Chapter 6 The mafic–ultramafic (ophiolitic) rocks of Myanmar

Abstract

Mafic and ultramafic rocks are widely distributed in Myanmar and form major tectonic belts and suture zones representing remnants of the Mesotethyan Ocean. They occur as deformed and disrupted ophiolitic sequences and in forearc slivers as part of an accretionary wedge, intimately associated with siliciclastic and limestone units. They commonly host chromite–nickel–manganese, copper (gold) and jadeite mineralization. In this chapter, the nature, distribution, geological setting, petrological, mineralogical and ore characteristics of the mafic and ultramafic rocks in Myanmar are reviewed and described, and their tectonic setting and mineralization potential are discussed. Myanmar is characterized by north–south-trending major tectonic domains. From west to east, these include: the Rakhine coastal strip, an ensimatic foredeep; the Indo-Myanmar Ranges, an outer arc or forearc; the Western Inner-Myanmar Tertiary Basin, an inter-arc basin; the Central Volcanic Belt (Central Volcanic Line), an inner magmatic-volcanic arc; the Eastern Inner-Myanmar Tertiary Basin, a back-arc basin; and the Shan-Tenasserim massif, the ensialic Sino-Myanmar Ranges (Bender 1983; Khin Zaw 1989, 1990, 2017; Khin Zaw et al. 2015). Among these tectonic domains, ophiolitic rock associations occur in three belts trending nearly north–south parallel with each other (from west to east): the Western Ophiolitic Belt (WOB); the Central Ophiolitic Belt (COB); and the Eastern Ophiolitic Belt (EOB) (Fig. 6.1). The narrow WOB forms the longest belt, extending from the north to the southern part of Myanmar covering the eastern hills of the Naga, Chin and Rakhine ranges. According to Hutchison (1975), there are two ophiolite belts in Myanmar: the Naga Hill Line and the Mandalay Line. In this chapter the Naga Hill Line is termed the WOB. The Mandalay Line is the combination of the COB and the EOB. The southern continuation of the Mandalay Line is uncertain, due to a lack of comprehensive geological information. These …