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60-781: The Lachlan Fold Belt is bordered on the west by the Delamerian Orogen from the early Palaeozoic (550 to 470 Mya). On the east side is found the Narooma Accretionary Complex (or Narooma Terrane ) from 445 Mya, and the New England Orogen from late Palaeozoic to early Mesozoic . These boundary orogens along with the Lachlan Orogen make up the Tasman Orogenic System In Australia, which along with

120-485: A 'Carpathian' type orogen, i.e. one where subduction 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). The Tasman Line outlines the Precambrian 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

180-671: 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. Turbidites from submarine fans, trench complexes, volcanic arcs, oceanic crust and micro continents dominate lithological components. The individual rock types are mostly sandstone and shale interbedded, with chert , and metavolcanics . Three broad subdivisions of Lachlan Fold Belt are Western, Central and Eastern. The Western Lachlan, which lies in Victoria includes

240-707: A subduction zone of the Palaeo-Pacific . After this time the region experienced an orogeny (mountain-building period) extending into the Ordovician . Foden et al. (2006) suggest that this orogeny lasted from ~514 Ma to 490 Ma. This event is called the Delamerian Orogeny , named after Delamere , a small town on the Fleurieu Peninsula where evidence was found for the event. The orogeny caused substantial folding, buckling, and faulting of

300-461: A thick pile of sedimentary rocks and minor volcanic rocks that were deposited on the eastern margin of Australia during the time of breakup of the supercontinent Rodinia . A number of authors have noted the similarity in these sedimentary rocks with rocks found in western North America and have suggested that they were formerly adjacent to each other in Rodinia. This is one major correlation in

360-504: A total cumulative thickness of about 24,000 m. The Adelaide Superbasin composed of several named basins and sub-basins. In total there are currently eight defined basins/sub-basins within the Adelaide Superbasin. The Adelaide Rift Complex is the oldest and most central part of the Adelaide Superbasin. It is a series of rift troughs and passive margins basins with protracted development from c. 840 Ma to c. 550 Ma with

420-416: Is transported by thermal conduction and below which heat transfer is mainly convective ; a rheological boundary, where the viscosity drops below about 10 Pa-s; and a chemical boundary layer, above which the mantle rock is depleted in volatiles and enriched in magnesium relative to the rock below. The lower boundary of the asthenosphere, the top of the tentatively defined mesosphere or mesospheric shell,

480-667: Is a region of platform deposits on the western rift shoulder that overlies the Gawler Craton . It experienced deposition in the late Neoproterozoic after the Sturtian Glaciation during a period of marine transgression and remains relatively undeformed to this day. The Coombalarnie Platform, like the Stuart Shelf, is a region of platform deposits; however, it overlies the Curnamona Province to

540-419: Is available to form greater quantities of melt. Another possible mechanism for producing mechanical weakness is grain boundary sliding, where grains slide slightly past each other under stress, lubricated by the traces of volatiles present. Weakening below oceanic plates is partly caused by their motion itself, thanks to the non-linear dislocation creep mechanism. Numerical models of mantle convection in which

600-593: 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. 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 asthenosphere rose towards

660-611: 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. The upper crust contains chevron folded turbidites. The lower crust contains duplexed oceanic lithosphere , and magmatic underplating . Structures in the Eastern thrust belt are oriented north–south. It has thick-skinned deformation in

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720-404: Is less well-defined, but has been placed at the base of the upper mantle. This boundary is neither seismically sharp nor well understood but is approximately coincident with the complex 670 km discontinuity. This discontinuity is generally linked to the transition from mantle rock containing ringwoodite to mantle rock containing bridgmanite and periclase . The mechanical properties of

780-422: Is not enough melt to fully wet grain boundaries in the rock, and the effects of melt on the mechanical properties of the rock are not expected to be significant if the grain boundaries are not fully wetted. The sharp lithosphere-asthenosphere boundary is also difficult to explain by partial melting alone. It is possible that the asthenosphere is a zone of minimum water solubility in mantle minerals so that more water

