Author Topic: MF 2/24-3/29  (Read 359 times)

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Re: MF 3/25-3/26
« on: March 26, 2017, 12:31:25 pm »
MF: Sat, March 25, 2017 10:31 PM
- In SD, all the mountain ranges were raised quickly by compressing continental crust.  Bending crust to form the Andes, the Rockies, the Himalayas, the Alps, etc. would activate the piezoelectric effect on a large scale, I would think.
- My website addresses cratons and continental roots on this page  http://www.newgeology.us/presentation41.html  from which excerpts are written below (quotes are sourced):
- Research is challenging the neat definitions of cratons.  "Generalizations of Archean cratons do not capture the variability between cratonic regions or the complexity within a single craton assemblage.  For example, not every craton is underlain by high-velocity roots, and the deepest roots do not always occur under Archean cratons."
- "Most geochemical characteristics of lithospheric mantle peridotites are most easily reconciled with a relatively low-pressure melting origin, albeit in the case of cratonic peridotites one taken to very high degrees of melting."
- "The geochemical evidence is consistent with the hypothesis that the roots are the residue of partial melting".
- "The North Atlantic Cratonic sub-continental lithospheric mantle and all other cratonic continental mantle roots studied here are the product of extreme melt extraction at relatively shallow depths (~90 km or less)."
- "The boundary between the lower crust and mantle may be open.  When magmatic or tectonic activity destabilizes and deforms the lithosphere, ultramafic cumulates tend to move downward.  This 'foundering' occurs during orogeny, rifting, and continental breakup."
- "Intracrustal melting produces granitoid magmas and dense mafic restites that return to the mantle.  The foundering of mafic restites from granitoid magmas is likely a major process."
- High temperature is required for dense lower crustal mafic-ultramafic cumulates to sink into the mantle.  Results of experiments show that "an initial strain rate can significantly reduce the Moho temperature required for an instability to develop."  "Instability times decrease because the initial effective viscosity is lower."
- In the Shock Dynamics model, lateral stress (pivoting or compression followed by extension) melted continental crust, and the residue foundered, producing a mantle root.  Melting and founder of dense residue must have occurred after the motion of the continents (which lasted only about 26 hours) had ceased.

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LK: Sun, March 26, 12:22PM
- That's great, Mike. I did a search on your site, but I didn't persist long enough to find that page about cratons and continental roots. It sounds like my suspicion about how the roots formed was correct. Now if we find which continents have roots and which don't, that will hopefully confirm SD further.
- I agree that a lot of piezoelectricity likely occurred during continental sliding and orogeny etc, but I was thinking it probably didn't contribute much to the SD and continental drift events. It's hard for me to distinguish in my mind between piezoelectricity, telluric currents, electron flow from tidal forces acting on current-free double-layers, and shock waves, etc. A few months ago I showed you an article about the shock effects of the Chixulub impact and you said you had read the same findings from last summer, I think. It talked about how the pressure from the impact shock waves caused solid rock to melt briefly and thus bend, similar to the bending seen in foldbelts or orogeny, I think. I don't think piezoelectricity was mentioned, but obviously it would have been involved, but I don't understand such things well enough to figure out exactly what it would have done. The momentum of an impact would do a lot. The shockwaves would cause brief melting and bending. I guess the piezoelectricity would be part of the ionization and melting. Do you think we should try to understand more thoroughly how piezoelectricity was involved?
- Another matter that seems important is to account for the surge channels that apparently exist in many locations, such as under ocean ridges, mountain ranges, foldbelts etc. Have you read what I copied from the Surge Tectonics book? They seem to detect the channels as lenses. If a lens has the same velocity P-waves all the way through, they call them inactive. If they had I think slower waves in the center, they call them active. That's if I understood what I read correctly. If their identification of active surge channels is correct, then it seems that the channels must have formed during the SD and continental drift events. Do you have an idea how molten channels would have formed in such locations during those events and why many of them would remain active/molten? I think Charles' model can help explain why they would remain active, i.e. because of tidal forces keeping the channels electrified each day. The channels under ocean ridges are said to be a few hundred km wide, but those within continents are much narrower.

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Sunday, March 26, 2017 7:26 PM
- Hi Lloyd, Continental "roots" are associated with cratons.  Radiometric dating of cratons puts them in particular eons.  Oldest to recent they are: archon, proton, tecton (see attached image).
- Meteorite shock effects should be separate from piezoelectric effects.  In the former, the crust is temporarily fluidized, which is confirmed by the report you mention about Chicxulub.  In the latter, the combination of momentum and sudden braking or collision (Himalayas) result in brittle folding/breaking.  My guess is that this would influence the geomagnetic field and magnetic striping that reflects alternating polarization of re-worked oceanic crust.

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LK: Thu, 3/29/17 9:50PM
- In the quote below from the book, Surge Tectonics, you can see they say the surge channels form at the top of the Moho.
- Here from the book is a Surge Channels Map I found online:
http://www.huttoncommentaries.com/images/ECNews/HeatFlow/WorldHeatFlowMap750.jpg
- The Webpage which seems religious is: http://www.huttoncommentaries.com/article.php?a_id=93
- They say the surge channels are within those warm bands. Many are said to be active channels and some are inactive, which I think means solidified.
- 3.9.3 ROLE OF THE MOHOROVIC DISCONTINUITY
Thus, when the postulated tholeiitic picrite magma reachs the Moho- (... between  8.0-km/s ... and 6.6-km/s ...), 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 velocities above and below the  Moho- surface suggest in turn that the discontinuity originated during the initial  cooling of the Earth.
- Here's a quote from the Conclusions section of the book.
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.
- QUESTION #1: Does it make sense to you that these magma "surge" channels would have formed at the top of the Moho under those many belts, bands etc? My guess is yes, starting during the SD event.  I wonder if the folding, rifting, fracturing etc caused the channels, instead of vice versa. Hmm?
- Here's a webpage of Pratt's on oceanization: http://davidpratt.info/sunken.htm
- Here's a map from there: http://davidpratt.info/earth/fig10.jpg
- The caption says Figure 13. Worldwide distribution of oceanic plateaus (black)
- The article says those locations on the seafloors have granite or continental rock. They think it means those are former continental areas and that there was no continental drift.
- QUESTION #2: How do you think that is best explained?
- I was surprised to see that Pratt seems to believe in Theosophy, which also seems to be his reason for having interest in geology.
- I posted the main points of the Surge Tectonics book on the forum at:
http://funday.createaforum.com/mike-messages/s/msg184/#msg184
- So it's a quicker read now.
« Last Edit: March 29, 2017, 09:55:54 pm by Admin »