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Lhasa Terrane in Southern Tibet Came from Australia Lhasa terrane in southern Tibet came from Australia Di-Cheng Zhu1*, Zhi-Dan Zhao1, Yaoling Niu1,2,3, Yildirim Dilek4, and Xuan-Xue Mo1 1State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China 2School of Earth Sciences, Lanzhou University, Lanzhou 730000, China 3Department of Earth Sciences, Durham University, Durham DH1 3LE, UK 4Department of Geology, Miami University, Oxford, Ohio 45056, USA ABSTRACT REGIONAL GEOLOGY AND DETRITAL The U-Pb age and Hf isotope data on detrital zircons from Paleozoic metasedimentary rocks ZIRCON ANALYSES ε in the Lhasa terrane (Tibet) defi ne a distinctive age population of ca. 1170 Ma with Hf(t) values The Lhasa terrane is one of the three large identical to the coeval detrital zircons from Western Australia, but those from the western east-west−trending tectonic belts in the Tibetan Qiangtang and Tethyan Himalaya terranes defi ne an age population of ca. 950 Ma with a similar Plateau. It is located between the Qiangtang ε Hf(t) range. The ca. 1170 Ma detrital zircons in the Lhasa terrane were most likely derived from and Tethyan Himalayan terranes, bounded by the Albany-Fraser belt in southwest Australia, whereas the ca. 950 Ma detrital zircons from both the Bangong-Nujiang suture zone to the north the western Qiangtang and Tethyan Himalaya terranes might have been sourced from the High and the Indus–Yarlung Zangbo suture zone to Himalaya to the south. Such detrital zircon connections enable us to propose that the Lhasa the south, respectively (Fig. 1). The sedimentary terrane is exotic to the Tibetan Plateau system, and should no longer be considered as part of cover in the Lhasa terrane is nearly continuous the Qiangtang–Greater India–Tethyan Himalaya continental margin system in the Paleozoic from the Cambrian (Ji et al., 2009) to the late reconstruction of the Indian plate, as current models show; rather, it should be placed at the Mesozoic, although the Upper Permian is locally northwestern margin of Australia. These results provide new constraints on the paleogeographic absent (Zhu et al., 2009). The crystalline base- reconstruction and tectonic evolution of southern Tibet, and indicate that the Lhasa terrane ment of the western Qiangtang terrane is cov- evolved as part of the late Precambrian–early Paleozoic evolution as part of Australia in a different ered primarily by Paleozoic metasedimentary paleogeographical setting than that of the Qiangtang−Greater India−Tethyan Himalaya system. rocks, in contrast to the eastern Qiangtang ter- rane, where Mesozoic sedimentary cover is INTRODUCTION and Hf isotope analysis on detrital zircons from predominant (Pan et al., 2004). The Tethyan The origin and evolution of the Tibetan Pla- sedimentary rocks (and their metamorphosed Himalaya in the northern Indian plate consists teau have been widely accepted to have resulted equivalents) has proven to be a powerful tool primarily of Paleozoic and Mesozoic sedimen- from several collisional events between Gond- for tracing their provenance and for paleogeo- tary sequences (Pan et al., 2004). The Lhasa wana-derived terranes (e.g., Qiangtang, Lhasa) graphic reconstruction of continents in Earth and western Qiangtang terranes are generally or continents (e.g., India) and Eurasia since history (cf. Veevers et al., 2005). In this paper considered to have originated from the Hima- the early Paleozoic (e.g., Allègre et al., 1984; we use a combined method of detrital zircon layan (or Indian) Gondwana (cf. Metcalfe, Yin and Harrison, 2000; Zhu et al., 2009). The chronology, geochemistry, and provenance 2009), whereas the eastern Qiangtang terrane is Lhasa and the Tethyan Himalayan terranes, discrimination for Paleozoic metasedimentary thought to have derived from the Yangtze craton immediately north and south of the Indus– rocks in the Lhasa, Qiangtang, and Tethyan (or pan-Cathaysian) continental margin (cf. Pan Yarlung Zangbo suture (Fig. 1), respectively, Himalayan terranes to show that the Lhasa et al., 2004). have thus received much attention as they terrane most likely originated from Australian We have undertaken laser ablation–induc- best record the entire history of continental Gondwana, as proposed by Audley-Charles tively coupled plasma–mass spectrometry U-Pb breakup, rift-drift, subduction, collision, and (1983, 1984), rather than Indian Gondwana. age and Hf isotope analyses of 446 detrital zir- collision-related tectonism, magmatism, and This result also offers a new understanding cons recovered from Permian–Carboniferous metamorphism. However, the origin of the of the tectonic evolution of the Tethyan ocean metasedimentary rocks in the Lhasa terrane Lhasa terrane remains enigmatic. The domi- systems in a global context. (samples 