CompuServe Messages

Doug >>You cannot mean the 3 plates meeting at the mid-oceanic ridges in the Indian Ocean since they are diverging, not converging; I figure you are worried about how Africa is almost surrounded by spreading ridges.<< Bad wording… This is a biggie for me… The meeting of the three plates have places of converging forces.. 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. try it with your hands on a globe…there would have to be a relative motion along the interface of the other two plates. There are two problems with this…while the eastern interface with the african plate "looks" like it has been sliding there is no evidence of sliding along the other interface with the australian ridge. Its shape would prevent that. Also the shift faults would have been sliding and would not line up. Face this one down and you will see the start of the Global motion problem. >>Imagine two plates are being pulled apart, but there is a third plate between them with a spreading ridge on either side of the middle plate. The two outer plates will move away and the ridges will follow them at half speed as I described before (the plate pulls away, both sides of the separation are added to equally, so the center of the seam has moved halfway with the plate; repeat indefinitely). The middle plate just sits there, no pressure, no movement, except it grows. This is how I see Africa when looking at the east-north-east to west-south-west components of forces upon it – they mostly cancel.<< The shift faults would not line up like they do think about it they would be sliding on one side or the other. Simulate the motion..take a small piece of paper and mark the shift faults. Now move the paper in the direction you think the plate went and notice the faults would be curved( the easter antarctic& australian plate connection works in one direction sort of..don't let that one give you hope..the rest of the motions would all cause slanted shift faults in every direction. Worse look at the forces of the motion.. there are three plates each one has motions along this interface that show converging forces…the australian arc converges at borneo, the antarctic triangle converges at a 45 degree angle and the african plate converges just above South Africa. This area just doesn't work on paper or in theory if you plot the motion. Its worse on a globe than on a flat map. >>Looking at the north-south stresses, the big picture is spreading south of Africa and subduction/compression to the north (at the Alps – Italy was part of the African plate). Africa is moving generally northward.<< Not at the north end it is moving west on the east side and east on the west side. You can't reconcile all these motions and keep the shift faults and transform faults aligned across the Mid Ocean Ridges. I can see africa as the place where the whole world is spreading away from…but not antarctica also as well as not enough subduction..There is no direct evidence of subduction on the northern part of India either, looks like its folding or bunching to me. >>The southwestern Indian ridge is indeed a confuser. One map I see appears to suggest is that it is changing character from a spreading ridge to a transform fault. It may be simply a retired spreading ridge. The angling of the transform faults would seem to be a response to the Carlsberg ridge – transforms from both seem to line up at first glance. The Carlsberg is more clearly active, as evidenced by its carving of the Gulf of Aden; perhaps it is "taking over" all the action.<< There is a big shift at Owen fracture Zone that breaks and shifts the carlsberg ridge as you say. The Carlsberg Ridge is part of the three leg split we discussed before, but it is spreading at a tapered rate terminating in the crotch of the rifts. 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? >>Here you are really getting into flat map distortion. On a map that attempts to avoid distortion, it looks reasonable to me.<<< Look at it on a globe and you will think again. >> Since the southwest Indian ridge was the first to split Gondwana, it is not difficult to imagine it is mostly dormant; taking the Carlsberg and Southeast Indian ridges<< I don't see a SE Indian Ridge but go ahead..It looks like India is part of Australia on my materials. >> (both of which got going later) as the main event for the Cenozoic, the angles of the transforms appear sensible to me. In particular, the last separation between Antarctica and Australia appears to be a simple case of the connect-the-dots principle.<< It has taken the longest for me to work out the original position of antarctica but I believe the Niney East ridge that 2500 mile straight long ridge South of calcutta and the Chagos Laccadive Ridge show us the path of Antarctica. Down then swing west with S. America one smooth three or four day event. >>It is derived from the simple basic principles of plate tectonics. I see no way to derive the connect-the-dots principle from your theory (the dots you should be connecting should have nothing to do with original juxtapositions, only with the shape of the continents and equal-speed meeting points).<< Not true the shape of the Mid Ocean Ridge and the mid point is approximately the location of the connect the dots locations of the continents drawn along the shift fault lines more or less. >>I expect transform faults to be generally perpendicular to spreading ridges when I am assuming there is no lateral slip along the direction of the ridge (as if the spreading zone were a transform fault itself). But as noted above, the Southwest Indian ridge may be undergoing such slipping as the younger upstart ridges fail to respect their feeble elder.<< Nice description Here you can still connect the dots along the shift faults from antarctica more or less up toward India. >>I gave a reason before which you ignored;<< Not ignored…the shift faults as I explained would not stay aligned when you plug in the motions of the Plates. See next post for balance. Kamron