HP–UHT granulites in the East Kunlun Orogen, NW China: Constraints on the transition from compression to extension in an arc setting of the Proto‐Tethys Ocean

Abstract

The East Kunlun Orogen (EKO) of the northwest part of the Central China Orogenic belt records long‐lived orogenic events from the Cambrian to the Triassic, involving the tectonic evolution from Proto‐Tethys to Palaeo‐Tethys. Although high‐ and ultra high pressure (HP‒UHP) metamorphism has been recognized in the EKO, other metamorphic events associated with the orogenic history are little known. The metamorphic history of high‐ and ultra high temperature granulites and their pressure–temperature–time (P‒T–t) path is keys to reconstructing tectonic events associated with a subduction‐to‐collision transition. In this contribution, we present P‒T–t results for the mafic and pelitic granulite facies metamorphic rocks in the Qingshuiquan region of the EKO, determined using phase equilibrium modelling and zircon geochronology. The Jingshuikou granulite terrane records a clockwise P–T path with high‐P and ultra high temperature (HP–UHT) conditions at Pmax ~900 to 950°C at 13 kbar, at Tmax of ~950°C at 9‒12 kbar, and a final stage of 800‒895°C at 6‒10 kbar. LA‐ICP‐MS U–Pb dating of zircons provides systemic constraints on a long‐lived metamorphic age span of 530‒465 Ma, with a peak of c. 503 Ma. The HP–UHT metamorphism of the Qingshuiquan granulite terrane reveals a complete process from arc compression at the early stage of subduction to extension on the active continental margin related to rollback of the subducted slab in the Early Palaeozoic, driven by heat transfer from upwelling of the sub‐arc hot asthenosphere. The timing and P‒T conditions of the high geothermal gradient metamorphism can be used to understand the subduction and collision process of the Proto‐Tethys Ocean, including the relationship between high‐P and high‐ to ultra‐temperature metamorphism in the East Kunlun and other orogenic belts.

Metamorphic evolution and geological significance of Early Palaeozoic high‐pressure granulites from the East Kunlun (NW China)

“…The temporal and spatial distribution of the subduction‐related rocks indicates that the NKT could have been an active continental margin setting and the SKT was subducted northward to the NKT (Dong et al, 2018; Fu et al, 2023; Xin et al, 2018). Granulite facies metamorphism mainly occurred in the Cambrian (Bi et al, 2021; Chen et al, 2008; Li et al, 2006; Zhang et al, 2003), with the peak value of 508 Ma in the age spectrum diagram (Figure 9b). This HT metamorphic event was contemporaneous with the formation of basic igneous rocks in the study area (Figure 9b; Li, Pei, et al, 2018; Wei, 2015; Yang et al, 1996).…”

“…(b) Histograms of zircon ages of the metamorphic (lower part) and intrusive (upper part) rocks. Metamorphic age data include eclogites (Du, 2018; Jia et al, 2014; Meng, Zhang, & Cui, 2013; Qi et al, 2014; Qi, Fan, et al, 2016; Song et al, 2018; Xiong & Ma, 2016), granulites (Bi et al, 2021; Li et al, 2006; Wang, Zhao, et al, 2022; Zhang et al, 2003; this study), amphibolites (Chen et al, 2008; Guo et al, 2018; Li et al, 2022; Wang, 2014), schists (Bi et al, 2020; Song et al, 2018) and gneisses (Bi et al, 2021; Chen et al, 2008, 2017; Gao et al, 2023; He et al, 2016; Liu et al, 2016; Meng et al, 2017; Meng, Cui, et al, 2013; Tang et al, 2022). The metamorphic rocks as a whole show three peak values (410 Ma, 430 Ma, and 508 Ma) on the probability density curve.…”

“…For other two mafic granulites, the protolith crystallization age and metamorphic age have been proposed to be 507 ± 3 and 455-457 Ma, respectively (He et al, 2023). These granulites are commonly regarded as components of the Baishahe formation or the Jinshuikou Group (Bi et al, 2021;Chen et al, 1999Chen et al, , 2007Sang et al, 2016;Wang & Chen, 1987). The protoliths of some mafic granulites have been suggested to represent Cambrian oceanic crust (He et al, 2023;Li et al, 2006).…”

“…Available zircon U–Pb ages indicate that metamorphism of the granulites occurred at 480–530 Ma, whereas metamorphism of the eclogites occurred at 400–450 Ma (e.g. Bi et al, 2021; Jia et al, 2014; Li et al, 2006; Meng, Zhang, & Cui, 2013; Song et al, 2018). Although the Early Palaeozoic granulites and eclogites in the East Kunlun can help to decipher its prolonged orogenic evolution, the relationship between these two rock types has been rarely investigated.…”

“…The East Kunlun Orogenic Belt (EKOB) situated in NW China forms part of the Central China Orogenic Belt, which also consists of several high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic belts, including the Dabie-Sulu, Tongbai, Qinling, North Qaidam, Qilian and Altyn Tagh (Figure 1a,b;Dong et al, 2021;Wu & Zheng, 2013). Previous studies have described the occurrence of Early Palaeozoic granulites in the East Kunlun, but details of the metamorphic evolution and tectonic setting of these rocks have not been fully established (Bi et al, 2021;Chen et al, 1999Chen et al, , 2008He et al, 2023;Li et al, 2006;Zhang et al, 2003). In recent years, the EKOB has been recognized as an Early Palaeozoic HP-UHP metamorphic belt, since eclogites and coesite inclusions in zircon have been discovered (e.g.…”