its laterally coeval and subparallel subduction zones. Two speculative solutions to the problem were suggested and, to the best of our knowledge, were accepted without benefit of additional research.
 The first solution was proposed by Drake and Nafe (1968, ...): "Velocity-depth data indicate that velocities in the range 7.2-7.7 km/s are almost completely absent in the deep ocean basins away from ridges or prominent seamounts and under the low-lying continental shields, but are present in all other regions to some degree. The material in this velocity range must be derived from the mantle but is of lower density than normal. If, as is suggested by the data, it is of a transient nature, its appearance and disappearance may be related to the changes in elevation associated with tectonic activity." Elsewhere in the same paper, Drake and Nafe (1968, ...) wrote that oceanic crustal layer 3 (the lowest ocean crustal layer which overlies the Moho-) "...would receive permanent additions of rock with the properties of gabbro, and a 7.2- to 7.7-km/sec layer would first develop and then vanish. In this view, the principal contribution of the 7.2- to 7.7-km/sec layer is to increase total thickness and, through isostatic adjustment, to increase surface elevation during the orogenic process, and then to disappear with an accompanying reduction in thickness and elevation."
 Referring to the 7.2- to 7.7-km/sec layer as low-velocity mantle, Vogt et al. (1969) wrote that, "The occurrence of low-velocity mantle under [the midocean ridge] crest could well be a steady-state phenomenon. That is, it may be constantly created under the axis and converted to normal mantle under the flanks" (..., 1969, ...). In further explanation, Vogt et al. (1969, ...) wrote that the low-velocity mantle "...under the ridge axis is most likely an ultrabasic crystal slush through which basaltic fluids must rise to feed the growing layers 2 and 3.... This slush then probably solidifies and becomes 'normal' mantle as it withdraws from the axis." This second explanation is no more satisfactory than that proposed by Drake and Nafe (1968).
 The problem has not been researched further, to the best of our knowledge, and remains unsolved. The problem is crucial, because these lenses are found under every type of tectonic belt. Under the continents, for example, long linear lenses of 7.2-7.8-km/s material underlie all rifts (..., 1983), all streamline (strike-slip) fault zones (..., 1989), and all foldbelts (..., 1968-1989). Under the ocean basins, identical lenses underlie the midocean ridges (..., 1959-1965), linear island and seamount chains (..., 1968), and other aseismic oceanic ridges (..., 1975). The lenses are a common denominator for all tectonic belts and, therefore, cannot be transient features, as maintained by Drake and Nafe (1968). Nor can the material that forms them become "normal" mantle as it withdraws from the axis of each tectonic belt, as suggested by Vogt et al. (1969). In plate tectonics, the midocean ridges are the only tectonic belts from which rock materials (i.e., the new crust formed at the axes of midocean ridges) can withdraw. If Vogt et al. (1969) are right, then a second explanation must be developed to explain the presence of identical lenses in other types of tectonic belts.
 In many foldbelts, the "anomalous" lenses have been deformed together with the shallower rocks (e.g., Figs. 2.13-2.15). Where a foldbelt has been found to be deformed bilaterally (i.e., the belt is bivergent), one side of the belt is said to have a zone of "backthrusts" (..., 1984-1986), although few of the "backthrusts" exhibit the criteria of backthrusts (..., 1951). In this work, we demonstrate that all foldbelts are bilateral (i.e., bivergent), an observation made long ago by Kober (1925), Vening Meinesz (1934), and many others. We call these bivergent foldbelts kobergens, a concept that we define and explain in detail in the following chapter. Examination of our many figures illustrating bivergent foldbelts reveals at once that such features combine the effects of compression and tension (Fig. 2.15). Along the two flanks of the foldbelts are folds, thrusts, and nappes whose vergence on one flank is the opposite of the on the other flank. Between the two flanks is a zone of tension. Thus compression and tension act together, side by side, in belts hundreds, even thousands, of kilometers long. Consequently, the seemingly contradictory evidence for stress regimes noted by workers in foldbelts (..., 1988a-1989) is not at all contradictory but is an inevitable consequence of tectogenesis. The literature on bivergent foldbelts dates at least to Suess (1885) and has increased steadily to the present (..., 1989).
« Last Edit: March 23, 2017, 01:34:41 pm by Admin »

