Postmelting hydrogen enrichment in the oceanic lithosphere
Veronique Le Roux1, Benjamin M Urann2,3, Daniele Brunelli4,5
1Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA. vleroux@whoi.edu.
Science Advances
|June 10, 2021
Summary
Water content in mantle rocks (H2O) varies significantly. This study shows H2O in pyroxenes increases in younger, more depleted oceanic peridotites due to post-melting hydrogen enrichment via diffusion.
Area of Science:
- Geochemistry
- Petrology
- Oceanography
Background:
- Interpreting water (H2O) content in exhumed mantle rocks is complex due to multiple geological processes.
- Previous studies faced challenges in understanding H2O variations in spatially isolated samples.
Purpose of the Study:
- To investigate temporal variations of H2O content in pyroxenes from abyssal peridotites.
- To understand the mechanisms controlling H2O incorporation in the oceanic mantle.
Main Methods:
- Analysis of a 24-million-year time series of abyssal peridotites from the Vema fracture zone.
- Measurement of H2O content in pyroxenes.
- Correlation analysis of H2O content with crustal age and pyroxene chemistry.
Main Results:
- H2O content in pyroxenes correlates with crustal age and pyroxene chemistry.
- H2O content increases in younger and more refractory peridotites.
- Observed trends are inconsistent with residual melting and differ from mantle xenoliths.
Conclusions:
- Post-melting hydrogen enrichment in peridotite residues occurs via ionic diffusion during cryptic metasomatism.
- Volatile-rich melts significantly contribute to hydrogen incorporation in the oceanic lithosphere.
- Widespread hydrous melts under mid-ocean ridges may lower mantle viscosity.
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