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首页> 外文期刊>Contributions to Mineralogy and Petrology >The genesis of arc dacites: the case of Mount St. Helens, WA
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The genesis of arc dacites: the case of Mount St. Helens, WA

机译：弧形Dacites的成因：瓦斯山，WA

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Throughout the last 35ka, Mount St. Helens has been the most active volcano in the Cascade arc, but the origin of its voluminous dacites remains controversial. These dacites were traditionally interpreted as a result of melting metabasaltic lower crust. Yet, recent studies have challenged this view and suggested an origin dominated by differentiation of mafic magmas through assimilation-fractional crystallization (AFC) processes. To address this discrepancy on the origin of dacites at Mount St. Helens, we conduct an interdisciplinary study using a combination of thermal and geochemical modeling. Our results show that 45% crystallization of a basaltic andesite parent reproduces the compositions of the dacites with a maximum of 20-30% assimilation of lower crustal lithologies. Amphibole textures and compositions support such a differentiation trend in a polybaric mush system. Combined with recent geophysical imaging and experimental data, we suggest that Mount St. Helens dacites are generated by (1) mantle-derived arc magma evolving by AFC to intermediate compositions in a lower crustal magma reservoir and (2) ascent of these magmas to a mid to upper crustal reservoir, where they reach high crystallinity without significant further chemical differentiation, and are subject to frequent recharge that leave a clear mixing/mingling overprint.
机译：在过去的35KA中，圣海伦山是级联弧中最活跃的火山，但它的巨大愚蠢的起源仍然存在争议。这些愚蠢的传统上被解释为熔化符合甲基抗性下外壳。然而，最近的研究已经挑战了这一观点，并建议通过同化分数结晶（AFC）过程来统治MAFIC岩浆的分化来源。为了解决St. Helens山的Dacces起源的这种差异，我们使用热和地球化学建模的组合进行跨学科研究。我们的研究结果表明，玄武岩矿石母体的45％结晶再现愚蠢的组合物，最多20-30％的较低地壳岩性同化。 Amphibole纹理和组合物支持多标压榨系统中的这种分化趋势。结合近期地球物理成像和实验数据，我们建议圣海伦山达克斯山型由（1）由AFC演变为下层地壳岩浆储存器中的中间组合物的披风衍生的弧形岩浆生成，（2）上升至这些岩浆到A.中到上层地壳储层，在那里它们达到高结晶度，没有显着进一步的进一步分化，并且经常再充电，留下清晰的混合/混合套印。

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