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Abstract

Ultramafic xenoliths from Mont Briançon, Ray Pic and Puy Beaunit in the French Massif Central show variable mineral compositions that indicate a residual origin after various degrees of partial melting of a fertile peridotite. Furthermore, trace element and Sr–Nd isotopic variations of clinopyroxenes indicate mixing processes between depleted mantle and enriched components such as asthenospheric melt and silicate carbonatite melt. Pyroxene geothermometer and CO2 geobarometer estimates are 860–1060 °C at 0.92–1.10 GPa for Mont Briançon, 930–980 °C at 0.89–1.04 GPa for Ray Pic and 840–940 °C at 0.59–0.71 GPa for Puy Beaunit. From south to north, the xenoliths show the following trends: (1) deeper to shallower origin; (2) more depleted mineral compositions, suggesting higher degrees of partial melting; and (3) more enriched isotopes and trace elements, indicating a mixing process with a silicate-rich carbonatite melt characterized by high H2O and K2O, possibly during Variscan subduction.

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