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The Hunter-Bowen Orogeny was a significant arc accretion event in the Permian and Triassic periods affecting approximately 2,500 km of the Australian continental margin. The Hunter-Bowen Orogeny occurred in two main phases, a Permian accretion of previously formed passive-marginal Devonian and Carboniferous sediments in the Hunter region and mid-west region of what is now New South Wales, separated by rifting, back-arc volcanism and a later Permian to Triassic event resulting in arc accretion and metamorphism during a subduction event. The Hunter-Bowen Orogeny has resulted in the New England Fold Belt, a tectonic accretion of metamorphic terranes and mid-crustal granitoid intrusions, flanked by Permian to Triassic sedimentary basins which were formed distally to the now-eroded orogenic mountain belt. While the Great Dividing Range north of Sydney is a prominent landform, this is more the result of Cainozoic volcanism and crustal uplift since the Jurassic than the result of the original orogenic belt which is essentially mimics. Gravity, magnetics and bathymetry indicate that several slivers of crust formerly from the Hunter-Bowen orogen are now spread out across the Indo-Australian plate east of the Australian continental landmass, forming some isolated submerged ocean plateaux and islands, notably Lord Howe Rise which includes Lord Howe Island.〔 Lord Howe Rise has a total area of about 1,500,000 square km, ==Prior tectonics== The Hunter-Bowen event produced a ~3,000 km long structural foredeep above a Late Carboniferous and Palaeozoic margin to the weakly consolidated Australian continental mass which was part of the Gondwana Supercontinent at this time; the orogen developed to the east of the Palaeozoic Lachlan Orogen and the Proterozoic terranes of the Mount Isa Inlier. Before the orogeny the rocks of the coastal area were formed. During Late Carboniferous there was a continental margin with an oceanic trench subducting the ocean floor off the coast. To the est there was a magmatic arch. This includes Connors Arch, Auburn Arch, Combarrago Volcanics and the Bathurst Batholith. A forearc basin in between included the Tamworth Belt and Yarrol Belt. Subduction resulted in blueschist metamorphism. At 309 Ma a mid oceanic ridge plate boundary encountered the subduction boundary near Tin Can Bay south of Fraser Island on the North D'Aguilar block. Another encounter point was near what is now Coffs Harbour. These ridge encounters with the trench stopped the subduction at those points and resulted in triple junctions moving north and south up the trench, and being replaced by a dextral transform fault. The northernmost triple junction, a ridge-trench-fault junction moved up the Queensland coast at 28 mm per year. As it moved the magmatism inland stopped and it reached Townsville about 290 Ma. The paired triple junction with this, a fault-trench-fault junction, moved south from Brisbane at about 12 mm per year. The triple junctions in the New England region stopped subduction very quickly because the mid ocean ridge was almost parallel to the trench. The merger converted the trench to a transform fault and turned off the volcanoes to the west. In between these two ridge trench encounter points, a small triangular shaped plate continued to subduct between Brisbane and Coffs Harbour. More time was available to build up a wide subduction complex.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hunter-Bowen orogeny」の詳細全文を読む スポンサード リンク
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