Recognition of a Devonian‐early Mississippian plutonic belt in the eastern Beishan area, Northwest China, and its tectonic implications

Abstract

The Beishan area, located in the southernmost part of the Central Asia Orogenic Belt, is crucial for understanding the tectonic evolution associated with the closure of the Paleo‐Asian Ocean. One intermediate and two granitic plutons from the eastern Beishan area between Mingshui–Shibanjing–Xiaohuangshan (MSX) and Niujuanzi–Xichangjing (NX) ophiolitic belts, including Tongchangkou gabbroic diorite, Northern Tongchangkou and Sandaomingshui plutons, are dated at 426 ± 3, 408 ± 2, and 365 ± 2 Ma by SIMS U–Pb zircon analyses. The Middle Silurian Tongchangkou gabbroic diorites with medium‐K calc‐alkaline metaluminous characteristics represent volcanic arc rocks. The Early Devonian Northern Tongchangkou pluton, a highly evolved calc‐alkaline mylonitic monzogranite with low εNd(t), −3.5 and −2.4, and relatively low initial 87Sr/86Sr (0.707095 and 0.707249), was mainly derived from Mesoproterozoic mafic to intermediate igneous protolith and shows both volcanic arc and postcollisional characteristics. The Late Devonian Sandaomingshui pluton, a calc‐alkaline granite with slightly positive εNd(t), 0.6 and 0.9, and low (87Sr/86Sr)t, 0.705543 and 0.705851, is likely from a more depleted source and represents a volcanic arc granite. Combined with previous studies of Late Paleozoic granites, we find that the widely distributed Permian granites in Central Asia Orogenic Belt are absent between MSX and NX ophiolitic belts. Given the regional geology, we conclude that the back‐arc basin represented by the NX ophiolitic belt closed during Early Devonian and afterward, flat subduction of the oceanic basin represented by the MSX ophiolitic belt occurred. It also indicates that the oceanic crust was still being produced in the Paleo‐Asian Ocean during the early Carboniferous.

Geochronology and geochemistry of granodiorite at Jinwozi Au deposit: Tectonomagmatic evolution for Palaeozoic Beishan Orogen (Central Asian Orogenic Belt) in NW China

“…This and previous studies (S. Li et al, 2013; Tian et al, 2014; X. Y. Wang et al, 2018; Yu et al, 2016; Yuan et al, 2018; W. Zhang et al, 2018) suggest that the magmatic activities in the Mazongshan arc are divided into four stages (Figure 12). The subduction‐related magmatism (ca.…”

“…At Mazongshan, intrusive rocks comprise mainly granitoids and minor mafic‐ultramafic rocks (Figure 1c). Palaeozoic granitoids are widespread, that is, Baitoushan muscovite granite (409–395 Ma; X. Y. Wang et al, 2018), Luotuojuan tonalite (434–433 Ma; Yu et al, 2016), Hongliuxia mylonitized granite (460–430 Ma; Yuan et al, 2018), Bagelengtai granodiorite (434 ± 6 Ma; Zheng et al, 2018), Haergen two‐mica granite (409 ± 3 Ma; X. Y. Wang et al, 2018), Tongchangkou granite (408 ± 3 Ma; W. Zhang et al, 2018), and Gongpoquan monzogranite (402 ± 3 Ma; Zheng, Wu, Zhang, Xu, & Meng, 2012). Mesozoic granitoids have not been reported in the Mazongshan arc, but are documented in the Heiyingshan, Huaniushan and Shuangyingshan arcs, including the Baixianishan monzogranite (224 ± 1 Ma), Dahuoluo granodiorite (240–238 Ma), and Daquan quartz syenite (221 ± 2 Ma; S. Li, Wang, et al, 2012).…”