Geochemical and geochronological constraints on the genesis of Pliocene post-collisional granite porphyry and shoshonite in Quanshuigou, western Kunlun Mountains, NW Qinghai–Tibet Plateau

ABSTRACT

Post-collisional K-rich magmatic rocks of the Qinghai–Tibet Plateau provide important information for understanding the continental collision and uplift of this plateau during the Cenozoic. However, the source of these K-rich rocks is still debated, and limited investigations have been conducted in the western Kunlun Mountains (WKM) in the northwestern margin of the plateau. In this paper, we present geochemical, geochronological, and Sr–Nd–Hf isotope data for Quanshuigou post-collisional K-rich igneous rocks from the WKM. Geochronological results show that these rocks were emplaced during two stages: (1) ca. 5.3 Ma, as an intrusive suite of granite porphyries; and (2) ca. 4.8 Ma, as a suite of shoshonites. These rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and depleted in heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs). Compositions of the granite porphyries classify these rocks as high-K calc-alkaline peraluminous A-type granites. Combining the negative zircon ε_Hf(t) values (−6.9 to −1.1) with Hf crustal model ages (T_DM2) of 1.16–1.53 Ga and negative ε_Nd(t) values (−5.31 to −4.96) with two-stage Nd model ages (T_DM2) of 1.22–1.46 Ga, these signatures suggest that the granite porphyries most probably originated from partial melting of thickened lower crust with limited input of mantle-derived magmas. In contrast, the shoshonites have low SiO₂ contents (50.84–53.94 wt.%), relatively high Mg^# values (50–57), and ε_Nd (t) values ranging from −6.18 to −5.34, with single-stage Nd model ages (T_DM1) of 0.97–1.02 Ga. Our analyses show that the parental magma of the shoshonites probably formed by partial melting of EMII-type lithospheric mantle, with the addition of subducted and recycled oceanic sediments. Hence, we conclude that these granite porphyries and shoshonites formed in a post-collisional, extension-related geodynamic setting and that the melting was probably triggered by motion on the Altyn Tagh strike-slip fault system.

GRAPHICAL ABSTRACT

KEYWORDS:

• Post-collisional K-rich igneous rocks
• geochronology
• geochemistry
• delamination
• Kunlun Mountains
• Qinghai–Tibet Plateau

Acknowledgments

We thank editor-in-chief Dr Robert J. Stern and two anonymous reviewers for their constructive and thoughtful reviews which greatly revise and improve the manuscript. Prof. Kai-Jun Zhang is thanked for discussions and for helping to revise the manuscript. We thank Profs. Hua-Ning Qiu and Wei Zhang for help with the chronology calculations, and Profs. Wei-Dong Sun, Xiang-Lin Tu, and Ke-Jun Hou for assistance with geochemical analyses. This work was supported by the National Natural Science Foundation of China (grant 41372208 and 41776056), the Natural Science Foundation of Guangdong Province (grant 2017A030310395), and China Postdoctoral Science Foundation (grant 2020M672671).

Article Highlights

• We analyse the petrogenesis/geodynamic setting of post-collisional extension-related rocks in Northwestern Tibetan Plateau

• Two stages of magma emplacement were determined: granite porphyry and shoshonite

• granite porphyry formed by partial melting of thickened lower crust with limited input of mantle-derived magmas

• EMII partial melting and subducted oceanic sediment were shoshonite sources

• Quanshuigou rocks were probably triggered by localized E–W extension in the horse-tail splay of the Altyn Tagh sinistral strike-slip faults.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was supported by the China Postdoctoral Science Foundation [2020M672671]; National Natural Science Foundation of China [41372208 and 41776056]; Natural Science Foundation of Guangdong Province [2017A030310395].