Lachlan Fold Belt
Encyclopedia
The Lachlan Fold Belt or Lachlan Orogen is a geological subdivision of the east part of Australia. It is a zone of folded and faulted rocks of similar age. It dominates New South Wales
and Victoria
, also extending into Tasmania
, the Australian Capital Territory and Queensland
. It was formed in the Middle Paleozoic from 450 to 340 Mya. It was earlier known as Lachlan Geosyncline. It covers an area of 200,000 km2.
) from 445 Mya, and the New England Orogen from late Palaeozoic to early Mesozoic
(310 - 210 Mya). These boundary orogens along with the Lachlan Orogen make up the Tasman Orogenic System In Australia, which along with the extension into the neighbouring parts of Gondwana make up the Tasmanides. North of the Lachlan Fold belt is the Thomson Orogen in the north east and centre of Queensland. Sometimes the Lachlan Orogen is included with the Thomson Orogen and known as the 'Lachlan-Thomson Orogen'. The Great Artesian Basin
has been laid down over the top of the LFB in northwestern New South Wales and western Queensland and the Murray-Darling Basin
covers the southwest of New South Wales. The Sydney Basin
is on the top of the LFB around Sydney and Wollongong on the east coast of New South Wales.
In Victoria the western limit of the LFB is defined by the Stawell-Ararat Fault. Westwards of this fault is the Moornambool Metamorphic Complex.
rate is greater than that of plate convergence. In such a case the 'hinge', at which subduction starts, tend to move further seawards over time (rollback).
margin of eastern Australia. The Delamerian Orogen follows this line, and the western side of the Lachlan Orogen also follows this curve. The central and east parts of the Orogen are aligned in a north south direction.
Before the concept of plate tectonics
was accepted, the LFB was described as the Lachlan Geosyncline.
The concept of terranes has been applied to the LFB with the term Lachlan Superterrane being used for the Lachlan Mudpile. Geomagnetic poles cannot be reliably determined for Devonian or older rocks thanks to the folding. In Victoria van den Berg used the terms Whitelaw Terrane for the Western Lachlan, and Benambra Terrane for the Central and Eastern Lachlan.
Other terrane subdivision have included Melbourne, Stawell, Howqua, Girilambone Terranes, as well as Cowra, Tumut and Hill End Troughs; and Parkes and Molong Zones; and the Wagga Omeo Belt.
Ordovician to Early Silurian Benambran Orogeny
(also led to the formation of the Wagga-Omeo Zone).
The Middle Devonian Tabberabberan Orogeny
affected the entire LFB and terminated the precratonic
stage of its development.
The Carboniferous Kanimblan Orogeny
was the
terminal event and converted the LFB into a
neocraton.
. The Wagga Omeo Metamorphic Belt is a large region in the Central Lachlan between the Kancoona-Kiera Shear Zone and the Gilmore Shear Zone. Other metamorphic complexes are Kuark, Camblong, Cooma, and Jerangle in the eastern side. These zones made up the Eastern Metamorphic Belt, named by Vallance in 1969. In these high temperature belts, the temperature peaked at 700°C and the pressure was 350 MPa, with a thermal gradient of 65 °/km. This same high temperature regime produced migmatite
and S-type granite from the Ordovician sediments.
Blueschist
formed by intermediate to high pressure metamorphism is found in melange at Port Sorell and the Arthur Lineament in Tasmania, and Howqua Melange and Heathcote Melange in Victoria.
Slate
has been formed in other parts of the fold belt indicating intermediate pressure and low temperature.
rose towards the surface. Granites cover 61000 km2. There are 875 lithological units of granite.
