Coexisting Discrete Bodies of Rhyolite and Punctuated Volcanism Characterize Yellowstone's Post‐Lava Creek Tuff Caldera Evolution
Coexisting Discrete Bodies of Rhyolite and Punctuated Volcanism Characterize Yellowstone's Post‐Lava Creek Tuff Caldera Evolution
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DOI：
10.1029/2019gc008321
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发表时间：
2019-08
期刊：
影响因子：
3.7
通讯作者：
C. Till;J. Vazquez;M. Stelten;H. Shamloo;J. Shaffer
中科院分区：
文献类型：
--
作者：
C. Till;J. Vazquez;M. Stelten;H. Shamloo;J. Shaffer
离子微探针206 Pb/238 U地质年代学和微量元素地球化学的未抛光边缘和切片内部的锆石从黄石火山口的最古老的后火山口熔岩提供洞察岩浆系统在火山口形成熔岩溪超级爆发的前奏和后果。火山口后熔岩组成了高原流纹岩的上盆地段，根据锆石结晶年龄分为两组：锆石年龄在~750和550 ka之间的早期熔岩和锆石年龄在~350和250 ka之间的晚期熔岩。从早期爆发的东Bislava盆地流的锆石产生U-Pb年龄和微量元素组成，当考虑到其共存的长石和辉石的Pb同位素组成时，指向在熔岩溪岩浆结晶期间存在的同位素不同的母体熔体，但未被超喷发利用。早、晚期上盆段群主要矿物的不同锆石结晶年龄和铅同位素组成表明岩浆库中的不同来源。作为熔体演化的代表，锆石表明黄石公园的后破火山口流纹在更新世中期至晚期之间变得更加演化，在同一时间段内，热液改变的围岩熔融和新的岩浆补给改变了它们的相对作用。这项研究的结果表明，离散的和短暂的身体的火山岩浆，有时在一个糊状为主的水库，包括在前奏的熔岩溪喷发，黄石公园的次火山水库的特点。
Ion‐microprobe 206Pb/238U geochronology and trace element geochemistry of the unpolished rims and sectioned interiors of zircons from Yellowstone caldera's oldest post‐caldera lavas provide insight into the magmatic system during the prelude and aftermath of the caldera‐forming Lava Creek supereruption. The post‐caldera lavas compose the Upper Basin Member of the Plateau Rhyolite and fall into two groups based on zircon crystallization age: early lavas with zircon ages between ~750 and 550 ka and late lavas with zircon ages between ~350 and 250 ka. Zircons from the early‐erupted East Biscuit Basin flow yield U‐Pb dates and trace element compositions, which when considered with the Pb isotopic compositions of their coexisting feldspars and pyroxenes, point to an isotopically distinct parental melt present during crystallization of the Lava Creek magma but untapped by the supereruption. Distinct zircon crystallization ages and Pb‐isotope compositions of major minerals between the early and late Upper Basin Member groups suggest contrasting sources in the magma reservoir. As proxies for melt evolution, the zircons indicate that Yellowstone's post‐caldera rhyolites became more evolved between mid‐ to late‐Pleistocene time, during the same interval that melting of hydrothermally altered wall rock and recharge by new silicic magmas changed in their relative roles. The results from this study indicate that discrete and ephemeral bodies of silicic magma, at times within a mush dominated reservoir and including during the prelude to the Lava Creek eruption, have characterized Yellowstone's subvolcanic reservoir.