Research Paper GEOSPHERE Jurassic sedimentation in the south-central Qiangtang terrane reveals successive terrane collisions in central Tibet 1, 2 1 3 4 GEOSPHERE, v. 15, no. 2 Lin Li *, Carmala N. Garzione , Majie Fan , Xiaowei Li , and Xiangzhong Li 1Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, Texas 76019, USA 2Department of Earth and Environmental Sciences, University of Rochester, Rochester, New York 14627, USA https://doi.org/10.1130/GES01649.1 3State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China 4Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710075, China 10 figures; 1 set of supplemental files CORRESPONDENCE: [email protected] ABSTRACT the Tibetan Plateau, especially of its southern and central parts (England and Searle, 1986; Murphy et al., 1997; Kapp et al., 2005, 2007b). The collision be- CITATION: Li, L., Garzione, C.N., Fan, M.J., Li, X.W., Our limited knowledge of Mesozoic tectonism in the Tibetan Plateau has tween the Lhasa and Qiangtang terranes along the Bangong-Nujiang suture and Li, X.Z., 2019, Jurassic sedimentation in the south-central Qiangtang terrane reveals successive hindered understanding of its geologic evolution. This study uses zircon U-Pb (shortened to Bangong suture hereafter; Fig. 1) is one of the most prominent terrane collisions in central Tibet: Geosphere, v. 15, geochronology to refine regional chronostratigraphy and infer the Jurassic tectonic events that occurred in the Mesozoic history of the Tibetan Plateau no. 2, p. 433–449, https://doi.org/10.1130/GES01649.1. sedimentary-tectonic evolution of the Bangong suture and the south-central (Dewey et al., 1988; Yin and Harrison, 2000). Despite the many studies that Qiangtang terrane in the central plateau. During the late Early–early Middle have been conducted to understand the processes of the Lhasa-Qiangtang Science Editor: Shanaka de Silva Associate Editor: Michael H. Taylor Jurassic, fan delta and alluvial fan deposits sourced from the Amdo basement collision (Yin and Harrison, 2000; Zhang et al., 2012a; Zhu et al., 2013), the to the south occurred within the Amdo suture zone, as a result of collision timing and nature of the collision remain controversial. Received 15 December 2017 between the Amdo basement and Qiangtang terrane. Since the Bajocian of The current understanding of the timing and nature of the Lhasa-Qiangtang Revision received 26 September 2018 the Middle Jurassic, continued sea-level rise transformed the Qiangtang ter- collision can be classified into two hypotheses. One of the hypotheses suggests Accepted 14 December 2018 rane into a south-facing shallow continental shelf, and sedimentary detritus that the collision did not occur until the early Late Cretaceous (ca. 100 Ma), was predominantly sourced from the Hoh Xil and Kunlun terranes to the based primarily on the presence of: (1) 120–108 Ma basaltic rocks with ocean Published online 29 January 2019 north. The contemporaneous magmatic arc in southern Qiangtang terrane island affinity within the Bangong suture zone (Zhu et al., 2006; Liu et al., 2014; was most likely submerged in a marine setting and did not contribute much Zhang et al., 2014a; Fan et al., 2015); (2) 170–140 Ma and 130–100 Ma intrusive detritus to the Middle Jurassic strata. Starting from the early Late Jurassic, rocks in the southern Qiangtang terrane, presumably formed by continental a depositional hiatus occurred in the southern Qiangtang terrane, whereas arc magmatism associated with the northward subduction of the Meso-Tethys the shallow marine to deltaic deposition in the central Qiangtang terrane oceanic lithosphere (Li et al., 2014; Hao et al., 2016; Liu et al., 2017; Liu et al., received detritus not only from the Hoh Xil and Kunlun terranes to the north, 2018); and (3) 131–121 Ma deep-marine radiolarian deposits near Gaize in the but also from the magmatic arc in southern Qiangtang terrane to the south. Bangong suture zone (Baxter et al., 2009). The other hypothesis suggests a The arrival of abundant Jurassic arc-derived detritus in central Qiangtang diachronous collision from east in the Amdo area during the Middle–Late Ju- terrane since ca. 163 Ma was most likely caused by the early Late Jurassic rassic (ca. 174–145 Ma; Dewey et al., 1988; Leeder et al., 1988), to west in the initial collision between the Lhasa and Qiangtang terranes, which raised the Shiquanhe area during the Early Cretaceous (ca. 145–110 Ma; Matte et al., 1996). southern Qiangtang magmatic arc to be a source region. This latter hypothesis is mainly based on: (1) obduction of ophiolite fragments onto the northern margin of the Lhasa terrane during the Middle–Late Jurassic near Amdo (Yin and Harrison, 2000); and (2) structural analyses that indicate INTRODUCTION major Early Cretaceous shortening in the southern Qiangtang terrane near Shiquanhe and Gaize (Kapp et al., 2005; Raterman et al., 2014). The Tibetan Plateau is a collage of terranes that was assembled during In addition to the uncertainty