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首页> 外文期刊>Contributions to Mineralogy and Petrology >High-temperature hydrothermal alteration of the Boehls Butte anorthosite: origin of a bimodal plagioclase assemblage
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High-temperature hydrothermal alteration of the Boehls Butte anorthosite: origin of a bimodal plagioclase assemblage

机译：Boehls Butte钙长石的高温热液蚀变：双峰斜长石组合的起源

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摘要

The Boehls Butte anorthosite consists predominantly of an unusual bimodal assemblage of andesine and bytownite-anorthite. Oxygen isotope compositions of the anorthosite were profoundly altered by high temperature, retrograde interaction with meteoric-hydrothermal fluids that varied in composition from iso-topically evolved to nearly pristine meteoric water. Oxygen isotope ratios of bulk plagioclase separates are in the range + 7.0 to -6.2 per thousand V-SMOW, however, secondary ion mass spectrometry indicates spot-sized isotope values as low as - 16 per thousand. Typical inter- and intra-plagioclase grain variability is 3-6 per thousand, and extreme heterogeneity of up to 20 per thousand is noted in a few samples. High-temperature hydrothermal alteration of intermediate plagioclase is proposed to explain the origin of bytownite-anorthite in the anorthosite and creation of its unusual bimodal plagioclase assemblage. The anorthite-forming reaction created retrograde reaction-enhanced permeability which, together with rapid decompression, extension, and unroofing of the anorthosite complex, helped to accommodated influx of significant volumes of meteoric-hydrothermal fluids into the anorthosite.
机译：Boehls Butte钙钛矿主要由安第斯山和副镇长-钙长石组成的不寻常的双峰组合。高温，逆流与陨石-水热流体的逆向相互作用极大地改变了钙硅钙石的氧同位素组成，而该流体的组成从同位素演化到近乎原始的陨石水。大部分斜长石分离物的氧同位素比在每7.0 V-SMOW + 7.0至-6.2范围内，但是，二次离子质谱法表明，点大小的同位素值低至每千V-16。典型的斜长石间和斜长石内部的晶粒变异性是千分之三至六，在一些样本中，异常异质性高达千分之二十。提出了中间斜长石的高温水热蚀变，以解释钙长石中钙钛矿-钙长石的起源及其异常的双峰斜长石组合的产生。形成钙长石的反应产生了逆行反应增强的渗透性，再加上快速的减压，伸展和无顶斜复合物的屋顶化，有助于容纳大量的陨石-水热流体涌入该斜长岩。

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