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首页> 外文期刊>Contributions to Mineralogy and Petrology >Construction of the granitoid crust of an island arc part I: geochronological and geochemical constraints from the plutonic Kohistan (NW Pakistan)
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Construction of the granitoid crust of an island arc part I: geochronological and geochemical constraints from the plutonic Kohistan (NW Pakistan)

机译：岛弧形花岗岩壳的构造第I部分：来自多面体Kohistan（巴基斯坦西北部）的年代学和地球化学约束

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We present major and trace element analyses and U–Pb zircon intrusion ages from I-type granitoids sampled along a crustal transect in the vicinity of the Chilas gabbronorite of the Kohistan paleo-arc. The aim is to investigate the roles of fractional crystallization of mantle-derived melts and partial melting of lower crustal amphibolites to produce the magmatic upper crust of an island arc. The analyzed samples span a wide calc-alkaline compositional range (diorite–tonalite–granodiorite–granite) and have typical subduction-related trace element signatures. Their intrusion ages (75.1 ± 4.5–42.1 ± 4.4 Ma) are younger than the Chilas Complex (~85 Ma). The new results indicate, in conjunction with literature data, that granitoid formation in the Kohistan arc was a continuous rather than punctuated process. Field observations and the presence of inherited zircons indicate the importance of assimilation processes. Field relations, petrographic observations and major and trace element compositions of the granitoid indicate the importance of amphibole fractionation for their origin. It is concluded that granitoids in the Kohistan arc are derivative products of mantle derived melts that evolved through amphibole-dominated fractionation and intra crustal assimilation. Communicated by T. L. Grove.
机译：我们介绍了主要和微量元素分析，以及在Kohistan古弧的Chilas gabbronorite附近沿地壳取样的I型花岗岩从U型铅锆石侵入年龄。目的是研究地幔衍生熔体的分步结晶和下部地壳闪石的部分熔融，以产生岛弧的岩浆上地壳的作用。分析样品的钙-碱组成范围很广（闪长岩—菱铁矿—闪长闪长岩—花岗岩），具有与俯冲有关的典型痕量元素特征。他们的入侵年龄（75.1±4.5–42.1±4.4 Ma）比奇拉斯情结（〜85 Ma）年轻。结合文献数据，新结果表明，科希斯坦弧中的花岗岩形成是一个连续的过程，而不是断断续续的过程。现场观察和遗传锆石的存在表明了同化过程的重要性。现场关系，岩相学观察以及花岗岩的主要和微量元素组成表明，闪石分离的重要性。结论是，科希斯坦弧中的花岗岩类是地幔衍生的熔体的衍生产物，这些熔体是通过闪石为主的分馏作用和地壳内同化作用演化而来的。由T. L. Grove沟通。

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