PROCEEDINGS OF SUNDALAND RESOURCES 2014 MGEI ANNUAL CONVENTION 17-18 November 2014, Palembang, South Sumatra, Indonesia 1 THE ORIGIN OF SUNDALAND Robert Hall Southeast Asia Research Group, Department of Earth Sciences Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom robert.hall@es.rhul.ac.uk ABSTRACT It is now accepted that the core of SE Asia was assembled from continental blocks that separated from Gondwana in the Palaeozoic and amalgamated with Asian blocks in the Triassic. Some fragments of these assembled blocks rifted and separated from Asia and later re-amalgamated with the oldest, western, part of the SE Asian continental core during the Mesozoic. There is increasing evidence that fragments of Cathaysian/Asian continental crust form parts of Northern Borneo and the offshore shelf to the north of Sarawak and east of Vietnam. Sarawak, the offshore Luconia–Dangerous Grounds areas, and Palawan include such Asian continental material. These probably represent a wide accretionary zone at the Asia–Pacific boundary, which was an active continental margin until early in the Late Cretaceous. Other continental blocks rifted from Australia in the Jurassic (SW Borneo, East Java–West Sulawesi, Sabah–NW Sulawesi, South Sulawesi–Sumba), and the Woyla intra-oceanic arc of Sumatra, and were added to Sundaland in the Cretaceous. After collision of these blocks subduction ceased around Sundaland in the early Late Cretaceous, and from about 80 Ma most of Sundaland was emergent, physically connected to Asia, but separated by deep oceans from India and Australia. INTRODUCTION This paper gives an overview of the origin and growth of Sundaland from the Late Palaeozoic until the Late Cretaceous. Sundaland was an exposed landmass during the Pleistocene sea level lowstands, and comprises southern Indochina, the Thai–Malay Peninsula, Sumatra, Java, Borneo, the shallow marine shelf (the ‘Sunda Shelf’) between these islands, and West Sulawesi (Fig. 1). Sundaland (van Bemmelen, 1949; Hutchison, 1973, 1989) is the continental core of SE Asia (Fig. 2). From the Late Cretaceous it formed the southeastern continental promontory of the Eurasian plate and was separated by deep oceans from India and Australia. It is now bordered to the west, south and east by subduction and collision zones (Hall and Morley, 2004; Metcalfe, 2011a,b). Its northern limit is poorly defined. It merges with the region deformed in the Cenozoic by India–Asia collision and is commonly separated from East Asia (Fig. 3) to the northeast along the Red River Shear Zone, which follows the Carboniferous Song Ma suture, and to the northwest from a Burma block along a Cretaceous suture and ophiolite zone (Hutchison, 1975). The western and southern margins of Sundaland follow the Sunda and Java Trenches. The eastern margin is irregular; a boundary has often been drawn through West Java, northeast into Borneo and then north-west towards the South China Sea, to exclude the ophiolitic and arc rocks added in the Cretaceous. However, we now know that further east, East Java, West Sulawesi, and potentially the area including Flores and Sumba, are underlain by continental crust that was at the edge of Sundaland and formed the SE Asian promontory of the Eurasian plate from the Late Cretaceous onwards. Sundaland has often been described as a shield or craton (e.g. van Bemmelen, 1949; Burton, 1972; Ben-Avraham and Emery, 1973; Gobbett and Hutchison 1973; Hutchison, 1989; Tjia, 1996; Barber et al., 2005) which is an idea inherited from geological thinking that pre-