Petrogenesis and tectonic setting of the Middle Permian A‐type granites in Altay, northwestern China: Evidences from geochronological, geochemical, and Hf isotopic studies

Abstract

The Jiangjunshan and Dakalasu alkali‐feldspar granites are located in the central part of the Chinese Altay orogen. In this paper, we present detailed geochemical, zircon U–Pb, and Hf isotopic data of these granites. The Jiangjunshan and Dakalasu alkali‐feldspar granites show a high content of SiO2 (72.05–73.27 and 69.55–71.04 wt%, respectively), total alkalis (Na2O + K2O = 8.41–8.71 and 7.24–8.66 wt%, respectively), and high‐field strength elements (Zr + Nb + Ce + Y = 400.3–482.9 and 156.7–339.3 ppm, respectively), as well as high Ga/Al ratios (10,000 × Ga/Al = 3.46–4.19 and 2.62–3.28, respectively) and depletion in Ba, Nb, Sr, and Ti, showing geochemical characteristics similar to those of A‐type granites. Zircon U–Pb dating of the Jiangjunshan and Dakalasu alkali‐feldspar granites yielded weighted mean dating 206Pb/238U ages of 268.3 ± 1.9 and 270.4 ± 1.9 Ma, respectively, indicating that these granites intruded during the Permian. The Jiangjunshan and Dakalasu alkali‐feldspar granites show highly variable zircon εHf(t) values ranging from −7.0 to +5.6, implying that these granites originated from a mixing of mantle‐derived magma with crustal materials. Our data on the Jiangjunshan and Dakalasu alkali‐feldspar granites, coupled with previous studies of Permian magmatism and metamorphism, suggest that the tectonic regime was in a postcollisional extensional environment in the Chinese Altay orogen during the Permian. Therefore, the change in stress from compression to extension and asthenospheric upwelling triggered by slab break‐off plays a significant role in the generation of Jiangjunshan and Dakalasu alkali‐feldspar granites.

Petrogenetic studies of Permian pegmatites in the Chinese Altay: Implications for a two‐stage post‐collisional magmatism model

“…The age versus ε Hf( t ) diagrams of the XLKS, DKLS, and YLM pegmatites, compared with Palaeozoic granites and sedimentary rocks in the Chinese Altay (the data are from Cai et al, 2011b; Y. Liu et al, 2018; Long et al, 2010; M. Sun et al, 2008; Yu et al, 2017; J. Y. Zhao et al, 2017; C. Zhang et al, 2018; C. Zhang, Liu, et al, 2017, J. Zhang, Wang, et al, 2017). DKLS, Dakalasu; XKLS, Xiaokalasu; YLM, Yelaman…”

“…Age distributions of the granites and pegmatites in the Chinese Altay (the data are from Cai et al, 2011b; Chai et al, 2010; Che et al, 2015; F. P. Gao et al, 2010; Z. X. Li et al, 2012; F. Liu et al, 2009, 2014, 2018; G. R. Liu, Dong, et al, 2010; Lv et al, 2012, 2015, 2018; Z. Ma et al, 2015; Ren et al, 2011; Song et al, 2010; M. Sun et al, 2008; G. Sun, Li, et al, 2009; M. Sun, Long, et al, 2009; Y. Tong et al, 2007, 2010; Y. Tong, Hong, et al, 2006; Y. Tong, Wang, et al, 2006; Y. Tong, Wang, et al, 2014; Wan et al, 2011; T. Wang et al, 2006, 2007, 2009; T. Wang et al, 2014; Yang et al, 2014; C. L. Zhang et al, 2012; X. Zhang et al, 2016; C. Zhang, Liu, et al, 2017, J. Zhang, Wang, et al, 2017; G. Zhou et al, 2007; Q. F. Zhou et al, 2018; Zhu et al, 2006)…”

“…Magmatism in this area reached a peak during the Devonian, roughly coeval with the felsic volcanic rocks (Cai et al, 2011a, 2011b, Chai et al, 2009; Long et al, 2010). The second magmatism peak in this area occurred in the Permian, coeval with the pegmatites and pyrometamorphism (Han et al, 1997; Y. Liu et al, 2018; Lv et al, 2012; Ren et al, 2011; Y. Tong, Wang, et al, 2014; L. Tong, Xu, et al, 2014; T. Wang et al, 2009; X. Zhang et al, 2016).…”

Geochronology, geochemistry, and petrogenesis of the Kezijiaer gabbros, southern Chinese Altai: Evidence for ridge subduction

“…Furthermore, the model of ridge subduction can readily account for the special rock association in this region, for example, adakites (393–390 Ma; Xiang et al, ; Zhang et al, ), boninites, and A‐type granites (382–367 Ma; Shen et al, ; Niu et al, ), as well as mid‐ocean ridge basalt (MORB)‐like gabbroic dykes (Xu et al, ) and Habahe mafic rocks (376 Ma; Cai et al, ). Contrastingly, the Permian granitic intrusions chiefly occur in the southern Chinese Altai and are dominated by undeformed A‐type granites (Liu et al, ). They generally possess high Ga/Al ratios and display depletions in Ba, Sr, Nb, and Ti (Shen et al, ).…”

Geochronology and trace elements of zircon in the Southern Chinese Altay: Implications for tectonic setting

“…The Central Asian Orogenic Belt (CAOB), which is one of the largest and longest-lived accretionary orogenic systems, has undergone complex geodynamic processes during the Phanerozoic continental growth of Central Asia (Hong et al, 2017(Hong et al, , 2020Li et al, 2017;Sengör et al, 1993;Windley et al, 2007;Xiao et al, 2009Xiao et al, , 2015. The Chinese Altay, a key segment of the CAOB, is an important region for studying the convergent processes and amalgamation of the Mongolian and Kazakhstan collage systems (Cai et al, 2016;Li et al, 2019;Liu et al, 2017;Xiao et al, 2015). Moreover, the Devonian was a crucial formation period of the voluminous magmatism that established the spatial framework of the Chinese Altay (Sun et al, 2009;Yu et al, 2017).…”