In situ characterization of serpentinites from forearc mantle wedges: Timing of serpentinization and behavior of fluid-mobile elements in subduction zones |
| |
| Authors: | Fabien Deschamps Stéphane Guillot Marguerite Godard Catherine Chauvel Muriel Andreani Kéiko Hattori |
| |
| Institution: | 1. IsTerre, Université Grenoble 1, CNRS, F-38041 Grenoble, Cedex 9, France;2. Laboratoire de Géologie, Ecole Normale Supérieure de Lyon, CNRS, France, Site Monod, 15 parvis René Descartes, Lyon, F-69342, France;3. LMV, Université Blaise Pascal, CNRS, Clermont-Ferrand, France;4. IMPMC, Université Pierre et Marie Curie - Sorbonne Universités, 4 place Jussieu, Tour 23, 75252 Paris Cedex 05, France;1. Istituto di Geoscienze e Georisorse, CNR, Pisa, Italy;2. Istituto di Scienze Marine, CNR, Bologna, Italy;3. Lamont Doherty Earth Observatory, Columbia University, New York, USA;4. Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Modena, Italy;5. Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy;6. Institute of Geochemistry and Petrology, ETH Zurich, Switzerland;7. Jackson School of Geosciences, University of Texas, Austin, USA;8. Géosciences Montpellier, Université Montpellier 2, Montpellier, France;1. Department of Earth Science, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan;2. Center for Northeast Asian Studies, Tohoku University, Aoba, Sendai 980-8576, Japan;3. Department of Solid Earth Geochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan |
| |
| Abstract: | The Tso Morari serpentinites in the Ladakh area, northwest Himalaya, originated from the forearc mantle overlying the northward subducting Neo-Tethys lithosphere and the margin of the Indian continent. The serpentinites are characterized by high concentration of fluid-mobile elements (FME: As, Sb, B, Li, and U) compared to ophiolitic or abyssal serpentinites. The Pb isotopic compositions of serpentinites show influence of the subducted Indian continental lithosphere. Trace element concentrations of antigorite determined in situ with Laser Ablation High Resolution Inductively Coupled Mass Spectrometer (LA-HR-ICP-MS) show high contents of FME including Pb, in contrast to the spatially associated iron oxides. Rare earth elements (REE) and compatible elements, such as Sc and Co, remained immobile during the hydration, allowing the identification of the primary minerals (olivine or orthopyroxene) from which serpentine formed. Serpentinized olivine displays higher Sb and As concentrations (up to 1000 × PM) than serpentinized orthopyroxenes that are enriched in Pb, Cs and Li (2 to up to 10 × PM).We propose that the observed FME distribution in two types of serpentine reflect the differential incorporation of FME during the downward movement of the serpentinite along the subduction plane. At temperature lower than 400 °C, at shallow depths, olivine is preferentially serpentinized and incorporates elements that are fluid soluble at low temperatures, such as Sb and As. Above 400 °C, orthopyroxene is hydrated and incorporates Pb, Cs, Li and possibly Ba. Boron and U are incorporated in both types of serpentine suggesting that they are released from slabs at temperatures around 300–400 °C. The serpentine acts as a sink for water, but also for FME and transports them to deeper and hotter levels in the mantle, down to the isotherm 600–650 °C where dehydration occurs. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