Admin

  • Administrator
  • Full Member
  • *****
  • Posts: 174
    • View Profile
SURGE TECTONICS HIGHLIGHTS
« Reply #3 on: March 29, 2017, 09:31:27 pm »
SURGE TECTONICS
3.1 Introduction
_Surge tectonics is based on the concept that the lithosphere contains a worldwide  network of deformable magma chambers (surge channels) in which partial magma melt  is in motion (active surge channels) or was in motion at some time in the past  (inactive surge channels).
_The presence of surge channels means that all of the compressive stress in the  lithosphere is oriented at right angles to their walls. As this compressive stress  increases during a given geotectonic cycle, it eventually ruptures the channels  that are deformed bilaterally into kobergens (Fig. 2.15).
_Thus, bilaterally deformed foldbelts in surge-tectonics terminology are called  kobergens.
_Surge tectonics involves
1. contraction or cooling of the Earth
2. lateral flow of fluid, or semifluid, magma through a network of interconnected  magma channels in the lithosphere
3. Earth's rotation, which involves differential lag between the lithosphere and  the strictosphere and its effects, i.e. eastward shifts (Table 2.3)
=the strictosphere is the hard mantle beneath the asthenosphere and lower crust
._lithosphere compression caused by cooling propels the lateral flow of magma  through surge channels

ST_3.2.2 CONTINENTS HAVE DEEP ROOTS
_Contrary to general belief continental roots are fixed to the strictosphere [as  shown] by large and increasing volumes of data, including neodymium and strontium  studies of crustal rocks (..., 1979).

_the deep roots of continents are a major obstacle to any hypothesis requiring  continental movements (..., 1985-1990).
_deep roots are seen beneath part of all of the Earth's ancient cratons.
_In places, however, lenses of 7.0-7.8-km/s material containing low-velocity zones  (Fig. 3.5) are present (..., 1989).
_Such lenses containing low-velocity layers postdate the establishment of the deep  cratonic roots, as we show in subsequent sections.

_3.3.2 Contraction Skepticism
_3.3.3 Evidence For a Differentiated, Cooled Earth
_1. The Earth includes several concentric shells, which are explicable only if the  Earth differentiated efficiently and at a much higher temperature than today.
_2. The outermost of these shells may be the oceanic crust whose thickness ranges  from about 4-7 km.
<<contradicts sed strata & oceanization
_This crust is characterized by relatively constant thickness and fairly uniform  seismic properties.
_This uniformity is explained if the oceanic crust is the outermost of the Earth's  concentric shells.
_5. A convincing evidence that huge segments of the lithosphere have been and are  being engulfed by tangential compression is the existence of Verschluckungszonen  (engulfment zones)
_In places along such zones, whole metamorphic and igneous belts that are  characteristic of parts of a given foldbelt simply disappear for hundreds of  kilometers along strike
_Although [some] considered these features to be former subduction zones, this  interpretation is difficult to defend because all of these zones, regardless of  age, are near-vertical bodies (1) reach only the top or middle of the asthenosphere  (150 to 250 km deep) and (2) do not deviate more than 10 to 25 from the vertical  (..., 1983-1984).
_6. The antipodal positions of the continents and ocean basins (unlikely a matter  of chance) mean that Earth passed through a molten phase
_7. Theory (..., 1970) and laboratory experiment (..., 1956) showed that heated  spheres cool by rupture along great circles. Remnants of two such great circles (as  defined by hypocenters at the base of the asthenosphere) are active today: the  Circum-Pacific and Tethys-Mediterranean fold systems. The importance of Bucher's  (1956) experiment to contraction theory, in which he reproduced the great circles,  is little appreciated.