There are 100 volcanic units derived from the same magma as the granites.
oceanic crust which was formed in a back arc basin or a fore arc basin. An ancient shoreline of Australia, called the cratonic margin existed off the east coast of the Delamerian Orogen in western New South Wales, Western Victoria and Western Tasmania. In the early Ordovician there was a shallow marine shelf called the Gnalta Shelf, over the top of the Koonenberry Belt near Broken Hill
. At the same time there were marine conditions in Amadeus Basin
where Horn Valley Siltstone was formed, and Georgina Basin where the Coolibah Formation deposited. The Larapintine Sea formed a shallow marine connection through central Australia to the Canning Basin in Western Australia. Sediments formed on the continental shelf of the continent from this time appear in western Tasmania and north west New South Wales. A subduction
zone consumed the Pacific crust
below the Delamerian coast, but this subduction moved 1000 km oceanwards. An island arc was formed on the northern end of the 900 km long trench. This was the Macquarie Volcanic Arc.
Between the continent and the island arc or trench, deep water sediments in the form of turbidite
s appeared in the Central Lachlan Orogen. These were derived from the western Delamerian Orogen and from the south west Ross Orogen, which is now left behind in Antarctica.
The Ordovician volcanoes of the arc are now found around Parkes, Wellington, Molong
and east of Condobolin
, Cowra
and Boorowa
. The east Lachlan Orogen containing Adaminaby Group Turbidites is now to the east and south of the Macquarie Arc. All its boundaries with the Macquarie Arc are faults, indicating that this is a separate terrane, also known as the Adaminaby Superterrane. In the Late Ordovician the turbidites were overlaid by a black shale. The back arc region was extended at this time.
Between in the Bolindian to Llandovery
, the arc collided with the back arc, ending the Benambran Cycle. The turbidites were deformed, biotite formed, and the arc was thrust over or under the turbidites..
In the Middle Llandovery, the Pacific plate boundary moved a few hundred km to the east. A new subduction zone dipping westwards lasted from the end of the Silurian into the Late Devonian. The whole of the Lachlan Fold Belt became a back arc area with a new volcanic arc formed to the east in what is now the New England Orogen. Extension stretched the LFB forming rifts, and shelves, along with intrusion of granites and volcanism. This was the Tabberabberan Orogeny.
Deformation happened in the west 450 to 395 Mya and in the east 400 to 380 Mya. Extensional basins occur in the central and east parts of the fold belt. Oceanic subduction (or underthrusting) is evidenced for the western and central parts by slivers of ophiolite and blueschist metamorphism. These are known as Coolac serpentinite
, and Honeysuckle Beds east of Tumut; The Kiandra Beds north of Batlow and the Tumut Pond Serpentinite Belt on the west side of Talbingo Dam
.
The Narooma Terrane
migrated 2500 km westwards on the moving Pacific plate and became attached to the Adaminaby Superterrane in Silurian
times. Conodont
fossils in the Narooma Chert prove the age of the terrane to be from late Cambrian to middle Ordovician. The Narooma Terrane exposure is between Narooma
and Eurobodalla and also between Burewarra Point and Durras around Batemans Bay
on the south coast of New South Wales.
The western parts under New South Wales and Queensland are mostly heavily weathered and or covered in younger sediments of the Great Artesian Basin
or Great Australian Basin and Murray-Darling Basin
. The underlying structure can still be explored through magnetic, gravity and seismic geophysical measurements.
About The Tasman Sea
started to form by seafloor spreading. This split off a segment of the coast to form the Lord Howe Rise
, part of Zealandia
. Around then, Bass Strait
was extended moving Tasmania away from the rest of Australian Mainland.
and shale
interbedded, with chert
, and metavolcanics.
The Macquarie Volcanic Arc formed about 1000 km off the coast. The Yarrimbah Formation is exposed west of Parkes
. It consists of siliceous siltstone
s, formed in deep water. It is the most western part of the Arc. The Rockley–Gulgong Volcanic Belt. Budhang Chert Member is found near Oberon
. The Molong Volcanic Belt lies between Cowra
and Boorowa
. The Adaminaby Group, from another terrane, was thrust northwards over the top of the Molong Volcanic Belt. The Kenyu Formation is from Late Ordovician
and contains conglomerate
. The Wagga Belt rocks are thrust eastwards over the top of the Junee-Narromine Volcanic Belt of the Macquarie arc. .
