Chapter 31 The pre-Cenozoic tectonic evolution of Myanmar

Abstract

Over the past few decades a synthesis has been developed in which Southeast Asia has been interpreted as composed of a number of continental tectonic units. There is a general consensus that these tectonic units originated during the Precambrian in the Southern Hemisphere, as part of the Gondwana Supercontinent. During the Palaeozoic these tectonic units were rifted off the northern margin of Gondwana by the formation and expansion of successive segments of the Tethys Ocean. They were then accreted to the southern margin of Eurasia following the subduction of Tethys during the latest Palaeozoic to early Mesozoic (e.g. Metcalfe 1988, 1996, 2011; Barber et al. 2011). Major pre-Tertiary tectonic units recognized in Southeast Asia are the Indochina Block and Sibumasu (Sino or Siam–Burma–Malaysia–Sumatra) Block, the latter extending from Yunnan in China, through the Shan States and southern Myanmar, Thailand, western Peninsular Malaysia to eastern Sumatra (Metcalfe 1996) (Fig. 31.1). Boundaries between the major blocks can be recognized, where they are marked by belts of ophiolites, including serpentinites, cumulate gabbros, pillow lavas and radiolarian cherts, representing the debris of the subducted Tethyan ocean floor. Fig. 31.1. Tectonic units of Myanmar and the immediately adjacent areas. Note that the ‘Indochina Block’ includes the Sukhothai Volcanic Arc (Sone & Metcalfe 2008). In Thailand to the south and east of Myanmar the broad outlines of this scenario are well established (Metcalfe 1996; Sone & Metcalfe 2008; Barber et al. 2011), but it is not clear how the Indochina and Sibumasu blocks can be traced into Myanmar. In addition, in Myanmar the Mt Victoria (Mitchell 1989) or West Burma Block (Metcalfe 1996) has been identified in the literature, but the eastern margin of this block against Sibumasu, conventionally identified as the Sagaing Fault, has not been clearly defined. The original position …