3.8 Evidence for the Existence of Surge Channels
3.8.1 SEISMIC-REFLECTION DATA
_As noted above, reflection-seismic techniques (...) have shown that the  continental crust of the upper lithosphere is divisible in a very general way into  an upper moderately reflective zone and a lower highly reflective zone (...).  Closer scrutiny of the newly-acquired data soon revealed the presence in the lower  crust of numerous cross-cutting and dipping events.
_When many of these cross-cutting events were preceived to be parts of lens-like  bodies, various names sprang up: .... Strictly nongenetic names include lenses,  lenticles, lozenges, and pods (...). Finlayson et al. (1989) found that the lenses  have P-wave velocities of 7.0-7.8 km/s, commonly with a low-velocity zone in their  middle.
_Thus we equate the lenses with the pods of "anomalous lower crust" and "anomalous  upper mantle" that we discussed in a preceding section. Klemperer (1987) noted that  many of the lenses are belts of high heat flow. Hyndman and Klemperer (1989)  observed that the lenses generally have very high electrical conductivity.
_Meyerhoff et al. (1992b) discovered that there are two types of undeformed  reflective lenses, and that many of these lenses have been severely tectonized. The  first type of lens is transparent in the middle (Fig. 3.29); the second type is  reflective throughout (Fig. 2.11). Tectonized lenses also may have transparent  interiors, or parts of interiors; many, however, are reflective throughout (Fig.  3.21). Where transparent zones are present (Fig. 3.20), bands of high heat flow,  bands of microearthquakes, belts of high conductivity, and bands of faults,  fractures, and fissures are present. Where a transparent layer is not present, high  heat flow and conductivity, however, are commonly still present. Meyerhoff et al.  (1992b) also found that lenses with transparent interiors are younger than those  without transparent interiors; moreover, there is a complete spectrum of lenses  from those with wholly transparent interiors to those without.

_The best explanations of thes observations are that (1) the lenses with  transparent interiors are active surge channels with a low-velocity zone sandwiched  between two levels of 7.0 to 7.8 km/s material; (2) the lenses with reflective  interiors are former surge channels now cooled and consisting wholly of 7.0 to 7.8  km/s material; and (3) the tectonized lenses are either active or former surge  channels since converted into kobergens by tectogenesis.

_3.8.3 SEISMOTOMOGRAPHIC DATA
_Seismotomographic data, wherever detialed studies have been made, indicate that  the lenses seen in seismic-refraction and seismic-reflection studies form an  interconnected, reticulate network in the lithosphere. Although only one highly  detailed seismotomographic study has been made on a continental scale---this in  China---it leaves no room for doubt that the 7.0-7.8-km/s lenses with transparent  interiors and the seismotomographically detected low-velocity channels in the  lithosphere are one and the same....
_Using seismotomographic techniques, it will be possible to map active surge  channels over the world with comparative ease.

_3.8.4 SURFACE-GEOLOGICAL DATA
_Direct evidence for the existence of surge channels comes from tectonic belts  themselves, and from one type of magma flood province. The latter include rift  igneous rocks that crop out nearly continuously for their full lengths. Examples  include the rhyodactic Sierra Madre Occidental-Sierra Madre del Sur extrusive and  intrusive belt of Mexico and Guatemala, some 2,400 km long; the 1,600-km-long  Sierra Nevada-Baja California batholith belt; the 4,000-km+ batholith and andesite  belt of the Andes south of the equator; the 4,000-km-long Okhotsk-Chukotka silicic  volcanic belt; the 5,800-km-long Wrangellia linear basaltic province extending from  eastern Alaska to Oregon, which erupted in less than 5 Ma; and many other similar  continental magma belts. The ocean basins are equally replete with them, ranging  from the 60,000-km-long midocean ridge system through the 5,800-km-long Hawaiian-  Emperor island and seamount chain to many similar belts of shorter lengths.  Geochemical studies also show that most of these belts are interconnected. Another  linear flood-basalt belt, which has been studied only relatively recently, is the  subsurface Mid-Continent province that extends 2,400 km from Kansas through the  Great Lakes to Ohio (Figs. 3.23, 3.24).

_3.8.5 OTHER DATA
_Other data mentioned in the preceding sections corroborate the interconnection of  active surge channels. One of these is the coincidence of the 7.0-7.8-km/s lenses  of the active surge channels (Figs. 2.9, 2.31, 3.6, 3.9, 3.14, 3.20) with the belts  of high heat flow (Fig. 2.26) and with belts of microseismicity. Both the presence  of high heat flow and microseismicity indicate that magma is moving within active  surge channels.

_However, an even more dramatic example is the June 28, 1992, Landers, California,  earthquake-related activity shown on Figure 3.25. This figure shows that the 7.5-  magnitude earthquake was strong enough to affect areas up to 1,250 km from the  epicenter (...) and provides an exampole of Pascal's Law in action. Given the  importance of Pascal's Law in surge-channel systems, the fact should be noted that  the viscosity of the magma in the surge channels affected by the Landers event is  sufficiently low that, when the stress was applied at a single hypocentral point  (Landers), the effects could still be transmitted for 1,250 km!

_3.9 Geometry of Surge Channels
_3.9.1 SURGE-CHANNEL CROSS SECTION
_Corry (1988) published the "Christmas Tree" model shown in Figure 2.8; Bridgwater  et al. (1974) published the more complex model shown in Figure 3.26. Either of  these could be cross sections of surge channels. Both are multitiered with one or  more magma chambers above the main chamber.

