EXPERIMENTAL STUDY OF TRACE ELEMENTS TRANSPORT DURING DEHYDRATION IN THE OCEANIC CRUST ALONG DIFFERENT SUBDUCTION PATHS

Dehydration of subducted oceanic crust in subduction zones is one of important process of element fractionation operating in Earth and dehydrated oceanic curst sinking into the deep mantle which may produce chemical heterogeneity in mantle. We carried out a series of high-pressure dehydration experiments on natural lawsonite blueschist in order to compare transportation of trace elements during dehydration process along different subduction paths. We found a new water-bearing mineral: Al-10Å phase in the hydrous MORB system along cold subduction path for the first time, which might be a continuous solid solution with muscovite on the 12 coordination site. By comparing the characteristics of trace elements before and after experimental simulation along different subduction paths, we conclude that previous reported decoupled mobility of trace element with dehydration derived by comparing the trace elements characteristics of rocks under different metamorphic grade in subduction zone is not reasonable. Part of LILE (such as Ba, Cs) will anyhow release companying by dehydration along different subduction zone, but the degree of mobility do not have substantial effect on the trace elemental distribution patterns of subducted rocks under different metamorphic grade. In comparison to hot ones, the cold subduction paths will keep some LILE (such as Rb, Sr) and LREE due to stability of water-bearing mineral. The subducted oceanic crust along cold subduction path is more reasonable to explain the formation of HIMU and EM II geochemical endmember in deep Earth mantle.