Petrogenetic connections between ash-flow tuffs and a granodioritic to granitic intrusive suite in the Sierra Nevada arc, California
Petrogenetic connections between ash-flow tuffs and a granodioritic to granitic intrusive suite in the Sierra Nevada arc, California
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DOI：
10.1130/ges00737.1
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发表时间：
2012-04
期刊：
影响因子：
2.5
通讯作者：
A. Barth;A. D. G. Feilen;S. Yager;S. Douglas;J. Wooden;N. Riggs;J. Walker
中科院分区：
文献类型：
--
作者：
A. Barth;A. D. G. Feilen;S. Yager;S. Douglas;J. Wooden;N. Riggs;J. Walker
微量元素分析的火山灰流凝灰岩和花岗质岩石在中东部的Sierran内华达州，结合U-Pb锆石年龄和微量元素丰度在整个岩石中，使我们能够解释一个共享的岩浆遗产广泛喷发的火山灰流凝灰岩和组装的一个典型的Sierran花岗闪长岩花岗岩侵入岩套。凝灰岩的石英、长石、黑云母和角闪石的斑晶含量为5%-15%，硅含量为70%-74%，碱丰度变化不定，但始终富含轻稀土，并伴有微弱的负Eu异常，表明凝灰岩的化学分类为热液蚀变、弧型、低硅流纹岩。凝灰岩的锆石U-Pb结晶年龄为232、224和219 Ma，表明爆发性火山作用在下面的226-218 Ma白钨矿侵入岩套（Sierra内华达州岩基中最古老和最大的侵入岩套之一）中花岗闪长岩到花岗质岩体侵位之前就开始了，并在整个侵位过程中持续进行。从灰流凝灰岩和同时代的长英质花岗闪长岩和花岗岩的锆石晶体显示出明显的化学分区和广泛的重叠微量元素丰度，表明结晶的锆石从非常相似的熔体组合物，尽管不同的后期冷却的历史。这些数据提供了一个统一的火山深成模型的Sierran弧岩浆作用，描述了一个长寿命的，多阶段的岩浆系统组成的增量侵位，花岗闪长岩花岗岩侵入套在上地壳，覆盖广泛的存款所产生的熔结凝灰岩喷发热再生长英质晶体泥。
Trace-element analyses of zircons from ash-flow tuffs and granitic rocks in the east-central Sierran Nevada, combined with U-Pb zircon ages and trace-element abundances in whole rocks, allow us to interpret a shared magmatic heritage for widespread eruption of ash-flow tuffs and assembly of a typical Sierran granodioritic to granitic intrusive suite. The tuffs have 5%-15% phenocrysts of quartz, feldspar, biotite, and amphibole, silica contents ranging from 70% to 74%, and have variable alkali abundances but are consistently light rare-earth enriched with weak negative Eu anomalies, suggesting chemical classification as hydrothermally altered, arc-type, low-silica rhyolites. The tuffs yielded U-Pb zircon crystallization ages of 232, 224, and 219 Ma, indicating that explosive volcanism began before and continued throughout emplacement of granodioritic to granitic plutons in the underlying 226-218 Ma Scheelite Intrusive Suite, one of the oldest and largest intrusive suites in the Sierra Nevada batholith. Zircon crystals from ash-flow tuffs and contemporaneous felsic granodiorite and granite show distinct chemical zoning and extensive overlap in trace-element abundances, indicating crystallization of zircons from very similar melt compositions despite dissimilar late cooling histories. These data provide evidence for a unified volcano-plutonic model for Sierran arc magmatism that describes a long-lived, multi-stage magma system composed of an incrementally emplaced, granodioritic to granitic intrusive suite in the upper crust, overlain by widespread deposits of ignimbrite eruptions generated by thermal rejuvenation of felsic crystal mushes.