Chapter 14 Tectonic Evolution

Abstract

The concept that SE Asia, and indeed Asia as a whole, has been built up during the Phanerozoic by the amalgamation of allochthonous terranes derived from the northern margin of East Gondwana, is now well established in the literature (e.g. Audley-Charles 1988; Sengor et al . 1988; Metcalfe 1996, 1999 and references therein). In Early Permian time all the major continental land masses, including East and West Gondwana, were joined together in the supercontinent of Pangaea (Fig. 14.1). At this time the continental blocks of North and South China, Indochina and Simao had already separated from East Gondwana. In Metcalfe's (1999) version of the concept a series of elongated terranes separated successively from the northern Gondwana margin by the development of ocean basins behind them. These oceans are referred to as Palaeo-Tethys, Meso-Tethys and Ceno-Tethys. The Indochina Block, with East Malaya, forms the core of SE Asia and is considered to have separated from Gondwana by Late Devonian times to amalgamate with the South China Block by the Early Carboniferous. Indochina is characterized by an Upper Palaeozoic to Mesozoic fauna and flora of Cathaysian and Tethyan type, exemplified by the Gigantopteris flora of Jengka Pass (Kon'no & Asama 1970; Hutchison 1994), related to those of the North and South China blocks, but with no relationship to the flora and fauna of Gondwana. To this core was added the Shan-Thai or Sibumasu Block, which separated from Gondwana in the Permian and amalgamated with the Indochina Block in the Late Permian or Triassic