https://doi.org/10.1130/G46855.1 Manuscript received 14 February 2019 Revised manuscript received 9 August 2019 Manuscript accepted 9 August 2019 © 2019 Geological Society of America. For permission to copy, contact [email protected]. Published online 30 August 2019 Plume-modified collision orogeny: The Tarim–western Tianshan example in Central Asia Yigui Han1,2, Guochun Zhao2,1*, Peter A. Cawood3,4, Min Sun2, Qian Liu5 and Jinlong Yao1 1State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Northern Taibai Street 229, Xi’an 710069, China 2Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong 3School of Earth, Atmosphere & Environment, Monash University, Melbourne, VIC 3800, Australia 4Department of Earth Sciences, University of St. Andrews, St. Andrews KY16 9AL, UK 5Graduate School of Life and Environmental Sciences, The University of Tsukuba, Ibaraki 305-8572, Japan ABSTRACT (CTS)–Yili block, forming the South Tianshan Plume-modified orogeny involves the interaction between a mantle plume and subducting (STS) suture zone, which contains ophiolite oceanic lithosphere at accretionary margins. We propose that a plume can also be involved relics and (U)HP metamorphic rocks (Fig. 1B; in collisional orogeny and accounts for the late Paleozoic geological relations in Central Asia. e.g., Gao et al., 2011; Han et al., 2011, 2016a; Continental collision between the Tarim and Central Tianshan–Yili blocks at the end Carbon- Klemd et al., 2011; Xiao et al., 2013; Bayet iferous resulted in an orogeny lacking continental-type (ultra)high-pressure [(U)HP] rocks et al., 2018; Zhang et al., 2019). A final stage, and significant syncollision surface erosion and uplift, features normally characteristic of involving north-directed oceanic subduction is continent-continent interactions. Their absence from the Tianshan region corresponded with evidenced by Carboniferous passive-margin the arrival of a mantle plume beneath the northern Tarim. Elemental and isotopic data reveal deposition along the STS–northern Tarim and an increasing influence of the mantle plume on magmatic petrogenesis from ca. 300 to 280 Ma, intense arc magmatism in the CTS-Yili block. immediately after collision at 310–300 Ma. The rising mantle plume interrupted the normal The collision time is commonly suggested at ca. succession of collisional orogenic events, destroying the deeply subducted continental crust 325–310 Ma, coinciding with the (U)HP meta- and hence preventing slab break-off–induced continental rebound. Plume-modified continen- morphism (e.g., Gao et al., 2011; Han et al., tal collision thus limited continental (U)HP rock exhumation and associated surface uplift. 2016b; Loury et al., 2018; Zhang et al., 2019). A large igneous province (∼4 × 105 km2) in the INTRODUCTION the late Paleozoic continental collision orog- Tarim and STS region includes ca. 300 Ma kim- Oceanic convergent zones have been shown eny in the western Tianshan and Tarim region berlites near Bachu, ca. 295–285 Ma flood ba- to be impacted by mantle plumes. The resul- in Central Asia was profoundly affected by the salts, and 285–265 Ma (ultra-)mafic intrusions tant “plume-modified orogeny” is exemplified impingement of the Tarim mantle plume. In par- and/or dikes, as well as rhyolites, granites, and by ancient orogens in North America and east- ticular, such plume-collision interaction explains syenites (Fig. 1B). These early Permian bimodal ern Australia (Murphy et al., 1998, 1999; Betts previously enigmatic features of the collisional magmatic suites have been ascribed to the in- et al., 2012), and the present Tonga subduction orogen, i.e., the lack of continental-type (ultra) cubation of a mantle plume beneath the Tarim zone and Samoa plume (Chang et al., 2016). high-pressure [(U)HP] rock suites and the ab- lithosphere (e.g., Zhou et al., 2009; Xu et al., Plume-slab interaction can cause prominent tec- sence of significant surface uplift during colli- 2014), as manifested by crustal uplift centered tonic changes such as flattening of the subduct- sion, and it extends our understanding of plume- in Tarim at the Carboniferous-Permian transition ing slab, development of a slab window or slab modified orogeny to collisional settings. (Li et al., 2014). break-off due to plume erosion, arc- to plume- Current models for the Tarim and CTS-Yili related magmatic transition, and supercontinent GEOLOGICAL OVERVIEW AND KEY collision invoke a classic Alpine-Himalayan–type fragmentation (e.g., Murphy et al., 1998, 1999; ISSUES belt, but this interpretation fails to reconcile the Dalziel et al., 2000; Betts et al., 2012). In con- The northern margin of the Tarim craton and lack of continental-type (U)HP rock suites and the trast to growing understanding of the interplay the adjoining Tianshan region in Central Asia are lack of significant upper-plate uplift in the CTS- between a mantle plume and an