Trace-element mobilization during dehydration reactions in slabs: constraints from eclogite-facies veins (Tianshan, China)

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Aqueous low- to high-solute fluids and/or supercritical hydrous melts released from the oceanic crust are believed to be responsible for trace element transport from the subducting slab to the overlying mantle wedge under UHP conditions. Reliable information on the nature and the composition of these UHP fluids as well as their capability to transport major and trace elements is scarce and stems exclusively from former subducted continental crust. A unique opportunity to study UHP veins in former subducted oceanic crust is given in the western Tianshan HP-LT metamorphic belt in north-western China. The aim of the intended study is to provide insight into fluid-rock interaction and element transfer during fluid flow under UHP conditions in subduction zones by means of a petrological (mineral chemistry, geothermobarometry) and geochemical (major and trace elements, fluid inclusions) investigation of the UHP veins and associated country rocks. In addition, it is intended to constrain the composition and type of fluid responsible for associated metasomatism and trace element transfer to the overlying mantle wedge.