Crust Mantle Recycling: Inputs and Outputs
Geochemical and isotopic compositions of continental derived materials that are available as inputs into modern subduction zones are assessed. Oceanic sediments from fore-arc, back-arc and continental margins have a wide range of isotopic and chemical compositions reflecting a variety of source terrains. Intra-oceanic forearc sediments have compositons similar to adjacent arc volcanics while sediments deposited in the passive margin of continental shelves have Proterozoic and in some cases Archean provenances. This indicates that a wide spectrum of materials are available for incorporation into modern and also presumeably ancient subduction zones. Studies of blue-schist and associated eclogite terrains indicate sediment subduction to depths of ~20km to 60 km, but direct constraints on the quantity of continental derived sediments subducted into the deep mantle remains elusive.
An attempt is also made to identify the outputs of crust mantle recycling, that is magmas derived from mantle sources containing components of ancient recycled sediments. A select class of ultra-potassic magmas, the olivine and leucite bearing lamproites, appear to have the appropriate geochemical signatures but their source regions may be located in the lower subcontinental lithosphere rather than the upper mantle.
KeywordsContinental Crust Subduction Zone Oceanic Crust Mantle Wedge Oceanic Sediment
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