_3.9.2 SURGE-CHANNEL SURFACE EXPRESSION
_Study of Figures 2.8, 2.9, 2.11, 2.31, 3.6, 3.9, 3.13, 3.14, 3.20, 3.23 and 3.24  might lead one to believe that surge channels are everywhere fairly simple  structures expressed at the surface by a single belt of earthquake foci, high heat  flow, bands of faults-fractures-fissures (streamlines), and related phenomena  which, during tectogenesis, deform into a single kobergen. Although this simple  picture is true of many kobergens, it is not true of all. Study of Figures 3.26 and  3.27 suggests that, during tectogenesis of the surge-channel complexes shown on  these figures, two or more parallel kobergens may exist at the surface. Such a  complex surface expression is in fact quite common. Well-documented examples are  found in the Western Cordillera of North America, the Mediterranean-Tethys orogenic  belt (including the Qinghai-Tibet Plateau), and the Andes, inter alia. Within the  Western Cordillera, the Qinghai-Tibet Plateau, and the Andes, we have found four or  more parallel kobergens side by side at the surface as documented and illustrated  by Meyerhoff et al. (1992b).

3.9.3 ROLE OF THE MOHOROVIC DISCONTINUITY
The principal forces acting on the lithosphere are compression, rotation, and  gravity.

Thus, when the postulated tholeiitic picrite magma reachs the Moho- (i.e., the zone  between 8.0-km/s mantle below and 6.6-km/s above), it has reached its level of  neutral buoyancy and spreads laterally. Under the proper conditions---abundant  magma supply and favorable crustal structure---a surge channel can form. We suggest  the possibility that the entire 7.0-7.8-km/s layer may have formed in this way. In  support of this suggestion, we note that the main channel of every surge channel  studied, from the Archean to the Cenozoic, is located precisely at the surface of  the Moho-. This indicates that the discontinuity is very ancient, perhaps as old as  the Earth itself. This fact and the great difference in P-wave ==velicities above and  below the Moho- surface suggest in turn that the discontinuity originated during  the initial cooling of the Earth. Hence, Mooney and Meissner's (1992) "transition  zone" was the level of neutral buoyancy at the time the 7.0-7.8-km/s material was  emplaced.

?>The formation of the Christmas-tree-like structures (Figs. 2.8, 3.26) at the  Moho- is simply an extension of the larger scale process of magma transfer from the  asthenosphere to the discontinuity. Once surge channels are established at the  discontinuity, the same processes take over that brought the magma to the  discontinuity in the first place, specifically, magma differentiation in the  channels and the Peach-Kohler climb force (...). After lighter magmas have formed  by differentiation and related processes, they rise to their own neutral buoyancy  levels, forming channels above the main surge channel (Figs. 3.23, 3.27).

SURGE TECTONICS
Chapter 6 Magma Floods, Flood Basalts, and Surge Tectonics
_6.1.1 SIGNIFICANCE OF FLOOD BASALTS
_Some 63% of the ocean basins are covered with flood basalts. At least 5% of the  continents are likewise covered with flood basalts. Thus 68%---a minimum figure---  of the Earth's surface is covered with these basaltic rocks. Flood basalts, then,  are not the oddities that many suppose them to be. In spite of this, they receive  little attention among the scientific community.
_ Engel et al. (1965) long ago demonstrated that deep ocean-floor tholeiitic  basalts are the oceanic equivalent of the continental flood basalts. The Basalt  Volcanism Study Project (1981) differentiated between the continental flood basalts  and "ocean-floor basalts," while recognizing that the principal differences were  the abundance of minor and rare-earth elements. Press and Siever (1974...)  recognized the fact that the ocean-floor basalts and continental flood basalts are  nearly the same, and that their differences are explained readily by contamination  in the continental crustal setting.

_6.1.2 CLASSIFICATION
_Continental flood-basalt provinces are geometrically of two types. The first is  broadly ovate, or even round, with the maximum diameter ranging from about 500 km  (Columbia River Basalt) to more than 2,500 km (Siberian Traps). The second is  distinctly linear, with a width of 100 to 200 km and lengths up to and even  exceeding 3,000 km.
_ Tectonism and metamorphism can severely disrupt any flood-basalt province after  its formation. For example, ... the Antrim Plateau Volcanics of northern Australia  ... parts ... have been removed by erosion. ... Similarly, only very scattered,  strongly flooded, and metamorphosed remains of the Willouran Mafic rocks are  preserved in ... South Australia, but their distribution shows that [it] is a  linear flood-basalt province.

