Paleozoic to early Mesozoic intrusive rocks in the East Kunlun Orogenic Belt, northwestern China: petrogenesis and implications for two Tethys evolution events

Igneous rocks can provide important insights into geodynamic evolution of orogenic belts. During the Paleozoic to early Mesozoic, the East Kunlun Orogenic Belt (EKOB) had experienced the evolution of Proto-Tethys and Paleo-Tethys Oceans successively. However, the precise ages of occurrence of specific geodynamic processes are still unclear. Here, we study the crystallization age and petrogenesis of Paleozoic to early Mesozoic intrusive rocks in the Eastern Kunlun Orogenic Belt (EKOB) to constrain regional geodynamic evolution. These intrusive rocks are located in the Paleozoic to early Mesozoic magmatic arc, which is parallel to the Tethys ophiolite belt. 440 Ma BDG (Baidungou) diorite and 430 Ma LTG (Luotuogou) granodiorite porphyry are probably derived from mixing-assimilation-storage-homogenization (MASH) zone in the lower crust and show significant depletions in high field strength elements (HFSEs, Nb, Ta, Ti) with characteristics of arc magmatic rocks. The 414 Ma LTG granite porphyry shows the geochemical characteristics of A2-type granites and was emplaced in an extensional setting. Permian to Triassic mafic dike swarm show low contents of SiO 2 and high MgO contents, combined with their depletions in HFSEs and enrichments in large ion lithophile elements (LILEs), it is concluded that they are derived from subduction-related fluid metasomatized mantle (SFMM). 247 Ma XSG granites display SiO 2 contents varying from 68.06 to 70.67 wt. % with high Rb/Sr (0.12–0.30), Th/Nb (1.25–1.38), but low Nb/Ta (9.1–13.0) ratios, which is similar to bulk continental crust. All the samples of XSG granites show (La/Yb) N ratios of 10.3–10.6 without adakitic affinity suggesting that they are derived from lower crust with normal thickness. Combined with previous research, it is suggested that the EKOB experienced two Wilson cycles during Paleozoic to early Mesozoic and the Paleo-Tethys Ocean reopened at Carboniferous after the Proto-Tethys Ocean was completely closed at late Silurian. Orogenic magmatism in the EKOB shows episodic characteristics and can be further divided into ten episodes (E1, E2, E3, E4, E5, E6, E7, E8, E9, and E10) corresponding to ten different geodynamic regimes.