Volcanic Time Scales, Eruption Rates, and Compositional Diversity at a Continental Arc

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This project, jointly supported by the Petrology and Geochemistry (EAR) and the Americas Programs (INT, is to perform an intensive 40Ar/39Ar dating study, coupled with quantitative estimates of erupted volumes, to fully characterize the volcanic history of three large central volcanoes in western Mexico and their surrounding peripheral vents. This proposed study would extend coverage of the total volcanic output (= 1 Ma) along a continuous 200 km arc segment, which is crucial in addressing global questions regarding the role of different subduction parameters on the eruptive output at arcs. In addition, new data on the eruptive history at individual volcanic fields significantly enhances geochemical and petrological data sets and allows more robust tests of the mechanisms and timescales for magma differentiation. The results of our proposed 40Ar/39Ar dating program will assist in the creation of volcanic hazards maps (independently, by Mexican scientists) in the proposed study area, which is the site of at least six, highly-explosive eruptions in the last 1 Myr, all from vents within = 40 km of Tepic, the capital of the state of Nayarit. Our collaboration with Dr. Hugo Delgado-Granados, from the Universidad Nacional Autonoma de Mexico (UNAM), has led to an extensive exchange of expertise and facilities between the University of Michigan and UNAM, as well as a series of student field trips that alternate between the U.S. and Mexico every other year. This project will provide training to two Ph.D. students (one female/one male), who will become skilled in Ar chronology, volcanic petrology, field mapping, and GIS (Geographic Information System) software tools.