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Githyanki
2013-Jul-20, 12:26 AM
So when two plates collide, on subducts under the other; what if they didn't subduct? What if they just smashed against each other? Is that possible? What would be the results if possible.

Solon
2013-Jul-20, 01:24 AM
So when two plates collide, on subducts under the other; what if they didn't subduct?

You get ohduction, seen at the Hawiian islands and southern Vancouver Island.

Gillianren
2013-Jul-20, 02:27 AM
Or the Himalayas.

geonuc
2013-Jul-20, 08:45 AM
So when two plates collide, on subducts under the other; what if they didn't subduct? What if they just smashed against each other? Is that possible? What would be the results if possible.

To any great extent, only oceanic crust subducts. Continental crust does not. So when two continents collide, as with the Himilaya Gillianren mentions, you get a large mountain range. There are many examples of this, the US Appalachians being a familiar one to Americans.

dgavin
2013-Jul-21, 05:11 PM
Actually when the continents first approach each other, one continents oceanic self does subduct under the other. However as the main body of the land meets, the ocean is pushed aside, eliminating the main lubricant for subduction (water). The subducting continental plate continues to be pulled down into the trench for about 90-140km (a few thousand years), then because if it's buoyancy and a lack of water for lubrication, that puts the brake on further subduction. The Subduction volcanism stops rather abruptly, in geologic terms, and then over time, the two plates as mentioned above push together and move up. Eventually the subduction trench is inverted into part of the new mountain range. The trench originating portion of these mountain rages can always be identified as they will have lifted ocean fossils high into the new mountain ranges. So if one side has ocean fossils high in the mountains, but the other side does not, you can identify the plate that was originally subducting, before it stopped.

geonuc
2013-Jul-21, 11:08 PM
Actually when the continents first approach each other, one continents oceanic s[h]elf does subduct under the other.

I believe I said that. Oceanic crust subducts; continental crust does not, to any great extent.

BigDon
2013-Jul-30, 02:38 PM
Shouldn't you mention to the folks at home that this is because ocean bottom crust is dense basalt and continental crust is lighter granite "foam" that floats on top of it?

It might help other people picture what is going on better.