Nature of the upper mantle and metasomatic processes on either side of the Sillon Houiller (French Massif central)

Peridotite xenoliths collected in two Mio-Pliocene volcanoes on either side of the Sillon Houiller (French Massif Central) have contrasting characteristics. East of the Sillon Houiller, the peridotites record anomalously high temperatures (1,250 degrees C) and extensive reequilibration with basaltic melts. To the west, equilibrium temperatures are much lower (950 degrees C) and the peridotites bear evidence for interaction with volatile-rich small melt fractions. In agreement with seismic tomographic data, these results indicate that the Massif Central lithospheric mantle is strongly affected by mantle plume upwelling to the east of the Sillon Houiller, while this effect is moderate to the west.