Host: Japan Association of Mineralogical Sciences
Calcic amphibole bearing spinel harzburgites from the Pinatubo 1991 dacite are characterized by depleted mineral chemsitry and abundant fluid inclusions composed of saline solutions and magnesite. Some xenoliths have zoned selvages in a boundary between harzburgite xenoliths and host dacite. Their outer zone consists of calcic amphibole, phlogopite and plagioclase, while their inner zone consists of fibrous orthopyroxene, olivine and phlogopite. We determined trace element and Sr-Nd isotopic compositions of amphibole of harzburgite xenoliths, an outer selvage and a host dacite. The compositional features suggest that the primary amphiboles were formed through a reaction between pyroxene and subduction related Si-rich aqueous fluids.