Petrogenesis and tectonic setting of Mid‐Triassic volcanic rocks in the East Kunlun orogenic belt, NW China: Insights from geochemistry, zircon U–Pb dating, and Hf isotopes

Abstract

The Elashan magmatic belt is located at the eastern margin of the East Kunlun orogenic belt (E‐KOB) in northwestern China, where voluminous magmatism occurred during the Late Permian to Late Triassic. Mid‐Triassic volcanism produced the Xilikete Formation, which shows a geochemistry similar to that of highly fractionated I‐type (HFI) volcanic rocks. These rocks are characterized by high SiO2 (73.82–74.97 wt%), differentiation index (DI; 91.01–94.69), and alkalis (e.g., high K2O + Na2O, with K2O/Na2O ratios greater than 1.0) and by enrichment in some large‐ ion lithophile elements (LILEs; e.g., Rb, K, and Pb) and depletion in other LILEs (e.g., Ba and Sr) as well as some high‐field‐strength elements (HFSEs; e.g., Nb, Ta, and Ti); these features confirm that they are HFI volcanic rocks. Zircon U–Pb ages indicate that the volcanic rocks were emplaced at ~239 Ma. These zircons have εHf(t) values ranging from −2.26 to +0.36, with two‐stage model ages (TDM2) of 1,441–1,221 Ma, indicating a magma source that involved partial melting of Mesoproterozoic lower crust accompanied by a minor juvenile mantle component. The ~240 Ma magmatism in the E‐KOB was probably developed in response to subduction of the Palaeo‐Tethys oceanic plate. Previous studies indicate that a tectonic transformation from subduction to continental collision occurred at ~240 Ma. Combining these data with regional geological observations, we conclude that the Daheba volcanic rocks formed in an active continental margin setting related to the subduction of the Palaeo‐Tethys oceanic plate beneath the E‐KOB.

Petrogenesis and Tectonic Implications of the Triassic Granitoids in the Ela Mountain Area of the East Kunlun Orogenic Belt

“…Among them, the granodiorite often contains MMEs, and the volcanic rocks are mostly rhyolite, dacite, andesite, and pyroclastic rocks of the same period. The zircon Hf isotope results showed that the magma was mainly derived from the partial melting of the lower crust of the Mesoproterozoic, and some of them mixed with a small amount of mantle material [2,3,5,6]. In terms of sedimentary assemblages, the Middle Triassic Xilikete Formation has the characteristics of marine-continental sedimentary assemblages [73] and an angular unconformity contact with the Late Triassic continental volcanic rocks (Elashan Formation and Babaoshan Formation, Figure 13), indicating that the East Kunlun Orogenic Belt was in a rapid uplift stage during the Middle Triassic, representing the collision between the BayanHar Block and the Eastern Kunlun Block and the disappearance of the Paleo-Tethys Ocean, resulting in local deposition.…”

“…The East Kunlun Orogenic Belt is a typical multi-cycle complex orogenic belt that retains information related to the evolution of the Proto-Teyhys Ocean and the Paleo-Tethys Ocean, and records the information and dynamic process of the formation and evolution of the northern Qinghai-Tibet Plateau. Among them, with the exposure of voluminous magmatic rocks related to the northward subduction of the Paleo-Tethys Ocean in the Late Paleozoic-Early Mesozoic as the main feature, many scholars have carried out relevant research on this area [1][2][3][4][5][6]. However, there has been controversy over the origin, petrogenesis, tectonic background, and deep process of the huge granitic magma in the late Permian-Triassic period in the East Kunlun Orogenic Belt at present.…”

“…In particular, different scholars have different views on the final closure time of the Paleo-Tethys Ocean. For example, (1) some researchers believe that the Paleo-Tethys Ocean in the East Kunlun Orogenic Belt was closed in the late Permian, and the Triassic granites are the products of the post-collision environment [4,7,8]; (2) some have proposed that the Permian-Early Triassic granites were mostly subduction magmatic rocks, and the collision orogenic movement began in the Middle Triassic [1,9]; (3) others have pointed out that the subduction of the Paleo-Tethys Ocean in the East Kunlun Orogenic Belt lasted until the Late Triassic, and the Early-Middle Triassic granite was the product of continental margin arc magmatism under subduction environment [5,6,10]; and (4) some believe that the oceanic basin was not closed in the Late Triassic, and that the Paleo-Tethys oceanic crust continued to subduct, with the Triassic magmatism related to the subduction of the oceanic crust [11,12].…”

Petrogenesis and tectonic implications of the quartz diorites and mafic microgranular enclaves in the Asiha gold ore deposit in the East Kunlun orogenic belt: Evidence from zircon U–Pb dating, geochemistry, and Sr–Nd–Hf isotopes

“…The EKOB in the Qinghai‐Tibetan Plateau is considered to undergo multi‐stages of tectonic‐magmatic evolution (Y. X. Chen, Pei, Li, Li, Liu, & Wang, 2017; Y. P. Dong et al, 2018; Du et al, 2017; J. J. Kong, Niu, He, Zhang, & Shao, 2020; Z. C. Li, Pei, et al, 2017; Y. G. Liu et al, 2018, 2019; X. Xu et al, 2020; Z. W. Zhang et al, 2018; M. J. Zhang et al, 2021). The evolutionary history of the Palaeo‐Tethys within the EKOB has attracted considerable attention over the past decades (Y. P. Dong et al, 2018; Gao & Sun, 2021; Hu et al, 2016; Huang et al, 2014; J. J. Kong et al, 2020; H. L. Kong et al, 2021; Y. Y. Liang, Xia, Ma, Zhao, & Guo, 2020; Richards, 2015; Shao et al, 2017; Song et al, 2020; Tian et al, 2021; J. Y. Zhang, Ma, Xiong, & Liu, 2012; Zhao et al, 2019). However, the precise timing of the termination of the continental collision and the beginning of the post‐collision of Palaeo‐Tethys along the EKOB remains poorly constrained.…”

“…L. Kong et al, 2021;Y. Y. Liang, Xia, Ma, Zhao, & Guo, 2020;Richards, 2015;Shao et al, 2017;Song et al, 2020;Tian et al, 2021;Zhao et al, 2019).…”