2.2.1 Main continental terranes
Many attempts have been made by previous workers to reconstruct the tectonic setting of Southeast Asia (e.g., Bunopas, 1982; Sengor, 1984; Hutchison, 1989, 2007; Metcalfe, 1988, 2011, 2013; Sone and Metcalfe, 2008; Barber and Crow, 2009; Hall, 2011, 2012; Morley, 2012; Khin Zaw et al., 2014). Generally, Southeast Asia is recognised to be made up of a collage of continental blocks or terranes including the South China Terrane, the Simao Terrane and the Indochina-East Malaya Terrane to the east and the Sibumasu Terrane, the West Myanmar (Burma) Terrane, the West Sumatra and the Woyla Terranes to the west (Fig. 2.1). The origin of all the Southeast Asia Terranes on the margin of Gondwana is also well discussed and detailed evidence can be found in a series of papers by Metcalfe (1988, 1996, 2006), Burrett and Stait (1985) and Burrett et al. (1990). As Peninsular Malaysia is located on the mainland Southeast Asia, an overview of the two major terranes; the Sibumasu Terrane and the Indochina-East Malaya Terrane (Metcalfe 1996, 2006) are discussed in detail in this thesis. The South China Terrane and the West Myanmar (Burma) Terrane are also discussed as they play significant roles in the formation of mainland Southeast Asia.
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Fig. 2.1. Distribution of principal continental fragments of Southeast Asia including the main suture zones, back- arc and volcanic arcs, and major fold belts in Southeast Asia (redrawn and modified after Sone and Metcalfe, 2008; Barber and Crow, 2009; Metcalfe, 2009, 2011, 2013; Hall, 2011; Ridd, 2013; Khin Zaw et al., 2014).
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a) Sibumasu Terrane
The Sibumasu Terrane forms the western region of Southeast Asia. Following Metcalfe (1988, 2013), the Sibumasu Terrane includes parts of western Yunnan (China), eastern Myanmar (Burma), western Thailand, western Peninsular Malaysia and the eastern part of Sumatra. It is bounded to the west by the Sagaing Fault, Andaman Sea and further southwest by the Medial Sumatra Tectonic Line (Fig 2.1). This terrane is characterised by the presence of glacial- marine diamictite (or pebbly mudstones: e.g., Barber and Crow, 2009) and Gondwana Palaeozoic flora and fauna (Metcalfe, 2011).
b) Indochina-East Malaya Terrane
The Indochina-East Malaya Terrane to the east covers a broad area of Vietnam, Cambodia, Laos, northeastern Thailand and continues to the eastern part of Peninsular Malaysia. In the northeast, the Indochina-East Malaya Terrane is bounded by the Ailaoshan-Song Ma Suture but its eastern and southern boundaries are poorly constrained (Fig. 2.1). This terrane is characterised by a Cathasyian Permian flora and fauna (Barber and Crow, 2009), and has experienced complex tectono-magmatic history that has been important for formation of different types of mineralised systems (e.g., Goldfarb et al., 2013; Khin Zaw et al., 2013; this study).
c) South China Terrane
The South China Terrane is a composite region and consists of two tectono-stratigraphic terranes: Yangtze and Cathaysia. The Yangtze and Cathaysia Terranes are separated by Jiangshao fault zone/tectonic suture zone (Zhou et al., 2002). Charvet et al. (1999) proposed that the amalgamation of the two terranes occurred around 900−950 Ma. Similar to the Indochina-East Malaya Terrane, this terrane has Early to Late Permian flora and fauna of Cathasyian type (Metcalfe, 1996).
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d) West Myanmar (Burma) Terrane
The West Myanmar (Burma) Terrane (Hutchison, 1989, 2007; Metcalfe, 1996) including the Mount Victoria Land of Mitchell (1989) lies to west of the Mogok Belt. Following Hutchison (1989), Barber and Crow (2009) argued that the West Myanmar (Burma) Terrane forms the whole of western Myanmar, and is defined at its eastern and western boundaries by the Sagaing strike-slip fault and the Indo-Burman Ranges. The presence of Middle Permian fauna of Cathaysian type (Oo et al., 2002) at the West Myanmar (Burma) Terrane suggests that this terrane belongs to the same group of crustal blocks as the Cathaysialand provinces (i.e., Indochina-East Malaya and South China Terranes).