08YR10, NX1–5, XM01, MB07–2, nant view is that the Lhasa terrane was rifted away from Indian Gondwana before it col- Figure 1. Tectonic frame- 80°E Detrital zircons in this study lided with the Qiangtang terrane to the north work of Tibetan Plateau JSSZ Detrital zircons in the literature CQMB in the Mesozoic (cf. Allègre et al., 1984; Yin and Himalayas, showing Western Dated magmatic rocks (Ma) and Harrison, 2000; Metcalfe, 2009), although sample locations of de- Qiangtang 364 LSSZ Eastern Qiangtang Audley-Charles (1983, 1984) proposed that the trital zircons of this study BNSZ GB-12 and previous work (data Spiti Rongma Shuanghu Lhasa terrane might have rifted from northern Valley Xungba Amdo sources in Table DR2; Gerze 32°N Australia in the Middle to Late Jurassic. How- 32°N see footnote 1). Suture 08YR10 Coqen Nyima XM01 Gongbo ever, this inferred Australian connection of the zones (SZ): JSSZ—Jin- gyamda Xainza 501 MB07-2 Lhasa terrane has not been widely considered sha; LSSZ—Longmu NX1-5 Lhasa Terrane GBJD by the scientifi c community because of the Tso–Shuanghu; BNSZ— N Lhasa Songdo Bangong-Nujiang; Selong IYZSZ 367 80°E lack of supporting data in the previous models. IYZSZ—Indus–Yarlung SL5-1 Nyalam Tethyan Himalaya 800km Using paleontology and stratigraphy to 28°N STDS Zangboe. STDS—South- 28°N reconstruct paleogeography has a long his- ern Tibetan detachment MCT system; MCT—Main Beijing tory of success (cf. Metcalfe, 2009), but a new 0 200 km MBT High Central thrust; MBT— Lesser Himalaya 90°E Himalaya approach that combines in situ U-Pb dating Main Boundary thrust; CQMB—Central Qiangtang Metamorphic Belt. Numbers indicate emplacement ages (Ma) of *E-mail: [email protected]. dated magmatic rocks (Ji et al., 2009; Dong et al., 2010; Pullen et al., 2011). © 2011 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, August August 2011; 2011 v. 39; no. 8; p. 727–730; doi:10.1130/G31895.1; 4 fi gures; Data Repository item 2011221. 727 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/39/8/727/3540777/727.pdf by guest on 24 September 2021 and GBJD from 82°E to 93°E; Fig. 1). We DETRITAL ZIRCON AGE spanning a wide range from 363 to 3602 Ma, also analyzed detrital zircons obtained from DISTRIBUTION AND HF ISOTOPES with two main peaks ca. 540 and ca. 1170 Ma a Lower Permian sandstone sample (SL5–1; ACROSS TIBET (Fig. DR2). A similar age distribution is also 98 grains) in the Tethyan Himalaya and from Ages of detrital zircons from the Ordovician conspicuous in inherited zircons from the Meso- an Ordovician quartzite sample (GB−12; quartzite sample (GB−12) in the central Qiang- zoic peraluminous granites in the Lhasa terrane 81 grains) in the western Qiangtang terrane tang metamorphic belt of the western Qiangtang (Zhu et al., 2009, 2011) (Fig. 2E). The zircons (Fig. 1) for comparison with the Lhasa sam- terrane range from 492 to 3564 Ma, with two in the ca. 1170 Ma age peak display a relatively ε ples. Sample descriptions and zircon details, peaks ca. 524 and ca. 942 Ma (Fig. DR2). This narrow range of Hf(t) values (–13.7 to +8.5) analytical techniques, concordia plots, and zir- age distribution is similar to detrital zircon ages with a narrow range of crustal model ages (2.8− con U-Pb age and Hf isotopic data of individual of metasedimentary rocks from the belt (Pullen 1.5 Ga) (Fig. 3B). analyses are provided in Tables DR1–DR3 and et al., 2008; Dong et al., 2011) (Fig. DR3). Figures DR1–DR3 in the GSA Data Reposi- The ca. 942 Ma age population yields varying DISCUSSION 1 ε tory . The zircon isotope data reported in this Hf(t) values (–28.2 to +7.5) with diverse crustal study and in the previous work are synthesized model ages (3.6–1.3 Ga) (Fig. 3A; Table DR3). Provenance of the Distinctive Detrital in Figs. 2 and 3. Detrital zircons of varying size The Lower Permian sandstone sample (SL5–1) Zircon Populations in Southern Tibet and shape were selected randomly, leaving out from the Selong area in the Tethyan Himalaya The similarity in age distributions (Figs. 2B grains with obvious cracks or inclusions. Thus (Fig. 1) contains zircons ranging in age from and 2F) recorded in detrital zircons from both the number of zircons in each population is sta- 498 to 2754 Ma, with two major age peaks the western Qiangtang (Pullen et al., 2008; tistically representative. ca. 535 and ca. 949 Ma (Fig. DR2). These ages Dong et al., 2011) and Tethyan Himalaya ter- also correspond well to the age distributions of ranes (DeCelles et al., 2000; McQuarrie et al., detrital zircons from a Neoproterozoic quartz- 2008; Myrow et al., 2010) suggests that zircons 70 Western Qiangtang: detrital 50 F zircons (N = 6; n = 547) ite and Cambrian–Permian sandstones from from these two terranes likely have a common 30 Spiti Valley and Nyalam (DeCelles et al., 2000; provenance.
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