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+ >> First, we know that plates are being subducted and that the subducted + plates plunge into the asthenosphere at a near 45 degree angle. This is + fact.<< + + How can you claim this as fact? + I understand that by seeing the different arrivals of groups of waves that + the different layers can be "seen". This is not enough to take it as fact that + the plate subducts. There is more to it than that. This is getting beyond me, but as I understand it, secondary waves are generated at the boundaries of density changes. It's not just the timing of the waves but the number and types of waves that enable geophyicist to determine the structure of unseen volumes. + + Could it be that subduction is so necessary to explain the new ocean basins + that we are interpreting the data in a convenient way? + No. What would be the point? + It seams odd that the plates being lighter and relatively thin that they + would go down …..seams as though they would break up in sections and pile up + at the surface like what happens to ice when broken by an icebreaker. + Doesn't seem odd at all. If you put one ice cube on top of another in a container of water the one on the bottom will sink (if it's movement is constrained in the horizontal direction) below the surface of the water. Same thing with the mafic rock of the crust. + >> The average time for a cooled subducted plate to be assimilated into the + mantle is about 12 million years. << + + Why would the lighter material be assimilated into the heavier material? + + >> With the time and pressures involved these "rigid" plates deform. << + + Ok but lets look at the facts…. Where the plate is being fabricated in the + rise the plate demonstrates brittleness in that it has regular fractures + across the ridge, transform and shift faults. In fact it is the most regularly + fractured area on earth. + Here the crust is newer and should be easy to deform…but it has rugged + craggy features with tremendous faulting. Why wouldn't it show huge cracks + where it turns to go down. Even millions of years couldn't cause it to bend + without cracking. You have tremendous faulting where plates subduct too. As the people of Alaska if they have ever noticed any side effects of the subducting plates (like earthquakes). Faulting and deformation are the trademarks of tectonics. Transform faults in the oceanic ridges are necessary for these large plates to move over a spherical surface. "Rugged and craggy" features are characteristic of the upwelling magma that produces the plates. You need to think large scale; both time and size. And rock does flow like plastic given millions of years. Most any metamorphic rock will show you this. Whole mountains have their lithology upside down and overturned. You can see layers of rock that make complete 180 degree bends over themselves. Take a look at Shelton's "Geology Illustrated" for examples of this. + + The appearance of the ocean basin crust looks more like material flowed out + from under the continents and met at the rise. The forces at play during + contact of the fronts caused the shift faults. + The motion of the plates have been measured. New material is added at the oceanic ridges. Two points, each on opposite sides of the ridge, are now further apart from each other than in the past. Rates of movement of up to 18.3 centimeters per year have been measured between the Pacific and Nazca plates. + When looking at the relative motions of the plates it appears like wide + expanses of plates are moving in a focusing manner into a much smaller area + without any wrinkling of the plate at all. + I'm looking at a plate map right now and don't see that at all. + I am not balking at accepting the standard explanation for the sake of being + iconoclastic…. I just need more proof to accept subduction. + Do you know of any source of graphic data on the subduction proving + soundings? + + Kamron Yes, you are balking. There is tons of evidence that plate tectonics is real. There is no widespead conspiracy to force everyone to believe tectonics exist. Why would there be? Most any library should have many geology books with more info. Here are a few at random: _Earth_, Press & Siever _Petrology_Igneous,_Sedimentary,_and_Metamorphic_, Ehlers & Blatt _Elementary Seismology_, Richter _Introduction_to_Geophysical_Prospecting_, Dobrin & Savit _Exploration_Geophysics_of_the_Shallow_Subsurface_, Burger _Geology_Illustrated_, Shelton You can also GO USENET here on CompuServe and check out sci.geo.geology. Take a look at GO ENCYCLOPEDIA as well. Mike