Petrogenesis and tectonic setting of the early-middle triassic subduction-related granite in the eastern segment of East Kunlun: evidences from petrology, geochemistry, and zircon U-Pb-Hf isotopes

ABSTRACT

The subduction process of the Paleo-Tethyan Ocean is still under controversy. We report zircon U-Pb ages and geochemistry (major and trace elements, and Hf isotopic compositions) for the Xiangjiananshan granitic plutons in the eastern segment of the East Kunlun Orogenic Belt, northern Tibetan Plateau, to constrain the subduction-related granitoids in its petrogenesis and to reconstruct the subduction prosess of the Buqingshan-A’nyemaqing Ocean. Zircon U-Pb dating yields coeval ages of 246.6 ± 4.1 Ma for granodiorite and 246.4 ± 3.9 Ma for biotite monzogranite of the Xiangjiananshan granitoid pluton. The granitoids include granodiorites, biotite monzogranites, and pseudo-porphyritic monzogranites. The granitoids have high contents of SiO₂ (66.60–73.19 wt.%) and Al₂O₃ (13.28–16.38 wt.%), consistent with the high-K calc-alkaline series. The A/CNK ratios range from 0.98 to 1.02, indicating that the granodiorite is metaluminous and weakly peraluminous. The mafic microgranular enclaves (MMEs) in granodiorite and biotite monzogranite have a restricted SiO₂ range (57.24–60.03 wt.%), and have higher Fe₂O₃^T, and MgO contents than the host granitoids, as well as higher total rare earth element (REE) concentrations. All samples are depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and are enriched in large ion lithophile elements (LILEs; e.g., Rb, Nd and La) and light rare earth elements (LREEs). Zircons from the pseudoporphyritic monzogranite yield two-stage model ages of 1137.32 to 1588.12 Ma, together with ε_Hf(t) values from −5.01 to +2.11. These results indicate that the parental magma of pseudoporphyritic monzogranite was generated by partial melting of Paleoproterozoic to Mesoproterozoic rocks of the lower crust with contamination of ancient crustal material. Field and petrological observations, together with elemental and Hf isotopic data, indicate that the Xiangjiananshan granitic plutons was formed by magma mixing of mafic and felsic magmas. The felsic magma was derived from partial melting of the lower crust, while the mafic magma was derived from partial melting of an enriched lithospheric mantle metasomatized by slab-derived fluid due to the subduction of the Buqingshan-A’nyemaqing Ocean. Therefore, we propose that the northward subduction of the Buqingshan-A’nyemaqing ocean north to the Bayan Hara block under East Kunlun initiated in the Middle Permian (ca. 270 Ma), yielding calcium metaluminous arc magmatic rocks with I-type granite characteristics at East Kunlun, including the XG pluton in this study. Subsequently, the Buqingshan-A’nyemaqing ocean closed and resulted in collision of the Bayan Hara and East Kunlun blocks from 240 to 230 Ma.

KEYWORDS:

• Geochronology
• geochemistry
• east Kunlun Orogenic Belt
• petrogenesis
• magma mixing
• paleo-Tethys Ocean

Highlights

• Early-Middle Triassic I-type granites emplaced in the East Kunlun orogenic belt

• They were derived from derived from partial melting of the lower crust, while the mafic magmas are derived from partial melting of an enriched lithospheric mantle metasomatized

• These findings fit in the overall evolution of the Paleo-Tethys system, the granites are associated with the subduction of the Paleo-Tethys Ocean

Acknowledgments

We thank Prof. Robert Stern, Editor in Chief, and three anonymous reviewers for their critical and constructive review and comments on this paper. We wish to acknowledge Dr. Sa-Ping Ding, Dr. Zhan-Qing Liu, Dr. Jun-Feng Guo and others for their help during the fieldwork. We wish to acknowledge Dr. Xiao-Ming Liu and Dr. Chun-Rong Diwu, at the Northwest University, State Key Laboratory of Continental Dynamics, for assistance with LA-ICP-MS dating; and He Li at the Institute of Geology and Geophysics, State Key Laboratory of Lithosphere Evolution, for assistance with conducting XRF and trace element analyses. The authors would like to thank Enago (www.enago.cn) for the English language review.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was financially supported by the National Nature Sciences Foundation of China [Grant Nos. 41872233, 41872235, 41802234, 41602229, 41472191, 41502191, 41172186, 40972136], China Scholarship Council (Grant No. 201806565026), the Commonweal Geological Survey, the Aluminum Corporation of China and the Land-Resources Department of Qinghai Province [Grant No. 200801], China Geological Survey [Grant Nos.12120114041201, DD2016007901], Natural Science Basic Research Plan in Shaanxi Province of China [Grant Nos. 2019JM-312, 2019JQ-090, 2019JQ-209], China Postdoctoral Science Foundation [Grant No. 2016M592726], and the Fundamental Research Funds for the Central Universities [Grant Nos. 300102270202, CHD2011TD020, 300103183081, 300104282717, 300102279204, and 201810710233];