Duobagou Permian–Triassic granites from the Dunhuang orogenic belt, NW China: implications for the tectonic evolution of the southernmost Central Asian Orogenic Belt

Abstract

The Duobagou Permian–Triassic granites of the Dunhuang orogenic belt are of great importance in understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt. LA-ICP-MS U–Pb zircon ages indicate that Permian–Triassic granitic intrusions from the Duobagou area formed at 276–274 Ma and 246 ± 1 Ma. These granites have high SiO2, Na2O and K2O, but low Al2O3, CaO and MgO contents and belong mainly to the high-K calc-alkaline I-type granite series. Based on whole-rock geochemistry and Sr–Nd and zircon Hf isotopes, the Duobagou Permian–Triassic granites were dominantly derived from the partial melting of lower continental crust formed during late Palaeoproterozoic to Mesoproterozoic times in a post-collisional extensional setting. Permian granites with zircon ϵHf(t) values of −5.4 to +3.1 and Hf model ages of TDM2 = 1.14–1.70 Ga indicate the involvement of a mantle component in their petrogenesis. Triassic granites with higher zircon ϵHf(t) values (+0.5 to +3.8) and TDM2 = 1.08–1.31 Ga suggest more juvenile sources caused by a greater contribution of mantle-derived melts, indicating a significant crustal growth. Regional extension from lithospheric delamination and heating from asthenospheric upwelling were proposed to have triggered the partial melting of lower crust, resulting in the generation of the Permian–Triassic magmatism. This may have been the mechanism for the significant crustal growth during Permian and Triassic times in the southernmost Central Asian Orogenic Belt.

Jurassic Evolution of the Dunhuang Basin and Its Implications for the Early History of the Altyn Tagh Fault, Northeast Tibet Plateau

“…(a–d) Detrital zircon ages in this study; (e) zircon age of magmatic and metamorphic rocks in the Dunhuang Basin (DHB) (L. M. Feng et al., 2020; Gan et al., 2021; Z. Y. He et al., 2014; Shi et al., 2020; Z. M. Wang et al., 2013, 2014; Z. D. Wang et al., 2021; H. Y. C. Wang, Chen, et al., 2017; H. Y. C. Wang, Wang, et al., 2017; J. X. Zhang et al., 2013; Y. Zhao et al., 2015, 2016, 2017, 2020; Y. Zhao, Ao, Yan, et al., 2019; Y. Zhao, Ao, Zhang, et al., 2019; Zong et al., 2013); (f) detrital zircon ages of Jurassic strata in the eastern DHB (Gehrels et al., 2003); (g) detrital zircon ages of modern river in the Bei Shan (W. T. Wang et al., 2016); (h) detrital zircon ages of Jurassic strata in the western Jiuxi Basin (K. X. An et al., 2018); (i) zircon U‐Pb age of magmatic rocks in the Qilian Shan (C. Wu et al., 2022); (j) zircon U‐Pb age in the North Altyn Tagh (X. D. Zhao et al., 2020); (k) detrital zircon ages of Middle Jurassic strata in the Lapeiquan area (X. D. Zhao et al., 2020); and (l) detrital zircon ages of Middle Jurassic strata in the Suganhu area (Cheng, Jolivet, et al., 2019; J. F. Zhao et al., 2020).…”

“…The younger age group results are in high accordance with the zircon age spectrum for the granites and modern rivers in the Bei Shan area. Although several researchers have reported on the existence of Permian‐Triassic granites in the Sanwei Shan area (L. M. Feng et al., 2020; Y. X. Wang et al., 2019; Z. D. Wang et al., 2021; Q. W. L. Zhang et al., 2020, 2022), the long distance from the Daba Sag, small exposure of the granites and main granite age range of 350–430 Ma indicate that the Sanwei Shan is unlikely to provide detritus for the Daba Sag during the Late Jurassic.…”

“…274 Ma may have originated from Permian granites in nearby areas (Y. X. Wang et al., 2019; Z. D. Wang et al., 2021). However, a distinct peak age of 253 Ma ranging from 245 to 291 Ma in the lenticular sandstone samples is present in northern Duobagou, and this age group was likely derived from the Bei Shan and Permian‐Triassic granites in Sanwei Shan (L. M. Feng et al., 2020; W. T. Wang et al., 2016; Y. X. Wang et al., 2019; Z. D. Wang et al., 2021; Q. W. L. Zhang et al., 2020, 2022) (Figure 10g). The schists and marble in the gravels are the principal lithologic composition of the Dunhuang Group, which is exposed in the Sanwei Shan (Figure 2b), and the vein quartz and granite are the intrusions of the schist of the Dunhuang Group (Y. Zhao et al., 2016, 2017).…”

“…A small amount of zircon with a peak age of ca. 274 Ma may have originated from Permian granites in nearby areas (Y. X. Wang et al., 2019; Z. D. Wang et al., 2021). However, a distinct peak age of 253 Ma ranging from 245 to 291 Ma in the lenticular sandstone samples is present in northern Duobagou, and this age group was likely derived from the Bei Shan and Permian‐Triassic granites in Sanwei Shan (L. M. Feng et al., 2020; W. T. Wang et al., 2016; Y. X. Wang et al., 2019; Z. D. Wang et al., 2021; Q. W. L. Zhang et al., 2020, 2022) (Figure 10g).…”

“…284–273 Ma) and Late Permian–Middle Triassic (ca. 255–238 Ma), which are interpreted as arc/subduction‐related and postcollisional extensional settings, respectively (L. M. Feng et al., 2020; Y. X. Wang et al., 2019; Z. D. Wang et al., 2021; Q. W. L. Zhang et al., 2020, 2022).…”