840-586: Is not well known due to much of the basin being buried beneath younger basins, including the Murray Basin , and is the subject of current research. It is thought that the Moyston Fault in Victoria marks the eastern boundary and the northern extension may continue underneath and potentially include the Warburton Basin ; however, this remains speculative. Most of the outcropping rock today

900-738: Is not well understood and is a focus of current geological research in South Australia. It is likely that deposition was continuous with the Arrowie Basin to the north. The Kanmantoo Province (also Kanmantoo Trough) is a deeply subsident rift formed in early Cambrian. It forms the eastern and southern portion of the Stansbury Basin, extending to the Glenelg River region of Victoria. Most rocks were highly deformed and experienced moderate to high grade metamorphism during

960-407: Is relatively sharp and likely coincides with the onset of partial melting or a change in composition or anisotropy . Various definitions of the boundary reflect various aspects of the boundary region. In addition to the mechanical boundary defined by seismic data, which reflects the transition from the rigid lithosphere to ductile asthenosphere, these include a thermal boundary layer, above which heat

1020-399: Is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere , at a depth between c. 80 and 200 km (50 and 120 mi) below the surface, and extends as deep as 700 km (430 mi). However, the lower boundary of the asthenosphere is not well defined. The asthenosphere is almost solid, but a slight amount of melting (less than 0.1% of

1080-408: Is thought to "float" or move about on the slowly flowing asthenosphere, enabling isostatic equilibrium and allowing the movement of tectonic plates . The asthenosphere extends from an upper boundary at approximately 80 to 200 km (50 to 120 miles) below the surface to a lower boundary at a depth of approximately 700 kilometers (430 mi). The lithosphere-asthenosphere boundary (LAB )

1140-683: Is within the two major mountain ranges of South Australia: the Flinders Ranges and the Mount Lofty Ranges . Much like the partly coeval Centralian Superbasin it contains several named basins and sub-basins. The oldest and largest of these is the Adelaide Rift Complex, with the adjoining and relatively undeformed Stuart Shelf, Torrens Hinge Zone and Coombalarnie Platform making up the remaining Neoproterozoic provinces. The Stansbury Basin (including its sub-province

1200-643: 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. The orogen is of the accretionary or 'Turkic' type. It has also been classified as

1260-602: The Peake and Denison Ranges in the central-north of South Australia down through the Flinders Ranges and Mount Lofty Ranges , narrowing at the Fleurieu Peninsula and extending onto Kangaroo Island . West–east it stretches about 700 km (430 mi) from the eastern margin of Lake Gairdner across to the Barrier Ranges of New South Wales. The true northern and eastern extent of the Adelaide Superbasin

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1320-724: The SWEAT (south-west USA against East Antarctica) reconstruction of Rodinia. Particularly notable events that are preserved in the rock record of the Adelaide Superbasin are the two Neoproterozoic Snowball Earth events (the Sturtian and Marinoan Glaciations), the Neoproterozoic Oxygenation Event , the Ediacaran Acraman bollide ejecta layer and the rise of Ediacaran Fauna . North–south it stretches over 850 km (530 mi) from

1380-423: The lithosphere that is involved in plate tectonic movement and isostatic adjustments. It is composed of peridotite , a rock containing mostly the minerals olivine and pyroxene . The lithosphere-asthenosphere boundary is conventionally taken at the 1,300 °C (2,370 °F) isotherm . Closer to the surface at lower temperatures, the mantle behaves rigidly; deeper below the surface at higher temperatures,

1440-677: 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. Most of the LFB was greatly affected by the Late Ordovician to Early Silurian Benambran Orogeny (also led to the formation of the Wagga-Omeo Zone). The Middle Devonian Tabberabberan Orogeny affected

1500-483: The Curnamona Province. The lithostratigraphy of the Adelaide Superbasin is divided into three supergroups with further division into numerous groups and subgroups and over 140 formations . Sedimentation in the Adelaide Superbasin ended in the middle Cambrian, when tectonic inversion occurred along the eastern margin of Neoproterozoic and Cambrian cratonic Australia and the margin became

