Development and Calibration of Rutile (U-Th)/He Geo- and Thermochronometry

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(U-Th)/He dating of phosphate and silicate minerals such as apatite, zircon, monazite, and titanite has attracted considerable interest; however, U- and Th-bearing Fe- or Ti-oxides have not been systematically investigated and developed as low-T thermochronometers. A common oxide mineral is rutile (TiO2), which is present as an accessory mineral in many magmatic rocks and also occurs widely in high-grade metamorphic rocks, especially in blueschists, eclogites, and granulites. We propose to develop and calibrate rutile (U-Th)/He geo- and thermochronometry by investigating its He diffusion characteristics; we will include such factors as grain size and chemical composition. Furthermore, we will test rutile (U-Th)/He dating on fast-cooled volcanic rocks as well as more slowly-cooled sample arrays from the KTB ultra-deep borehole and an exhumed extensional fault block in the Wassuk Range, western Basin and Range province. We will also apply rutile (U-Th)/He thermochronometry to date the cooling of high-pressure metamorphic rocks from Oman. The (U-Th)/He calibration of rutile will provide a new geo- and thermochronometer that will be widely applicable, but should be especially useful for studies of high-P to ultrahigh-P samples that are notoriously difficult or impossible to date at the present. The scientific results and methodologies developed during our study will be disseminated to the geosciences community through publication of research papers and presentations at international meetings. The study will significantly impact the education of two students that will work with the PIs in the KU (U-Th)/He and TIMS laboratories, providing them the opportunity for active learning and exposing them to state-of-the-art analytical facilities and new research directions. This background will be important to the intellectual growth of the students and give them experience in working in collaborative and group/team situations.