TRACING SUBDUCTION ZONE PROCESSES BY USING MG ISOTOPES

The key component during subduction is the subducting oceanic slab including marine sediments, altered basalts, abyssal peridotites and fresh mafic and ultramafic rocks. How these rocks interact with each other and the mantle wedge at elevated temperature and pressure during subduction controls the subduction zone processes such as earthquakes and volcano eruptions. The nature, behavior and fate of subducting materials however are still not well understood. Here, I will describe how Mg isotopes can be used to answer some of these questions and provide insights into subduction zone processes. In particular, I will focus on 1) Mg isotope systematics of subduction zone fluids and their implications on arc magmatism and seismicity; 2) the contribution and mechanisms of subducted sediments and altered basalts to arc magmatism; 3) the interactions between different types of rocks/fluids among the subducting slabs; 4) the roles of subducted materials in producing the mantle heterogeneity; and 5) the global elemental cycling and long-term climate change, including the deep time evolution, carbo recycling etc. The pioneer work of John Valley on stable isotope geochemistry and his inspiration on non-traditional stable isotopes at both low-T and high-T processes will be discussed.