Chapter 4 Geological and tectonic evolution of the Indo-Myanmar Ranges (IMR) in the Myanmar region

Abstract

The Indo-Myanmar Ranges (IMR) of Myanmar, also known as the Indo-Burman Ranges (IBR) or the Western Ranges, extend from the East Himalayan Syntaxis (EHS) southwards along the eastern side of the Bay of Bengal to the Andaman Sea, comprising the Naga Hills Tract in the north, the Chin Hills in the middle and the Rakhine (Arakan) Yoma in the south. The IMR is economically important; major discoveries of oil and gas have been made in the Bay of Bengal to the west of the Rakhine Yoma, and there are several occurrences of chromite and nickel deposits (e.g. Webula, Mwetaung in Chin State) and submarine volcanic-hosted massive sulphide deposits (e.g. Laymyetna in Ayerwaddy Region). The IMR occupies a complex tectonic zone as the southeastwards continuation of the Indian–Asian collision belt in Tibet and Assam, and lies north of the active subduction zone of the Sunda–Andaman arc (Figs 4.1 & 4.2). The IMR occurs along the western margin of the Myanmar Microplate, also known as the Burmese Platelet or the West Myanmar Terrane or Block, situated between the Eurasian Plate to the east and the Indian Plate to the west (e.g. Fitch 1972; Curray et al. 1979; Mukhopadhyay & Dasgupta 1988; Pivnik et al. 1998; Bertrand & Rangin 2003; Shi et al. 2009; Baxter et al. 2011; Garzanti et al. 2013; Soibam et al. 2015). The West Myanmar Block has been also described as a forearc sliver, bounded on the west by a subduction zone and a strike-slip margin, on the east by a strike-slip fault (Sagaing Fault), on the south by a spreading centre and on the north by a compressional plate boundary (Curray et al. 1979; Pivnik et al. 1998; Nielsen et al. 2004). Fig. 4.1. Tectonic map of Myanmar region …