Sr enrichment in mantle pyroxenes as a result of plagioclase alteration in lherzolite

The Sr enrichment within pyroxenes is neither caused by metasomatism nor modified by fluids involved in hydrothermal alteration because pyroxenes are extremely depleted in fluid-mobile and light rare earth elements. Also, Sr enrichment cannot be related to the melt impregnation, since the Sr supply from the impregnating melt was consumed by plagioclase crystallization. The Sr enrichment in the pyroxene postdates the melt impregnation and is due to the relatively high-temperature (375 °C-850 °C) of saussuritization, that is, the breakdown of plagioclase. Plagioclase decomposition has released appreciable amounts of Sr to enrich adjacent pyroxenes. Saussurite shows significantly lower Sr contents than the plagioclase. Sr enrichment in peridotite pyroxenes, which is ascribed primarily to the metasomatism of slab-derived fluids, should be treated carefully, particularly when altered plagioclase is present.