A Long Section of Depleted Mantle Peridotite

Abstract

The upper mantle is critical for our understanding of terrestrial magmatism, crust formation, and element cycling between Earth’s solid interior, hydrosphere, atmosphere, and biosphere. Mantle composition and evolution have been primarily inferred by surface sampling and indirect methods. We recovered a long (1268-meter) section of serpentinised abyssal mantle peridotite interleaved with thin gabbroic intrusions. We find depleted compositions with notable variations in mantle mineralogy controlled by melt flow. Dunite zones have predominantly intermediate dips, in contrast to the originally steep mantle fabrics, indicative of oblique melt transport. Extensive hydrothermal fluid-rock interaction is recorded across the full depth of the core and is overprinted by oxidation in the upper 200 meters. Alteration patterns are consistent with vent fluid composition in the nearby Lost City hydrothermal field.

A pretty huge advance. This one will run for years to come, I think.

Edited December 2Dec 2 by sethoflagos

Could be useful for new options for C sequestration, too. Peridotite is a good C02 absorber. Carbonates formed.

MIT Technology Review

Carbon-Capturing Rock

Geologists discover that certain rock formations could sequester large amounts of carbon dioxide.

Anything that adds to our knowledge of element cycling between biosphere and asthenosphere is pretty important right now.

14 hours ago, sethoflagos said:

A Long Section of Depleted Mantle Peridotite

A pretty huge advance. This one will run for years to come, I think.

Lot of geochemistry in this. I got a bit lost reading about serpentinisation in bed last night and went to sleep before I understood it properly. Seems these rocks can reduce water, releasing H2 while themselves oxidising (by acquisition of OH?) into a suite of minerals including chrysotile, a.k.a. white asbestos. I was interested in the potential role of the hydrogen as an energy source for life around hydrothermal vents. The reaction is said to be strongly exothermic, I see.

The ability to take up CO2 is also interesting but I'll need to read about that separately. I recall there was a suggestion that slag from iron and/or cement kilns could do that, but this is obviously different.

14 hours ago, sethoflagos said:

A pretty huge advance. This one will run for years to come, I think.

Thanks +1

For those interested in a simpler yet more general discussion of the mantle for backgound material I recommend this book.

Peridotite is first discussed on page 119

18 hours ago, TheVat said:

Could be useful for new options for C sequestration, too. Peridotite is a good C02 absorber. Carbonates formed.

MIT Technology Review

Carbon-Capturing Rock

Geologists discover that certain rock formations could sequester large amounts of carbon dioxide.

Anything that adds to our knowledge of element cycling between biosphere and asthenosphere is pretty important right now.

Absolutely. I was also intrigued by the efficiency with which it removed uranium from seawater.

5 hours ago, exchemist said:

Lot of geochemistry in this. I got a bit lost reading about serpentinisation in bed last night and went to sleep before I understood it properly. Seems these rocks can reduce water, releasing H2 while themselves oxidising (by acquisition of OH?) into a suite of minerals including chrysotile, a.k.a. white asbestos. I was interested in the potential role of the hydrogen as an energy source for life around hydrothermal vents. The reaction is said to be strongly exothermic, I see.

Up to present, the sequential order of serpentinisation reactions has been largely inferred from terrestrial ophiolites which have been strongly overprinted with later processes. It will be interesting to see how much of the old guesswork holds up now the geologists have an extensive fresh section to study.

5 hours ago, studiot said:

Thanks +1

For those interested in a simpler yet more general discussion of the mantle for backgound material I recommend this book.

Peridotite is first discussed on page 119

I wonder how much of that chapter will need to be rewritten. 🙂

Edited December 3Dec 3 by sethoflagos

52 minutes ago, sethoflagos said:

I wonder how much of that chapter will need to be rewritten. 🙂

Not much, the book is from different point of view and much more general picture.

Your information is additive and I'm sure further work elsewhere across the globe will gradually build up a more complete picture.