Volcanic Hazard Assessment in the Southwestern US Based on High-precision Ar/Ar Geochronology of Late Quaternary Eruptive Centers

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The goal of the proposed research is to assess the volcanic hazards in the southwestern US by establishing the periodicity and temporal-spatial patterns of late Quaternary (i.e., 500,000 yrs) volcanism in the region. One of the fundamental components of volcanic hazard assessment is determining the timing and location of previous eruptions. The location of young eruptive centers in the southwestern US is well established. However, the existing geochronology for these volcanoes is not sufficiently precise or complete for an accurate hazard assessment. Ultra-high precision Ar/Ar ages will be generated for Quaternary volcanic rocks using state of the art mass spectrometers. Ages will be used to calculate eruption recurrence and repose intervals, and magma supply rates. A comprehensive age-based assessment of volcanic hazards will be generated for the region. Information regarding volcanic hazards for the southwestern US will be made available to government agencies and the general public through a variety of outreach activities.The central theme to the proposed research is using geochronology to develop a comprehensive understanding of volcanic hazards in the southwestern US. Recent acquisition and development of two low-volume, high-sensitivity, multicollector ARGUS VI mass spectrometers at the New Mexico Geochronology Research Laboratory routinely yield ages that are about an order of magnitude more precise than previous noble gas mass spectrometers. With these analytical improvements, the temporal-spatial patterns of late Quaternary volcanic systems can be characterized at a level that was previously unobtainable. Initial efforts will focus on the numerous basaltic centers and sparse silicic domes in the Rio Grande Rift and Jemez Lineament within New Mexico. Some of these centers, especially those 50 ka, have been dated by other methods providing a means to assess the accuracy of our ages. In addition to assessing volcanic hazards, the ultra-high precision ages will likely be useful for understanding the evolution of the Rio Grande Rift, crust-mantle dynamics, and landscape evolution of the southwestern US.