_6.6 Flood-Basalt Provinces and Frequency in Geologic Time
As we observed near the beginning of this chapter, the commonly used textbooks of  physical geology, structural geology, and geotectonics rarely list more than 10 to  20 flood-basalt provinces. However, the magnificent review of basalts by the  participants in the Basalt Volcanism Study Project (1981) mentions or figures not  less than 56 flood-basalt provinces and 45 additional provinces of dike swarms  which the project participants thought might have fed flood-basalt provinces that  have since been removed by erosion.
_ Yoder (1988, ...) wrote that "Great basaltic 'floods' have appeared on the  continents throughout geologic time (Table 1)," but showed on his Table 1 none  older than 1,200+/- 50 Ma. He also ... made it clear that he regards midocean-ridge  and other oceanic basalts as flood basalts, as have a number of earlier workers  (..., 1974). We concur absolutely with their interpretation. We also concur with  the participants of the Basalt Volcanism Study Project (1981) that evidence of the  existence of flood provinces extends back in time to at least 3,760 Ma, and very  likely to the Earth's earliest (but nowhere preserved) history.

_6.7 Non-Basalt Flood Volcanism in Flood-Basalt Provinces
The bimodal nature of many flood-basalt provinces has been known and stressed for  many years (..., 1981). Time seems not to be a major factor (the idea being that,  the longer an underlying magma chamber is present, the more the magma will interact  with the continental crust above it). The most important factor may be the crustal  stress state.
_ We believe that the evidence from these examples demonstrates convincingly that  there is a complete gradation from all-basalt and basaltic andesite flood provinces  to bimodal provinces containing mainly rhyolite and ignimbrite. Hence, there are  basalt floods and rhyolite floods.
_ ... The volumetric predominance of these ash-flow tuffs has led to recognition of  the [Sierra Madre Occidental] as the world's largest rhyolite-dominated volcanic  province" (Fig. 6.28).
_ Thus, from 38 Ma until 17 Ma, a truly bimodal column of extrusive rocks  accumulated in northern Mexico and adjoining parts of the United States, with  rhyolite at one end, basaltic andesite at the other, and very little rock of  intermediate compositions. ... [Skipping remainder of paragraph]
_ We believe that these basalts of the "southern cordilleran basaltic andesite"  suite are flood basalts. And if they are flood basalts, then we have demonstrated  that the same mechanism that leads to continental and oceanic basalt outpourings  also produces the "orogenic andesite suite".
_ The Okhotsk-Chukotka Volcanic Belt, a linear belt of Cretaceous volcanics, is  similar to the Sierra Madre Occidental. It extends 3,000 km from the mouth of Uda  Bay (northwestern Sea of Okhotsk) to the Bering Sea almost at St. Lawrence Island.  It seems to have every type of volcanic from andesitic through rhyolite. Basalts  are scarce. Soviet geologists either ignore it or say that it is the remnant of a  volcanic arc.
 
