Geochemical Character of Serpentinites Associated with High- to Ultra-High-Pressure Metamorphic Rocks in the Alps, Cuba, and the Himalayas: Recycling of Elements in Subduction Zones

Geochemical Character of Serpentinites Associated with High- to Ultra-High-Pressure Metamorphic Rocks in the Alps, Cuba, and the Himalayas: Recycling of Elements in Subduction Zones

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dc.contributor.author Hattori, Keiko
dc.contributor.author Guillot, Stéphane
dc.date.accessioned 2012-04-16T17:28:18Z
dc.date.available 2012-04-16T17:28:18Z
dc.date.created 2007 en_US
dc.date.issued 2012-04-16
dc.identifier Geochemistry Geophysics Geosystems 8, Q09010 en_US
dc.identifier.other 10.1029/2007GC001594 en_US
dc.identifier.uri http://hdl.handle.net/10393/22708
dc.description.abstract Serpentinites associated with eclogitic rocks were examined from three areas: the Alps, Cuba, and the Himalayas. Most serpentinites have low Al/Si and high concentrations of Ir-type platinum group elements (PGE) in bulk rock compositions, indicating that they are hydrated mantle peridotites. A few samples contain high Al/Si and low concentrations of Ir-type PGE, suggesting that they are ultramafic cumulates. Among the hydrated mantle peridotites, we identified two groups, primarily on the basis of Al/Si and Mg/Si ratios: forearc mantle serpentinites and hydrated abyssal peridotites. Forearc serpentinites occur in the Himalayas and along a major deformation zone in Cuba. All serpentinites in the Alps and most serpentinites in Cuba are hydrated abyssal peridotites. Himalayan serpentinites have low Al/Si and high Mg/Si ratios in bulk rock compositions, and high Cr in spinel; they were serpentinized by fluids released from the subducted Indian continent and enriched in fluid-mobile elements, and show high 87Sr/86Sr, up to 0.730, similar to the values of rocks of the subducted margin of the Indian continent. Although Himalayan serpentinites have a similar refractory geochemical signature as the Mariana forearc serpentinites, the former contain markedly high concentrations of fluid-mobile elements and high 87Sr/86Sr compared to the latter that were hydrated by subducted Pacific Ocean crust. The data indicate that the enrichment of fluid-mobile elements in forearc serpentinites depends on the composition of subducted slabs. Alpine serpentinites and most Cuban serpentinites show moderate Al/Si similar to abyssal peridotites. Hydration of peridotites near the seafloor is supported by micro-Raman spectra of earlier formed lizardite, high δ 34S (+11 to +17‰) of sulphides, and elevated 87Sr/86Sr, ranging from 0.7037 to 0.7095. The data support the contribution of S and Sr from seawater and sediments. These serpentinites are not highly enriched in fluid-mobile elements because serpentinization occurred at a high water/rock ratio. Alkali elements are conspicuously unenriched in all serpentinites. This lack of alkali enrichment is explained by slab retention of alkalis. This is also consistent with the observation of relatively low alkali concentrations in volcanic front magmas, since partial melting related to the volcanic fronts is triggered by dehydration of serpentinites. en_US
dc.language.iso en en_US
dc.subject Forearc Mantle Peridotites. en_US
dc.subject Element Recycling en_US
dc.subject Subduction Zones en_US
dc.subject UHP and HP Rocks en_US
dc.subject Arc Magmas en_US
dc.subject Mantle Peridotites. en_US
dc.title Geochemical Character of Serpentinites Associated with High- to Ultra-High-Pressure Metamorphic Rocks in the Alps, Cuba, and the Himalayas: Recycling of Elements in Subduction Zones en_US
dc.type Article en_US

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