Late Palaeozoic and Mesozoic tectonic and palaeogeographical evolution of SE Asia

SE Asia comprises a collage of continental terranes derived directly or indirectly from the India–Australian margin of eastern Gondwana. The Late Palaeozoic and Mesozoic evolution of the region involved the rifting and separation of three elongate continental slivers from eastern Gondwana and the successive opening and closure of three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Sukhothai Island Arc System, including the Linchang, Sukhothai and Chanthaburi terranes, is identified between the Sibumasu and Indochina–East Malaya terranes in SE Asia and was formed by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo sutures represent the closed back-arc basin. The Palaeo-Tethys is represented to the west by the Changning–Menglian, Chiang Mai/Inthanon and Bentong–Raub suture zones. The West Sumatra and West Burma blocks rifted and separated from Gondwana, along with Indochina and East Malaya in the Devonian, and together with South China formed a composite terrane ‘Cathaysialand’ in the Permian. They were translated westwards to their positions outboard of the Sibumasu Terrane by strike-slip tectonics in the Late Permian–Early Triassic at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates. SW Borneo is tentatively identified as possibly being the missing ‘Argoland’ that separated from NW Australia in the Jurassic. Palaeogeographical reconstructions for the Late Palaeozoic and Mesozoic illustrating the tectonic and palaeogeographical evolution of SE Asia are presented. SE Asia is a unique natural laboratory for studying collisional plate tectonics, suture formation and mountain building (Hall 2002, 2009). The region is also one of the best for studying long-lived terrane dispersion and accretion processes (Metcalfe 1999) and the effects of rapid changes in continent– ocean configurations on biogeographical patterns and ecosystems (Hall & Holloway 1998; Kershaw et al. 2001; Metcalfe et al. 2001). The tectonic evolution, terrane accretion, and assembly of SE Asia during the Late Palaeozoic and Mesozoic has resulted in complex changes in the palaeogeography of SE Asia and in the juxtaposition of contrasting but temporally coincident palaeo-ecosystems in the region. Changing continent–ocean configurations, palaeogeography and climate changes in the Late Palaeozoic and Mesozoic of what is now SE Asia have resulted in complex patterns of both marine and terrestrial ecosystems of SE Asia both in space and time. This paper presents an overview of the tectonic and palaeogeographical evolution of SE Asia in the Late Palaeozoic and Mesozoic. Tectonic framework of SE Asia SE Asia is located at the zone of convergence between the Eurasia, Pacific and Indo-Australian plates (Fig. 1). The region comprises a complex assemblage of continental terranes (bounded by suture zones or other major tectonic features), island arcs and small ocean basins. The older Palaeozoic and Mesozoic portions of the region comprise allochthonous continental terranes (small to medium-sized allochthonous continental blocks that have distinctive tectonostratigraphic histories) that were assembled prior to the current collision of Australia with the region. The Cenozoic evolution of the region has been well studied, and the evolution and reconstruction models of Hall (2002) are considered the most reliable. This paper focuses on the Late Palaeozoic and Mesozoic evolution. Continental terranes and their origins The principal continental terranes and sutures of SE Asia are shown in Figures 2 and 3. Terranes are grouped according to their interpreted origins and are discussed briefly under these origin groupings below. Descriptions of the terranes have been given by Metcalfe (2006). All the continental terranes of East and SE Asia are interpreted to have been directly or indirectly derived from the eastern Gondwana margin at different times and some small terranes were subsequently derived indirectly from larger Gondwana-derived terranes or composite terranes (see Metcalfe 1986, 1988, 1990, 1991, 1993, 1996a, b, 1998, 2001, 2002, 2005, 2006; Table 1). I have previously described the successive rifting and northwards drift of three From: BUFFETAUT, E., CUNY, G., LE LOEUFF, J. & SUTEETHORN, V. (eds) Late Palaeozoic and Mesozoic Ecosystems in SE Asia. The Geological Society, London, Special Publications, 315, 7–23. DOI: 10.1144/SP315.2 0305-8719/09/$15.00 # The Geological Society of London 2009. Gondwana-derived continental slivers (now disrupted into various terranes), with the successive opening and closure of the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys ocean basins. This broad scenario is still advocated here (Fig. 4), but recent new data demand modification of the terrane make-up of these continental slivers, and also reinterpretations of the origins and boundaries of some of the terranes in the region. Terranes derived from Gondwana in the Devonian. A group of East and SE Asian terranes are interpreted to have rifted and separated from Gondwana as an elongate continental sliver in the Devonian (Fig. 4) and comprise North China, South China (including Hainan), Indochina–East Malaya (including the Qamdao–Simao/Simao and disrupted West Sumatra and West Burma terranes) and Tarim (including the disrupted Kunlun, Qaidam and Ala Shan terranes). The West Sumatra terrane was proposed by Hutchison (1994) and Barber & Crow (2003), and is interpreted to have been translated westwards from ‘Cathaysialand’ (combined South China–Indochina–East Malaya composite terrane in Permo-Triassic times) as suggested by Barber et al. (2005) and Metcalfe (2005). A Devonian separation of these terranes from Gondwana is still advocated here based on palaeomagnetic and biogeographical data from the terranes themselves and also from Devonian age data for oceanic radiolarian cherts in the Palaeo-Tethys (for details, see Metcalfe 1988, 1990, 1998, 2005). Jablonski & Saitta (2004) have, however, on the basis of transgressive–regressive sequences in western Australian basins, argued for a later Early Carboniferous (Viséan) separation of South China, Indochina and Simao terranes. This timing seems too young in view of the fact that the Palaeo-Tethys suture zone includes oceanic sediments of Devonian age and no post-Devonian Gondwana biota is reported from the terranes in question. Terranes derived from Gondwana in the Early Permian. The second continental sliver that rifted and separated from Gondwana in the Early Permian (with opening of the Meso-Tethys) was the Cimmerian continent of Sengor (1979, 1984), which included the Sibumasu terrane (Metcalfe 1984) of SE Asia and the Baoshan and Tengchong terranes of Yunnan in western China. I have presented evidence for the NW Australian origin and Early Permian rifting and separation of the Sibumasu portion of the Cimmerian continent from Gondwana in a series of papers (e.g. Metcalfe 1986, 1988, 1990, 1991, 1993, 1996a, b, 1998, 2001, 2002, 2005, 2006) and this will not be repeated here. Recent studies (Sone & Metcalfe 2008) have led to the recognition of an island arc system, the Sukhothai Island Arc system, through SE Asia (Fig. 5) situated between Sibumasu and Indochina–East Malaya (from which it was derived by back-arc spreading). This interpretation, Fig. 1. Principal tectonic plates of SE Asia. Arrows show plate motions relative to Eurasia. I. METCALFE 8