How ophiolitic mélanges can be defined as sutures is controversial with regard to accretionary orogenesis and continental growth. The Chinese Altay, East Junggar, Tianshan, and Beishan belts of the southern Central Asian Orogenic Belt (CAOB) in Northwest China, offer a special natural laboratory to resolve this puzzle. In the Chinese Altay, the Erqis unit consists of ophiolitic mélanges and coherent assemblages, forming a Paleozoic accretionary complex. At least two ophiolitic mélanges (Armantai, and Kelameili) in East Junggar, characterized by imbricated ophiolitic mélanges, Nb-enriched basalts, adakitic rocks and volcanic rocks, belong to a Devonian–Carboniferous intra-oceanic island arc with some Paleozoic ophiolites, superimposed by Permian arc volcanism. In the Tianshan, ophiolitic mélanges like Kanggurtag, North Tianshan, and South Tianshan occur as part of some Paleozoic accretionary complexes related to amalgamation of arc terranes. In the Beishan there are also several ophiolitic mélanges, including the Hongshishan, Xingxingxia–Shibangjing, Hongliuhe–Xichangjing, and Liuyuan ophiolitic units. Most ophiolitic mélanges in the study area are characterized by ultramafic, mafic and other components, which are juxtaposed, or even emplaced as lenses and knockers in a matrix of some coherent units. The tectonic settings of various components are different, and some adjacent units in the same mélange show contrasting different tectonic settings. The formation ages of these various components are in a wide spectrum, varying from Neoproterozoic to Permian. Therefore we cannot assume that these ophiolitic mélanges always form in linear sutures as a result of the closure of specific oceans. Often the ophiolitic components formed either as the substrate of intra-oceanic arcs, or were accreted as lenses or knockers in subduction-accretion complexes. Using published age and paleogeographic constraints, we propose the presence of (1) a major early Paleozoic tectonic boundary that separates the Chinese Altay–East Junggar multiple subduction systems of the southern Siberian active margin from those of the northern Tarim; and (2) a major Permian suture zone that separates the Tianshan–Beishan from the northern active margin of the Tarim Craton. These new observations and interpretations have broad implications for the architecture and crustal growth of central Asia and other ancient orogens as well

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 ε_Nd(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.