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首页> 外文会议>Geothermal Resources Council annual meeting >Dynamic Open-System Volatile Evolution of a Shallow Magmatic System, China Hat, SE Idaho: Implications for Magmatic Associated Blind Geothermal Systems
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Dynamic Open-System Volatile Evolution of a Shallow Magmatic System, China Hat, SE Idaho: Implications for Magmatic Associated Blind Geothermal Systems

机译：浅岩浆系统的动态开放系统挥发性演化，爱达荷州中国帽子：对岩浆相关的盲地热系统的启示

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The Blackfoot Volcanic Field (BVF) of SE Idaho has received renewed interest in recent years as a region with geothermal potential, despite a paucity of surface features often associated with geothermal activity. This study builds upon recently discovered indications for a robust heat source at shallow depth under the BVF that is driven by open-system evolution of a topaz-rhyolite magmatic system at depths of 10-15 km. Primitive mantle derived basaltic magmas periodically transfer heat and mass into this rhyolite-dominated reservoir. We present new magmatic enclave data from the BVF's youngest topaz-rhyolites that are evidence for arrested mixing and homogenization between basalt and rhyolite end-members in this system. Episodic eruptions of highly evolved, volatile-rich topaz rhyolite magma ascending from the upper crustal magmatic system have occurred at least three times, with the most recent eruptions at ~75 and ~57 ka, forming the dome complexes of China Cap, China Hat, and North Cone. Pre-emptive magmatic conditions are inferred from new major-element and volatile quartz-hosted melt inclusion SIMS analyses that indicate three different populations of melt inclusions with variable H_2O contents between <1 and 4.5 wt % H_2O. We use this data to construct a model in which basaltic magma injection into the rhyolitic magma reservoir adds heat and mass into the system, driving an interaction of different regions of rhyolitic melt prior to eruption. Assuming volatile degassing upon rhyolite ascent, we calculated a release of 7.5-12 MT of H_2O from China Cap, and 36-60 MT of H_2O from China Hat and North Cone, over brief timescales. Incompatible elements, such as lithium, would be partitioned into this exsolved volatile phase, which may be the source of high Li contents measured in a brine sample collected from a deep high heat-flow well in the sedimentary geothermal reservoir adjacent to the BVF. Lithium therefore would play an important role as a tracer in tracking the magmatic component of deep fluids.
机译：爱达荷州的黑脚火山场（BVF）近年来作为具有地热潜力的地区重新引起了人们的兴趣，尽管通常与地热活动相关的地表特征很少。这项研究基于最近发现的在BVF下浅深度有坚固热源的迹象，该热源是由黄玉-流纹岩岩浆系统在10-15 km深度的开放系统演化驱动的。原始地幔衍生的玄武岩浆周期性地将热量和质量传递到该流纹岩为主的储层中。我们提供了BVF最年轻的黄玉-流纹岩的新岩浆飞地数据，这些数据证明了该系统中玄武岩和流纹岩最终成员之间的混合和均质化被阻止。从上地壳岩浆系统上升到高度演化，富含挥发性的黄玉流纹岩岩浆的间歇性喷发至少发生了三次，最近的喷发发生在〜75和〜57 ka，形成了中国帽，中国帽，和北锥。从新的主要元素和挥发性石英主导的熔体夹杂物SIMS分析可以推断出先发岩浆条件，该分析表明H_2O含量在<1至4.5 wt％H_2O之间的三种不同的熔体夹杂物种群。我们使用这些数据来构建一个模型，在该模型中，向流纹岩浆储层注入玄武岩浆会增加系统的热量和质量，从而在喷发之前驱使流纹岩熔体的不同区域相互作用。假设流纹岩上升时存在挥发性脱气，我们计算了在较短的时间范围内，从China Cap释放了7.5-12 MT的H_2O，从China Hat和North Cone释放了36-60 MT的H_2O。不相容的元素（例如锂）将被分配到该溶解的挥发性相中，这可能是在盐水样品中测得的高Li含量的来源，该盐水样品是从与BVF相邻的沉积地热储层中的深部高热流井收集的。因此，锂在追踪深层流体的岩浆成分方面将扮演重要的角色。

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