Lithospheric mantle processes beneath Kurose islet, Southwest Japan

Abstract

Upper mantle xenoliths enclosed in Cenozoic alkali basalts in Southwest Japan were found at Kurose Islet. The xenoliths consist primarily of harzburgite and minor lherzolite and exhibit a porphyroclastic texture. Trace element data showing relative depletion in light rare earth elements (REEs) and general spoon‐shaped patterns suggest that xenoliths experienced depletion and slight enrichment processes. Incompatible trace element patterns for the spinel peridotite xenoliths indicate varying degrees of modification by fractional melting (from 6 to 11%). The Kurose spinel peridotites appear to have undergone melt extraction followed by an episode of cryptic mantle metasomatism. A nearby silicate melt may have been the metasomatic agent affecting spinel peridotites. The spinel peridotites originated from depths of 48 to 51 km at equilibrium temperatures ranging from 1030 to 1082 °C.