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,Geological Journal

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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
Geological Journal ( IF 1.4 ) Pub Date : 2021-02-15 , DOI: 10.1002/gj.4100
Nan Tian ₁ , Fengyue Sun ₁ , Zhongcui Pan _{1,

2} , Liang Li _{3,

4} , Jiaming Yan ₁ , Dongqian Wu ₁ , Yan Gu ₂ , Jiafang Deng ₁ , Zhedong Liu ₅ , Li Wang ₁ , Yajing Zhang ₁

Affiliation

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 ε_Hf(t) values ranging from −2.26 to +0.36, with two-stage model ages (T_DM2) 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.

更新日期：2021-02-15

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