in the timing of the Lhasa-Qiangtang colli- the Phanerozoic (Yin and Harrison, 2000); from south to north, they are the sion, the presence of the Amdo basement, with ophiolite fragments on both Himalaya, Lhasa, Qiangtang, Hoh Xil-Songpan-Ganzi (shortened to Hoh Xil its northern and southern sides (Coward et al., 1988; Fig. 1B), remains enig- hereafter), Kunlun-Qaidam, and Qilian terranes (Fig. 1A). Mesozoic tectonism, matic. Yin and Harrison (2000) considered the Amdo basement as a part of prior to the final Cenozoic India-Asia collision, contributed to the growth of the Lhasa terrane, and suggested that closure of the Meso-Tethys Ocean and collision between the Lhasa and Qiangtang terranes occurred to the north This paper is published under the terms of the *Current address: Géosciences Rennes, UMR–CNRS 6118, Université de Rennes 1, 35042 Rennes of the Amdo basement. To the contrary, Guynn et al. (2006) proposed that CC-BY-NC license. Cedex, France the Amdo basement was rifted from the Qiangtang terrane before the Early © 2019 The Authors GEOSPHERE | Volume 15 | Number 2 Li et al. | Jurassic terrane collisions in central Tibet Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/433/4663908/433.pdf 433 by guest on 26 September 2021 Research Paper 84 E 86 88 90 92 B Tr Hoh Xil terrane Tr K2-Ts JSS 35 JSS K2-Ts N Ts 35 Tr-Jr Tr-Jr N C-P Tuotuohe 34 Ts 34 Tr-Jr K2-Ts Ts Qiangtang Q Fig. 2A iangtan g terrane anti clinorium Yanshiping Ts 33 C-P Tr-Jr Shuanghu 33 Tr-Jr Tr-Jr Ts Tr-Jr Gaize Amdo BNS Ts 32 32 Nima BNS Amdo Jr-K Lhasa Jr-K basement terrane Jr-K Naqu 84 E 86 88 90 92 40 Abbreviations: A F N Qiangtang Paleozoic Central Qiangtang N asin AT QL Qi C-P im B l KL-QD: Kunlun-Qaidam metasedimentary rocks metamorphic rocks Tar KL-QD S ia n SCB: Sichuan Basin Qiangtang Mesozoic Late Cretaceous– ATF: Altyn Tagh strike- Tr-Jr K2-Ts Hoh X KLS sedimentary rocks Cenozoic sed. rocks 35 il slip fault Hoh Xil Triassic Cenozoic JS LMT: Longmenshan thrust Ts Qiangtang S Songpan Tr sedimentary rocks sedimentary rocks MBT: Main boundary thrust Ganzi B B T BNS: Bangong-Nujiang Lhasa Mesozoic Suture zone ophiolite NS Jr-K LM suture sedimentary rocks and sedimentary rocks Lhasa B 30 Hi IYS: Indus-Yurlong suture Qiangtang Eocene– ma IYS SC Amdo gneiss laya JSS: Jinshajiang suture Oligocene volcanics 400 km KLS: Kunlun suture MBT Mesozoic granites Thrust faults Indian QLS: Qilian suture 80 E 85 90 95 100 105 Figure 1. (A) Tibetan Plateau above the 2000 m elevation contour, showing major tectonic subdivisions and suture zones (dotted lines). Rectangular box shows location of B. (B) Simplified geologic map of the west-central Tibetan Plateau. Modified from Kapp et al. (2005). Rectangular box shows location of Fig. 2A. sed.—sedimentary. Jurassic and then collided with the Qiangtang terrane during the Early–Middle and detrital provenance can be distinctive in different tectonic settings; e.g., a Jurassic (ca. 190–170 Ma), which was followed by the major Lhasa-Qiangtang retroarc foreland basin would receive detritus mainly from the magmatic arc, collision to the south of the Amdo basement. whereas a passive continental margin basin would have major sediment sources The Qiangtang terrane holds the largest Jurassic marine deposits in the from the adjacent exposed continent. This study applies the zircon U-Pb geo- Tibetan Plateau. Previous sedimentological studies have suggested that these chronology method to both sandstone and igneous samples from the Jurassic Jurassic strata were deposited in shallow marine to marginal marine environ- sedimentary successions in the Amdo-Yanshiping area, south-central Qiangtang ments (Wang et al., 2001; Wang et al., 2010a). However, the tectonic setting of terrane (Fig. 2), to infer the history of the Lhasa-Qiangtang collision and the role these deposits is not well understood, with proposed models ranging from a that the Amdo basement played during the collision. We found that: (1) the retroarc foreland basin (Li et al., 2001) to a passive continental margin basin (Guo Amdo Formation received detritus mainly from the Amdo basement as a result et al., 2008) to a passive rift basin (Wang et al., 2010b). Depositional environment of late Early–early Middle Jurassic collision between the Amdo basement and GEOSPHERE | Volume 15 | Number 2 Li et al. | Jurassic terrane collisions in central Tibet Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/15/2/433/4663908/433.pdf 434 by guest on 26 September 2021 Research Paper 91.50 E 92.00 92.50 93.00 92.00 E 92.10 92.20 Q A Highway E B Tr3 E Q Q Tr3b J2-3 J C-P 2b J J2q Q Yanshiping C-P 2q Yanshiping 0 N J 0 N 3x J B 2q 16MZ01D 36.6 3.5 N Q J J2-3 Tr3 2b 3 J2-3 J3s 16MZ02D J2b J3 J3 x J2 x J2q J b 16MZ03D Q 2b J 0 0 10 20 km 3x J3K1x Q Q J2-3 J2-3 J2q J2b 0 Q J2-3 0 0 2.5 5 km Q 36.5 0 Tr J2-3 Tan ac J2b g e Q gul of a r 33.0 ang Q K2 91.60 E 91.80 92.00 e N K2 Pass Q Q Tr3t C J2ba J2-3 J2b 16AD03D 32.50 K2a Q Q 16QS01D J2 J2s K2d J2b 2d 2a K2d Q K K 5 J2s 3 50 K2d C 2.