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首页> 外文期刊>Contributions to Mineralogy and Petrology >Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling
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Genesis of the post-caldera eastern Upper Basin Member rhyolites, Yellowstone, WY: from volcanic stratigraphy, geochemistry, and radiogenic isotope modeling

机译：威斯康星州黄石市火山后东部上盆地成员流纹岩的成因：来自火山地层学，地球化学和放射性同位素建模

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摘要

An array of samples from the eastern Upper Basin Member of the Plateau Rhyolite (EUBM) in the Yellowstone Plateau, Wyoming, were collected and analyzed to evaluate styles of deposition, geochemical variation, and plausible sources for low δ~(18)O rhyolites. Similar depositional styles and geochemistry suggest that the Tuff of Sulphur Creek and Tuff of Uncle Tom's Trail were both deposited from pyroclastic density currents and are most likely part of the same unit. The middle unit of the EUBM, the Canyon flow, may be composed of multiple flows based on a wide range of Pb isotopic ratios (e.g., ~(206)Pb/~(204)Pb ranges from 17.54 to 17.86). The youngest EUBM, the Dunraven Road flow, appears to be a ring fracture dome and contains isotopic ratios and sparse phenocrysts that are similar to extra-caldera rhyolites of the younger Roaring Mountain Member. Petrologic textures, more radiogenic ~(87)Sr/~(86)Sr in plagioclase phenocrysts (0.7134-0.7185) than groundmass and whole-rock ratios (0.7099-0.7161), and δ~(18)O depletions on the order of 5‰ found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving an initial source rock formed by assimilation and fractional crystallization processes, which cooled and was hydrothermally altered. The source rock was then lowered to melting depth by caldera collapse and remelted and erupted. The presence of a low δ~(18)O extra-caldera rhyolite indicates that country rock may have been hydrothermally altered at depth and then assimilated to form the Dunraven Road flow.
机译：收集并分析了来自怀俄明州黄石高原高原流纹岩东部上盆地成员的一系列样品，以评估低δ〜（18）O流纹岩的沉积方式，地球化学变化和合理来源。类似的沉积样式和地球化学表明，硫磺河凝灰岩和汤姆叔叔径的凝灰岩都是由火山碎屑密度流沉积的，很可能是同一单元的一部分。 EUBM的中间单元Canyon流可以基于多种Pb同位素比（例如〜（206）Pb /〜（204）Pb范围从17.54至17.86）由多个流组成。最年轻的EUBM（邓拉文路流）似乎是一个环形破裂的穹顶，其同位素比和稀疏的隐晶岩与年轻的咆哮山脉成员的破火山口流纹岩相似。岩石质地，斜长石隐晶（0.7134-0.7185）中的放射性（〜87）Sr /〜（86）Sr比地面质量比和整岩比（0.7099-0.7161）多，δ〜（18）O损耗约为5在硫磺河凝灰岩和峡谷流中发现的‰至少表明了两阶段的成岩作用，涉及由同化和分步结晶过程形成的初始烃源岩，该烃源岩冷却并热液化。然后通过破火山口塌陷将源岩降低到融化深度，然后重新融化并喷发。低δ〜（18）O破火山口流纹岩的存在表明，乡村岩石可能在深度发生了热液蚀变，然后被吸收形成了Dunraven Road流。

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