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
and Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
, also extending into Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
, the Australian Capital Territory and Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
. It was formed in the Middle Paleozoic from 450 to 340 Mya. It was earlier known as Lachlan Geosyncline. It covers an area of 200,000 km2.
Location
On the west is the Delamerian Orogen from the early Palaeozoic (550 to 470 Mya). On the east side is found the Narooma Accretionary Complex (or Narooma TerraneNarooma Terrane
The Narooma Accretionary Complex or Narooma Terrane is a geological structural region on the south coast of New South Wales, Australia that is the remains of a subduction zone or an oceanic terrane...
) from 445 Mya, and the New England Orogen from late Palaeozoic to early Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
(310 - 210 Mya). These boundary orogens along with the Lachlan Orogen make up the Tasman Orogenic System In Australia, which along with the extension into the neighbouring parts of Gondwana make up the Tasmanides. North of the Lachlan Fold belt is the Thomson Orogen in the north east and centre of Queensland. Sometimes the Lachlan Orogen is included with the Thomson Orogen and known as the 'Lachlan-Thomson Orogen'. The Great Artesian Basin
Great Artesian Basin
The Great Artesian Basin provides the only reliable source of freshwater through much of inland Australia. The basin is the largest and deepest artesian basin in the world, stretching over a total of , with temperatures measured ranging from 30°C to 100°C...
has been laid down over the top of the LFB in northwestern New South Wales and western Queensland and the Murray-Darling Basin
Murray-Darling Basin
The Murray-Darling basin is a large geographical area in the interior of southeastern Australia, whose name is derived from its two major rivers, the Murray River and the Darling River. It drains one-seventh of the Australian land mass, and is currently by far the most significant agricultural...
covers the southwest of New South Wales. The Sydney Basin
Sydney Basin
The Sydney Basin is a sedimentary basin on the east coast of New South Wales, Australia consisting of Permian and Triassic sedimentary rocks...
is on the top of the LFB around Sydney and Wollongong on the east coast of New South Wales.
In Victoria the western limit of the LFB is defined by the Stawell-Ararat Fault. Westwards of this fault is the Moornambool Metamorphic Complex.
Classification
The orogen is of the accretionary or 'Turkic' type. It has also been classified as a 'Carpathian' type orogen, i.e. one where subductionSubduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
rate is greater than that of plate convergence. In such a case the 'hinge', at which subduction starts, tend to move further seawards over time (rollback).
Shape
The Tasman Line outlines the PrecambrianPrecambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
margin of eastern Australia. The Delamerian Orogen follows this line, and the western side of the Lachlan Orogen also follows this curve. The central and east parts of the Orogen are aligned in a north south direction.
Size
At the present time the fold belt is about 1000 km wide. However the original width was 2000 to 3000 km wide, with the excess size absorbed by folding and thrusting.Structure
Rock beds are folded in chevron folds. They are cut by thin skinned thrusts. Other faults separate the different terranes making up the orogen.Before the concept of plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
was accepted, the LFB was described as the Lachlan Geosyncline.
The concept of terranes has been applied to the LFB with the term Lachlan Superterrane being used for the Lachlan Mudpile. Geomagnetic poles cannot be reliably determined for Devonian or older rocks thanks to the folding. In Victoria van den Berg used the terms Whitelaw Terrane for the Western Lachlan, and Benambra Terrane for the Central and Eastern Lachlan.
Other terrane subdivision have included Melbourne, Stawell, Howqua, Girilambone Terranes, as well as Cowra, Tumut and Hill End Troughs; and Parkes and Molong Zones; and the Wagga Omeo Belt.
Orogenies
Most of the LFB was greatly affected by the LateOrdovician to Early Silurian Benambran Orogeny
(also led to the formation of the Wagga-Omeo Zone).
The Middle Devonian Tabberabberan Orogeny
affected the entire LFB and terminated the precratonic
stage of its development.
