Abstract
AbstractThe southeastern Central Asian Orogenic Belt (CAOB) records the assembly process between several micro-continental blocks and the North China Craton (NCC), with the consumption of the Paleo-Asian Ocean (PAO), but whether the S-wards subduction of the PAO beneath the northern NCC was ongoing during Carboniferous–Permian time is still being debated. A key issue to resolve this controversy is whether the Carboniferous magmatism in the northern NCC was continental arc magmatism. The Alxa Block is the western segment of the northern NCC and contiguous to the southeastern CAOB, and their Carboniferous–Permian magmatism could have occurred in similar tectonic settings. In this contribution, new zircon U–Pb ages, elemental geochemistry and Sr–Nd isotopic analyses are presented for three early Carboniferous granitic plutons in the southwestern Alxa Block. Two newly identified aluminous A-type granites, an alkali-feldspar granite (331.6 ± 1.6 Ma) and a monzogranite (331.8 ± 1.7 Ma), exhibit juvenile and radiogenic Sr–Nd isotopic features, respectively. Although a granodiorite (326.2 ± 6.6 Ma) is characterized by high Sr/Y ratios (97.4–139.9), which is generally treated as an adikitic feature, this sample has highly radiogenic Sr–Nd isotopes and displays significantly higher K2O/Na2O ratios than typical adakites. These three granites were probably derived from the partial melting of Precambrian continental crustal sources heated by upwelling asthenosphere in lithospheric extensional setting. Regionally, both the Alxa Block and the southeastern CAOB are characterized by the formation of early Carboniferous extension-related magmatic rocks but lack coeval sedimentary deposits, suggesting a uniform lithospheric extensional setting rather than a simple continental arc.
Highlights
The Phanerozoic Central Asian Orogenic Belt (CAOB), one of the largest long-lived accretionary orogens worldwide, is situated to the north of the Tarim–North China cratons (Fig. 1a) and formed by complex subduction, accretion and collision processes related to the consumption of the Paleo-Asian Ocean (PAO), with significant crustal growth (Han et al 1997, 2011; Jahn et al 2000; Wu et al 2003; Windley et al 2007; Xiao et al 2018)
The third set of models infer that the large-scale PAO closed before the Late Devonian Epoch, but a new orogenic cycle began with intra-continental rifting within the southeastern CAOB during early Carboniferous time and resulted in the formation of a Red-Sea-like limited ocean basin, with the Solonker suture marking its closure during the Early Triassic Epoch (e.g. Zhang et al 2015a; Luo et al 2016; Pang et al 2016; Zhao et al 2017; Xu et al 2018)
Granodiorite 17WAL-35 displays relatively higher CaO (1.52–2.51 wt%) and lower total REE concentrations (114.30– 206.16 ppm), with significantly enriched light rare earth elements (LREEs; (La/Yb)N = 35.75–56.24) and positive Eu anomalies. It is characterized by enriched lithophile elements (LILEs) (Cs, Rb, Ba, Th, Pb and Sr) and depleted highfield-strength elements (HFSEs; Y, Yb and Lu), with negative Nb–Ta and positive Zr–Hf anomalies, respectively (Fig. 5d)
Summary
The Phanerozoic Central Asian Orogenic Belt (CAOB), one of the largest long-lived accretionary orogens worldwide, is situated to the north of the Tarim–North China cratons (Fig. 1a) and formed by complex subduction, accretion and collision processes related to the consumption of the Paleo-Asian Ocean (PAO), with significant crustal growth (Han et al 1997, 2011; Jahn et al 2000; Wu et al 2003; Windley et al 2007; Xiao et al 2018). In the first set of models, the subduction of the PAO was continuous from the early Palaeozoic Era to Late Permian–Early Triassic time and led to the successive accretion of micro-continental blocks and magmatic arcs to the northern NCC, with the northern margin of the NCC as a continental arc during Carboniferous–Permian time and the Solonker suture as the final closure site of the PAO The third set of models infer that the large-scale PAO closed before the Late Devonian Epoch, but a new orogenic cycle began with intra-continental rifting within the southeastern CAOB during early Carboniferous time and resulted in the formation of a Red-Sea-like limited ocean basin, with the Solonker suture marking its closure during the Early Triassic Epoch The lithospheric extension may be triggered by slab
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call