Petrogenesis of Permian to Triassic granitoids from the East Kunlun orogenic belt: implications for crustal evolution during oceanic subduction and continental collision

ABSTRACT

The study of Permian-Triassic granitoids, which widely occur within the East Kunlun Orogenic Belt (EKOB), is relevant for a better understanding of the evolution of the Paleo-Tethys Ocean and regional crustal evolution. This study focuses on the Permian-Triassic granitoids from the Nagengkangqieer region, east segment of EKOB. The Late Permian granodiorite (ca. 252 Ma) shows high-K calc-alkaline and metaluminous features with moderate SiO₂ (63.31–67.04 wt.%), relatively high Mg# (48–52), and low Sr/Y ratios. The granodiorite is enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) and shows enriched isotopic compositions (ε_Nd (t) = −5.53 to −5.14, ε_Hf (t) = −5.6 to −1.1). These geochemical characteristics imply that the Late Permian granodiorite was derived from a mixing source of mafic lower crust and mantle materials (<30%). The Middle Triassic porphyritic monzogranite (ca. 239 Ma) and monzogranite (ca. 239 Ma) are high-K calc-alkaline to shoshonitic and weak peraluminous with high SiO₂ (70.58–76.54 wt.%) contents and low Mg# (19–36). They display relatively higher FeO^T/MgO ratios, lower P₂O₅ contents, and more enriched isotopic compositions (ε_Nd (t) = −7.87 to −6.71, ε_Hf (t) = −13.7 to −1.2) than those of granodiorites. These findings indicate that the Triassic granites belong to fractionated granites derived from partial melting of the lower continental crust. In combination with the results of this study and the spatio-temporal distribution of regional magmatic, metamorphic, and sedimentary events, we conclude that Late Permian granodiorite formed in a subduction setting, whereas the Middle Triassic granites were formed in a syn-collision setting. Closing of the Paleo-Tethys Ocean occurred in the Middle Triassic (ca. 240 Ma). Additionally, only a small proportion of juvenile materials (<30%) was involved in magmatism and contributed to continental crustal growth during Late Permian subduction, whereas crustal reworking dominated regional magmatism and resulted in a higher crustal maturity.

KEYWORDS:

• Eastern Kunlun orogenic belt
• magma mixing
• Paleo-Tethys
• crustal evolution

Acknowledgments

We would like to thank the valuable help from Huiwen Bai, Deding Kong, and Songtao Zhang during the fieldwork.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Research highlights

1. Identification of 252 and 239 Ma granitoids in the EKOB, East Tethys.

2. Subduction of the Paleo-Tethys Ocean terminated in the late Middle Triassic in the EKOB.

3. Only less than 30% juvenile material contributed to bulk crustal growth in a subduction setting.

4. Crustal reworking dominated regional magmatism and resulted in a high crustal maturity.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2022.2106587

Additional information

Funding

This work was supported by the China Postdoctoral Science Foundation (project number 2021M693191), the Fundamental Research Funds for the Central Universities (project number CUGL170413), the National Natural Science Foundation of China (project number 41772071) and the China Geological Survey (project number 12120100400150017-37).