Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations
Introduction
The Cenozoic was a period of major tectonic events, which influenced life and climate in SE Asia and the SW Pacific. Early in the Cenozoic, the collision of India with Eurasia enlarged the area of land in SE Asia. Later, the continuing collision with Australia led to connections between Australia, Eurasia and the Pacific, accompanied by the disappearance of some volcanic arcs and initiation of others. Subduction maintained volcanic arcs, which formed discontinuously emergent island chains crossing the region. The geological evolution of this region is complex, fascinating and important. Many geological ideas of great significance have originated here, from the links between gravity and ocean trenches of Vening Meinesz (1934), the mobilist ideas of Carey (1958), to the development of island arcs in the West Pacific (Karig, 1974). It is neither coincidence that Wallace's ideas on evolution developed here, nor that these original thoughts were closely linked to ideas of geological evolution (Wallace, 1869). Much of the region has emerged from the sea very recently, providing opportunities for new life and the incredible diversity of plant and animal species (e.g. Fischer, 1960, Stehli, 1968, Briggs, 1974, Brown, 1988, Gentry, 1988, Paulay, 1997, Morley, 1999), and the region continues to change at a rapid rate. Although it is a spectacular region of volcanic activity and seismicity, this wonderful natural laboratory is still not geologically well known.
This paper attempts to give an account of the Cenozoic evolution of this vast region (Fig. 1, Fig. 2, Fig. 3), using computer animations to illustrate its plate tectonic evolution. Because the region is so large, there is extensive literature (the Royal Holloway SE Asia Research Group's bibliography, primarily concerned with SE Asia, contains approximately 18,000 references). The coverage of the region is not even. For some areas like the Banda Arcs, the amount of geological literature is daunting, whereas for similar sized and equally complex parts of New Guinea, there is very little. I have tried to provide a basic commentary on the regional geology and constraints on reconstructions, before discussing the sequence of events. In order to do this, I have often cited references, which provide some of this information and review earlier literature, but may not be the primary work (for example, there are large amounts of important data in early Dutch publications, which are generally not cited here). This has been done to keep the reference list manageable, while providing adequate information on the background, justification for the interpretations made, and to provide a starting point for those who wish to research specific areas in more detail. Important sources for information on regional tectonics, and overviews of the geology of different parts of SE Asia and the SW Pacific, can be found in Visser and Hermes, 1962, van Bemmelen, 1970, Dow, 1977, Hamilton, 1979, Hayes, 1980, Hayes, 1983, Kroenke, 1984, Hutchison, 1989, Hutchison, 1996b, Mitchell and Leach, 1991, Hall and Blundell, 1996.
Section 2 of the paper briefly discusses present-day plate motions, as known from global plate models, GPS and tomography, considers the limitations of plate tectonics for continental and oceanic parts of the region, and discusses the value of a plate tectonic model for SE Asia and the SW Pacific. Section 3 summarises the techniques used in constructing the model, the value and sources of information and outlines routine features of the animations, such as the colours used on the maps and their meaning, and the file types and animation software. 4 Circum-Asia regions, 5 Asia–Pacific–Australia margins, 6 Circum-Australia regions then summarise the present tectonic and geological background for the many geographical sub-areas between Asia and the SW Pacific, and the essential features of the model for these areas. For this purpose, I have subdivided the region into three major sub-regions, and then discussed areas within these sub-regions. Section 4 deals with mainland Asia, areas peripheral to Asia, and the Sundaland region. Section 5 deals with Asia–Pacific–Australian margins and considers the smaller plates at these plate boundaries, including the Philippine Sea Plate, the Philippines and eastern Indonesia. Section 6 deals with the smaller plates and arcs around northern and eastern Australia, including New Guinea, the Caroline Plate and the Melanesian Arcs. 7 The plate tectonic model, 8 Cenozoic history discuss the plate tectonic model and Cenozoic history of the region for time slices of 5 million years from 55 Ma to the present. Section 9 discusses the implications of the interpretations for the region and attempts to draw some more general conclusions of relevance to other orogenic belts.
Section snippets
The region discussed
The region of SE Asia and the SW Pacific (Fig. 1, Fig. 2, Fig. 3) includes two major continental regions, Sundaland–Eurasia and Australasia, separated by oceanic plates. The whole of the western Pacific region is a mosaic of microplates, mainly of oceanic character, but at the margins of Australia, Sundaland and Asia are numerous small fragments of broadly continental character. How useful can a plate tectonic model be for such a region? The following parts of Section 2 consider present plate
Plate model
This paper gives an account of a plate tectonic model for the Cenozoic development of the region, based on my interpretations of a large range of geological data. It summarises the regional tectonic development of SE Asia and the SW Pacific, using a plate model which has been animated using 1 Ma time-slices. The animations are provided on a CD, which accompanies this paper, and it is intended that the paper will be read in conjunction with these, which can be run on any modern personal computer.
