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Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties.

ABSTRACT: Recently, high electrical conductors have been detected beneath some fore-arcs and are believed to store voluminous slab-derived fluids. This implies that the for-arc mantle wedge is permeable for aqueous fluids. Here, we precisely determine the dihedral (wetting) angle in an olivine-NaCl-H₂O system at fore-arc mantle conditions to assess the effect of salinity of subduction-zone fluids on the fluid connectivity. We find that NaCl significantly decreases the dihedral angle to below 60° in all investigated conditions at concentrations above 5?wt% and, importantly, even at 1?wt% at 2?GPa. Our results show that slab-released fluid forms an interconnected network at relatively shallow depths of ~80?km and can partly reach the fore-arc crust without causing wet-melting and serpentinization of the mantle. Fluid transport through this permeable window of mantle wedge accounts for the location of the high electrical conductivity anomalies detected in fore-arc regions.

SUBMITTER: Huang Y

PROVIDER: S-EPMC6895192 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties.

Huang Yongsheng Y Nakatani Takayuki T Nakamura Michihiko M McCammon Catherine C

Nature communications 20191205 1

Recently, high electrical conductors have been detected beneath some fore-arcs and are believed to store voluminous slab-derived fluids. This implies that the for-arc mantle wedge is permeable for aqueous fluids. Here, we precisely determine the dihedral (wetting) angle in an olivine-NaCl-H<sub>2</sub>O system at fore-arc mantle conditions to assess the effect of salinity of subduction-zone fluids on the fluid connectivity. We find that NaCl significantly decreases the dihedral angle to below 60 ...[more]

PMID: 31804479

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Project description:We present new partition coefficients for various trace elements including Cl between olivine, pyroxenes, amphibole and coexisting chlorine-bearing aqueous fluid in a series of high-pressure experiments at 2 GPa between 900 and 1,300 °C in natural and synthetic systems. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA-ICP-MS. The chlorine and fluorine contents in mantle minerals were measured by electron microprobe, and the nature of OH defects was investigated by infrared spectroscopy. Furthermore, a fluorine-rich olivine from one selected sample was investigated by TEM. Results reveal average Cl concentrations in olivine and pyroxenes around 20 ppm and up to 900 ppm F in olivine, making olivine an important repository of halogens in the mantle. Chlorine is always incompatible with Cl partition coefficients DClolivine/fluid varying between 10-5 and 10-3, whereas DClorthopyroxene/fluid and DClclinopyroxene/fluid are ~10-4 and DClamphibole/fluid is ~5 × 10-3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered as Damph/fluid ≈ Dcpx/fluid > Dopx/fluid > Dol/fluid but that Dmineral/fluid for Li and P is very similar for all observed silicate phases. Infrared spectra of olivine synthesized in a F-free Ti-bearing system show absorption bands at 3,525 and ~3,570 cm-1. In F ± TiO2-bearing systems, additional absorption bands appear at ~3,535, ~3,595, 3,640 and 3,670 cm-1. Absorption bands at ~3,530 and ~3,570 cm-1, previously assigned to humite-like point defects, profit from low synthesis temperatures and the presence of F. The presence of planar defects could not be proved by TEM investigations, but dislocations in the olivine lattice were observed and are suggested to be an important site for halogen incorporation in olivine.

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Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties.

Publications

Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties.

Similar Datasets

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