Geochemistry and petrogenesis of the early Palaeozoic appinite-granite complex in the Western Kunlun Orogenic Belt, NW China: implications for Palaeozoic tectonic evolution

Abstract

The Datong pluton, the largest early Palaeozoic granitoid in the Western Kunlun Orogenic Belt (WKOB) in NW China, is a typical appinite-granite complex. It consists of diorites, quartz diorites, monzodiorites, quartz monzodiorites, monzonites, quartz monzonites, syenites, granodiorites and monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yielded crystallization ages of 459 ± 3 Ma for the quartz monzonites and 452 ± 5 Ma for the monzogranites (Late Ordovician). The rocks possess a wide range of SiO2 (56.0–73.4 wt %), MgO (0.17–4.55 wt %) and Mg no. (25–60), with high K2O (2.83–5.29 wt %) contents, exhibiting high-K calc-alkaline to shoshonitic traits. They are characterized by enrichments in large-ion lithophile elements (LILEs) and light rare Earth elements (LREEs), as well as depletions in high-field-strength elements (HFSEs). The rocks have initial 87Sr/86Sr ratios of 0.7086–0.7185, negative εNd(t) values of –3.72 to –1.79 and εHf(t) values vary from –1.6 to +4.7. These features are modelled to show that they were most likely derived from an enriched lithospheric mantle source and that fractional crystallization with minor crustal contamination was involved in their petrogenetic process. Considering the distribution and chronology of the Palaeozoic intrusions – such as Kegang, Bulong, Qiukesu, Yierba, North Kudi, Dongbake, Buya, Ayilixi and Warengzilafu granitoid plutons with ages of c. 420–530 Ma – in conjunction with the Palaeozoic metamorphic overprinting in the WKOB, we propose a divergent double-subduction model to explain the destruction of the Proto-Tethys Ocean and suggest that the Datong pluton was likely emplaced in a post-collisional setting following the termination of subduction in response to slab break-off.

Accretionary orogenesis triggered by collision across continent distance: Evidence from the Proto‐Tethyan West Kunlun, China

“…La/Yb‐based crustal thickness estimates show episodic crustal thickening and thinning processes, which were divided into four cycles (I to IV). These crustal thickening and thinning events are supported by accompanying geological evidences including A‐type or bimodal rocks (~523 Ma Taxkorgan rocks, ~478 Ma Kusilafu pluton and ~405 Ma North Kudi pluton; Gao et al, 2013; Li et al, 2019; Xiao et al, 2005; Yuan et al, 2002), adakitic rocks (~513 Ma Datongdong and Yirba plutons, 470–452 Ma Datong and Akedala plutons and 430 Ma Buya pluton; Hu, Guo, et al, 2017; Li et al, 2019; Liao et al, 2010; Liu et al, 2014; Wang et al, 2017; Xu et al, 2021; Ye et al, 2008; Yin et al, 2020; Zhu et al, 2018), ~520 Ma northward migration of arc magmatism (Yin et al, 2020) and ~440 Ma amphibolite‐facies metamorphism (Zhang, Zou, et al, 2019). Crustal thickness estimates from magmatic zircons are in agreement with those from the whole‐rock La/Yb method.…”

“…Admittedly, Cycle III accretionary orogenesis in West Kunlun could be a rather local event. Co-existence of subducted oceanic crust-and thick lower crust-derived adakites (e.g.Datong pluton;Li et al, 2019;Liao et al, 2010;Wang et al, 2017;Zhu et al, 2018) together with a sharp shift in zircon Hf isotopic compositions toward positive values at 460 Ma are somewhat consistent with the subduction of oceanic ridges or slab breakoff, which deserves further study.5 | IMPLIC ATIONSSignificant accretionary orogeneses at 520-450 Ma were identified before the 450-400 Ma collisional orogenesis in Proto-Tethyan West Kunlun. In West Kunlun, 520-480 Ma accretionary orogenesiswas a geodynamical response to the final collision among blocks within Gondwana.…”

“…Key magmatic rocks are specially marked. These rocks were compiled from (Cui et al, 2006; Cui, Wang, Bian, Zhu, et al, 2007; Cui, Wang, Bian, Luo, et al, 2007; Gao et al, 2013; Hu, 2018; Hu et al, 2016; Hu, Wang, et al, 2017; Hu, Guo, et al, 2017; Jia et al, 2013; Li et al, 2019; Liao et al, 2010; Liu et al, 2014, 2016, 2019; Wang et al, 2013, 2017; Xiao et al, 2005; Xu et al, 2021; Ye et al, 2008; Yin et al, 2020; Yuan et al, 2002; Zhang et al, 2007; Zhang, He, et al, 2016; Zhang, Liu, et al, 2016; Zhang et al, 2018a; Zhang, Wu, Chen, et al, 2019; Zhang, Wu, Li, et al, 2019; Zheng et al, 2013; Zhu et al, 2016, 2018; Zhuan et al, 2018). Please see Table S2 for more details.…”

Late Palaeozoic to Late Triassic northward accretion and incorporation of seamounts along the northern South Pamir: Insights from the anatomy of the Pshart accretionary complex

“…Our geochronological study reveals that the sediments were mainly derived from Karakul‐Mazar and Bashgumbaz magmatic arcs, and older zircons were derived from the Central and South Pamir terranes, which are mainly composed of metamorphosed Palaeozoic–Triassic passive margin rocks (Rutte et al, 2017; Schwab et al, 2004). However, we do not exclude the possible derivation of detritus material from the Kunlun Terrane, which is composed of composite igneous rocks of Palaeozoic–Mesozoic age (Jiang et al, 2013; Xiao, Windley, Chen, Zhang, & Li, 2002; Zhang et al, 2016; Zhu et al, 2018) that were marked by several episodes of calcic to calc‐alkaline magmatism ranging in age from 260 to 240, 290 to 260, and 450 to 420 Ma (Cowgill, Yin, Harrison, & Xiao‐Feng, 2003; Harris, Ronghua, Lewis, Hawkesworth, & Yuquan, 1988; Zhang et al, 2014).…”

Petrogenesis of high Ba–Sr plutons with high Sr/Y ratios in an intracontinental setting: evidence from Early Cretaceous Fushan monzonites, central North China Craton

“…High Sr/Y magmatic rocks usually have adakitic signatures (high Sr and low Y and Yb concentrations with high Sr/Y and La/Yb ratios), which are related to continental crustal evolution and recycling, specific geodynamics and porphyry-type Cu ± Mo ± Au deposits (Xu et al 2002;Martin et al 2005;Castillo, 2012). Meanwhile, high Ba-Sr intrusions usually vary from appinite to granite and are characterized by high alkali, Ba-Sr and light rare earth element (LREE) concentrations and low heavy REE (HREE) concentrations, carrying important information on their petrogenesis and geodynamics in orogenic belts or subduction zones (Tarney & Jones, 1994;Fowler et al 2008;Bruand et al 2014;Pan et al 2016;Zhu et al 2018).…”