The Liuyuan complex in the Beishan, NW China: a Carboniferous–Permian ophiolitic fore-arc sliver in the southern Altaids

Abstract

The tectonic history and time of closure of the Palaeo-Asian ocean of the Altaids are issues of lively current debate. To address these issues, this paper presents detailed geological, petrological and geochemical data of the Liuyuan complex (LC) in the Beishan region in NW China, located in the southernmost Altaids, in order to constrain its age, origin and tectonic setting. The LC mainly comprises massive basalts, pillow basalts, basaltic breccias, gabbros and ultramafic rocks together with cherts and tuffs. Most prominent are gabbros and large volumes of basaltic lavas. These mafic rocks have high TiO2 contents, flat rare earth element (REE) patterns and show high-field-strength elements (HFSEs) similar to those of mid-ocean ridge basalts (MORB). The mafic rocks exhibit positive εNd(t) (6.6–9.0) values, representing magmas derived from the mantle. But these basic rocks are also enriched in Th relative to REEs, and are systematically depleted in Nb–Ta–(Ti) relative to REEs. There is also a large range in initial 87Sr/86Sr (0.7037–0.7093). All these variables indicate that mantle-derived magma was contaminated by fluids and/or melts from a subducting lithospheric slab, and formed in a supra-subduction zone (SSZ) setting. A gabbro intruded in the complex was dated by LA-ICP-MS on 20 zircons that yielded a 206Pb–238U weighted average age of 286 ± 2 Ma. Considering the fact that all these basalts are imbricated against Permian tuffaceous sediments and limestone, we propose that the LC formed as an ophiolite in a fore-arc in Carboniferous–Permian time. This indicates that the Palaeo-Asian ocean still existed at 286 ± 2 Ma in early Permian time, and thus the time of closure of the Palaeo-Asian ocean was in or after the late Permian.

Provenance and tectonic settings of Permian turbidites from the Beishan Mountains, NW China: Implications for the Late Paleozoic accretionary tectonics of the southern Altaids

“…1a) contain the Liuyuan complex, arcs, ophiolites, and possibly micro-continents, which are all bounded by brittle faults and/or ductile shear belts ( Fig. 1b) (Zuo et al, 1990a;Hsü et al, 1992;Liu and Wang, 1995;Nie et al, 2002;Mao, 2008;Mao et al, 2011;Xiao et al, 2010b). The Liuyuan subduction-accretionary complex, which is situated between the Huaniushan and Shibanshan arcs on the southern margin of the Beishan Mountains (Fig.…”

“…;Mao, 2008;Mao et al, 2011;Li et al, 2009a;Xiao et al, 2010b). Tectonic setting discrimination diagrams with trace elements for the Beishan Permian turbidites.…”

Polyphase deformation of a Paleozoic forearc–arc complex in the Beishan orogen, NW China

“…Zhang et al, 2011;Zhang et al, 2012a). However, there is still much debate about the accretionary-collisional processes and the timing of termination of the orogen Guo et al, 2012;Mao et al, 2012b;Su et al, 2013;Zhang et al, 2012b). To date, the scarcity of systematic studies of the deformation history of the arcs and their accretionary complexes has hampered detailed understanding of the subduction-accretion-collision processes of the Beishan orogenic collage.…”

Petrogenesis and implications for tectonic setting of Cambrian suprasubduction-zone ophiolitic rocks in the central Beishan orogenic collage, Northwest China

“…1). A strong focus on the geochemistry of the Beishan ophiolites has inferred most to be supra-subduction zone in their nature (Wang et al, 2011;Mao et al, 2012b;Zheng et al, 2013;Tian et al, 2014), and the interpretations that follow have furthered the argument for multiple, contemporaneous subduction, obduction and accretion events that may have had varying subduction polarity. http://dx.doi.org/10.1016/j.jseaes.2014.10.038 1367-9120/Ó 2014 Elsevier Ltd. All rights reserved.…”

“…The magmatic record of the Beishan holds information of Early Cambrian, Silurian-Devonian and Carboniferous seafloor spreading, with diachronous Paleozoic arc-and collision-related magmatism. Complications arise considering that all have been transpressionally packaged between island arc accretionary complexes (Qu et al, 2011;Xiao et al, 2010;Song et al, 2013a) and cratonic margins to the north and south during the Silurian (He et al, 2014) through Permian (Mao et al, 2012b;Cunningham, 2013;Tian et al, 2013). Analogues have been found for the Beishan, and the CAOB as a whole, within the Lachlan orogen in Australia (Spaggiari et al, 2004;Schulmann and Paterson, 2011) or with modern (pre-collision) scenarios such as the southwestern Pacific archipelago with its collection of variously sized island arcs and complex arrays of subduction zones (Hsü et al, 1994;Hsü, 2003;Safonova et al, 2011;Xiao et al, 2010).…”