Hunter-Bowen orogeny
Encyclopedia
The Hunter-Bowen Orogeny was a significant arc accretion event in the Permian
and Triassic
periods affecting approximately 2,500 km of the Australia
n 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 Island
.
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.
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:
has identified several episodes of deformation, accretion, subduction and magmatism.
Gympie Block
Permian
The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...
and Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
periods affecting approximately 2,500 km of the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n continental margin
Continental margin
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....
.
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
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
intrusions, flanked by Permian to Triassic sedimentary basins which were formed distally to the now-eroded orogenic mountain belt.
While the Great Dividing Range
Great Dividing Range
The Great Dividing Range, or the Eastern Highlands, is Australia's most substantial mountain range and the third longest in the world. The range stretches more than 3,500 km from Dauan Island off the northeastern tip of Queensland, running the entire length of the eastern coastline through...
north of Sydney
Sydney
Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...
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
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
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
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
.
The Sydney-Gunnedah-Bowen Basin
The Hunter-Bowen event produced a ~3,000 km long structural foredeep above a Late CarboniferousCarboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
and Palaeozoic margin to the weakly consolidated Australian continental mass which was part of the Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
Supercontinent at this time; the orogen developed to the east of the Palaeozoic Lachlan Orogen and the Proterozoic terranes of the Mount 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
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
. 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:
- Deformation
- MetamorphismMetamorphismMetamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
of both greenschistGreenschistGreenschist is a general field petrologic term applied to metamorphic or altered mafic volcanic rock. The term greenstone is sometimes used to refer to greenschist but can refer to other rock types too. The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the...
and rare blueschistBlueschistBlueschist is a rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to ~500 degrees Celsius....
facies - thrustingThrust faultA thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
- Transtension pull-apart basins such as the
- Esk Trough, a thin pull-apart rift infill fluvialFluvialFluvial is used in geography and Earth science to refer to the processes associated with rivers and streams and the deposits and landforms created by them...
coalCoalCoal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
-bearing basin - Clarence-Moreton Basin, including the Ipswich Basin
- Esk Trough, a thin pull-apart rift infill fluvial
- Transpressional faulting and widespread deformation
- Metamorphism
- Arc volcanismVolcanismVolcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
, namely in the GympieGympieGympie may refer to:* Gympie, a city in Queensland, Australia** Gympie Airport** Electoral district of Gympie** Gympie Region, its local government authority* Gympie Gympie , a stinging plant...
province, offshore of the Hunter valley and Sydney BasinSydney BasinThe Sydney Basin is a sedimentary basin on the east coast of New South Wales, Australia consisting of Permian and Triassic sedimentary rocks... - Back-arc basin formation,
- Gunnedah Basin
- Sydney basinSydney BasinThe Sydney Basin is a sedimentary basin on the east coast of New South Wales, Australia consisting of Permian and Triassic sedimentary rocks...
- Bowen BasinBowen BasinThe Bowen Basin contains the largest coal reserves in Australia. This major coal producing region contains one of the world's largest deposits of bituminous coal. The Basin contains much of the known Permian coal resources in Queensland including virtually all of the known mineable prime coking coal...
- GraniteGraniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
emplacement- New England I-type and S-type suites during accretion (330-260Ma)
- Gympie M-type and I-type suites in back-arc position (4 suites; 260-245; 240-235, 231-225 and 220-215Ma)
- AndesiteAndesiteAndesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
, rhyoliteRhyoliteThis page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
and basaltBasaltBasalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
volcanism in the- In-arc at the Permo-Triassic boundary
- Back-arc in the early to mid Triassic
- Gold, tin, tungsten mineralisation in the Gympie Block, the New England orogen and throughout the Queensland hinterlands
- CoalCoalCoal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
formation in the Sydney basinSydney BasinThe Sydney Basin is a sedimentary basin on the east coast of New South Wales, Australia consisting of Permian and Triassic sedimentary rocks...
, Esk Trough, Gunnedah Basin, Bowen BasinBowen BasinThe Bowen Basin contains the largest coal reserves in Australia. This major coal producing region contains one of the world's largest deposits of bituminous coal. The Basin contains much of the known Permian coal resources in Queensland including virtually all of the known mineable prime coking coal...
and Ipswich Basin
Geochronology
GeochronologyGeochronology
Geochronology is the science of determining the age of rocks, fossils, and sediments, within a certain degree of uncertainty inherent to the method used. A variety of dating methods are used by geologists to achieve this, and schemes of classification and terminology have been proposed...
has identified several episodes of deformation, accretion, subduction and magmatism.
Gympie Block
- Deformation occurred at 250-240 Ma
- Tholeiitic suite of magmatism, including M-type and I-type granites at ~250-245 Ma
- Transitional tholeiitic to calc-alkaline granite and andesite suite ~245-240 Ma
- I-type granite suite and basalt suite ~229 Ma associated with gold mineralisation
- Late I-type and S-type high-level caldera complexes 225-221 Ma
See also
- Geology of AustraliaGeology of AustraliaAustralia is a continent situated on the Indo-Australian Plate.The geology of Australia includes virtually all known rock types and from all geological time periods spanning over 3.8 billion years of the Earth's history.-Components:...
- OrogenyOrogenyOrogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
- Subduction zone
- Shear (geology)
- GraniteGraniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
; particularly the section on S-type and I-type