Accessory Minerals and Crustal Processes

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WatsonEAR-0073752This research program involves experimental investigations at high pressures and temperatures that address the properties and behavior of rare-element minerals (i.e., ac-cessory minerals) in the Earth's crust. Accessory minerals - for example, zircon (ZrSiO4), apatite (Ca5[PO4]3F), monazite (CePO4), xenotime (YPO4), titanite (CaTiSiO5), and rutile (TiO2)-are the principal hosts of radioactive isotopes (e.g., of U, Th, Lu, Sm) and their decay products (e.g., isotopes of Pb, Hf, Nd) and also of trace elements such as the rare earths that are useful in deciphering geochemical processes. The research con-ducted under this grant is aimed at learning how these minerals participate in melting processes and metamorphic reactions, and how effectively they retain radiometric age in-formation and stable isotope ratios. Several types of experiments and measurements are conducted in order to characterize: 1) ionic diffusion in accessory minerals (e.g., of oxy-gen, Pb, Th and REE); and 2) solubility of zircon in silicic magmas and pelagic sediment-derived melts in subduction environments. We are also exploring cathodoluminescence (CL) as a means of semi-quantitative mapping of trace-element distribution in experi-mental samples. The intended long-range impact of the work is to enhance the ability of geochemists to understand and model the processes that redistribute the chemical elements in the Earth's crust.