Can serpentinite dehydration release sulfate-rich fluids into the subarc mantle?

The dehydration of serpentinite is crucial for the recycling of water in subduction zones, the fluids launched are thought of a vital component within the oxidation of the sub-arc mantle. Nonetheless, whether or not serpentinite-derived fluids are oxidized or lowered stays hotly debated.

A analysis staff led by Professor Zeng Zhigang from the Institute of Oceanology of the Chinese language Academy of Sciences (IOCAS), in collaboration with co-researchers from Tianjin College and the Guangzhou Institute of Geochemistry of CAS, revealed {that a} subarc coat chilly subduction zones could be metasomatized by sulphate-rich fluids derived from serpentinite.

Related outcomes have been revealed in Journal of Geophysical Analysis: Stable Earth October 13.

On this examine, the researchers analyzed the isotopic compositions of copper (Cu) and sulfur (S) of contemporary lavas from three subduction areas of the Western Pacific. They discovered that arc-bound lavas had heavier Cu and S isotopic compositions in comparison with mid-ocean ridge basalts and back-arc lavas, and their δ⁶⁵Cu values ​​had been positively correlated with geochemical proxies for slab-derived fluids (eg, B/Nb, Ba/Th, and Ba/La). This proof means that fluids containing isotopically heavy Cu and S metasomatize their mantle sources.

Theoretically, the Cu²⁺-SO₄^2– provider fluids launched by serpentinite dehydration have extraordinarily heavy Cu and S isotopic compositions. Consequently, sulfate-rich fluids seeped into the sub-arc mantle and produced heavy Cu and S isotopes within the arc-bound magmas.

In distinction, sulfate-rich fluids had been absent at back-arc depths as a result of full decomposition of serpentine minerals in the course of the early phases of subduction, resulting in the remark of δ-type basalts mid-ocean ridge (MORB).⁶⁵Cu and δ³⁴S-values ​​(~-1‰) in back-arc basalts.

“Heavy Cu isotopes in arc-bound magmas reveal that the sub-arc mantle has been metasomatized by sulfate-rich fluids (oxidants) derived from serpentinite, explaining the oxidation properties of magmas of arc in chilly subduction zones,” stated first creator Chen Zuxing. of the examine.

“This examine means that Cu isotopes might present new perception into the transport of oxidized fluids throughout subduction,” Prof Zeng stated.