Magmachronology and the Chemical Dynamics of Rhyolites

我们将利用锆石和allanite结晶史提供的独特时间框架，通过演化流纹岩系统来研究热通量和质量通量的相对量级。将研究四个主要的硅火山活动中心：1)美国加州长谷的主教凝灰岩和玻璃山流纹岩；2)印度尼西亚苏门答腊岛最年轻的多巴凝灰岩；3)怀俄明州黄石火山口杂岩中央高原段流纹岩；4)加州的科索火山场。通过原位离子探针238U-206Pb和238U-230Th定年，获得了单个晶域的年龄。在年龄分布的指导下，离子探针将用于确定晶体的微量元素分带分布及其熔体包裹体的组成。互补的同位素分析将通过微钻孔对特征良好的颗粒进行。我们的目标是：1)确定在火山口形成系统（长谷、多巴和黄石火山口）中分化的时间和晶体的分化“记忆”；2)研究富斑岩和贫斑岩（多巴和科索火山田）演化流纹岩体系的化学动力学。总的来说，这些研究将为流纹岩演化过程中长期冷却、岩浆补给和地壳同化之间的动态相互作用提供更深入的理解。

EAR-0003601ReidWe will utilize the unique chronological framework provided by the crystallization history of zircon and allanite to investigate the relative magnitudes of thermal and mass fluxes through evolving rhyolite systems. Four major centers of silicic volcanism will be studied: 1) the Bishop Tuff and Glass Mountain rhyolites of Long Valley, California; 2) the Youngest Toba Tuff of Sumatra, Indonesia; 3) the Central Plateau Member rhyolites of the Yellowstone caldera complex, Wyoming; and 4) Coso volcanic field, California. Ages of individual crystal domains will be obtained by in situ ion microprobe 238U-206Pb and 238U-230Th dating. Guided by the age distributions, the ion microprobe will be used to determine the trace element zoning profiles of the crystals and of the compositions of their melt inclusions. Complementary isotopic analyses will be performed by microdrilling of well-characterized grains. Our goals are: 1) to determine the timing of differentiation and the differentiation "memory" of crystals in caldera-forming systems (Long Valley, Toba, and Yellowstone calderas); and 2) to investigate the chemical dynamics of evolving rhyolite systems which are relatively phenocryst-rich and poor (Toba and Coso volcanic fields). Collectively, these studies will provide a deeper understanding of the dynamic interplay between secular cooling, magmatic recharge, and crustal assimilation in rhyolite evolution.