Early Jurassic intra‐oceanic arc system of the Neotethys Ocean: Constraints from andesites in the Gangdese magmatic belt, south Tibet

Abstract

The Gangdese magmatic belt is located in the southern margin of the Lhasa terrane, south Tibet. Here zircon U–Pb ages and Hf isotopic data, as well as whole‐rock geochemistry and Sr–Nd isotopes on andesites from the Bima Formation with a view to evaluating the history of the Gangdese magmatism and the evolution of the Neotethys Ocean. Zircon U–Pb dating yields an age of ca 170 Ma from six samples, representing the eruptive time of these volcanic rocks. Zircon Hf isotopes show highly positive εHf(t) values of +13 to +16 with a mean of +15.2. Whole‐rock geochemical and Sr–Nd isotopic results suggest that the magma source of these andesites was controlled by partial melting of a depleted mantle source with addition of continental‐derived sediments, similar to those in the southern arcs of the Lesser Antilles arc belt. In combination with published data, the volcanic rocks of the Bima Formation are proposed to have been generated in an intra‐oceanic arc system, closely associated with northward subduction of the Neotethyan oceanic lithosphere.

Composition and age of Jurassic diabase dikes in the Xiongcun porphyry copper–gold district, southern margin of the Lhasa terrane, Tibet, China: Petrogenesis and tectonic setting

“…The tectonic setting of Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane remains controversial. Some researchers suggest that the Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane were formed in a magmatic arc setting (continental margin arc or intra‐oceanic arc) related to the northward subduction of the Neo‐Tethys oceanic lithosphere (Huang et al, ; Ji et al, ; Kang et al, ; Lang et al, ; S. W. Ma, Meng, et al, , X. X. Ma, Xu, et al, , X. X. Ma, Yi, et al, ; Meng, Dong, et al, , Meng, Xu, et al, ; Pan et al, ; J. X. Tang et al, ; J. X. Tang et al, ; C. Wang et al, ), whereas others suggest that they were formed in a back‐arc setting in response to the southward subduction of the Bangong‐Nujiang oceanic lithosphere (Geng et al, ; Hsü et al, ; Liao et al, ; Shui et al, ; Song et al, ; D. C. Zhu et al, ; D. C. Zhu et al, ). Effective discrimination diagrams are key to discriminating the tectonic setting and addressing this controversy.…”

“…Some scholars have recently reported Early Mesozoic magmatic rocks that are similar to intra‐oceanic arc volcanic rocks in the southern margin of the Lhasa terrane (Huang et al, ; Kang et al, ; X. X. Ma, Yi, et al, ; J. X. Tang et al, ). In addition, in the south of the Xiongcun porphyry copper–gold district, a suite of intra‐oceanic arc volcanic–sedimentary rocks has been identified (X. X. Ma, Xu, et al, ; Z. Y. Yang et al, ), implying the existence of an intra‐oceanic arc system within the Xiongcun region during the Early–Middle Jurassic (X. X. Ma, Xu, et al, ; J. X. Tang et al, ; Z. Y. Yang et al, ). Therefore, it is also possible that the Xiongcun diabase dikes were generated in an oceanic arc setting.…”

“…This study mainly focused on the southern Lhasa subterrane (Figure b,c), which is characterized by juvenile crust (Z. Q. Hou et al, ). This subterrane experienced the subduction of the Neo‐Tethys oceanic slab and the India–Asia continental collision (M. F. Chu et al, ; M. F. Chu et al, ; Ding, Kapp, & Wan, ; Guo et al, ; Z. Q. Hou et al, ; Ji et al, ; Kang et al, ; Lang et al, ; Lee et al, ; S. W. Ma, Meng, et al, , X. X. Ma, Xu, et al, , X. X. Ma, Yi, et al, ; Meng, Dong, et al, , Meng, Xu, et al, ; Mo et al, ; Mo, Dong, Zhao, Zhou, et al, ; J. X. Tang et al, ; C. Wang et al, ; W. Y. Xu et al, ; B. Xu et al, ; A. Yin & Harrison, ; H. F. Zhang, Xu, et al, ). To the south of the Lhasa terrane, a Late Cretaceous–Early Tertiary Xigaze fore‐arc basin is locally well preserved within the YZSZ (Figure c; Durr, ; A. Yin et al, ).…”

“…The Miocene intrusions, which formed in a post‐collisional geologic setting and have adakite‐like affinity, were commonly emplaced as small stocks and/or dikes in the southern Lhasa subterrane (Chung et al, ; Z. Q. Hou, Gao, Qu, Rui, & Mo, ; Qu, Xin, & Xu, ; R. Wang, Richards, Hou, & Yang, ; R. Wang, Richards, Hou, Yang, & DuFrane, ). However, Early Mesozoic magmatic rocks are relatively rare in the southern margin of the Lhasa terrane, and the petrogenesis and tectonic setting of these rocks remain controversial subjects (Figure c; Geng et al, ; Huang et al, ; Hsü et al, ; Ji et al, ; Kang et al, ; Lang et al, ; Liao et al, ; S. W. Ma, Meng, et al, , X. X. Ma, Xu, et al, , X. X. Ma, Yi, et al, ; Meng, Dong, et al, , Meng, Xu, et al, ; Shui et al, ; Song et al, ; J. X. Tang et al, ; J. X. Tang et al, ; C. Wang et al, ; D. C. Zhu et al, , D. C. Zhu et al, ).…”

“…Compared with Cretaceous and Cenozoic magmatism, Early Mesozoic (Late Triassic to Jurassic) magmatic rocks are relatively rare in the southern margin of the Lhasa terrane. The petrogenesis and tectonic setting of these rocks remain controversial subjects (Figure c), with some researchers suggesting that the Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane were formed in a magmatic arc setting (continental margin arc or intra‐oceanic arc) related to the northward subduction of the Neo‐Tethys oceanic lithosphere (Huang, Xu, Chen, Kang, & Dong, ; Ji et al, ; Kang et al, ; Lang et al, ; S. W. Ma, Meng, Xu, & Liu, ; X. X. Ma, Xu, Meert, & Santosh, ; X. X. Ma, Yi, & Xu, ; Meng, Dong, Cong, Xu, & Cao, ; Meng, Xu, et al, ; Pan et al, ; J. X. Tang et al, ; J. X. Tang et al, ; C. Wang et al, ), whereas other researchers suggesting that they are formed in a back‐arc setting in response to the southward subduction of the Bangong‐Nujiang oceanic lithosphere (Geng, Pan, Wang, Zhu, & Liao, ; Hsü, Pan, & Sengör, ; Liao et al, ; Shui, He, Zhang, & Lu, ; Song et al, ; D. C. Zhu et al, ; D. C. Zhu et al, ). To discuss the genesis and tectonic setting of Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane, most geochemical and geochronological studies on the Early Mesozoic magmatic rocks in the southern margin of the Lhasa terrane have focused on felsic rocks (M. F. Chu et al, ; Guo et al, ; Ji et al, ; Lang et al, ; S. W. Ma, Meng, et al, ; Meng, Dong, et al, ; Qu, Hou, Zaw, & Li, ; Tafti, Mortensen, Lang, Rebagliati, & Oliver, ; J. X. Tang et al, ; C. Wang et al, ; Wen et al, ; Z. M. Yang, Hou, Xia, Song, & Li, ; H. F. Zhang, Xu, et al, ).…”