CompuServe Messages

// >> Bore threw the continent? I have no idea what you're talking about here either. << Yes… thats the explanation of volcanic activity away from the "subduction zone" the melting crust dissolves the lithosphere and arrives at the surface. // Ahh…I see. 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…kinda like a lava lamp. Now, your next question will be why is this magma so much less dense than the plate that is being subducted (which sinks)? Well, it's not much lighter. The time for this magma to rise to the surface and form granitic plutons or what-have-you is measured in millions of years. Also, there is some complex geochemistry going on as well. The under-riding oceanic plate is, well, to put it simply, waterlogged. The role of this presence of water, not to mention the pressure, is very important in the compostion of these magmatic melts. The chemistry is way beyond me. Now you need a good text on geochemistry or Petrology.<grin> // Convection forces cannot pull something floating down very far or for long. When you read the text how did you solve the apparent problem?// I don't see a problem. Let's look at it another way. The oceanic plates are about 70 km thick. When two of these plates collide something has to happen. The most logical thing is for one plate to override the other. So due when end up with 70 km high mountains as one plate rises above the sea and flops down on top of the other? No. Why? Weight. The mantle won't support that much weight in a given area. Thus one is forced under the other as the "engine" that pushes these plates around doesn't stop. As the bottom of a plate gets more than about 100 – 150 km down it starts to melt from the greater heat at that depth. How that? Let me know if you have other questions. I'm frustrated as these medium makes it kinda hard to present data of this type in a clear, logical manner. It would help if I was a better teacher, too. Mike