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首页> 外文期刊>Contributions to Mineralogy and Petrology >The Blacktail Creek Tuff: an analytical and experimental study of rhyolites from the Heise volcanic field, Yellowstone hotspot system
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The Blacktail Creek Tuff: an analytical and experimental study of rhyolites from the Heise volcanic field, Yellowstone hotspot system

机译：Blacktail Creek凝灰岩：黄石热点系统中Heise火山场流纹岩的分析和实验研究

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摘要

The magma storage conditions of the 6.62 Ma Blacktail Creek Tuff eruption, belonging to the Heise volcanic field (6.62-4.45 Ma old) of the Yellowstone hotspot system, have been investigated by combining thermobarometric and experimental approaches. The results from different geothermometers (e.g., Fe-Ti oxides, feldspar pairs, apatite and zircon solubility, and Ti in quartz) indicate a pre-eruptive temperature in the range 825-875 degrees C. The temperature estimated using two-pyroxene pairs varies in a range of 810-950 degrees C, but the pyroxenes are probably not in equilibrium with each other, and the analytical results of melt inclusion in pyroxenes indicate a complex history for clinopyroxene, which hosts two compositionally different inclusion types. One natural Blacktail Creek Tuff rock sample has been used to determine experimentally the equilibrium phase assemblages in the pressure range 100500 MPa and a water activity range 0.1-1.0. The experiments have been performed at fluid-present conditions, with a fluid phase composed of H2O and CO2, as well as at fluid-absent conditions. The stability of the quartzo-feldspathic phases is similar in both types of experiments, but the presence of mafic minerals such as biotite and clinopyroxene is strongly dependent on the experimental approach. Possible explanations are given for this discrepancy which may have strong impacts on the choice of appropriate experimental approaches for the determination of magma storage conditions. The comparison of the composition of natural phases and of experimentally synthesized phases confirms magma storage temperatures of 845-875 degrees C. Melt water contents of 1.5-2.5 wt% H2O are required to reproduce the natural Blacktail Creek Tuff mineral assemblage at these temperatures. Using the Ti-in-quartz barometer and the Qz-AbOr proportions of natural matrix glasses, coexisting with quartz, plagioclase and sanidine, the depth of magma storage is estimated to be in a pressure range between 130 and 250 MPa.
机译：结合热压法和实验方法，研究了黄石热点地区Heise火山场（6.62-4.45 Ma老）的6.62 Ma Blacktail Creek Tuff喷发的岩浆储存条件。来自不同地热仪的结果（例如，Fe-Ti氧化物，长石对，磷灰石和锆石的溶解度以及石英中的Ti）表明火山爆发前的温度在825-875摄氏度范围内。使用两个py对估计的温度会有所不同在810-950摄氏度的温度范围内，辉石可能彼此不平衡，而且辉石中熔融夹杂物的分析结果表明，斜辉石的历史很复杂，其包含两种成分不同的夹杂物类型。一种天然黑尾溪凝灰岩岩石样品已被用于实验确定压力范围为100500 MPa和水活度范围为0.1-1.0的平衡相组合。实验是在流体存在的条件下，由H2O和CO2组成的流体相以及没有流体的条件下进行的。在这两种类型的实验中，石英长石相的稳定性都相似，但是黑镁铁矿如黑云母和斜辉石的存在强烈依赖于实验方法。对于这种差异给出了可能的解释，这可能会对确定岩浆储存条件的适当实验方法的选择产生重大影响。天然相和实验合成相组成的比较证实了岩浆的储存温度为845-875摄氏度。在这些温度下，要重现天然的Blacktail Creek Tuff矿物组合，需要1.5-2.5 wt％H2O的熔融水含量。使用石英石英气压计和Qz-AbOr比例的天然基质玻璃与石英，斜长石和山梨碱共存，可以估计岩浆的储藏深度在130 MPa至250 MPa之间。

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