The Carboniferous Kanimblan Orogeny
Kanimblan Orogeny
Kanimblan orogeny was a mountain-building event in eastern Australia toward the end of Early Carboniferous time . It was a terminal orogeny episode forming the Lachlan Fold Belt, also called Lachlan Geosyncline before the advent of the plate tectonics theory.Uplift and deformation occurred in a...
was the
terminal event and converted the LFB into a
neocraton.
Metamorphism
There are two high temperature low pressure regions of metamorphismMetamorphism
Metamorphism 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...
. The Wagga Omeo Metamorphic Belt is a large region in the Central Lachlan between the Kancoona-Kiera Shear Zone and the Gilmore Shear Zone. Other metamorphic complexes are Kuark, Camblong, Cooma, and Jerangle in the eastern side. These zones made up the Eastern Metamorphic Belt, named by Vallance in 1969. In these high temperature belts, the temperature peaked at 700°C and the pressure was 350 MPa, with a thermal gradient of 65 °/km. This same high temperature regime produced migmatite
Migmatite
Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...
and S-type granite from the Ordovician sediments.
Blueschist
Blueschist
Blueschist 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....
formed by intermediate to high pressure metamorphism is found in melange at Port Sorell and the Arthur Lineament in Tasmania, and Howqua Melange and Heathcote Melange in Victoria.
Slate
Slate
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering...
has been formed in other parts of the fold belt indicating intermediate pressure and low temperature.
Plutonism
Granite plutons have formed in many parts of the LFB where there has been significant heating. They were formed at the time of extension, when hot asthenosphereAsthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...
rose towards the surface. Granites cover 61000 km2. There are 875 lithological units of granite.
There are 100 volcanic units derived from the same magma as the granites.
History
The basement of the belt is CambrianCambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
oceanic crust which was formed in a back arc basin or a fore arc basin. An ancient shoreline of Australia, called the cratonic margin existed off the east coast of the Delamerian Orogen in western New South Wales, Western Victoria and Western Tasmania. In the early Ordovician there was a shallow marine shelf called the Gnalta Shelf, over the top of the Koonenberry Belt near Broken Hill
Broken Hill, New South Wales
-Geology:Broken Hill's massive orebody, which formed about 1,800 million years ago, has proved to be among the world's largest silver-lead-zinc mineral deposits. The orebody is shaped like a boomerang plunging into the earth at its ends and outcropping in the centre. The protruding tip of the...
. At the same time there were marine conditions in Amadeus Basin
Amadeus Basin
The Amadeus Basin is a large intracratonic sedimentary basin in central Australia, lying mostly within the southern Northern Territory, but extending into the state of Western Australia. It is named after Lake Amadeus which lies within the basin...
where Horn Valley Siltstone was formed, and Georgina Basin where the Coolibah Formation deposited. The Larapintine Sea formed a shallow marine connection through central Australia to the Canning Basin in Western Australia. Sediments formed on the continental shelf of the continent from this time appear in western Tasmania and north west New South Wales. A subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
zone consumed the Pacific crust
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
below the Delamerian coast, but this subduction moved 1000 km oceanwards. An island arc was formed on the northern end of the 900 km long trench. This was the Macquarie Volcanic Arc.
Between the continent and the island arc or trench, deep water sediments in the form of turbidite
Turbidite
Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...
s appeared in the Central Lachlan Orogen. These were derived from the western Delamerian Orogen and from the south west Ross Orogen, which is now left behind in Antarctica.
The Ordovician volcanoes of the arc are now found around Parkes, Wellington, Molong
Molong, New South Wales
Molong is a small town in the Central West region of New South Wales, Australia, in Cabonne Shire.Molong is located on the Mitchell Highway about 300 kilometres west of Sydney and about 30 kilometres from the city of Orange. It is elevated at 529 metres above sea level. At the 2006 census, Molong...
and east of Condobolin
Condobolin, New South Wales
Condobolin is a town in the west of the Central West region of New South Wales, Australia, on the Lachlan River. At the 2006 census, Condobolin had a population of 2,847.- History :...
