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首页> 外文期刊>Contributions to Mineralogy and Petrology >The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes, Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction
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The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes, Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction

机译：喀斯喀特弧（加利福尼亚州）沙斯塔山和梅迪奇湖火山中高镁岩浆的起源：高于和低于地幔氧同位素特征，归因于当前和过去的俯冲

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摘要

We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ~(18)O (δ~(18)O_(O1)) values of 5.9-6.l%o, which are about l%o higher than those observed in olivine from normal mantle-derived magmas. In contrast, HAOT lavas from Medicine Lake have δ~(18)O_(O1) values ranging from 4.7 to 5.5%o, which are similar to or lower than values for olivine in equilibrium with mantle-derived magmas. Other magma types from both volcanoes show intermediate δ~(18)O_(O1) values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace element composition of olivine phenocrysts precludes a pyroxenitic mantle source.
机译：我们报告了Mt Shasta和Medicine Lake火山的主要岩浆类型中熔岩中橄榄石和邻苯二甲酚表型的氧同位素组成：原始高铝橄榄石胆石（HAOT），玄武质安山岩（BA），原始镁质安山岩（PMA）和达西斯。来自山的最原始的HAOT（MgO> 9 wt％）。 Shasta的橄榄石δ〜（18）O（δ〜（18）O_（O1））值为5.9-6.l％o，比正常地幔衍生岩浆中的橄榄石观测值高约1％o。相比之下，Medicine Lake的HAOT熔岩的δ〜（18）O_（O1）值在4.7％至5.5％o之间，与与地幔源性岩浆处于平衡状态的橄榄石的值相似或更低。两个火山的其他岩浆类型均显示出中等的δ〜（18）O_（O1）值。大多数镁质熔岩的氧同位素组成不能用地壳污染来解释，并且橄榄石表晶的痕量元素组成排除了热释铁质地幔源。

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