An interesting article from National Geographic notes that seismic studies of the Earth’s interior have discovered a large amount of water trapped within rock below the Asian continent.
Map courtesy of Washington University in St. Louis
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While the title of the National Geographic article makes me cringe (Huge Underground “Ocean” Found Beneath Asia), it does raise some interesting points in terms of plate tectonics and the subduction of ocean crust. It seems to makes sense that the ocean crust has a higher water content than other rocks and that these show up in the mantle after they have already been subducted.
Map courtesy of Washington University in St. Louis
This map shows an interesting distribution of the water logged rock though. I would expect to see a similar distribution beneath the Andes Mountains of South America, but there isn’t much that shows up in that area.
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5 comments
Monday, March 5, 2007 at 7:50 am
Chris Rowan
My guess would be that the lack of an anomaly under South America is due to differences in the age of the crust being subducted. The crust being subducted beneath Asia is almost 200 million years old, so has had plenty of time for large amounts of hydrated minerals to accumulate through reactions with seawater. In contrast, the crust being subducted beneath the Americas is much closer to the spreading ridges which created it, and is therefore much younger, so will be relatively ‘dry’
Monday, March 5, 2007 at 2:27 pm
Dave Schumaker
Thanks for that reply. It sounds like an excellent hypothesis to me actually. Though I would still expect to see even a small amount of water saturated rock in that subduction zone though. Then again, I’m not exactly sure how their scale is setup and what sort of concentrations they correlated with certain wave anomaly. But since the water in subducted sheets are thought to lead to more melting of mantle material (which help drive those volcanoes in subduction zones), I would expect something to show up.
I may try to shoot off an email to the authors later this evening and see if I can get some of their thoughts on it. Though I’m sure they are being inundated with emails asking whether or not we can sail these seas and if the “oceans” found down there are somehow valuable for drinking water. ;)
Tuesday, March 6, 2007 at 3:41 am
Chris Rowan
The image you have is (I think) set to 1000 km depth - this is way below where the melting which leads to arc volcanoes occurs. A cross-section through their model does seem to show a high attenuation zone beneath South America at shallower depths.
Tuesday, March 6, 2007 at 3:43 am
Chris Rowan
…and you’re probably right about the authors, although probably the worst are the creationists congratulating them on finally discovering where the water from The Flood went…
Saturday, March 10, 2007 at 9:11 am
Javi
Well, Chris, I think so, the age of the subduction is the most important factor, but maybe the different angle of the subduction slab at South America and the high velocity of the plate could help in the matter as well.
I mean….the cooling velocity is very different one each other place because of the proof and dip angle of the subduction slab.
Cheers from Spain.
Javi