EAR-PF: Tracking rocks from depth to the surface: Coupled (U-Th)/(Pb-He) dating of monazite

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Dr. Emily M. Peterman has been granted the NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at Stanford University. This research will develop and calibrate a new technique to determine particle paths within the crust from a single key mineral that is present in many rocks. Monazite is a uranium- and thorium-bearing phosphate that can be analyzed by multiple methods to provide isotopic age information that bear upon both the timing of high-temperature crystallization and subsequent lower-temperature cooling during crustal residence. Furthermore, the trace element and isotopic composition of monazite can be linked to growth conditions within the crust. By combining all of this information, the newly developed approach will improve our ability to quantitatively reconstruct the spatial and temporal nature of crust-forming processes.This comprehensive analysis of the use of monazite as a chronometer for elucidating the formation and evolution of continental crust will impact a broad range of geoscience disciplines, including tectonics, geomorphology, metamorphic petrology, landscape evolution and continental dynamics. By improving the accuracy and precision of monazite isotopic age analysis, this research will improve our ability to constrain geodynamic models of crustal evolution. The details of the new methodology - including the calibration of compositionally dependent effects - may have application to other techniques, and should benefit the geoochronologic community at large. Research methods developed in this project will be integrated into a field-based course to be taught by Peterman in Death Valley. Through this course, undergraduate and graduate students will be taught how to collect samples, analyze data, and publish a paper that constrains the timing of deformation along a major fault that exposes some of the deepest-known exposures of southwestern North American crust. The results from this study will also be incorporated into an outreach demonstration that uses coupled monazite chronometry to provide an animated module that illustrates the mechanics, timing and rates of processes responsible for creating dynamic orogens such as the Himalaya.