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Chapter 1 Geological Background 1.1 Tectonic Setting The New England Orogen is the easternmost and youngest component of the Tasmanide orogenic collage of eastern Australia (Glen�� 2005; Offler and Murray�� 2011)�� which comprises various terranes that interacted�� accreted or amalgamated with each other. It is a major north-trending Palaeozoic structure that extends over approximately 1300 km from Bowen (20° S) in Queensland to Newcastle (33° S) in New South Wales (Figure 1.1). Furthermore�� it developed over a period of approximately 300 million years along the East Gondwana margin and underwent pulses of contraction and extension resulting in folding�� oroclinal bending�� metamorphism�� and basin formation. In the latter part of its history�� a Carboniferous volcanic arc�� fore-arc basin�� and accretionary wedge terranes formed (Leitch�� 1975; Cawood and Leitch�� 1985; Flood and Aitchison�� 1988). The arc�� particularly in the south�� is mostly buried under the Sydney�� Gunnedah�� and Bowen basins. The fore-arc and subduction complex is separated by a major fault�� the Peel-Manning-Yarrol Fault System which is marked by serpentinite bodies that may represent a disrupted�� early Cambrian ophiolite succession (Aitchison et al.�� 1992). The orogen can be subdivided into a northern segment and a southern segment�� separated by Mesozoic sedimentary rocks of the Clarence-Moreton Basin. Furthermore�� the Northern New England Orogen can be subdivided into: 1) a northern region within which deformation is characterized by open folds and variable�� but generally minor thrusting; 2) a central region of thin-skinned�� fold-thrust deformation with cross-orogen tear faults�� and within which strain is strongly partitioned�� and cleavage development is variable (Gogango Thrust Belt and more eastern terranes) (Figure 1.1�� Cawood et al.�� 2011); and 3) a southern region of thick-skinned deformation within which the basement appears to be involved in deformation. The Southern New England Orogen constitutes a weakly deformed fore-arc basin in the west (Tamworth Belt) and an accretionary wedge of metasedimentary rocks in the east (Tablelands Complex) (Figure 1.2). These are separated by the Peel-Manning Fault System (Leitch�� 1974; Korsch�� 1977). Figure 1.1: Geological map of the Hastings Block. (a) Location and tectonic setting of the Hastings Block within eastern Australia and within the Southern New England Orogen. (b) Major tectonic units and faults within and adjacent to the Hastings Block (simplified from Roberts et al.�� 1995).(c) Simplified geological map of the Hastings Block with the suggested boundary between the SHB and NHB shown by the dashed line. Numerous tectonic models have been proposed for the development of the New England Orogen (Scheibner�� 1973; Leitch�� 1974; Cawood�� 1982; Murray et al.�� 1987). Most infer a long-lived�� east-facing convergent plate margin configuration with progressive accretion of younger rocks at the eastern margin of Gondwana. Offler and Murray (2011) showed that intra-oceanic island arc and back-arc basin (BAB) settings dominate throughout the Devonian and those basalt compositions in the Late Devonian sequences of the Southern New England Orogen and the Northern New England Orogen become more arc-like to the west�� suggesting that the subduction zone dipped to the east beneath intra oceanic arcs at this time. Buckman et al. (2014) proposed that the NEO contains a large�� far-traveled oceanic and island arc terrane that was emplaced over the Gondwanan margin during the latest Devonian to Early Carboniferous. 1.2 Local Setting The Southern New England Orogen (SNEO) buried volcanic arc�� concave to the east fore-arc (Tamworth Belt)�� and an accretion-subduction complex (Tablelands Complex) associated with a west-dipping subduction zone consists of Cambrian to Carboniferous buried volcanic arc�� a fore-arc basin sequences of the Tamworth Belt and a Silurian to Early Carboniferous accretion-subduction complex rocks of the Tablelands Complex (Figure 1.2). The Tamworth Belt is separated from the Tablelands Complex by the Peel-Manning Fault System. The Tamworth Belt is faulted against the Sydney Basin�� along with the Hunter-Mooki Thrust System. To the southeast�� near Maitland�� sediments of the Sydney basin overlap those of the Tamworth Belt (Figure 1.2). Assemblages in the Southern New England Orogen are predominantly Devonian and Carboniferous volcanic and sedimentary units intruded by younger S- and I-type granite plutons�� with several major occurrences of ultramafic rocks and serpentinite-matrix melange which have ��ophiolitic�� affinities (Aitchison and Ireland�� 1995). In the Tamworth Belt�� the rocks record burial metamorphism with diagenetic to sub-greenschist facies assemblages (Offler et al.�� 1997; Offler�� 2005); while in the Tablelands Complex�� sub-greenschist to greenschist facies rocks occur as well as high P - low T (Phillips et al.�� 2010) and higher grade high T - low P metamorph