CompuServe Messages

Mike >> The friction and pressure from one plate sliding under the other produces a felsic magma. This magma is less dense then the surrounding country rock and slowly "pushes" it's way to the surface<< I can see that it could rise straight up once it got started but it seams some of it would go back up the seam of the subducted crust …and there isn't any at all around the deepest trenches where the subduction is thought to be occuring. >>Now, your next question will be why is this magma so much less dense than the plate that is being subducted (which sinks)?<< No problem with that. The liquid form would be lighter than the solid. Making it likely that some trace would leak back up the seam. If the crust is floating on a liquid (which I agree with) and the pressure of magma at the rise is sufficient to cause leaks….then the pressure in the deep trenches were subduction is said to occur would much higher…the subducting crust would open up a path for the magma and it should be squirting out all along that zone. But there is no evidence of magma flows along the trenches that I know of…. >> the "engine" that pushes these plates around << This is very tough for me also …I see no forces in play that could translate into plate subduction. No pushing or pulling force. Convection doesn't have enough grip to force the subduction especially where there is no breaking of the surface. How do you see the engine? Kamron