Petrogenetic evolution of a Late Jurassic calc-alkaline plutonic complex, Klamath Mountains Province, U.S.A.: quantification by major- and trace-element modelling

IF 1.1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
L. Medaris, M. Svojtka, L. Ackerman, Spencer J. Cotkin
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Abstract

This investigation illustrates the use of major and trace elements to evaluate the petrogenetic evolution of the Late Jurassic Russian Peak Plutonic Complex in the Klamath Mountains Province, northern California, U.S.A. The two principal plutons in the complex consist of quartz diorite and granodiorite, both of which were most likely derived by partial melting of amphibolitic oceanic crustal sources and ultimately emplaced at a shallow level of ~10 km (Ptotal ~ 3 kbar). The major-element compositional variations in quartz diorite are consistent with crystallization of plagioclase (45 %) and amphibole (69 %) and resorption of clinopyroxene (–14 %). Major-element variations in granodiorite could have resulted from crystallization of plagioclase (60 %), amphibole (26 %), and biotite (14 %). Trace elements in whole-rocks and amphibole record different degrees of fractional crystallization, whole-rocks reflecting differentiation on a plutonic scale, and amphibole crystals reflecting differentiation on the scale of an individual sample. Quartz diorite experienced 10% fractional crystallization for the suite as a whole and 45% for individual samples; in contrast, granodiorite experienced 40% crystallization for the suite and 80% for individual samples. For both quartz diorite and granodiorite, comparisons of whole-rock REE patterns with those for melts calculated to be in equilibrium with amphibole demonstrate that the whole-rock REE compositions represent a combination of crystals and melts from evolving magmas, rather than melts alone.
美国克拉马斯山脉晚侏罗纪钙碱性深成岩体杂岩的岩石成因演化:通过主元素和微量元素模型进行量化
本次调查说明了主要元素和微量元素的使用,以评估美国加利福尼亚州北部克拉马斯山脉晚侏罗纪俄罗斯尖峰Plutonic杂岩体的岩石成因演化。该杂岩体中的两个主要深成岩体由石英闪长岩和花岗闪长岩组成,两者很可能是由角闪岩海洋地壳源的部分熔融引起的,并最终侵位在约10km的浅层(Ptotal~3kbar)。石英闪长岩中的主要元素组成变化与斜长石(45%)和角闪石(69%)的结晶以及斜辉石(-14%)的再吸收一致。花岗闪长岩中的主要元素变化可能是由斜长石(60%)、角闪石(26%)和黑云母(14%)结晶引起的。全岩和角闪石中的微量元素记录了不同程度的分级结晶,全岩反映了深成规模的分化,角闪石晶体反映了单个样品规模的分化。石英闪长岩整体经历了10%的分级结晶,单个样品经历了45%的分级结晶;相比之下,花岗闪长岩组经历了40%的结晶,单个样品经历了80%的结晶。对于石英闪长岩和花岗闪长岩,全岩REE模式与计算出与角闪石平衡的熔体的REE模式的比较表明,全岩稀土元素组成代表了来自演化岩浆的晶体和熔体的组合,而不是单独的熔体。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Geosciences
Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-MINERALOGY
CiteScore
2.30
自引率
7.10%
发文量
15
审稿时长
>12 weeks
期刊介绍: The Journal of Geosciences is an international peer-reviewed journal published by the Czech Geological Society with support from the Czech Geological Survey. It accepts high-quality original research or review papers dealing with all aspects of the nature and origin of igneous and metamorphic rocks. The Journal focuses, mainly but not exclusively, on: -Process-oriented regional studies of igneous and metamorphic complexes- Research in structural geology and tectonics- Igneous and metamorphic petrology- Mineral chemistry and mineralogy- Major- and trace-element geochemistry, isotope geochemistry- Dating igneous activity and metamorphic events- Experimental petrology and mineralogy- Theoretical models of igneous and metamorphic processes- Mineralizing processes and mineral deposits. All the papers are written in English, even though they may be accompanied by an additional Czech abstract. Each contribution is a subject to peer review by at least two independent reviewers, typically at least one from abroad. The Journal appears 2 to 4 times a year. Formally it is divided in annual volumes, each of them including 4 issues.
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