_6.9 Surge-Tectonics Origin of Magma Floods
In the preceding pages we have referred to the presence of several flood-basalt  provinces around the world, and have shown that some flood provinces include large  volumes of silicic rocks, usually rhyolite and/or dacite. We have also shown by the  northern Mexican example that flood basalts can interfinger with the andesite  orogenic suite.
_The available evidence has led us to the conclusion that the same mechanism causes  volcanism in the midocean ridges, linear island and seamount chains, oceanic  plateaus, island arcs, and continental interiors. We next attempt an explanation of  our conclusion.
_ Many attempts have been made to explain flood volcanism in the framework of the  plate-tectonics hypothesis. The two principal explanations involve (1) hot spots,  or mantle plumes and (2) an extraterrestrial cause (e.g., an asteroid impact).
_ Extraterrestrial causes have been proposed by Alt et al. (1988), who applied this  hypothesis to the Columbia River flood-basalt province. A major problem with this  concept is that it does not explain linear flood-basalt provinces such as the  Keweenawan (Mid-Continent) rift and Wrangellia. Furthermore, Mitchell and Widdowson  (1991) pointed out that impact and shock phenomena should be present in the area  surrounding the Columbia River province if it resulted from extraterrestrial  action, but they are entirley absent.
_ As we noted in Chapters 3 and 4, Mooney et al. (1983) observed that all active  rifts studied by them have an anomalous lower crust with P-wave velocities in the  7.0 to 7.7 km/s range (Fig. 6.36). [Others] obtained the identical result.... Fuchs  (1974) believed that this pod of anomalous lower crustal material houses the  mechanism that causes rifting. It is interesting to note that all midocean ridges  have a pod of 7.0-7.7 km/s as well (..., 1959-1965). (Furthermore, each island arc  and foldbelt also has a pod of 7.0-7.7 km/s material that pinches out from the  center of the arc or foldbelt (..., 1987-1989 ... for the Japan arc ... [and] for  the Appalachians.)
_ Figure 3.6 is a cross section across the Baykal rift, from Krylov et al. (1979)  and Sychev (1985). Years of refraction work have shown [that] Lake Baykal is  underlain at about 32 km by a pod that is connected to the deeper asthenosphere.  The shallow pod contains a low-velocity zone that presumably is a partial melt. The  pod extends the full length of the rift. It is, in short, a channel containing  partly molten magma and an excellent example of one of our surge channels. Were it  to burst, we believe that it would produce another linear flood-basalt province.
_ According to our surge tectonic hypothesis, magma in surge channels moves both  vertically and horizontally. When two surge channels come in contact, their magmas  join together. If they are oriented at an appreciable angle to one another, we  believe that the result is a "collision". These5 "collisions" are responsible for  the eruption of round or ovate flood-basalt provinces worldwide.

