Chapter 12 Tectonic and metamorphic evolution of the Mogok Metamorphic and Jade Mines belts and ophiolitic terranes of Burma (Myanmar)

Abstract

The Mogok Metamorphic Belt is a north–south-aligned belt of mainly high-grade metamorphic rocks and granites that extends the length of Burma (Myanmar) along the western margin of the Sibumasu block from the Andaman Sea to the East Himalayan (Namche Barwa) Syntaxis (Figs 12.1 & 12.2). The Mogok metamorphic rocks host some of the world's finest rubies and sapphires, the former mainly from high-grade phlogopite + corundum marbles and the latter from a heterogeneous suite of syenite and charnockites that intrude the metamorphic rocks (Chhibber 1934 a , b ; Iyer 1953; Searle & Haq 1964; Bender 1983; Mitchell et al. 2007; Searle et al. 2007; Themelis 2008). Gem spinels are also found in forsterite-bearing marbles. Gemstones have been mined in the Mogok region since at least the mid-1800s (O'Connor 1888; Gubelin 1965 a , b ; Keller 1982, 1983; Kane & Kammerling 1992). Together with the adjacent Mergui Slate Belt these rocks lie to the west of the Shan Scarp and the Paung Laung-Mawchi Zone, interpreted by Mitchell et al. (2012) as a possible suture zone. We refer to this entire zone of metamorphic rocks, plus the Slate Belt and pre-collisional granites east of the Sagaing Fault and west of the Paung Laung-Mawchi Zone, as the Mogok–Mandalay–Mergui (MMM) Belt; the metamorphic rocks are referred to solely as the Mogok Metamorphic Belt (MMB). Fig. 12.1. Geological terrane map of the Eastern Himalaya, SE Tibet, Burma (Myanmar), Yunnan and Thailand. Lines of cross-sections in Figures 12.2 and 12.5 are shown. NLB, North Lhasa Block; SLB, South Lhasa Block; ITS, Indus-Tsangpo Suture Zone; GHS, Greater Himalayan sequence; LHS, Lesser Himalayan sequence; SH, Shillong Plateau; IBR, Indo-Burman Ranges; CB, Central (Chindwin) Basin; SFZ, Sagaing Fault Zone; TPFZ, Three Pagodas Fault Zone; MPFZ, Mae Ping Fault Zone; ST, Shan-Thai …