Residence Times of Silicic Magmas

9706519雷德大型、高度爆炸性的喷发反映了岩浆在地壳浅层的积累，这反过来又需要输入的热量远远超过输出的热量。因此，岩浆堆积和成分修改的持续时间是火山热史的记录，对于大量的流纹岩岩浆来说，火山可能在数万到数百万年的时间尺度上运行。为了确定岩浆堆积的动力学，将改进和使用三种新的方法来测定流纹岩岩浆中矿物的结晶年龄。其中两种方法将利用高分辨率的离子微探针，这将使单个锆石和尿晶石晶体的年龄，并获得晶体生长的详细记录。第三种方法将根据它们所含玻璃包裹体的年龄来确定石英结晶的时间。主要的流纹岩火山活动中心，包括长谷(加利福尼亚州)，黄石公园(怀俄明州)和托巴(苏门答腊岛)火山口，将被调查。从这些研究中收集的见解将与结晶的温度依赖性结合起来，开发与大体积硅质系统有关的流纹岩岩浆的热演化模型。

9706519 Reid Large, highly explosive eruptions reflect the accumulation of magma at shallow crustal levels, which in turn, requires a heat input significantly in excess of output. The duration of magma accumulation and compositional modification is therefore a record of the thermal history of a volcano which, for voluminous rhyolitic magmas, may operate over timescales of tens of thousands to millions of years. To delimit the dynamics of magma accumulation, three new methods for dating the crystallization of minerals from rhyolitic magmas will be refined and employed. Two of these methods will utilize a high resolution ion microprobe which will enable individual zircon and allanite crystals to be dated and a detailed record of crystal growth to be obtained. The third method will determine the timing of quartz crystallization from age of the glass inclusions they contain. Major centers of rhyolitic volcanism, including Long Valley (California), Yellowstone (Wyoming), and Toba (Sumatra) calderas, will be investigated. The insights gathered from these studies will be used in conjunction with the temperature-dependence of crystallization to develop models for the thermal evolution of rhyolitic magmas associated with large-volume silicic systems.