Magmachronology and the Chemical Dynamics of Rhyolites

EAR-0003601Reid我们将利用锆石和尿晶石结晶历史提供的独特年代学框架，研究流纹岩系统演化过程中热通量和质量通量的相对大小。硅质火山作用的四个主要中心将被研究：1)加利福尼亚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托巴凝灰岩；3)怀俄明州黄石火山口杂岩的中央高原成员流纹岩；以及4)加利福尼亚州的科索火山场。通过原位离子探针238U-206Pb和238U-230Th测年，可以获得单个晶区的年龄。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剖面及其熔体包裹体的成分。补充同位素分析将通过对特征良好的颗粒进行微钻来进行。我们的目标是：1)确定火山口形成系统(Long Valley、Toba和Yellowstone火山口)中晶体的分化时间和晶体的分化“记忆”；以及2)研究相对斑晶丰富和相对贫乏的流纹岩系统(Toba和Coso火山田)的化学动力学。总而言之，这些研究将对流纹岩演化中长期冷却、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.