AAPG Foundation 2019 Grants-in-Aid Projects

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High-resolution paleomagnetic and 40Ar/39Ar age characterization of volcanic sequences at the Goat Rocks volcanic complex, Washington State

Abstract

My work at the Goat Rocks volcanic complex is aimed at understanding the long-lived chemical feedbacks between magma and crust, which applies to the formation of hydrothermal ore deposits (e.g. 1, 2). The proposed project emphasizes the stratigraphic reconstruction of the eruption chronology by way of magnetostratigraphy, taking advantage of an extremely rare opportunity to sample multiple geomagnetic instabilities in high resolution at the same location. Paleomagnetic field orientation and intensity in lava flow sequences will not only provide a chronologic framework for eruptions (e.g. 3, 4), but precise 40Ar/39Ar dating of such sequences will in turn refine the geomagnetic polarity time scale (4, 5). I plan to sample detailed transects across the short-lived magnetic instabilities recorded at Goat Rocks (6), including the Punaru’u excursion (~1115 ka; 7), Matuyama-Brunhes reversal (~773 ka; 8), and Big Lost and/or West Eifel 4 excursions (~570 ka and ~555 ka; 9). Oriented samples will be demagnetized at the Caltech paleomagnetism lab, and argon ages will be determined at Oregon State University for key samples that bracket or transect major events. Results will significantly improve correlation of disconnected lava sequences at Goat Rocks, yielding better estimates of the eruptive history and magma flux rates at this major arc volcano. Furthermore, the proposed work will provide data toward a more accurate and complete geomagnetic polarity time scale, directly benefitting magnetostratigraphic studies of sedimentary sequences and the correlation of stratigraphic sections across the globe.