Provenance and tectonic setting of the Early and Middle Devonian Xueshan Formation, the North Qilian Belt, China

Abstract

The North Qilian orogenic belt is the key in the exploration of the formation and assembly of Asia. The Early–Middle Devonian Xueshan Formation, which is deposited in the north area of North Qilian Orogenic Belt, is the most important for revealing the evolution basin–mountain transition of the North Qilian Belt. In order to reveal the tectonic evolution of the central orogenic belt in China and Paleozoic global plate reconstruction, it is necessary to perform provenance analysis of the Xueshan Formation. Eighteen samples were collected from Yumen and Yongchang profiles in the west of North Qilian Belt (WN), and 16 samples were obtained from Gulang and Jingtai profiles in the east of North Qilian Belt (EN). The compositions of clastic conglomerates and the sandstones suggested that felsic volcanic was the main source of the WN Xueshan Formation deposits and that the sedimentary and metamorphic rocks were the main source of the EN sediments. According to major geochemistry indexes, such as Al2O3/SiO2 ratio ranging from 0.08 to 0.37 and the chemical index of alteration less than 80, the source rocks were moderately weathered and of moderately matured. The samples from the EN were relatively enriched in Cr, Ni, Sc, and V elements and depleted in Hf element. However, those from the WN were enriched in Hf without the enrichment of Cr, Ni, Sc, or V. The samples from WN showed a strong negative Eu anomaly, but the samples from EN showed a weak negative Eu anomaly or a positive Eu anomaly. All the above geochemical characteristics suggested the prominent input of felsic clasts with granitic rocks into the WN. Meanwhile, the discrimination diagrams of trace elements implied that WN rocks were derived from continental island arc and that the EN rocks were derived from orogenic belt and the passive continental margin. The North China Plate subducted southwards and formed subduction‐related arc magmatism along the southern margin of the North Qilian Terrane during the Early–Middle Devonian. In conclusion, the WN is a fore‐arc basin, but EN is a foreland basin.

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

“…These, combined with the duration time and volumes of the high Sr/Y magmatism, the absence of the extensionrelated magmatism (e.g., A-type granite), and the fact that the Lower to Upper Silurian is completely preserved in the western North Qilian (Xu et al, 2013), suggest that crustal thickening, thinning, and uplift in the western North Qilian were not as strong as in the eastern North Qilian during the Early Paleozoic period. On the other hand, the occurrence of detrital zircons of 550-500 Ma corresponding with the age of the North Qilian ophiolites within the Early-Middle Devonian sandstones in the eastern North Qilian (Xu et al, 2013) and the distinctly higher Fe 2 O 3 , MgO, Cr, Ni, Sc, and V, lower Zr and Hf contents, and higher Eu*/ Eu ratios of the Early-Middle Devonian clastic sedimentary rocks in the eastern North Qilian and more metamorphic fragments within them as compared with those of the time equivalent strata in the western North Qilian (Hou et al, 2018) indicate that the eastern North Qilian could have experienced stronger uplift and erosion than the western North Qilian, which could account for the fewer occurrences of Early Paleozoic ophiolites, high pressure metamorphic rocks, and arc-related magmatic rocks in the eastern North Qilian.…”

Petrography and geochemistry of the Lower Silurian sandstones from the Angzanggou Formation in the North Qilian Belt, China: implications for provenance, weathering and tectonic setting

“…The high ratio of volcanic lithic fragments indicates that the lithic clasts in the sandstone of the Angzanggou Formation were derived from felsic volcanic and granitoid rocks (Dickinson & Valloni, 1980). The detrital mode of the sandstones suggests that these fragments were derived from a continental arc (Hou et al 2016(Hou et al , 2018a (Fig. 5), indicating that unstable component contents in the sandstones gradually decreased with the increase in the maturity of the clastic rocks.…”

“…Xiao et al (2009), Gehrels et al (2003) and Zuo & Liu (1987) interpreted the Angzanggou Formation as an arc-related basin fill based on its sandstone and detrital mode. However, the petrology and geochemistry of volcaniclastic material in the Silurian sandstones indicate that the sediments were fore-arc basin fill (Xiao et al 2009;Yan et al 2010;Hou et al 2016Hou et al , 2018aYuan & Yang, 2015).…”

Textural and geochemical characteristics of late Pleistocene to Holocene fine-grained deep-sea sediment cores (GM6 and GM7), recovered from southwestern Gulf of Mexico

“…The composition of terrigenous sediments is largely influenced by the nature of parent rocks and sedimentary processes during transportation and within the depositional basin (Armstrong-Altrin 2015; Basu 2017). Hence, the spatial and temporal variations during sedimentation can be able to understand by the mineralogical and geochemical compositions of sediments, and numerous studies utilized these as a device to understand sediment provenance (Bhattacharjee et al 2017;Craigie 2018;Hou et al 2017;Mitra et al 2017;Paikaray et al 2008;Saha et al 2010Saha et al , 2018Verma et al 2016a;Verma and Armstrong-Altrin 2016;Wang et al 2017aWang et al , 2017b. In sediments, unstable minerals and mobile elements can be affected easily by weathering and erosional processes during transportation.…”