Early Paleozoic Ocean Plate Stratigraphy of the Beishan Orogenic Zone, NW China: Implications for Regional Tectonic Evolution

Abstract

The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well‐enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Paleozoic deposits. From the Cambrian to the middle Ordovician, this region was characterized by geographically extensive, flat‐bedded siliceous mudstone, indicating the existence of a large ocean basin. The oceanic plate entered the convergence phase in terms of the Wilson Circle during the Middle Ordovician, when numerous magmatic arcs formed along two opposite sides of the ocean. The magmatic arcs became the widest during the Silurian, suggesting that the Hongliuhe‐Niujuanzi‐Xichangjing Ocean (HNX; a southern branch of the Paleo Asian Ocean) was reduced to a small residual ocean in the central Beishan region by that time, and probably lasted till the Carboniferous or later by newly published data.

Petrogenesis of Early Carboniferous Alkaline Basalt from the Wusun Mountain: Implications for Tectonic Evolution of the Western Yining Block, NW China

“…Combined with the discoveries of numerous magmatic rocks with zircon U-Pb ages of 466 to 447 Ma (Hu et al, 2008;Wang et al, 2012) in the northern BY, it is suggested that the initial southward subduction of the northern Tianshan Ocean began in the Middle Ordovician (Huang Z Y et al, 2013), and terminated in the latest Early Carboniferous . Contrastingly, the STAC was related to the northward subduction of the southern Tianshan Ocean and Late Paleozoic collision between the Tarim Craton and the BY-CTAT (Li et al, 2018a), an event which is characterized by a highultrahigh pressure (HP-UHP) metamorphic belt and associated ophiolitic mé langes (Gao and Klemd, 2003;Zhang et al, 2013;Zhang et al, 2020). The metamorphic belt is dominated by metapelites, eclogites, blueschists and marbles (Gao and Klemd, 2003), with the peak metamorphism time probably representing an important orogenic event (Su et al, 2010).…”

“…The Central Asian Orogenic Belt (CAOB) represents the largest Phanerozoic accretionary tectonic orogen in the world (Jahn et al, 2004;Windley et al, 2007;Shen et al, 2008), and is mainly composed of a series of microcontinents, island arcs, seamounts, and ophiolitic mé langes (Xiao et al, 2014;Yang et al, 2015;Wang et al, 2020). The formation of the CAOB was closely associated with the gradual contraction and final closure of the Paleo-Asian Ocean (PAO) (Wilhem et al, 2012;Li et al, 2013;Li S et al, 2016), and its closure displayed diachronous characteristics in different areas (Li et al, 2013;.…”