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

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

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


Authors

Xin Tong

Jingjing Yan

Zhidan Zhao

Yaoling Niu

Ningyuan Qi

Qingshang Shi

Dong Liu

Qing Wang

Liang-Liang Zhang

Guochen Dong

Di-Cheng Zhu



Abstract

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 (87Sr/86Sr = 0.713941–0.718417, εNd(t) = −14 to −9.8, 206Pb/204Pb = 18.806–18.936, 207Pb/204Pb = 15.739–15.764, 208Pb/204Pb = 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 εHf(t) of −15.9 to −0.2 and − 13.8 to −7.4, respectively. These samples also show varying δ26Mg ranging from −0.40 to −0.18, with an average δ26Mg = −0.27 ± 0.06‰ (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.

Citation

Tong, X., Yan, J., Zhao, Z., Niu, Y., Qi, N., Shi, Q., …Zhu, D. (2022). Middle-Late Jurassic magmatism in the west central Lhasa subterrane, Tibet: Petrology, zircon chronology, elemental and Sr-Nd-Pb-Hf-Mg isotopic geochemistry. Lithos, 408-409, Article 106549. https://doi.org/10.1016/j.lithos.2021.106549

Journal Article Type Article
Acceptance Date Nov 23, 2021
Online Publication Date Nov 27, 2021
Publication Date 2022-01
Deposit Date Dec 1, 2021
Publicly Available Date Mar 29, 2024
Journal Lithos
Print ISSN 0024-4937
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 408-409
Article Number 106549
DOI https://doi.org/10.1016/j.lithos.2021.106549

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