CompuServe Messages

Hi, Kamron– First, I will respond to your message in the "All" thread, since this is a better place. Then I will respond to the your message in this thread. >> I have a major problem with the continent compressing though. I see continental collisions as resembling car collisions. A light impact just crumples the bumper (shoves the sediments and older-rifting detritus on from the continental margins up on top). A heavier impact crumples the whole front end of the car (including the continental craton). Granite is no more ultimately rigid than basalt or any other rock. Rigidity is relative, as we have discussed before, and looks different in geological time frames when there is enough time to push solids along cleavage planes (like slowly but surely pushing those magnet-studded boards one space at a time). In human time frames, there is time only to push them hard so they shatter or melt (if you are in too much of a rush, you can only kick the boards apart or rip the magnets loose), so granite appears utterly rigid. It is more rigid than the deep mantle, but not absolutely rigid – if it were, there would be no granitic gneiss. >> It would bulge downward to match the upward motion. But why would this occur rather than the thin ocean basin give way and buckle up? We were talking about _continents_ colliding; how did the ocean floor get involved? There may be a seafloor-like underlayer to the colliding continents, which along with lithosphere may still be subducting out from under the collision point to keep pulling the continents together even after first impact; I gather this has been proposed in the Himalayas case. The ocean floor that was following the colliding continents may start subducting at the outer edges of both continents, but only after some of the impact has been absorbed. >> Slow motion would absorb and dissipate the heat… Is this supposed to mitigate the impact? >> …and transmit the pressures to the other side better than a rapid event where the enormous inertias would help create the upthrusts. Transmitting pressures to the other side is what the collision-crumpling is all about. Slowness might allow the pressures to be transmitted back away from the collision zone, so the crumpling might be allowed elsewhere. Indeed, I expect subduction and compression at the far sides of the continents in some cases. >>it appears like the results were caused by a rapid event rather than a slow steady process But rapidity would not allow time for smooth deformation of solid rock – it would all have to be brittle breakage or liquefaction. Signs of faults and melting appear to be much too modest where the Himalayas and other fold mountains are concerned. >> If there is no real speed then the inertia required to smash and compress is not there. There is less inertia, but still a lot. And as noted above there are likely forces still being applied while the collision is underway. Indeed, I have heard that the Himalayas have been measured as still rising, though I cannot recall where. Your way has _too much_ inertia given the mind-staggering masses involved; again, fault blocks rather than folds would be expected, if not a total meltdown – which we do not see. >> There is an excellent match between the east coast of N. America and the northern part of the eastern African Coast. As the cookie matches the dough mat it was cut from, so do the modern coasts match because the mid-Atlantic ridge cut them from one supercontinent. The coasts that collided to form the Appalachians may not have been such a good fit, and may have needed a lot of jamming together. >> What evidence is there that this eastern US coast was separated from the the rest of the Continent? I am not familiar with this case. I dimly remember something about some seafloor-rock trapped in the Appalachians. If there are pre-Carbonifereous fossils east of the Appalachians, I expect them to match African counterparts better than other N. American. Note that I am not really talking about the entire Appalachians; I think parts, like the Adirondacks (?) came from different events. –Doug