GeologyRocksKimberlites
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Jon
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Hi there, I asked a collegue
Thu, 05/31/2007 - 08:38Hi there,
I asked a collegue of mine whose PhD involved kimberlites in Canada and South Africa (He was exminaing the diamond chemistry). I pointed him to your post and he replied with this:
Forget the 'molten sphere' idea. Kimberlites come up in dykes and then wittle away a pipe-shaped diatreme on pressure release at the surface. Also kimberlites do not form diamonds...they just transport them from the base of the mantle lithosphere. The old, cold parts under canada are suitable for diamond stability, whereas there are no great cool spots in the US, the mantle is too hot for a given depth!
Hope that helps a bit 
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Kimberlites
Submitted by MakeTheBedrock on Fri, 05/18/2007 - 23:49.Kimberlites are truly fascinating. I just learned that they form from CO2 outgassing that sends a molten sphere into the crust of the Earth. I wondered if the CO2 could be pushed out of the rocks in the mantle in a large enough quantity or if the CO2 came from some pocket. I also wondered what allows a Kimberlite to form diamonds. I recently looked at different Kimberlites in Kansas with my class, but didn't understand exactly why ones in Arkansas had signatures of diamond formation and the ones here didn't.