Prolonged Late Mesoproterozoic to Late Triassic Tectonic Evolution of the Major Paleo-Asian Ocean in the Beishan Orogen (NW China) in the Southern Altaids

Abstract

The accretionary processes and the continental growth of the Altaids are still controversial. The Beishan orogen is situated in the southernmost Altaids and is an ideal tectonic site to address these issues. In this study, we report the results of new field-based lithological mapping and structural analysis on the Huaniushan complex in the Beishan orogen, which is composed of blocks of serpentinized ultramafic, gabbro, basalt, chert, limestone, and other rocks within a strongly deformed and cleaved matrix of sandstone and schist. Our new zircon U-Pb date reveal that a gabbro block formed at 504 ± 3 Ma. Our geochemical and isotopic data of gabbroic and basaltic blocks show that they are relics of the Mid-Ocean-Ridge (MORB)-type and Ocean-Island-Basalt (OIB)-type oceanic lithosphere, with high values of εNd(t) (+4.3–+14.5) and εHf(t) (+8.07–+17.74). The maximum depositional ages (MDAs) of two sandstone blocks were dated at 309 ± 5 Ma and 502 ± 11 Ma, respectively. U-Pb ages and Hf isotopes of detrital zircons from the matrix sandstones indicate that they were derived only from the Shuangyingshan–Huaniushan arc to the north. Accordingly, the Huaniushan complex was part of the Liuyuan accretionary complex that fringed the Huaniushan arc, and, therefore, formed by the northward subduction of the Liuyuan oceanic plate. Combined with the basalt yields zircon U-Pb age of 1,071 ± 5 Ma, we concluded that the Huaniushan complex has an age of 1,071 Ma to 309 Ma. Furthermore, the oceanic blocks and sedimentary matrix of the Liuyuan accretionary complex have an age of 1,071–270 Ma and 920–234 Ma, respectively, suggesting that the Liuyuan Ocean was still open at ca. 234 Ma. Thus, the studies reveal that the Liuyuan Ocean, a major branch of the Paleo-Asian Ocean, may have experienced a prolonged tectonic history, starting in the late Mesoproterozoic (1,071 Ma) and terminating later than the late Triassic (234 Ma), with a long subduction and development of a series of seamounts and/or plateaus emplaced into the Liuyuan accretionary complex.

Subduction Initiation of the Southern Branch of the Paleo‐Asian Ocean in the Middle Ordovician in the Southern Beishan Orogen

“… ε Hf ( t ) versus age diagram for the Huaniushan volcanic rocks in the Beishan orogen. The Hf isotope data of the sediments from the Heiyingshan block (Song et al., 2013); sediments and N‐MORB type gabbro in the Huaniushan complex (Mao et al., 2022); Gubaoquan eclogite (Soldner et al., 2019); parogeneiss in Gubaoquan (Liu, Zhao, et al., 2015); 424 Ma adakite (Mao, Xiao, Fang, et al., 2012). …”

“…The Huaniushan arc, is one of the major accretionary arcs in the southern Beishan orogen, and experienced a complicated long‐lived subduction–accretion process from the Cambrian to Triassic (Liu & Wang, 1995; Mao et al., 2022; Nie, Jiang, Bai, et al., 2002; Xiao et al., 2010; Zuo et al., 1991), even from the late Mesoproterozoic (Mao et al., 2022; Soldner et al., 2019). The zircon U‐Pb dates reveal that the crystallization times for the basaltic andesite, high‐Mg andesite and dacite are 449–422 Ma, 460–455 Ma and 437 Ma, respectively, suggesting that the magmatism acted from the Middle Ordovician to the early Silurian (460–437 Ma).…”

“…The Liuyuan accretionary complex is located south of the Huaniushan arc (Figure 1c), and contains the Liuyuan, Houhongquan, Huaniushan, Zhangfanshan, Huitongshan complexes and Gubaoquan eclogite. These ophiolitic complexes contain metamorphic basalts, gabbros, hornblendites, ultramafic rocks, cherts, limestones, sediments, and metamorphic tectonic blocks (Liu et al., 2011; Liu & Wang, 1995; Mao, Xiao, Fang, et al., 2012; Mao et al., 2022; Wang et al., 2016; Xiao et al., 2010; Yu et al., 2012; Zuo et al., 1991). The Huaniushan volcanic complex is located in the northernmost part of the Liuyuan accretionary complex along the Huaniushan fault (Figures 1c and 2).…”

“…The Paleo‐Asian Ocean (PAO) formed during the breakup of the Rodinia supercontinent between 1,000 and 700 Ma (Dobretsov et al., 1995, 2003; Mao et al., 2022). The Paleo‐Asian Ocean is a branch of the Pacific or a Pacific‐type outer ocean (Coney, 1992; Dobretsov et al., 1995, 2003; Liu, Xu, et al., 2015) that experienced continual Neoproterozoic to Mesozoic subductions and accretions of island arcs, continental arcs, seamounts, microcontinents, and accretionary complexes as part of circum‐Pacific orogenic system.…”

“…It lies among the European, Siberian, and Tarim‐North China cratons, and was formed by the convergence of the Tarim and North China cratons along the South Tianshan‐Solonker suture zone (Liu et al., 2021; Şengör et al., 1993; Xiao et al., 2018). The Beishan orogen is the middle segment of the Tianshan‐Solonker suture of the southern Altaids (Domeier & Torsvik, 2014; Mao, Xiao, Windley, et al., 2012; Xiao et al., 2010, 2018) and was formed by long‐lived episodic amalgamation and accretion of continental margin arcs, and island arcs, ophiolites, and accretionary wedges (Liu & Wang, 1995; Mao et al., 2022; Qu et al., 2011; Xiao et al., 2010; Zuo et al., 1991). The Huaniushan arc and Liuyuan accretionary complex are located in the southern part of the Beishan orogen.…”