Fluid-mobile element budgets in serpentinized oceanic lithospheric mantle: Insights from B, As, Li, Pb, PGEs and Os isotopes in the Feather River Ophiolite, California
| Autor: | William P. Leeman, Zheng-Xue A. Li, Arnaud Agranier, Cin-Ty A. Lee |
|---|---|
| Přispěvatelé: | Domaines Océaniques (LDO), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Observatoire des Sciences de l'Univers-Institut d'écologie et environnement-Centre National de la Recherche Scientifique (CNRS), Department of Earth Science [Houston], Rice University [Houston], National Science Foundation [Arlington] (NSF) |
| Rok vydání: | 2007 |
| Předmět: |
010504 meteorology & atmospheric sciences
Geochemistry Platinum group element 010502 geochemistry & geophysics Ophiolite 01 natural sciences [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry Geochemistry and Petrology Boron 0105 earth and related environmental sciences Peridotite geography geography.geographical_feature_category Radiogenic nuclide Trace element Geology Platinum group Osmium [SDE.MCG.CPE]Environmental Sciences/Global Changes/domain_sde.mcg.cpe Seafloor spreading Volcanic rock Feather River Fluid-mobile elements Primitive mantle Serpentinite |
| Zdroj: | Chemical Geology Chemical Geology, Elsevier, 2007, 245 (3-4), pp.23-241. ⟨10.1016/j.chemgeo.2007.08.008⟩ |
| ISSN: | 0009-2541 |
| DOI: | 10.1016/j.chemgeo.2007.08.008 |
| Popis: | International audience; Serpentinized oceanic lithosphere may be an important source for boron and other fluid-mobile elements that are anomalously enriched in arc volcanic rocks. However, the integrated water/rock ratios associated with different styles of serpentinization may be variable. For example, large water/rock ratios are involved in the serpentinization of abyssal peridotites exhumed to the seafloor, whereas much lower water/rock ratios are likely to dictate serpentinization along deep faults and fractures. To address how fluid-mobile element enrichments vary with serpentinization at different settings, we investigated serpentinized harzburgites from the Feather River Ophiolite (FRO) in northern California. Major and trace element systematics indicate that serpentinization of the FRO ultramafics involved seawater. However, FRO serpentinites have unradiogenic Os isotopic compositions and near-chondritic platinum group element relative abundances, contrasting with serpentinized abyssal peridotites, which have radiogenic Os isotopic compositions and disturbed platinum group element systematics. These observations indicate that the integrated water/rock ratio involved in FRO serpentinization was smaller than that involved in abyssal peridotite serpentinization. B concentrations in the FRO (5–15 ppm), while substantially higher than primitive mantle (< 0.1 ppm), are still lower than in abyssal peridotites (10–170 ppm). These low values are not due to metamorphic loss as there is no petrographic evidence for prograde metamorphism (the serpentine minerals are low temperature forms like chrysotile and lizardite) and there is no consistency between observed fluid-mobile element (B, As, Pb, and Li) contents and depletions predicted from metamorphic dehydration models. Low B and fluid-mobile element contents in the FRO may thus be an intrinsic feature of low water/rock ratio serpentinization. Such values may be more representative of serpentinized oceanic lithospheric mantle rather than abyssal peridotites, which sample only the top veneer of the lithosphere. |
| Databáze: | OpenAIRE |
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