CHAPTER 7
CONCLUSIONS
We have proposed a new hypothesis of global tectonics in this book, one that is  different and will be considered unorthodox by many scientists and non-scientists  alike. However, we believe that current tectonic hypotheses cannot adequately  explain the increasing volume of data being collected by both old and new  technologies. We believe that the hypothesis of surge tectonics does explain these  data sets, in a way that is simple and more accurate.
 The major points of the surge-tectonics hypothesis can be summarized as follows:
 1. All linear to curvilinear mesoscopic and megascopic structures and landforms  observed on Earth (and similar features seen on Mars, Venus, and the moons of  Jupiter, Saturn and Uranus), and all magmatic phenomena are generated, directly or  indirectly, by surge channels. The surge channel is the common denominator of  geology, geophysics, and geochemistry.
 2. Surge channels formed and continue to form an interconnected worldwide network  in the lithosphere. They contain fluid to semifluid magma, or mush, differentiated  from the Earth's asthenosphere by the cooling of the Earth. All newly  differentiated magma in the asthenosphere must rise into the lithosphere. The newly  formed magma has a lower density and therefore, is gravitationally unstable in the  asthenosphere. It rises in response to the Peach-Kohler climb force to its level of  neutral buoyancy (that is, to form a surge channel).
<<So no vertical channels are needed
 3. Lateral movements in the Earth's upper layers are a response to the Earth's  rotation. Differential lag between the more rigid lithosphere above and the (more)  fluid asthenosphere below causes the fluid, or mushy, materials to move relatively  eastward.
 4. Surge channels are alternately filled and emptied. A complete cycle of filling  and emptying is a geotectonic cycle.
<<I rather think they don't empty; they solidify
The geotectonic cycle takes place along this sequence of events:
 a. Contraction of the strictosphere is always underway, because the Earth is  cooling;
<<...with minor exceptions due to major impacts
 b. The overlying lithosphere, which is already cool, does not contract, but  adjusts its basal circumference to the upper surface of the shrinking strictosphere  by large-scale thrusting along lithosphere Benioff zones and normal-type faulting  along the strictosphere Benioff zones.
<<Benioff zones were caused by recent impacts, so little shrinkage has occurred  since then, though major local and sometimes minor global effects have likely  occurred
 c. Thrusting of the lithosphere is not a continuous process, but occurs when the  lithosphere's underlying dynamic support fails. When the weight of the lithosphere  overcomes combined resistance of the asthenosphere and Benioff zone friction,  lithosphere collapse begins in a episodic fashion. Hence, tectogenesis is episodic.
<<Such collapse is likely frequent and minor, due to daily electrified tides
 d. During anorogenic intervals between lithosphere collapses, the asthenosphere  volume increases slowly as the strictosphere radius decreases and decompression of  the asthenosphere begins.
 e. Decompression is accompanied by rising temperature, increased magma generation,  and lowered viscosity in the asthenosphere, which gradually weakens during the time  intervals between collapses.
 f. During lithosphere collapse into the asthenosphere, the continentward (hanging  wall) sides of the lithosphere Benioff zones override (obduct) the ocean floor. The  entire lithosphere buckles, fractures, and founders. Enormous compressive stresses  are created in the lithosphere.
<<Again, the stresses should be minor, since they're frequent
 g. When the lithosphere collapses into the asthenosphere, the asthenosphere-  derived magma in the surge channels begins to surge intensely. Where volume of  magma in the channels exceeds volumetric capacity, and when compression in the  lithosphere exceeds the strength of the lithosphere that directly overlies the  surge channels, the surge-channel roofs rupture along the cracks that comprise the  fault-fracture-fissure system generated before the rupture. Rupture is bivergent  and forms continental rifts, foldbelts, strike-slip zones, and midocean rifts. We  call such bilaterally deformed belts kobergens.
<<This all occurred during the relatively recent major impact event
 h. Once tectogenesis is completed, another geotectonic cycle or subcycle sets in,  commonly within the same belt.
<<Surge channels likely only form during major impact events
 5. Movement in the surge channel during the taphrogenic phase of the geotectonic  cycle is parallel with the channel. It is also very slow, not exceeding a few  centimeters per year. Flow at the surge-channel walls is laminar as evidenced by  the channel-parallel faults, fractures, and fissures observed at the Earth's  surface (Stoke's Law). Such flow also produced the more or less regular  segmentation observed in tectonic belts.
 6. Tectogenesis has many styles. Each reflects the rigidity and thickness of the  overlying lithosphere. In opcean basins where the lithosphere is thinnest, massive  basalt flooding occurs. At ocean-continent transitions, eugeosynclines with  alpinotype tectogenesis form. In continental interiors where the lithosphere is  thicker, either germanotype foldbelts or continental rifts are created.
 7. During the geotectonic cycle, and within the eugeosynclinal regime, the central  core (crest of the surge channel) evolves from a rift basin to a tightly compressed  slpinotype foldbelt. Thus a rift basin up to several hundred kilometers wide  narrows through time until it is a zone no more than a few kilometers wide that is  occupied by a streamline (strike-slip) fault zone (e.g. the San Andreas fault).  Then as compression takes over and dominates the full width of the surge-channel  crest, the streamline fault zone is distorted, surge channel still contains any  void spaces, the overlying rocks may collapse into it, and through this process of  Verschluckung (engulgment) become a Verschluckungzone.
 8. The Earth above the strictosphere resembles a giant hydraulic press that  behaves according to Pascal's Law. A hydraulic press consists of a containment  vessel, fluid in that vessel, and a switch or trigger mechanism. In the case of the  Earth, the containment vessel is the interconnected surge-channel system; the fluid  is the magma in the channels; and the trigger mechanism is worldwide lithosphere  collapse into the asthenosphere when that body becomes too weak to sustain the  lithosphere dynamically. Thus tectogenesis may be regarded as surge-channel  response to Pascal's Law.
 9. Surge channels, active or inactive, underlie nearly every major feature of the  Earth's surface, including all rifts, foldbelts, metamorphic belts, and strike-slip  zones. These belts are roughly bisymmetrical, have linear surface swaths of faults,  fractures, and fissures, and belt-parallel stretching lineations. Aligned plutons,  ophiolites, melange belts, volcanic centers, kimberlite dikes, diatremes, ring  structures and mineral belts are characteristic. Zoned metamorphic belts are also  characteristic. In some areas, linear river valleys, flood basalts, and/or vortex  structures may be present. A lens of 7.8-7.0 km/s material always underlies the  belt.
 10. Active surge channels are most easily recognized by the presence of high heat  flow (Fig. 2.26), microseismicity, lines of thermal springs, small negative Bouguer  gravity anomalies, and a 7.8-7.0 km/s lens of material that is transparent in the  center or throughout.
 11. Inactive surge channels possess a linear positive magnetic anomaly, a linear  Bouguer positive gravity anomaly, and a linear, lens-shaped pod of 7.8-7.0 km/s  material that is reflective throughout.
 12. A surge-tectonics approach to geodynamics provides a new means for determining  the origin of the Earth's features and their evolution through time, for analyzing  regions prone to earthquakes and volcanism, and for predicting the location and  formation of mineral deposits throughout the globe.