CompuServe Messages

Hi, Kamron– >> Looking at the point at the top of the Antarctic plate it has a spreading rate along each side..picture the triangle …it would really move sort of straight down towards the pole here as a result of the two motions leaving each of the sides motion in reference to the adjoining plates north of it.. would need to slide along the mid ocean ridge. That is what I said, there may be sliding along the southwest Indian ridge, which in any case is not spreading fast, and/or sliding along those angled transform faults across that ridge. The Antarctic plate appears to me to be moving mostly parallel to the southwest Indian ridge, which leaves me seeing no problem. >> there is no evidence of sliding along the other interface with the australian ridge. I do not need or want such sliding; I expect Antarctica is moving pretty close to directly away from Australia. With no sliding along ridges except in the southwest Indian, I expect the others to have perpendicular transform faults, which they more or less do. >> The shift faults would not line up like they do I assume the northward movement of Africa since the S. Atlantic opened has been modest compared to the rate of east-west spreading, hence the predominantly east-west transform faults on the east-west ridges. Africa may have stopped all northward motion for all I know. >> the australian arc converges at borneo Toward Borneo maybe, but all the action is in the subduction zones surrounding Indonesia + Phillipines. The north-moving Australian plate hits the Asian plate and subducts at the generally east-west Java trench; the generally east-west motions of the Asian and Pacific plates meet at generally north-south trenches east of Indonesia+Phillipines. For all I know, there may be weaknesses in our understanding of some of the details at many points; maybe 10-20% of the puzzle pieces have not been fit into plate tectonics yet, and they may hold a few surprises. But with 80-90% of the pieces in place, fitting together and forming a sensible big picture, I am confident the missing pieces will be found and placed. The theory may take some revisions; Newton's physics was overthrown by both relativity and quantum mechanics in turn, but it works so well in normal realms that it is still used, and the revisions continue to use large parts of Newton's infrastructure. Given the degree of coordination in independent lines of evidence (radioactive datings, paleomagnetism, deep quake mappings, seamount chain orientations, etc.), and its ability to predict, plate tectonics has surely achieved that Newtonian status. Concerning the predictions of plate tectonics: the Scientific American of Nov. 1986 has an article about how plate motions had already been measured directly before the advent of GPS, by long-baseline interferometric measurements using radio telescopes keying on quasars. A decade ago they had already measured long term movements between stations in Germany, Sweden Connecticut, Texas, Hawaii, Alaska, Kwajalein and Japan, and found them almost entirely in accord with predictions based on plate tectonics (all right, so they found CT and TX moving together a bit, but 8 out of 9 is not at all bad – what other theory predicted half as many of the observations?). After another decade of measurements, if they had found any great problem for plate tectonics we would have heard the great hullabaloo by now. >>There is no direct evidence of subduction on the northern part of India either, looks like its folding or bunching to me. Correct, as far as I know. It was mentioned in a hedging way, as if not enough seismic evidence was available to know whether the lithosphere underneath the Himalayas is still subducting. >> Why would the Indian side of the Owen shift zone be further south where the India smashed up the Himalayas that where the African side has a split between it and the arabian plate? I see no Owen shift zone on my maps, thus no comment. >> I don't see a SE Indian Ridge but go ahead..It looks like India is part of Australia on my materials. The southeast Indian ridge is the third leg of the junction in the mid-Indian Ocean – it passes between Antarctica and Australia. India was wedged between S. Africa and Antarctica in Pangaea. It took off in a sprint (geologically speaking) towards Asia in the late Triassic, before Australia and Antarctica split. Between it and Australia there must have been a fast-moving transform fault; I have assumed without evidence that the 90-East ridge is associated with that fault. The fault must be mostly inactive since India hit Asia, thus India would seem to be part of the Australian plate. But I expect it is a rather loose association; since India has this problem with Asia that the rest of the Australian plate does not, it would not be surprising to see them go their separate ways. If subduction has stopped or slowed under the Himalayas, this might be happening already. I do not see what the 90-East ridge would have to do with Antarctica, which was a neighbor of S. Africa in Pangaea, nowhere near Asia. Are you claiming otherwise? If so, we are going to get you because I am sure we can find geo formations that correlate Antarctica with S. Africa, not Asia, from the Triassic. >> Here you can still connect the dots along the shift faults from antarctica more or less up toward India. What I expect to work in that case is a connection of India's margins with points on the southwest Indian ridge corresponding to where India was connected to Africa and Antarctica before that earliest split of Gondwana. –Doug