Late Paleozoic Tectonic Evolution of the Paleo‐Asian Ocean in the Northern Alxa Block (NW China)

Abstract

The northern Alxa Block occupies a key position in the southern margin of the Central Asian Orogenic Belt (CAOB) and records late Paleozoic subduction and closure processes of the Paleo‐Asian Ocean (PAO). However, there are still controversies regarding the timing and location of the final closure of the PAO. This study presents structural deformation data and geochronological and geochemical data for Permian volcanic rocks, as well as detrital zircon provenance analysis of Permian sedimentary rocks along the Nuoergong‐Langshan Zone (NLZ) in the northern Alxa Block. During the early to middle Permian, the PAO lithospheric slab subducted beneath the northern Alxa Block, rendering a continental volcanic arc in the NLZ and also giving rise to extensive folding, thrusting, and crustal thickening. The crustal thickening in the NLZ may trigger the early Permian magmatic flare‐up that constructed much of the continental arc plutons. In the middle to late Permian, a retroarc foreland basin was formed, within which the Dahongshan Formation deposited. Significant active tectonic movements led to regional unconformity occurring during this period. A large‐scale dextral ductile shear deformation in the NLZ resulting from the lateral extrusion of the thickened crust after the terminal amalgamation of the southern CAOB was constrained between 272 and 249 Ma, suggesting a late Permian tectonic transition from compression to transpression. Combining these findings with published data, we suggest that the final consumption of the PAO occurred in the late Permian, probably along the Enger Us suture zone in the northern margin Alxa Block.

Closure of the Paleo‐Asian Ocean in the Middle‐Late Triassic (Ladinian‐Carnian): Evidence From Provenance Analysis of Retroarc Sediments

“…Our proposed timing of the final closure of the PAO is in general agreement with multi‐disciplinary data from regional studies along the whole southern CAOB. For example, Permian subduction‐related arc magmatism and arc‐flanking basins have been well documented along the northern margins of the Alxa Block and North China Craton (Eizenhöfer et al., 2014; D. Song et al., 2018, 2021; Tian et al., 2020; Zhang, Zhao, et al., 2016). Middle to late Permian pelagic radiolarians were reported in accretionary complexes and ophiolitic mélanges along a ∼3,000 km distance from Tianshan, through northern Alxa to the northern margin of the North China Craton, indicating the existence of a continuous deep marine basin between the Central Asian arcs and the Tarim and NCC until the late Permian (Y. Li et al., 2002; Shang, 2004; Xie et al., 2014).…”

Carboniferous and Permian integrative stratigraphy and timescale of North China Block

“…The closure of the PAO marks that the North China, Tarim and Qaidam blocks joined with Siberian-eastern European plates as parts of Pangea (Zhao et al, 2018). However, the final closure timing of the PAO is still controversial, ranging from Late Devonian to Triassic (Xiao et al, 2003;Zhang et al, 2009;Kröner et al, 2010;Cocks and Torsvik, 2013;Xiao et al, 2015;Zhu and Ren, 2017;Eizenhöfer and Zhao, 2018;Niu et al, 2021;Tian et al, 2020;Zhang et al, 2020).…”