Accessory Minerals and Crustal Processes

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9527014 Watson The objective of the proposed research is to increase our understanding of accessory minerals (particularly zircon) in the physiochemical environment of the mid- to lower-crust. This project will include a combination of experiments, analyses of natural materials and numerical modeling. Several sub-projects are planned, including: (1) continuation of lattice diffusion measurements by Rutherford backscattering spectroscopy on the parent and daughter isotopes of key isotopic systems (U-Pb, Sm-Nd, Lu-Hf); (2) calibration of geothermometers involving zircon coexisting with a phosphate mineral; (3) numerical modeling of crystal growth and dissolution and the processes that lead to chemical zoning; (4) imaging of internal structures (e.g. zoning, overgrowths) and correlation of these features with in situ isotopic analyses; and (5) development of cathodluminescence spectroscopy (CL) in combination with electron microprobe analysis as a means of identifying and distinguishing the origin of various growth regions within individual zircons. The proposed work will provide the tools and insights needed to take full advantage of accessory minerals as recorders of the timing and temperature of crustal events.