Residence Times of Silicic Magmas

大的、高度爆炸性的喷发反映了岩浆在地壳浅层的积累，而这反过来又需要大大超过输出的热量输入。因此，岩浆聚集和成分变化的持续时间是火山热史的记录，对于大量流纹岩岩浆来说，火山热史可能在数万年到数百万年的时间尺度上发生作用。为了确定岩浆聚集动力学，本文将改进并采用三种新的流纹岩岩浆矿物结晶测年方法。其中两种方法将使用高分辨率离子微探针，这将使单个锆石和allanite晶体能够确定年代，并获得晶体生长的详细记录。第三种方法将根据它们所含的玻璃夹杂物的年龄来确定石英结晶的时间。流纹岩火山活动的主要中心，包括长谷（加利福尼亚）、黄石（怀俄明州）和多巴（苏门答腊）火山口，将被调查。从这些研究中收集到的见解将与结晶的温度依赖性相结合，用于开发与大体积硅系统相关的流纹岩岩浆热演化模型。

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.