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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.
Additional recommended knowledge
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 Island.
The Sydney-Gunnedah-Bowen Basin
The Hunter-Bowen event produced a ~3,000km 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 Mt Isa Inlier.
This structural foredeep filled with marine deepwater sediments and later fluviatile sandstones, which during the Permian and Triassic formed vast accumulations of coal. The Sydney and Bowen Basins were flanked by an offshore island arc system during continued accretion and subduction during the Permian.
Thrusting of the Permian sequences westward in a Rocky Mountains style foreland basin system continued as metamorphism began affecting the lower parts of the offshore island arcs, composed primarily of Devonian marine sediments of continental origin, and Carboniferous flysch. Metamorphism resulted in the generation of S-type and I-type granites which intruded this Palaeozoic sedimentary sequence in the New England Fold Belt. To the north, significant deformation affected the Carboniferous Marlborough and Yarrol Terranes, resulting in magmatism and restricted granite emplacement.
The results of the Hunter-Bowen event were:
Geochronology has identified several episodes of deformation, accretion, subduction and magmatism.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hunter-Bowen_orogeny". A list of authors is available in Wikipedia.|