Eurasia
Although there is considerable evidence for Cenozoic deformation within eastern Asia (Fig. 6, Fig. 7), most strain seems to have been concentrated south of the Red River Fault (e.g. England and Houseman, 1986, Peltzer and Tapponnier, 1988, Huchon et al., 1994, Jolivet et al., 1994, Houseman and England, 1993, Wang and Burchfiel, 1997). In all the reconstructions, South China is fixed to Eurasia, and is considered as a rigid plate. Deformation of Asia north of South China is not included in the
The Philippine Sea Plate
Today, south of Japan the Philippine Sea Plate and Philippine islands separate the Asian margin from the Pacific Plate (Fig. 1, Fig. 3, Fig. 6, Fig. 9). It is the major plate separating the Pacific, Australian and Eurasian plates, and therefore it must be considered in order to understand Australia–Pacific and Australia–Eurasia boundaries. The Philippine Sea Plate is clearly of great importance to models of the western Pacific, but it is difficult to link to the global plate circuit because it
Eastern Australia
At present the eastern Australian margin (Fig. 2, Fig. 3, Fig. 11, Fig. 12) consists of a wide region of marginal basins whose history is still not well known. The margin was essentially in its present form by the early Eocene. Recent work by Gaina et al., 1998, Gaina et al., 1999 has modified early tectonic models (Weissel and Hayes, 1977, Weissel and Watts, 1979). The Coral Sea was fully open by 52 Ma according to Gaina et al. (1999) and the Tasman Sea ceased spreading at around 52 Ma (Gaina et
The plate tectonic model
Below, the geological evolution of the region, based on the information summarised earlier, is described for 5 Ma intervals. In this section, I have deliberately avoided re-citing references which have been discussed earlier in the paper, in the hope that it will be easier to follow. It is hoped and assumed that the reader will use the computer animations when reading this account. Throughout the text the ages given should all be accompanied by the word ‘about’, although the resolution of this
Reconstruction at 55 Ma (Fig. 14)
At 55 Ma the Asian margin from Japan northwards was an active continental margin. Further south the situation is less clear, and different plate boundaries can be inferred from the limited evidence that exists. It seems plausible that Taiwan, Palawan and the now extended crust of the South China Sea margins formed a passive margin, established during the late Cretaceous after the cessation of earlier subduction. Ru and Pigott, 1986, Zhou et al., 1995 report the earliest episode of extension of
Discussion
There were three important periods in the regional development of SE Asia and the SW Pacific. At about 45 Ma plate boundaries changed, probably as a result of India–Asia collision, but possibly after Pacific Plate motion change. At about 25 Ma plate boundaries and motions changed again, perhaps due to Ontong Java–Melanesian Arc collision, Australia–Philippine Sea Arc collision, and/or changes related to India–Asia collision. Plate motions and boundaries changed again at about 5 Ma, for uncertain
Acknowledgements
Financial support has been provided at different times by NERC, the Royal Society, the London University Central Research Fund, and the London University and Royal Holloway SE Asia Research Groups, supported by a number of industrial companies. Work in Indonesia has been facilitated by GRDC. I am especially grateful to Alan Smith and Lawrence Rush for advice, discussion and considerable practical support in using the ATLAS program and their constant willingness to modify the application to help
References (482)
Neogene tectonic reconstruction of the Adelbert–Finisterre–New Britain collision, northern Papua New Guinea
Journal of Southeast Asian Earth Sciences
(1995)- et al.
Geochronology of some Banda Arc volcanics
The Geology and Tectonics of Eastern Indonesia
Geological Research and Development Centre, Bandung, Special Publication
(1981) - et al.
Structural evolution of a modern arc–continent collision in Papua New Guinea
Tectonics
(1994) - et al.
The evolution of Sumba Island (Indonesia) revisited in the light of new data on the geochronology and geochemistry of the magmatic rocks
Journal of Asian Earth Sciences
(2000) - et al.
Geochronological cross-section through northern Thailand
Journal of Southeast Asian Earth Sciences
(1993) - et al.
Eocene arc–continent collision in New Caledonia and implications for regional Southwest Pacific tectonic evolution
Geology
(1995) - et al.
Regional implications of U/Pb SHRIMP age constraints on the tectonic evolution of New Caledonia
Tectonophysics
(1998) - Allagu, B., 2001. Tectonic Evolution and Sedimentation of the Southern Sabah Basin, Malaysia. Unpublished Ph.D. Thesis,...
Origin and tectonic evolution of the Caroline Ridge and the Sorol Trough, western tropical Pacific, from admittance and a tectonic modeling analysis
Tectonophysics
(1999)- et al.
Geologic evolution and petroleum system of Thailand Andaman Sea Basins