Middle-Late Jurassic magmatism in the west central Lhasa subterrane, Tibet: Petrology, zircon chronology, elemental and Sr-Nd-Pb-Hf-Mg isotopic geochemistry

文献类型： 外文期刊

第一作者： Tong, Xin

作者： Tong, Xin;Yan, Jingjing;Zhao, Zhidan;Niu, Yaoling;Qi, Ningyuan;Shi, Qingshang;Liu, Dong;Wang, Qing;Zhang, Liang-Liang;Dong, Guochen;Zhu, Di-Cheng;Tong, Xin;Tong, Xin;Yan, Jingjing;Niu, Yaoling;Niu, Yaoling;Niu, Yaoling

作者机构：

关键词： Tonalite; Sr-Nd-Pb-Mg isotope; Geochronology; Tethyan Bangong-Nujiang Ocean; Lhasa terrane

期刊名称：LITHOS （ 影响因子：4.02； 五年影响因子：4.808 ）

ISSN： 0024-4937

年卷期： 2022 年 408-409 卷

页码：

收录情况： SCI

摘要： Mesozoic magmatic rocks are widespread in the Lhasa terrane, but most of them are of cretaceous age. Because Jurassic rocks are relatively rare and our knowledge on such earlier magmatism in the context of the tectonic setting and evolution is limited. In this study, we focus on the mid-late Jurassic granitoids that occur in the west central Lhasa subterrane. We present the results of a systematic study of these granitoid rocks of tonalite composition together with the hosted mafic magmatic enclaves. We dated 4 representative tonalite samples and 2 enclaves using zircon U-Pb method that gives the age range of 167-154 Ma. All these samples have Sr-Nd-Pb isotopic compositions (Sr-87/Sr-86 = 0.713941-0.718417, epsilon(Nd)(t) = -14 to -9.8, Pb-206/Pb-204 = 18.806-18.936, Pb-207/Pb-204 = 15.739-15.764, Pb-208/Pb-204 = 39.257-39.798) similar to the composition of gneisses from the basement of the Lhasa terrane, suggesting that magmas parental to these mid-late Jurassic granitoids of tonalitic composition are of largely crustal origin, which is also supported by the petrographic observations. Both of the tonalite samples and the mafic enclaves have a wide span of zircon epsilon(Hf)(t) of -15.9 to -0.2 and -13.8 to -7.4, respectively. These samples also show varying delta Mg-26 ranging from -0.40 to -0.18, with an average delta Mg-26 = -0.27 +/- 0.06 parts per thousand (2SD) that is best understood as representing the Mg composition of the continental crust of the Lhasa terrane. All these observations allow us to conclude that basaltic melts derived from metasomatized mantle were involved in the petrogenesis of these granitoids. Specifically, southward subduction of the Bangong-Nujiang Ocean lithosphere and subsequent slab rollback metasomatized the mantle wedge and the lithospheric mantle above, whose melting produced basaltic magmas. Underplating and intrusion of these basaltic magmas caused crustal melting and generation of granitoid magmas parental to the tonalite and enclaves we study.

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