Magmachronology and the Chemical Dynamics of Rhyolites

我们将利用锆石和褐帘石结晶历史提供的独特年代框架，通过不断演变的流纹岩系统来研究热通量和质量通量的相对大小。 将研究四个主要的火山活动中心：1）加州长谷的主教凝灰岩和玻璃山流纹; 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复合体的中央高原段流纹;和4）加州的科索火山场。 用原位离子探针~（238）U-~（206）Pb和~（238）U-~（230）Th测年方法获得各晶畴的年龄。 在年龄分布的指导下，离子探针将用于确定晶体及其熔体包裹体成分的微量元素分带剖面。 将通过对特征明确的颗粒进行微钻来进行补充同位素分析。 我们的目标是：1）确定火山口形成系统（长谷、多巴和黄石火山口）中晶体的分异时间和分异“记忆”; 2）研究相对富斑和贫斑的演化流纹岩系统（多巴和科索火山区）的化学动力学。 总的来说，这些研究将提供一个更深入的了解长期冷却，岩浆补给和地壳同化流纹岩演化之间的动态相互作用。

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.