, Cowra
Cowra, New South Wales
Cowra is a town in the Central West region of New South Wales, Australia in the Cowra Shire. It is located on the Mid-Western Highway, 317 kilometres west of Sydney on the banks of the Lachlan River at an altitude of 310 metres above sea level. At the 2006 census Cowra had a population of 8,430...
and Boorowa
Boorowa, New South Wales
Boorowa is a farming town in the South West Slopes of New South Wales, Australia. At the 2006 census, Boorowa had a population of 1,070 people. It is located in a valley 243 km west of Sydney and 487 m above sea-level...
. The east Lachlan Orogen containing Adaminaby Group Turbidites is now to the east and south of the Macquarie Arc. All its boundaries with the Macquarie Arc are faults, indicating that this is a separate terrane, also known as the Adaminaby Superterrane. In the Late Ordovician the turbidites were overlaid by a black shale. The back arc region was extended at this time.
Between in the Bolindian to Llandovery
Llandovery
Llandovery is a market town in Carmarthenshire, Wales, lying on the River Tywi and the A40 road.The town is served by Llandovery railway station, where there is a park and ride to Llanelli and Shrewsbury via the Heart of Wales Line...
, the arc collided with the back arc, ending the Benambran Cycle. The turbidites were deformed, biotite formed, and the arc was thrust over or under the turbidites..
In the Middle Llandovery, the Pacific plate boundary moved a few hundred km to the east. A new subduction zone dipping westwards lasted from the end of the Silurian into the Late Devonian. The whole of the Lachlan Fold Belt became a back arc area with a new volcanic arc formed to the east in what is now the New England Orogen. Extension stretched the LFB forming rifts, and shelves, along with intrusion of granites and volcanism. This was the Tabberabberan Orogeny.
Deformation happened in the west 450 to 395 Mya and in the east 400 to 380 Mya. Extensional basins occur in the central and east parts of the fold belt. Oceanic subduction (or underthrusting) is evidenced for the western and central parts by slivers of ophiolite and blueschist metamorphism. These are known as Coolac serpentinite
Serpentinite
Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...
, and Honeysuckle Beds east of Tumut; The Kiandra Beds north of Batlow and the Tumut Pond Serpentinite Belt on the west side of Talbingo Dam
Talbingo Dam
Talbingo Dam is located on the Tumut River in southern New South Wales. It is the largest dam in the Snowy Mountains Scheme, with the associated Tumut 3 Power Station also the largest in the project...
.
The Narooma Terrane
Narooma Terrane
The Narooma Accretionary Complex or Narooma Terrane is a geological structural region on the south coast of New South Wales, Australia that is the remains of a subduction zone or an oceanic terrane...
migrated 2500 km westwards on the moving Pacific plate and became attached to the Adaminaby Superterrane in Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
times. Conodont
Conodont
Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
fossils in the Narooma Chert prove the age of the terrane to be from late Cambrian to middle Ordovician. The Narooma Terrane exposure is between Narooma
Narooma, New South Wales
Narooma is a town in the Australian state of New South Wales on the far south coast. The town is on the Princes Highway. The name is said to be derived from the Aboriginal word meaning ‘clear blue waters’. At the 2006 census, Narooma had a population of 3,100 people.Montague Island, a National...
and Eurobodalla and also between Burewarra Point and Durras around Batemans Bay
Batemans Bay, New South Wales
- Media :Radio Stations*East Coast Radio 2EC *Power FM NSW South Coast - POWER FM from Nowra can also be received in parts of Batemans Bay on FM 94.9....
on the south coast of New South Wales.
The western parts under New South Wales and Queensland are mostly heavily weathered and or covered in younger sediments of the Great Artesian Basin
Great Artesian Basin
The Great Artesian Basin provides the only reliable source of freshwater through much of inland Australia. The basin is the largest and deepest artesian basin in the world, stretching over a total of , with temperatures measured ranging from 30°C to 100°C...
or Great Australian Basin and Murray-Darling Basin
Murray-Darling Basin
The Murray-Darling basin is a large geographical area in the interior of southeastern Australia, whose name is derived from its two major rivers, the Murray River and the Darling River. It drains one-seventh of the Australian land mass, and is currently by far the most significant agricultural...
