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

这项拟议研究的目标是通过建立该地区第四纪晚期(即50万年)火山活动的周期性和时空模式来评估美国西南部的火山灾害。火山危险性评估的一个基本组成部分是确定以前喷发的时间和地点。在美国西南部，年轻的喷发中心的位置是确定的。然而，现有的这些火山的地质年代学不够精确或完整，无法进行准确的危险评估。使用最先进的质谱仪将产生第四纪火山岩的超高精度Ar/Ar年龄。年龄将被用来计算喷发复发和休息间隔，以及岩浆供应率。将对该地区的火山灾害进行基于年龄的全面评估。有关美国西南部火山灾害的信息将通过各种外展活动向政府机构和公众提供。拟议研究的中心主题是利用地质年代学来全面了解美国西南部的火山灾害。新墨西哥州地质年代学研究实验室最近获得和开发了两台小容量、高灵敏度、多收集器的Argus VI质谱仪，常规地得出的年龄比以前的惰性气体质谱仪精确一个数量级。有了这些分析上的改进，晚第四纪火山系统的时空格局可以在以前无法获得的水平上得到表征。最初的努力将集中在新墨西哥州里奥格兰德裂谷和杰梅兹线条的众多玄武岩中心和稀疏的硅质穹顶上。其中一些中心，特别是那些50ka的中心，已经用其他方法测定了年代，为评估我们年龄的准确性提供了一种手段。除了评估火山灾害，超高精度的年龄可能有助于了解里奥格兰德裂谷的演化、壳-地幔动力学以及美国西南部的地形演化。

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.