2.2.2 Main suture zones
Most known boundaries of the terranes that made up Southeast Asia are marked by major geological discontinuities, either by the suture zones of the main Palaeo-Tethys Ocean or the back-arc basins. In addition, a volcanic arc system is also identified (e.g., Sone and Metcalfe, 2008; Metcalfe, 2011) and has been established as part of the terranes. Furthermore, mineralised fold belts were also developed (e.g., Goldfarb et al., 2013; Khin Zaw et al., 2014). The main suture zones, back-arc basins, volcanic arc terranes and fold belts are shown in Figure 2.1, and are briefly discussed below:
The Changning-Menglian, Inthanon (Chiang Mai) and Bentong-Raub Sutures are regarded as the main Palaeo-Tethys Suture Zones (Fig. 2.1). In addition, according to Metcalfe (2011), the Ailaoshan and Song Ma Sutures are also included in other branches of the Palaeo-Tethys Ocean. Other postulated Palaeo-Tethys sutures include the Sagaing Fault in Myanmar and its southward extension the Medial Sumatra Tectonic Zone in Sumatra (Fig. 2.1) (e.g., Barber and Crow, 2003; Wakita and Metcalfe, 2005), both of which are currently present as a strike- slip shear zone (Barber and Crow, 2009).
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The Jinghong-Nan-Sra Kaeo Suture is indicated by Sone and Metcalfe (2008) as the back-arc basin for the Sukhothai Arc System. This indication is based on the short age range of the chert found in these sutures from Early to Late Permian (Metcalfe, 2011) and they are considered to link the Sukhothai Island Arc System (Fig. 2.1) to the Permian volcanic arc terrane that was developed on the western margin of the Indochina-East Malaya Terrane during the Permian (e.g., Sone and Metcalfe, 2008).
The southern continuation of the arc system in Peninsular Malaysia is still controversial. Sone and Metcalfe (2008) and Metcalfe (2011, 2013) extended this Permian arc system to the entire East Malaya Terrane of the Peninsular Malaysia based on the widespread distribution of Permo-Triassic I-type subduction-related granitoids within the Central and Eastern Belts. However, Khin Zaw et al. (2014) prefer to call the eastern part of Peninsular Malaysia including the Central and Eastern Belts of East Malaya Terrane, the East Malaya Fold Belt (Fig. 2.1), which contains orogenic Au mineralisation, as detailed lithostratigraphic and magmatic-volcanic correlations are lacking for the correlation. In this study, the Central Belt and Eastern Belt are considered similar in origin at the earliest stage of East Malaya Terrane, but later separated by back-arc spreading and re-assembled by back-arc collapse (Chapter 4). Thus, it is suggested that the Central Belt of Peninsular Malaysia (Fig. 2.1) represents the volcanic arc system, and the Lebir Fault zone to the east as a possible of the back-arc suture. The extent of these island arc and back-arc systems in Peninsular Malaysia, are interpreted here extending towards the SE through the Bintan and Bangka islands of Indonesia following Hutchison (1989) and Barber et al. (2005) (Fig. 2.1).
The Truong and Loei Fold Belts are regarded as major fold belts within the Indochina Terrane (Fig. 2.1) (Khin Zaw et al., 2014). The NW-trending Truong Son Fold Belt is characterised by volcanic, plutonic and metamorphic rocks from Late Carboniferous to Late Triassic (310−230 Ma) ages, which formed as a result of a long−lived subduction−collision−extension with two
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magmatic events between the Indochina and South China Terranes (e.g., Khin Zaw et al., 2010; Meffre, et al., 2011; Manaka et al., 2014). This fold belt contains skarn, epithermal and orogenic/sediment hosted deposit systems (Goldfarb et al., 2013; Khin Zaw et al., 2014; Manaka et al., 2014). The Permian Loei Fold Belt or Loei−Phetchabun Volcanic Belt hosts abundant of skarn and epithermal mineralisation systems (e.g., Goldfarb et al., 2013; Khin Zaw et al., 2014). It is dominated by volcaniclastics and marine sedimentary rocks that range in age from Devonian through Early Permian to Triassic (e.g., Goldfarb et al., 2013), and which experienced multiple magmatic tectonic events (e.g., Khin Zaw et al., 2014).