Low-temperature Sr enrichment in mantle pyroxenes as a result of crustal alteration in plagioclase lherzolite

Abstract

Melt-impregnated plagioclase lherzolites from Nain melange, Iran, contain pyroxenes which are enriched and chemically zoned in Sr. The pyroxenes are characterized by extremely low contents of LREE, being in equilibrium with an ultra-depleted MORB-like melt. The Sr enrichment of the pyroxenes cannot be linked to the melt impregnation because of the high compatibility of Sr in plagioclase. The Sr-enrichment is due to breakdown of plagioclase at low-temperature condition. During saussuritization, appreciable amounts of Sr have been released from plagioclase to enrich adjacent pyroxenes. The limited Sr uptakes by saussurite (assemblage of hydrogarnet and amphibole) support this fact.