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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Understanding the isotopic and chemical evolution of Yellowstone hot spot magmatism using magmatic-thermomechanical modeling
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Understanding the isotopic and chemical evolution of Yellowstone hot spot magmatism using magmatic-thermomechanical modeling

机译：利用岩浆热力学模型了解黄石热点岩浆活动的同位素和化学演化

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Large-scale melting and reworking of the crust and the upper mantle occurs in areas of mantle plume-crust interaction, generating voluminous and bimodal basaltic and silicic magmatism. Continental hot spot track magmas preserve geochemical and temporal records of these processes. Here, we apply and further develop the large scale (crust and the upper mantle) I2VIS magmatic-thermomechanical modeling code to investigate the potential origins of chemical and isotopic trends in the Yellowstone hot spot track, perhaps the best studied and constrained subcontinental mantle plume system on Earth. We model the propagation of melt via dikes in solid crust and via percolation in partially molten crust by using Lagrangian markers which also track the chemical and isotopic compositions of the melts that eventually erupt at the surface. Confirming the results of earlier geophysical and geochemical studies, we show that the eruptive activity at Yellowstone is best explained in terms of the formation of a similar to 15 km-thick mid-crustal mafic sill complex with its top at a depth of similar to 8 km that develops over a period of similar to 3 Myr. This sill complex releases rhyolitic fractionates and creates additional rhyolites by melting the surrounding crust, driving the voluminous rhyolitic volcanism which characterizes the Yellowstone system.We recognize three key trends in the evolution of a continental hot spot volcanic center such as Yellowstone: (1) frequent, small eruptions results in in larger erupted rhyolite volumes compared to rare and large eruptions, (2) erupted magmas tend to be initially comprised of a large degree of crustal melt, and the relative contribution of fractionates of basalts from the mantle increases with time, and (3), the initial depth of the crust which melts to produce eruptible rhyolites becomes shallower with time. The first of these trends is simply a function of the continuous supply of new basalt to the crust from the mantle. The latter trend, which is responsible for low-delta O-18 rhyolites, is produced by a combination of progressive melting of shallower crust as the system becomes hotter, repeated caldera collapses adverting shallow crust to a depth where it can melt, and the overplating and burial of shallow crust by repeated intrusions of basalt. The mid- and lower crust is not a significant source of erupted rhyolitic melts, as both the crustal melting and basalt fractionation takes place in the sill complex which forms near the bottom of the upper crust. The resulting modeled isotopic evolution of erupted magmas are a good match with the actual stable and radiogenic isotopic record of Yellowstone hot spot track volcanism preserved in zircon phenocrysts, and further replicates the results of recent geophysical imaging campaigns, giving us confidence that the assumptions and results of these thermomechanical models are broadly correct. (C) 2018 Elsevier B.V. All rights reserved.
机译：地幔柱与地壳相互作用的区域发生了地壳和上地幔的大规模熔化和返工，产生了大量的和双峰的玄武质和硅质岩浆作用。大陆热点轨道岩浆保留了这些过程的地球化学和时间记录。在这里，我们应用并进一步开发大规模（地壳和上地幔）I2VIS岩浆-热力学建模代码，以研究黄石热点轨迹中化学和同位素趋势的潜在起源，也许是研究得最好和受约束的次大陆架地幔柱系统。在地球上。我们使用拉格朗日标记对通过固体壳中的堤坝和部分熔融的壳中的渗透进行的熔体传播进行建模，该拉格朗日标记还跟踪最终在表面喷出的熔体的化学和同位素组成。证实了较早的地球物理和地球化学研究的结果，我们表明，黄石的喷发活动可以通过形成类似于15 km厚的中地壳铁镁质基岩复合体的方式得到最好的解释，其顶部的深度类似于8 km的发展类似于3 Myr。这种基石复合物释放流纹岩级分，并通过融化周围的地壳，驱动黄石系统特有的大量流纹岩火山作用而形成额外的流纹岩。我们认识到大陆热点火山中心（如黄石）演化的三个关键趋势：（1）频繁发生，与稀有和大型喷发相比，小喷发导致流纹岩的喷发量更大；（2）喷出的岩浆起初通常由大量的地壳融化组成，而地幔中玄武岩馏分的相对贡献随时间增加， （3）随着时间的流逝，融化产生易爆流纹岩的地壳的初始深度变浅。这些趋势中的第一个仅是不断从地幔向地壳供应新玄武岩的函数。后一种趋势是由低δO-18流纹岩造​​成的，这是由于随着系统温度的升高，浅层地壳逐渐融化，破火山口反复崩塌，使浅层地壳逐渐融化到一定深度而形成的，这种趋势是由反复侵入玄武岩并埋藏浅层地壳。中地壳和下地壳并不是流纹岩熔岩喷出的重要来源，因为地壳熔融和玄武岩分馏都发生在靠近上地壳底部的基岩复合物中。由此产生的岩浆喷发同位素演化模型与锆石斑岩中保存的黄石热点径迹火山活动的实际稳定和放射性同位素记录非常吻合，并进一步复制了最近的地球物理成像活动的结果，使我们相信这些假设和结果这些热力学模型中的大部分是正确的。 （C）2018 Elsevier B.V.保留所有权利。

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