Petrogenesis of Early Paleozoic high Sr/Y intrusive rocks from the North Qilian orogen: Implication for diachronous continental collision

Abstract

A combination of U-Pb zircon ages and geochemical and Sr-Nd-Hf isotopic data are presented for the Early Paleozoic granodiorites from the Haoquangou and Baimawa plutons in order to probe the crustal thickness variation of the eastern North Qilian and the diachronous evolution of the North Qilian orogen. The granodiorites formed at 436–435 Ma and have high Sr/Y ratios (63–117). Elemental and isotopic data combined with geochemical modeling and comparisons with experimental data suggest that they were produced from the melting of relatively juvenile mafic rocks in the thickened lower crust. Together with other petrological and geochemical data and the calculation of variation in crustal thickness, this indicates that the eastern North Qilian experienced clear crustal thickening and thinning from the Late Ordovician to Late Silurian. Based on available data, we suggest that diachronous collision from east to west, which probably resulted in the distinct intensity of orogenesis between eastern and western North Qilian, can well account for the differential distribution of Early Paleozoic high Sr/Y magmatism and other geological differences between the eastern and western parts of the North Qilian. Our study also implies that diachronous collision may lead to, apart from distinct metamorphic, structural and sedimentary responses, the large differences in magmatism and deep crustal processes along the orogenic strike.

Petrogenesis of Syn-Collisional Adakitic Granitoids and Their Copper Mineralization Potential in the North Qilian Suture Zone

“…One date of 517 ± 6 Ma for the sample 12QL-181 could be affected by the old core of the zircon grain as indicated by CL images and, thus, is geologically insignificant. The 24 data-points for the sample 12QL-181 display Th contents of 155-446 ppm, U contents of 411-829 ppm, and Th/U ratios of 0.38-0.74, and yield 206 Pb/ 238 U ages of 428-443 Ma with a weighted mean 206 Pb/ 238 U age of 435 ± 2 Ma (MSWD = 3.7) (Table S1, Figure 3a), the same as the literature data of 436 ± 2 Ma within errors [31], interpreted as the crystallization age of the HQG pluton. The zircon grains from the granodiorite sample (12QL-190) give Th contents of 206-463 ppm, U contents of 306-692 ppm, and corresponding Th/U ratios of 0.49-0.78.…”

“…457-430 Ma Quwushan granodiorite [16,29], and ca. 436-435 Ma HSS granodioritetrondhjemite [31], suggesting an extensive pulse of adakitic magmatism ca. 457-430 Ma in the NQSZ.…”

“…3 km north of Baiyi showing major tectonic units and the Heishishan (HSS) pluton (modified after [30], the location of copper mineralization is after [33]), and (b) sketch map of the HSS granitic complex in the eastern NQSZ (modified after 1:50,000 geological map). Data sources include Chen et al, 2012 [6], Chen et al, 2016 [16], Tseng et al, 2009 [28], Yu et al, 2015 [29], Chen et al, 2023 [30], and Yang et al, 2020 [31].…”

Petrogenesis and tectonic evolution of the Palaeozoic to Mesozoic Niuxinshan granitoids in the North Qilian orogen,NWChina

“…Moreover, various models were proposed on the collisional process between the Qilian and Alxa blocks (Song et al, 2013). By comparing the inhomogeneous variation of the Early Palaeozoic high Sr/Y rocks between the western and eastern segments of the North Qilian orogen, Yang, Zhang, et al (2020) concluded a diachronous collision between the Qilian and Alxa blocks from east to west. The magmatic rocks with adakitic affinities are dominantly exposed in the eastern part of the North Qilian orogen, whereas those low Sr/Y calc-alkaline granitoids occur in its western segment.…”

Petrogenesis of mafic‐intermediate dykes from the Central Qilian belt, NW China: Significance of the role of subducted compositions in sub‐arc mantle

“…Long‐lived early Palaeozoic arc magmatism in the Qilian Orogen, northeastern Tibet Plateau, formed an extensive linear belt of plutonic and volcanic rocks as a result of subduction of the Proto‐Tethyan Ocean (Figure 1a; Liu et al, 2006; Song et al, 2013; Zhang et al, 2013; Wang et al, 2017; Wu et al, 2020; Fu et al, 2020; Zhao et al, 2020; Yu et al, 2021). Previous studies have concluded that these arc magmas reflect a sub‐arc mantle that is composed of distinct slab‐derived components (Yang et al, 2015, 2016, 2018,Yang, Song et al, 2019a, Yang, Zhang et al, 2019b; Wang et al, 2017; Tao et al, 2018; Fu et al, 2020; Zhao et al, 2020; Sun et al, 2022). Subduction‐related mafic‐intermediate dykes are well exposed in the western part of the Central Qilian belt (Figure 1b).…”