CompuServe Messages

Doug >>This underlayer is not the seafloor from oceans surrounding colliding continents – I am talking about _directly_ under the collision, where the lithosphere is also converging. Since the lithosphere is comparable in mass to the continents, and since it is denser and closer to the "escape hatch", it would be no surprise if the lithosphere from one of the plates took a dive even if the colliding continents on top do not.<< I see the entire continental crust as about 5 miles thick on top of a base that is more like 10 or 12 miles thick. I don't see this subducting with the relative forces that may exist. But even if I simulate it it doesn't want to keep going down after it softens up. >>I am saying the seafloor south of India might have started subducting (but I do not see that it has), and may yet start subducting (it is still early in that particular collision, as I said) near the coast of India. Continents in collision are too light to "want" to subduct, but let a following seafloor be confronted with the choice of crumpling and subducting, it is likelier to choose the latter.<< I would think it would crumble like ice in front of an ice breaker. >> Once ocean crust is old enough to be cooler and denser than the mantle, it is just looking for any excuse to subduct.<< If it floats as a cold solid it would surely float as it reheated. >> One caveat – if the pull that brought the continents together has ceased during the collision, there is less incentive for trailing seafloor to dive.<< I agree there is no incentive. >>You were just expressing surprise at continents crumplng in slow plate collisions, implying they should be ultimately rigid. They are not, as I have explained, but there is some rigidity that _might_ allow the pressure to be released at some remote place from the collision site in some cases. This does not seem to be the case where the Himalayas are concerned.<< True …I am not surprised that the folding can occur…it apparently has…my surprise is that the ocean plate on the opposite side would buckle before the ten times stronger continent would unless the speeds take advantage of the inertia. >>If the undercarriage of a car crumples, why shouldn't the body also crumple? If the bumper crumples, the rest may or may not crumple – it all depends on the force and angle of collision, the point(s) of impact, and the construction of the car.<< I would…my point or what I tried to question was if the craton can adjust its bonds and flow why doesn't the upper crust do the same instead of folding? >>Whaddaya mean "we"?<< The agreements of which there have been many is the we. >> You are the one asserting any collisions took place within days, and trying to claim solid rock cannot bend/fold/crumple without melting or faulting even on the long time scales of plate tectonics.<< I have not claimed that rock cannot bend and fold without melting. It definitely has done this. >> In your short time scale, your own assertions become correct – I very much doubt solid rock can fold so much within a week without very obvious melting and/or faulting.<< well it is very faulted, crumbled and broken so that happened. >>Seafloor might crumple if compressed, but as noted above subduction is more to be expected. If it crumpled, I do not expect the evidence to last long. Continental mountains can force down "roots" of light rock that will buoy the mountains up until the mountains erode.<< This process of floating would create a constant height..as it eroded the area would rise upward and so maintain its height. >> Seafloor material is already too heavy (except the youngest seafloor) to "float", and I expect it would just sink again soon after being uplifted, if indeed it does not all fold downwards instead of upwards. Any projection deeper into the lithosphre may be subject to being "dissolved" by that lithosphere (since it closely resembles the lithosphere in composition, or seemingly more likely, to starting a subduction.<< If it is heavier than the material then why doesn't it just sink downward? >>The old continental craton edges would have met underneath what is now the Appalachians; burying the best evidence under mountains seems a good enough disguise for me. The only thing that was surprising me in this matter was a possible hint that the eastern seaboard did _not_ come from Africa, which proved not to be an intended implication.<< If the east and west sides of the App. Mts. were different sections of crust it would go 15 miles deep or more..I would expect to see remnants of the crack…and how did they get welded together so well? >>Don's mention of seafloor chunks caught up in the Green Mts. is probably about as much as one gets in the way of direct evidence for an earlier coastline thereabouts.<< thats a start >>He listed some fossil-bearing formations that seem to bear out my "prediction", provided they are old enough; it seems there is better fossil evidence for some coastal exchanges between N. America and Europe. It seems we traded Scotland for coast from east Newfoundland south to maybe RI; they tried to run off with Greenland also, but got caught.<< I say they were all together also…. with Greenland in between. Greenland looks like it drifted north while Iceland drifted south. The gap at the top of N. America could be closed as well as the whole Atlantic gap if these two motions occurred. Kamron