. The underlying structure can still be explored through magnetic, gravity and seismic geophysical measurements.
About The Tasman Sea
Tasman Sea
The Tasman Sea is the large body of water between Australia and New Zealand, approximately across. It extends 2,800 km from north to south. It is a south-western segment of the South Pacific Ocean. The sea was named after the Dutch explorer Abel Janszoon Tasman, the first recorded European...
started to form by seafloor spreading. This split off a segment of the coast to form the Lord Howe Rise
Lord Howe Rise
The Lord Howe Rise is an underwater plateau that extends from southwest of New Caledonia to the Challenger Plateau, west of New Zealand. To its west is the Tasman Basin and to the east is the New Caledonia Basin. Lord Howe Rise has a total area of about 1,500,000 square km, and generally lies about...
, part of Zealandia
Zealandia
SS Zealandia, nicknamed Z was a historically significant Australian cargo and passenger ship. It served as a troopship in both World War I and World War II. Zealandia transported the ill-fated Australian 8th Division. Its crew were the last Allied personnel to see HMAS Sydney, which was lost with...
. Around then, Bass Strait
Bass Strait
Bass Strait is a sea strait separating Tasmania from the south of the Australian mainland, specifically the state of Victoria.-Extent:The International Hydrographic Organization defines the limits of the Bass Strait as follows:...
was extended moving Tasmania away from the rest of Australian Mainland.
Lithology
Turbidites from submarine fans, trench complexes, volcanic arcs, oceanic crust and micro continents dominate lithological components. The individual rock types are mostly sandstoneSandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
and shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
interbedded, with chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
, and metavolcanics.
Subdivisions
Broad subdivisions are the Western Lachlan, which lies in Victoria including the Stawell and Melbourne Zones. The eastern boundary is the Mount Wellington—Mount Useful Fault Zone (east of Melbourne). The Central Lachlan includes the Tabberabbera Zone and the Wagga-Omeo Metamorphic Belt. The Eastern Lachlan extends to the east of the Gilmore Fault Zone, a shear zone on the edge of the WOMB.The Macquarie Volcanic Arc formed about 1000 km off the coast. The Yarrimbah Formation is exposed west of Parkes
Parkes, New South Wales
- Transport :Parkes has a local bus service provided by Western Road Liners, which acquired Harris Bus Lines in March 2006. The Indian Pacific also stops twice a week, as well as the Broken Hill Outback Xplorer service, run by CountryLink, which heads to Broken Hill on Mondays and Sydney on...
. It consists of siliceous siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s, formed in deep water. It is the most western part of the Arc. The Rockley–Gulgong Volcanic Belt. Budhang Chert Member is found near Oberon
Oberon, New South Wales
-See also:*Oberon Correctional Centre*Mount Trickett*Mount Bindo*Shooters Hill-External links:***...
. The Molong Volcanic Belt lies between Cowra
Cowra, New South Wales
Cowra is a town in the Central West region of New South Wales, Australia in the Cowra Shire. It is located on the Mid-Western Highway, 317 kilometres west of Sydney on the banks of the Lachlan River at an altitude of 310 metres above sea level. At the 2006 census Cowra had a population of 8,430...
and Boorowa
Boorowa, New South Wales
Boorowa is a farming town in the South West Slopes of New South Wales, Australia. At the 2006 census, Boorowa had a population of 1,070 people. It is located in a valley 243 km west of Sydney and 487 m above sea-level...
. The Adaminaby Group, from another terrane, was thrust northwards over the top of the Molong Volcanic Belt. The Kenyu Formation is from Late Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
and contains conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
. The Wagga Belt rocks are thrust eastwards over the top of the Junee-Narromine Volcanic Belt of the Macquarie arc. .