• Abstract and Figures
• Public Full-text

Lithos 364–365 (2020) 105549 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos Research Article Rushan-Pshart Paleo-Tethyan suture deduced from geochronological, geochemical, and Sr-Nd-Hf isotopic characteristics of granitoids in Pamir Shifeng Wang a,WenkunTanga,⁎, Yiduo Liu b, Xinghong Liu a, Xin Yao a a Key Laboratory of Paleomagnetism and Tectonic Reconstruction, Ministry of Land and Resources, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China b Department of Earth and Atmospheric Sciences, University of Houston, TX 77204, USA article info abstract Article history: Correlation of blocks comprising the Pamir plateau with blocks in the Tibetan plateau is debated due to the com- Received 24 September 2019 plex tectonic history of amalgamated orogenic belts, followed by widespread Cenozoic intracontinental deforma- Received in revised form 20 April 2020 tion within the Pamir plateau. Of particular interest is the Rushan-Pshart suture along the southern edge of the Accepted 21 April 2020 Central Pamir. It is uncertain if the suture zone is a Meso-Tethyan or a Paleo-Tethyan suture and if it is the west- Available online 25 April 2020 ern extension of the Bangong-Nujiang suture. This study presents new in-situ zircon U-Pb geochronology, whole- Keywords: rock geochemistry, and Sr-Nd-Hf isotopes of three granitic plutons (Tahman, Tash, and Mingtie) along the south- Central Pamir block ern edge of the Central Pamir block. Emplacement ages of the three plutons range from ~206 Ma to ~201 Ma. Rushan–Pshart Paleo-Tethyan Suture Samples from Tahman and Tash contain 67% to 76% SiO2, and yield A/CNK values between 0.92 and 1.17. They Indosinian granite exhibit high LILE/HFSE ratios, negative Eu anomalies (Eu/Eu* = 0.41–0.77), pronounced negative Nb, Ta, P, and Zircon U-Pb age Ti anomalies, negative εNd(t) values (between −7.3 and −6.9), and negative zircon εHf(t) values (between Geochemistry −15.5 and −1.4). Geochemical data indicate that the Tahman and Tash samples represent metaluminous or peraluminous, I-type arc-related granitoids. The Tahman granites are inferred to have formed by partial melting of the Precambrian metaigneous and metasedimentary rocks in the lower crust, while the Tash pluton was formed by partial melting of the infracrustal medium-to-high K basaltic compositions within the garnet stability field of the lowermost crust. We suggest that these newly discovered Late Triassic granite plutons are related to the closure of the Rushan-Pshart suture. This is supported by recent geochronological, paleontological, and strat- igraphic studies. Thus, the Rushan-Pshart suture is a Paleo-Tethyan suture. We further notice that the Central Pamir block is bounded by the Tanymas and Rushan-Pshart Paleo-Tethyan sutures to the north and south, respec- tively, which is structurally similar to the North Qiangtang and the Indochina blocks that are also bounded by two Paleo-Tethyan sutures from both sides. This indicates that the Central Pamir block is the western extension of the Tianshuihai-North Qiangtang block, both of which underwent oblique convergence during the closure of the Paleo-Tethys ocean. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Late Cretaceous), and Neo-Tethys (Late Triassic–Late Cretaceous) (Metcalfe, 2013; Robinson, 2015; Sengör, 1984; Xiao et al., 2002, The Himalayan–Tibetan–Pamir orogenic plateau witnessed the se- 2005; Zhang et al., 2018a). Some blocks, such as the Cimmerian block quential accretion of blocks onto the southern margin of Eurasia since (which includes the Turkey, Iran, Afghan, Qiangtang, Baoshan, and the Neo-Proterozoic (e.g., Robinson, 2015; Yin and Harrison, 2000). In Sibumasu micro-blocks), extend over a distance of N7000 km from the the Tibet Plateau, from north to south, these blocks include: the Mediterranean Sea in the west to the Sumatra arc in the east (Fig. 1a). Qaidam-Kunlun, Songpan-Ganzi, Qiangtang, Lhasa, and Himalayan Due to the complex tectonic history of the amalgamated orogenic blocks. In the Pamir plateau, similarly, there exist the North, Central, belts, as well as subsequent widespread Cenozoic intracontinental de- and South Pamir blocks (Fig. 1a). Rifting and drifting of these blocks formation, correlation of the blocks comprising the Pamir plateau with from Gondwana and their subsequent accretion onto Eurasia are gener- those in Tibetan plateau remains unresolved. In particular, intense ally related to the successive opening and closing of four intervening strain localized at the western Himalayan syntaxis in the Pamir region oceans, namely, the Proto-Tethys (Neo-Proterozoic–Ordovician), during the Cenozoic has resulted in discussion on whether the South Paleo-Tethys (Devonian–Triassic), Meso-Tethys (late Early Permian– or Central Pamir is the western continuation of the Qiangtang block, and whether the Rushan-Pshart Suture (RPS) corresponds to the – ⁎ Corresponding author. Bangong Nujiang suture (BNS) (Fig. 1a) (e.g. Angiolini et al., 2013; E-mail address: [email protected] (W. Tang). Lacassin et al., 2004; Schwab et al., 2004). https://doi.org/10.1016/j.lithos.2020.105549 0024-4937/© 2020 Elsevier B.V. All rights reserved. 