At The Mariana Trench Southern Peridotite

The mantle wedge is the key part of the subduciton factory. Subducting slab derived fluids (melts) return to surface through this part and lead to fluids (melts)-rocks interaction. In order to better understand the influence of the mantle wedge relating to subducting, the peridotites from the southern Mariana fore arc is checked in this paper. The mineralogical and geological characteristics show that the peridotites are the products of two major processes: an early partial melting depletion event that was overprinted by hydrous melts-rock interaction. The compositions of whole rock and minerals indicate that the peridotites are the residues of higher partial melting event than abyssal peridotites. Clinopyroxene in peridotites is relatively more depleted than orthopyroxene and olivine, which indicates the hydrous melting event induced by water. The infiltration of hydrous melts enriched in Al, Ca, Na and trace elements, which leads to the Ca and Na enrichment in whole rock and LILE, LREE and Zr enrichment in cpx. The melts-rock interaction also changes the composition of spinel and formed amphibole and opx. The forming of amphibole in peridotites is a long time stage and controlled by temperature and pressure. Earlier stage amphibole joined hydrous melting of peridotites. The composition of hydrous melts is also influenced by temperature. REE and HFSE content of hydrous melts increase due to the increase of temperature, but the lower dissolution of HREE and HFSE compared to LILE and LREE indicates the hydrous melts derived from the subducting slab.