Time scales of magma storage and differentiation of voluminous high-silica rhyolites at Yellowstone caldera, Wyoming
Time scales of magma storage and differentiation of voluminous high-silica rhyolites at Yellowstone caldera, Wyoming
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DOI：
10.1007/s00410-002-0400-7
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发表时间：
2002-12
影响因子：
3.5
通讯作者：
J. Vazquez;M. Reid
中科院分区：
文献类型：
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作者：
J. Vazquez;M. Reid
黄石火山口崩塌后流纹岩中锆石的离子探针测年揭示了岩浆在不同岩浆库中结晶和储存的时间尺度，火山口形成岩浆作用中晶体再循环的作用，以及晶体-熔体分离的时间和功效。在70 ~ 160 ka之间逐渐喷发的大量（~900 km ~ 3）中央高原段熔岩中，锆石的238 U-230 Th不平衡年龄主要跨越从各自喷发到~200 ka的范围，平均年龄为~200 ka。喷发前60，000年。当考虑到与微量元素和Sr-和Nd-同位素组成的主机熔体，CPM锆石的年龄分布表明，韵律是同生和分化的数万年前喷发的不断发展的岩浆库。因此，后破火山口CPM流纹岩并没有从一个长期存在的流纹岩岩浆从破火山口形成的喷发遗留下来的身体，也不代表显着的火山口的深成根的再动员。相反，CPM岩浆的产生和分化的情节有效的晶体熔体分离在~200和~125万年，持续的热输入，存储的时间尺度上与其他大量的破火山口相关的rhythmic估计。
Ion microprobe dating of zircons from post-collapse rhyolites at Yellowstone caldera reveals the time scales of crystallization and storage of silicic magma in a differentiating magma reservoir, the role of recycling of crystals from the caldera-forming magmatism, and the timing and efficacy of crystal-melt separation. Zircons in the voluminous (~900 km3) Central Plateau Member lavas, which progressively erupted between 70 to 160 ka, yield238U-230Th disequilibrium ages dominantly spanning the range from those of their respective eruptions to ~200 ka; mean zircon ages range to ca. 60,000 years before eruption. When considered together with the trace element and Sr- and Nd-isotope compositions of their host melts, the age distributions of the CPM zircons show that the rhyolites are cogenetic and differentiated tens of thousands of years prior to eruption from an evolving magma reservoir. Thus, the post-caldera CPM rhyolites were not erupted from a long-standing body of rhyolitic magma left over from the caldera-forming eruption, nor do they represent significant remobilization of the plutonic roots of the caldera. Rather, the CPM magma was generated and differentiated by episodes of effective crystal-melt separation at ~200 and ~125 ka and, sustained by thermal inputs, stored for timescales on par with estimates for other voluminous caldera-related rhyolites.