Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Deformed continental arc sequences in the South Tianshan: New constraints on the Early Paleozoic accretionary tectonics of the Central Asian Orogenic Belt Linglin Zhong a,b , Bo Wang a, ⁎ , Koen de Jong c , Yazhong Zhai a , Hongsheng Liu a a State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, 210023 Nanjing, China b Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA c Seoul National University, College of Natural Science, School of Earth and Environmental Sciences, Gwanak-guu Seoul 151-742, Republic of Korea ARTICLEINFO Keywords: Accretionary orogeny Continental arc Volcanic rocks Early Paleozoic South Tianshan (Tien Shan) Central Asian Orogenic Belt ABSTRACT The tectonic afnity and structural evolution of the South Tianshan are key issues to understand the Paleozoic accretionaryorcollisionalorogenesisinthesouthwesternCentralAsianOrogenicBelt,butremaincontroversial. Geological and structural investigations on the Early Paleozoic low-grade metamorphic volcanic-sedimentary sequences around the Bayinbuluk basin demonstrate that they were prevalently reworked by north-vergent ductile deformation and overlain unconformably by Devonian to Carboniferous carbonates. Zircon U–Pb dating indicates that the volcanic rocks erupted during the Middle Ordovician to Early Devonian time (460–410Ma), and contain Neoarchean to Neoproterozoic zircon xenocrysts (~2.75Ga, ~2.46Ga, ~1.60Ga, 997–963Ma and 827Ma). Their whole-rock elemental, Sr–Nd isotopic (εNd(t)=−5.0 to +3.6) and zircon Lu–Hf isotopic (εHf (t)=−13.5 to +11.6) features resemble those of Andean-type continental arc volcanic rocks. The coexisting tufaceous sedimentary rocks indicate a depositional environment amidst a continental volcanic arc at 421 to 404Ma.Thenewlyobtainedandavailablegeochronological,geochemicalandstructuraldatasuggestthat:(1)a wideactivecontinentalmargincoveringtheSouthandCentralTianshanandnorthernTarimwasformeddueto Early-Mid Paleozoic southward subduction of the Paleo-Tianshan Ocean beneath the Tarim Craton; and (2) a Mid-Paleozoic transition from advancing to retreating accretionary orogeny was followed by opening of the SouthTianshanback-arcbasinsandbreak-upofthenorthernTarimcontinentalmargin.TheSouthTianshanwas subsequentlysubjectedtoregionaldeformationduringthesuccessivediachronousclosureofthemajorandback- arc oceanic basins, and locally reworked by the ductile strike-slip faulting (307–255Ma). 1. Introduction Accretionary orogens form at convergent boundaries due to sub- duction of oceanic slabs and can be subdivided into retreating and advancing types (Cawood and Buchan, 2007; Cawood et al., 2009). Along modern circum-Pacifc accretionary orogens, like the Andes Mountains of western South America (Babeyko and Sobolev, 2005; Ramos and Folguera, 2009) and New Zealand (e.g., Collins, 2002), some regions are extending, whereas others are contracting, controlled by subduction angles refecting slab buoyancy. Zones of orogenic con- tractioncanbecorrelatedwithfatsubductionofbuoyantoceaniccrust (e.g., young ocean foor, thicker and less dense aseismic ridges, or ba- salt plateaux), whereas contractional deformation is considerably re- duced or absent where the slab is steeply dipping (Cross and Pilger, 1982).Retreatingaccretionaryorogensoccuratplateboundarieswhere therateofconvergenceislessthanthatofsubduction,usuallyinvolving large plates of old oceanic lithosphere inducing upper-plate extension and crustal thinning, causing widespread arc splitting and formation of basalt-foored back-arc basins (Collins, 2002; Martinez and Taylor, 2003),suchasinthewesternPacifc(UyedaandKanamori,1979; Hall, 2012). By contrast, advancing accretionary orogens are characterized by propagating crustal shortening, thickening and anatexis (Cawoodetal., 2009), often focused in the thermally softened back-arc region, usually present on at least one side of the interacting plates (Collins, 2002; Hyndman, 2010). This process forms narrow orogens and closure of back-arc basins and produces suture zones situated between earlier stabilized lithosphere. Because continental arcs tend to have longer life spans than oceanic arcs (Ducea et al., 2015), accretionary belts formed at active continental margins are likely to undergo multiple orogenic https://doi.org/10.1016/j.tecto.2019.228169 Received 27 November 2018; Received in revised form 30 July 2019; Accepted 2 August 2019 ⁎ Corresponding author. E-mail address: bwang@nju.edu.cn (B. Wang). Tectonophysics 768 (2019) 228169 Available online 09 August 2019 0040-1951/ © 2019 Elsevier B.V. All rights reserved. T