Element Mobility During Subduction-Zone HP-UHP Metamorphism

The presence of subduction zones is one of the characteristic tectonic features different from other terrestrial planets. Series of physical and chemical changes occur while the subduction of oceanic lithosphere sinking in the deep mantle, and induce the formation of arc lavas. Actually, the physical and chemical changes is subduction-zone metamorphism, it is significance for mass transfer in crust-mantle interaction, evolution of oceanic lithosphere and geochemical dynamics of the entire earth.HP-UHP rocks exposed on Southwestern Tianshan mountain recorded the subduction and exhumation process of the oceanic lithosphere component completely, which is the living fossil of geological-geochemical processes of deep subduction zone, In order to understand the elemental mobility in SZM, we collected various types of metamorphic rocks, including eclogite, blueschist and quartz-albite schist for meticulous petrographic observations and whole rock geochemical analysis. Based on immobile elements analysis, indicating diverse components of protoliths of HP-UHP rocks exposed in Southwestern Tianshan, including normal mid-ocean ridge basalt(N-MORB)component,ocean island basalt (OIB)component, altered oceanic crust(AOC)component, continent/arc-derived sediments component, which represent scattered subduction complex composed of normal ocean crust, seamounts and sediments.Frequent fluids activities occurs through the evolution of subduction and exhumation, but it is not necessarily lead to migration of water-soluble elements along with fluids, such as LILEs etc.,. Elemental mobility is essentially controlled by stability of their host minerals, which also constrain the geochemical characteristics of arc lavas.