An Early Permian transpressional continental arc and arc–arc collision recorded in the Baidunzi Complex, southern Central Asian Orogenic Belt, NW China

Our multidisciplinary study of the southern Beishan Orogen in NW China, located between the Tienshan and Solonker suture zones, sheds light on the closure of the Palaeo-Asian Ocean and the termination of orogenesis in the Central Asian Orogenic Belt. We identify the Baidunzi Complex, an exotic Permian transpressional continental arc terrane, which is characterized by sheared and isoclinally folded metasedimentary and syn-kinematic plutonic rocks transformed into upper greenschist to amphibolite tectonites. The complex consists of basement rocks of thick-bedded orthoquartzite and orthogneiss, Carboniferous–Permian metasedimentary strata (including volcaniclastic sedimentary rocks, marble and marl interlayered with psammite) and the Baidunzi Intrusive Suite featuring 294–289 Ma hornblende diorite, tonalite, granodiorite and granite. The late intrusive rocks, including leucogranite to trondhjemite sills and a stitching gabbro unit, suggest an amalgamation age of 281–280 Ma between the Baidunzi and Ganquan arcs. The spatial and temporal linkage between the Baidunzi continental arc and the Liuyuan back-arc–Ganquan arc suggests that they were either built on a coeval doubly vergent subduction system or from the same north-vergent subduction system and then structurally juxtaposed by sinistral convergence. Geochronological and Hf isotope evidence, along with the continental rock affinity, indicates a close association between the Baidunzi Complex and the northern margin of the Tarim Craton during the break-up of Gondwana and the assembly of Pangaea.