Sediment-peridotite interaction in a temperature gradient: transport of trace elements and growth of diamonds

点击翻译按钮获取中文摘要

Subduction zones have a very complex compositional and thermal structure. The slab-mantle juxtaposes relatively cold sediment with hotter mantle peridotite. Mass transfer processes between the downgoing slab and the overlying mantle wedge are fundamental to our understanding of deep-Earth element cycling and the generation of arc magmas. In a previous project, the effect of a thermal gradient on sediment-peridotite interaction at 7.5-10 GPa was investigated. A number of changes in petrology and major element composition were observed in these complex experiments as a function of temperature gradient and time. This project is an extension of the preceding project where we aim to investigate mass transfer in more detail by analyzing trace element compositions of the minerals and different mineralogical layers produced during sediment-peridotite interaction. Several new experiments will be carried out with the sediment mixture (K-GLOSS) alone in a comparable temperature gradient to provide us with better boundary conditions for our element transport modeling. This composition represents a subducting sediment and contains H2O, carbonate and graphite and is doped with trace elements that will be measured by LA-ICP-MS. Several additional experiments will be performed to further study the nucleation and growth of diamond in complex chemical and thermal gradients. Recent experience has indicated that somewhat higher temperatures than previous experiments are needed to promote spontaneous nucleation of diamond throughout the sample