The Lhasa Terrane: Record of a microcontinent and its histories of drift and growth Di-Cheng Zhu a, ⁎, Zhi-Dan Zhao a , Yaoling Niu a,b,c , Xuan-Xue Mo a , Sun-Lin Chung d , Zeng-Qian Hou e , Li-Quan Wang f , Fu-Yuan Wu g a State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China b Department of Earth Sciences, Durham University, Durham DH1 3LE, UK c School of Earth Sciences, Lanzhou University, Lanzhou 730000, China d Department of Geosciences, National Taiwan University, Taipei 106, China e Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China f Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China g Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China abstract article info Article history: Received 15 May 2010 Received in revised form 30 October 2010 Accepted 2 November 2010 Available online 26 November 2010 Editor: T.M. Harrison Keywords: zircon U–Pb dating and Hf isotope Mesozoic–early Tertiary magmatic rocks lithospheric architecture tectonomagmatic evolution Lhasa Terrane Tibet The Lhasa Terrane in southern Tibet has long been accepted as the last geological block accreted to Eurasia before its collision with the northward drifting Indian continent in the Cenozoic, but its lithospheric architecture, drift and growth histories and the nature of its northern suture with Eurasia via the Qiangtang Terrane remain enigmatic. Using zircon in situ U–Pb and Lu–Hf isotopic and bulk-rock geochemical data of Mesozoic–Early Tertiary magmatic rocks sampled along four north–south traverses across the Lhasa Terrane, we show that the Lhasa Terrane has ancient basement rocks of Proterozoic and Archean ages (up to 2870 Ma) in its centre with younger and juvenile crust (Phanerozoic) accreted towards its both northern and southern edges. This finding proves that the central Lhasa subterrane was once a microcontinent. This continent has survived from its long journey across the Paleo-Tethyan Ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the Qiangtang Terrane to the north and with the Indian continent to the south. Zircon Hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks (e.g., ~ 50–90%, 0–70%, and 30–100% to the Mesozoic magmatism in the southern, central, and northern Lhasa subterranes, respectively). We suggest that much of the Mesozoic magmatism in the Lhasa Terrane may be associated with the southward Bangong–Nujiang Tethyan seafloor subduction beneath the Lhasa Terrane, which likely began in the Middle Permian (or earlier) and ceased in the late Early Cretaceous, and that the significant changes of zircon ε Hf (t) at ~113 and ~52 Ma record tectonomagmatic activities as a result of slab break-off and related mantle melting events following the Qiangtang–Lhasa amalgamation and India–Lhasa amalgamation, respectively. These results manifest the efficacy of zircons as a chronometer (U–Pb dating) and a geochemical tracer (Hf isotopes) in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The Tibetan Plateau is a geological amalgamation of several continental collision events since the Early Paleozoic (cf. Dewey et al., 1988; Kapp et al., 2007; Yin and Harrison, 2000; Zhu et al., 2009a, 2010). The Lhasa Terrane is the southernmost Eurasian block speculated as having rifted from Gondwana in the Triassic or the mid- to late Jurassic and drifted northward across the Tethyan Ocean basins before it collided with Eurasia along the Bangong–Nujiang suture (BNSZ; Fig. 1a) in the Cretaceous (earlier in the east and later in the west) (cf. Audley-Charles, 1983, 1984, 1988; Dewey et al., 1988; Kapp et al., 2007; Matte et al., 1996; Metcalfe, 2010; Sengör, 1987; Yin and Harrison, 2000; Zhang et al., 2004), and as having an Andean-type active continental margin in the south prior to the collision with the northward moving Indian continent in the Cenozoic marked by the Indus–Yarlung–Zangbo suture (IYZSZ; Fig. 1a) (e.g., Aitchison et al., 2007; Mo et al., 2008; Rowley, 1996; Yin and Harrison, 2000). However, the lithospheric architecture of the Lhasa Terrane (e.g., the age, composition and spatial distribution of crustal lithologies) and the nature of its northern suture (BNSZ) with Eurasia via the Qiangtang Terrane remain poorly understood. Geological studies in this regard have been hampered by complex crustal deformation as a result of continued convergence of the Indian lithosphere against the Lhasa Terrene through underthrusting (e.g., Kosarev et al., 1999). For example, despite much research on the Mesozoic geology of the Lhasa Earth and Planetary Science Letters 301 (2011) 241–255 ⁎ Corresponding author. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 29# Xue-Yuan Road, Haidian District, Beijing 100083, China. Tel.: +86 10 8232 2094; fax: +86 10 8232 2094. E-mail address: dchengzhu@163.com (D.-C. Zhu). 0012-821X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2010.11.005 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl