Subduction v. intraplate metasomatism fingerprints
Published:January 01, 2010
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.
Figures & Tables
Petrological Evolution of the European Lithospheric Mantle
Several different databases and models have been developed over many years of petrological study carried out by several European and non-European groups on mantle xenoliths, peridotite massifs, ophiolites and mafic magmas spanning in age from Archaean to Recent times. This volume aims to bring together these different approaches and to integrate the geochemical perceptions of the European upper mantle. The papers include regional petrological studies of the European lithospheric mantle, from Spain to the Pannonian Basin, from Corsica and Serbia as far north as Svalbard. Six contributions are based on studies of mantle xenoliths, while the remaining three deal with ophiolitic and peridotitic complexes. A further article provides an update on the textural classification of mantle rocks using a computer-aided approach and there is an introductory overview.