2 S. Wang et al. / Lithos 364–365 (2020) 105549 Fig. 1. Simplified geologic map of the eastern Pamir (after Xinjiang BGMR, 2005), part of geochronological data in the study area also shown. Abbreviations: ① - Caledonian granite belt; ② - Indosinian granite belt; ③ - Yanshanian granite belt; TSH-NQ-Tianshuihai-North Qiangtang; SQ-south Qiangtang; SC-South China; NC -North China; SG- Songpan-Ganzi; L = Lhasa;JS- Jinshajiang suture; LSS- Longmu Co-Shuanghu suture; BNS- Bangong-Nujiang suture; YS- Yalong–Indus suture; TS- Tanymas suture; KS- Kudi suture; RPS- Rushan-Pshart suture; ShS- Shyok suture; CMS- Changning-Menglian suture; ATF: Altyn Tagh fault; KKF: Karakorum fault; Tash. F-Tashikurgan fault. S. Wang et al. / Lithos 364–365 (2020) 105549 3 Recent petrological, geochronological, and geochemical studies on to the west of Tashkurghan town yields a zircon U–Pb age of 12–8Ma ophiolitic, magmatic, and metamorphic rocks in central Qiangtang (Jiang et al., 2012), and a granite intruded into the Bulunkuole have shown that the Longmu Co–Shuanghu Suture represents a primary Palaeoproterozoic gneiss yields an age of 855 ± 14 Ma (Bian et al., Paleo-Tethyan suture (Li et al., 2006, 2009; Li et al., 2019; Wang et al., 2013). Three magmatic belts developed in the eastern Pamir, which 2018, 2019; Zhai et al., 2011, 2013, 2016). The North Qiangtang block are, from north to south, the Cambro-Ordovician, Permo-Triassic, and is interpreted as having a Cathaysian affinity, whereas the South Jurassic-Cretaceous magmatic belts (Bi et al., 1999; Kang et al., 2012, Qiangtang block is ascribed to represent the eastern segment of the Cim- 2015; Li et al., 2016; Schwab et al., 2004; Zhang et al., 2005). Based on merian block (Li et al., 2006, 2009; Li et al., 2019; Metcalfe, 2013; Wang geochronological and geochemical characteristics of the granites, these et al., 2016b, 2018, 2019). On the west side of the Karakorum Fault magmatic belts are considered to be associated with the closure of the (KKF), the Rushan-Pshart suture has been conventionally interpreted Kudi Proto-Tethys, Jinshajiang (Tanymas) Paleo-Tethys, and Bangong- as a Meso-Tethyan suture that correlates with the Bangong-Nujiang Nujiang (Rushan-Pashart or Shyok) Meso-Tethys oceans, respectively Meso-Tethyan suture (Burtman and Molnar, 1993; Lacassin et al., (Mattern and Schneider, 2000; Xiao et al., 2002, 2005; Zhang et al., 2004; Schwab et al., 2004). However, recent studies proposed alterna- 2004, 2016, 2018a, b; Li et al., 2007a; Qu et al., 2007; Yang et al., 2010). tively that the Rushan-Pshart suture is a Paleo-Tethyan suture rather Although no ophiolitic rocks have been identified, the presence of than a Meso-Tethyan one, based on new studies on biostratigraphy, the Longmu Co–Shuanghu suture in the southern part of the study mafic dikes, and granites in Central Pamir (Angiolini et al., 2013; area is inferred from the juxtaposition of Cathaysian- and Chapman et al., 2018; Hong et al., 2017). These competing interpreta- Gondwanan-affinitive biostratigraphy (Fig. 1). The strata to the north tions of the tectonic architecture in Pamir highlight the uncertainties of the Longmu Co-Shuanghu Suture is comprised of Upper Devonian in block correlation between Pamir and Tibet. Therefore, more research to Lower Permian sandstone and shale that contain warm-water is needed to document the evolution of the Rushan-Pshart suture and its Cathaysian fossil assemblages, similar to those observed in the North relationship to the sutures in the Tibetan Plateau. Qiangtang area; in contrast, Upper Devonian to Lower Permian units Geochronological and geochemical data from granitic rocks can pro- to the south of the Longmu Co Suture are characterized by cold-water vide important information regarding the timing and nature during sub- assemblages of Gondwanan affinity (Huang, 2001; Bureau of Geology duction and collision of plate convergence. In Pamir, the emplacement of and Mineral Resources of Xinjiang Uygur Autonomous Region the Caledonian granite belt is related to the closure of the Kudi Proto- (Xinjiang BGMR), 2006; Cui et al., 2006; Xia et al., 2006; Li et al., 2006, Tethys, the emplacement of the Indosinian granite belt to the closure of 2009; Metcalfe, 2013). Thus, the Tianshuihai-North Qiangtang block is the Jinshajiang Paleo-Tethys, and the emplacement of the Yanshanian bounded by the Jinshajiang suture to the north and the Longmu Co- granite belt to the closure of the Bangong-Nujiang Meso-Tethys oceans Shuanghu suture to the south, both of which are in the Paleo-Tethyan (e.g. Jiang et al., 2002, 2013; Xiao et al., 2002, 2005; Schwab et al., 2004; domain. The magmatic records around Mazar also support this double Zhang et al., 2004, 2005, 2016, 2018a,b;Fig.

Load more

  15

Copy Link