Much of the dynamic activity of the Earth and aposis surface is concentrated at convergent boundaries of tectonic plates, i.e. where oceanic plates are thrust under various types of overriding tectonic plates. Most material in the down-going plate in the subduction process is recycled into the Earth and aposis interior. This recycled material releases fluids from the down-going plate into the mantle, which triggers mantle melting. These melts are responsible for most of the hazardous volcanic activity on Earth, and the processes that govern melt generation have been the subject of vigourous scientific research. Numerous geochemical studies of subduction related volcanic rocks have established particular element and isotopic ratios as tools to fingerprint processes operating within subduction zones.
However, current models of subduction zone processes are largely based on empirical assumptions on the composition and nature of the fluids derived from the subducted material. What is required is ground truthing of the geochemistry of fluids from recycled crust by in situ analyses on high-pressure metamorphic rocks and minerals in combination with targeted experimental studies. This project therefore focuses on the evolution of lithium and other commonly-used geo chemical trace elements and their isotopes in subduction zones.
The plan is to analyse high-pressure metamorphic rocks that have been through part of the subduction process and to study experimentally diffusion of the two isotopes of Li, which are extensively used to infer crystal recycling. These data will be integrated into new models of trace-element concentrations and isotope ratios in rocks and fluids during subduction. The goal is to characterise the redistribution of trace elements and isotopes in high-pressure metamorphic rock types from subduction settings.
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