Extreme Gropundwater

[amigocabal]

Dehydration melting at the top of the lower mantle

The high water storage capacity of minerals in Earth’s mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone.

Note: 410-660 km translates to about 256 to 413 mi.

[slebetman]

Gropund Water?

[madd0ct0r]

there's water mixed into the top layer of crust, trapped in mineral formations?
huh.

what the fuck is dehydration melting?

[Executor32]

Per this article from Northwestern University about the paper:

The melting the researchers have detected is called dehydration melting. Rocks in the transition zone can hold a lot of H2O, but rocks in the top of the lower mantle can hold almost none. The water contained within ringwoodite in the transition zone is forced out when it goes deeper (into the lower mantle) and forms a higher-pressure mineral called silicate perovskite, which cannot absorb the water. This causes the rock at the boundary between the transition zone and lower mantle to partially melt.

“When a rock with a lot of H2O moves from the transition zone to the lower mantle it needs to get rid of the H2O somehow, so it melts a little bit,” Schmandt said. “This is called dehydration melting.”

I learned a thing.

[cosmicalstorm]

Flood by Stephen Baxter should be mentioned here since this is a sci-fi forum. The premise of Flood is that this water starts to move up out of the crust. It features some pretty harrowing maps. After reading the book I noticed myself smiling condescendingly when newspeople discuss the possibility of a few meters of rising ocean

[SpottedKitty]

there's water mixed into the top layer of crust, trapped in mineral formations?

Lots of different types of rock include water; sometimes the amount of water determines what kind of rock it is, assuming no other differences in chemical composition.

For a moderately weird example, look at opals used in jewellery; if they're stored the wrong way, they can lose water, which ruins the quality of the stone.