oceanic subduc- an accretionary orogen that recorded the con- Yili region during collision. Such collision zones tion zone, the influences of a plume at a zone of sumption of the Paleozoic Paleo-Asian Ocean are normally characterized by intense and rapid continental collision have not been investigated. (Fig. 1; e.g., Windley et al., 2007; Cawood et al., surface uplift and exhumation of continental-type This study proposes such a case by providing 2009; Charvet et al., 2011; Xiao et al., 2015; (U)HP rocks, mainly induced by break-off of the age, geochemical, and isotopic evidence that Zhao et al., 2018). In the late Paleozoic, oceanic lower plate around the ocean-continent bound- subduction and closure resulted in collision be- ary and prompt continental slab rebound, as the *E-mail: [email protected] tween the Tarim craton and the Central Tianshan subducting dense oceanic slab fails to resist the CITATION: Han, Y., et al., 2019, Plume-modified collision orogeny: The Tarim–western Tianshan example in Central Asia: Geology, v. 47, p. 1001–1005, https://doi.org/10.1130/G46855.1 Geological Society of America | GEOLOGY | Volume 47 | Number 10 | www.gsapubs.org 1001 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/47/10/1001/4830278/1001.pdf by Northwest Univ Dept of Geology user on 06 January 2020 t o o o is at odds with the oceanic-crust origin for the C el 80 E 82 E 84 E 86°E A entr ic B N al Asian Orogen (U)HP rocks outlined above. The (U)HP meta- Karakum China 100 km B Yining North o morphism indicates the persistence of oceanic- Tarim Kazakhstan 44 N China CTS-Yili Block Urumqi slab subduction until ca. 310 Ma (Bayet et al., 30°N Fig.1B Yili region 2018). We suggest continental collision at ca. South Indian China Central Tianshan 310–300 Ma, corresponding to the main exhu- 500km 80°E 100°E 20°N an Suture h Tiansh Zone mation stage of the (U)HP rocks (Klemd et al., n Sout South Akeyazi Kule Tianshan 2005). This inference accords with numerical Heiyingshan Naryn Central Tiansha 42oN modeling that suggests that (U)HP rocks were Kuche Lake Kyrgyzstan Baicheng South Tianshan Korla exhumed during the transition from oceanic to Wushi Aksu continental subduction, as is the case for the Atbashi western Alps, New Caledonia, and Cuba (Agard o Keping 40 N Piqiang et al., 2009; Burov et al., 2014). The 310–300 Ma Flood basalts China (ca. 295-285 Ma) collision is also supported by magmatic records Bachu Kashi Syenites and (ultra) in the region. Compiled crystallization ages of mafic intrusions Tarim Craton Compiled data points: (ca. 285-270 Ma) Kimberlites magmatic rocks indicate a quiescence between (ca. 300 Ma) Yili Central Tianshan 310 and 300 Ma along the southern part of the South Tianshan CTS-Yili block, particularly in the CTS region N Tarim (Keping-Kuche) 38oN (Fig. 2A; Table DR1). Such a suppression of Yecheng NW Tarim (Piqiang) 76oE 78oE 80oE 82oE 84oE W-C Tarim (Bachu) magmatic activity can be accounted for by the continental subduction of the Tarim cratonic Cratonic block Micro-continent Accretionary orogenic domain Main Fault margin beneath the southern CTS-Yili block. Main suture zone and ophiolite relics Phanerozoic granitoids (U)HPbelt Precambrian and early Paleozoic Late Paleozoic Cenozoic and Mesozoic This interpretation coincides with a dramatic decrease of whole-rock εNd(t) and zircon εHf(t) Figure 1. (A) Tectonic overview map of Asia and major continental blocks (modified after Zhao values of magmatic rocks in the CTS domain (the et al., 2018). (B) Simplified geological map of Tarim and western Tianshan (modified after Gao upper plate), from juvenile to evolved signatures et al., 2011; Han et al., 2011; Xu et al., 2014), showing main tectonic units and sample locations of compiled age and geochemical data. Thick dotted line indicates inferred influential extent of after the 310–300 Ma age interval (Fig. 2C; Table Tarim mantle plume. CTS—Central Tianshan; N, NW, and W-C Tarim—northern, northwestern, DR2). The prominent decrease of Nd-Hf isotopes and western-central Tarim, respectively; (U)HP—(ultra)high-pressure. implies a significant input of old continental ma- terials into the magma source, probably inher- buoyancy of the continental crust (e.g., Davies and in magma source characteristics, based on data ited from the subducted lower plate, i.e., Tarim von Blanckenburg, 1995; van Hunen and Allen, from 330–260 Ma magmatic rocks in the Tarim continental crust commencing at 310–300 Ma. 2011; Zheng and Chen, 2016). In contrast, the and western Tianshan regions. This included 276 In the Tarim region, the first sign of man- South Tianshan belt preserves the world’s largest radiometric ages (Table DR1 in the GSA Data tle plume–related magmatism occurred at ca. oceanic-type (U)HP terrane but lacks continental- Repository1), 1297 major- and trace-element 300 Ma, i.e., the extrusion of kimberlites in type counterparts (Fig.