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  Systematic changes in serpentine Si isotope signatures across the Mariana forearc – a new proxy for slab dehydration processes

Geilert, S., Albers, E., Frick, D. A., Hansen, C. T., von Blanckenburg, F. (2021): Systematic changes in serpentine Si isotope signatures across the Mariana forearc – a new proxy for slab dehydration processes. - Earth and Planetary Science Letters, 575, 117193.
https://doi.org/10.1016/j.epsl.2021.117193

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Item Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5008004 Version Permalink: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5008004_1
Genre: Journal Article

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Geilert, Sonja1, Author
Albers, Elmar1, Author
Frick, Daniel A.2, Author              
Hansen, Christian T.1, Author
von Blanckenburg, F.2, Author              
Affiliations:
1External Organizations, ou_persistent22              
23.3 Earth Surface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146037              

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 Abstract: The Mariana forearc is a unique location for exploring the role serpentinization plays in the marine Si cycle by means of Si stable isotope variations. Here, active mud volcanism transports deep, serpentinized mantle wedge material to the surface and thus offers a natural window to slab dehydration processes in dependence of changing temperature and pressure with depth. Si isotopes were measured in situ by femtosecond laser ablation MC-ICPMS in serpentine within ultramafic clasts from three mud volcanoes (Yinazao, Fantangisña, and Asùt Tesoru) sampled during International Ocean Discovery Program Expedition 366. To corroborate the results, serpentinization of olivine was studied in batch experiments. The Si isotope ratios show large variations between the mud volcanoes and between individual serpentine generations within a given mud volcano. Serpentine that formed early under low water/rock ratios exhibits Si of −0.41 ± 0.04‰ (1SD) similar to unaltered olivine which agrees well with experimental findings predicting no significant isotope fractionation during early serpentinization. In contrast, late serpentine veins formed under higher water/rock ratios span a wide range of Si isotope ratios that differ significantly between the individual mud volcanoes. With increasing distance to the trench, Si of late veins are −0.10 ± 0.07‰, −1.94 ± 0.13‰, and −0.80 ± 0.22‰ and −0.93 ± 0.21‰. These Si values are interpreted to record the isotopic composition of the fluid source, namely subducted biogenic silica and pore fluids, clays, and altered oceanic crust that dehydrate as consequence of rising pressure and temperature with depth. We show that Si isotopes of mantle wedge serpentinites can be used as a reliable new proxy for slab dehydration processes. They may be used in paleo-forearc systems to unravel oceanic sediment and silica biomineralization evolution through geological time.

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 Dates: 2021-09-162021
 Publication Status: Finally published
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 Identifiers: DOI: 10.1016/j.epsl.2021.117193
GFZPOF: p3 PT5 Georesources
OATYPE: Hybrid Open Access
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Title: Earth and Planetary Science Letters
Source Genre: Journal, SCI, Scopus
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Pages: - Volume / Issue: 575 Sequence Number: 117193 Start / End Page: - Identifier: ISSN: 0012-821X
ISSN: 1385-013X
CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals99
Publisher: Elsevier