Development of a Micro-baddeleyite (ZrO2) U-series Chronometer for Recent Mafic Lavas

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Reconstructing the pre- and post-eruptive chronology of past volcanic eruptions is essential for understanding the patterns of human response to natural disasters, and to devise mitigation strategies for extant volcanic hazards. Despite the maturity of many geochronological techniques applied to date Quaternary volcanic eruptions, considerable uncertainties remain with regard to the timing of magmatic processes culminating in violent eruptions, as well as their environmental impact even for fairly recent events. This research will develop a dating tool for common types of volcanoes characterized by comparatively low silica abundances, which can be difficult to date using existing chronometers. Ultimately, improved age constraints on the eruptive history of such volcanoes will lead to better assessments of their volcanic hazards.The new chronometer is based on the radioactive decay of uranium intrinsic to the crystal lattice of baddeleyite, a zirconium oxide mineral. Crystal sizes for baddeleyite are typically small, and therefore this research will improve electron-beam techniques for locating micro-baddeleyite crystals in rocks, and develop analytical procedures to analyze baddeleyite via secondary ionization mass spectrometry to detect trace abundances of uranium and its radioactive decay products. Representative volcanoes will be investigated to calibrate the baddeleyite chronometer against other dating techniques. For this, University of California Los Angeles researchers are collaborating with domestic and international volcanologists. Case studies include volcanoes in the Cascades (USA) and the Campanian volcanic province (Italy). These volcanoes represent long-lived volcanic systems with a protracted history of recurrent eruptions over tens to hundred thousands of years. Establishing precise and accurate volcanic chronostratigraphies through baddeleyite uranium disequilibrium dating will ultimately contribute to an improved understanding of magma output rates and eruptive recurrence intervals in a broad range of magmatic environments.