1560-634: The Delamerian Orogeny. The Arrowie Basin is second of the two known Cambrian basins of the Adelaide Superbasin. It extends from the Stuart Shelf in the west across the Flinders Ranges to western New South Wales where it forms part of the Neoproterozoic–Cambrian cover on the Curnamona Province. The Yalkalpo Sub-basin is the easternmost part of the Arrowie Basin. Its western boundary is the basement high Benagerie Ridge of

1620-551: The Earth's crust move about. Due to the temperature and pressure conditions in the asthenosphere, rock becomes ductile , moving at rates of deformation measured in cm/yr over lineal distances eventually measuring thousands of kilometers. In this way, it flows like a convection current, radiating heat outward from the Earth's interior. Above the asthenosphere, at the same rate of deformation, rock behaves elastically and, being brittle, can break, causing faults . The rigid lithosphere

1680-547: The Kanmantoo Province/Trough) and Arrowie Basin (including its sub-province the Yalkalpo Sub-basin) are the two known Cambrian provinces within the Adelaide Superbasin. Deposition in the Adelaide Superbasin began just prior to 830 Ma as Laurentia (and possibly an intervening continent, see Rodinia for alternative reconstructions) began to rift away from Australia during the breakup of

1740-498: The LVZ alerted seismologists to the existence of the asthenosphere and gave some information about its physical properties, as the speed of seismic waves decreases with decreasing rigidity . This decrease in seismic wave velocity from the lithosphere to the asthenosphere could be caused by the presence of a very small percentage of melt in the asthenosphere, though since the asthenosphere transmits S waves , it cannot be fully melted. In

1800-826: 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 84  million years ago The Tasman Sea started to form by seafloor spreading. This split off

1860-475: The Orogen are aligned in a north–south direction. 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. 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

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1920-872: The Stawell and Melbourne Zones. The eastern boundary of the Western Lachlan 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

1980-418: The asthenosphere are widely attributed to the partial melting of the rock. It is likely that a small amount of melt is present through much of the asthenosphere, where it is stabilized by the traces of volatiles (water and carbon dioxide) present in the mantle rock. However, the likely amount of melt, not more than about 0.1% of the rock, seems inadequate to fully explain the existence of the asthenosphere. This

2040-793: 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 Silurian, 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

2100-561: The coast. The Yarrimbah Formation is exposed west of Parkes . It consists of siliceous siltstones , 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

2160-620: 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

2220-506: The distinctive mid-ocean ridge basalt (MORB) of the ocean crust. Magmas are also generated by decompressional melting of the asthenosphere above subduction zones and in areas of continental rifting . Decompression melting in upwelling asthenosphere likely begins at a depth as great as 100 to 150 kilometers (60 to 90 mi), where the small amounts of volatiles in the mantle rock (about 100  ppm of water and 60 ppm of carbon dioxide ) assist in melting not more than about 0.1% of

2280-835: 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

2340-545: 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 447 to 443 million years ago in the Ordovician to Silurian , the arc collided with

2400-541: 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

2460-537: 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

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2520-809: The end of the Neoproterozoic , and in 2004 the location gave its name to the last geological period of the era, the Ediacaran . The ranges formed during the Delamerian orogeny continue to erode, and intra-plate subsidence is occurring. In the South Mount Lofty Ranges this has resulted in rifting and the formation of graben structures, creating the long parallel faults which shape the Adelaide Plains . Asthenosphere The asthenosphere (from Ancient Greek ἀσθενός ( asthenós )  'without strength')

2580-671: 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. There are two high temperature low pressure regions of metamorphism . 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

2640-666: 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

2700-405: The form of turbidites 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

2760-473: The granites at Victor Harbor were intruded at this time, as were those at Palmer in the eastern South Mount Lofty Ranges. Fossils of the earliest Animalia are found in the Adelaide Superbasin. The first of these might be the probable sponges found in the Trezona Formation, although the first confirmed Animalia are the world-renowned Ediacaran fauna , named for the Ediacara Hills where they were first discovered in South Australia in 1946. They occur at

2820-437: The lower boundary of the LVZ lies at a depth of 180 to 220 kilometers (110 to 140 mi), whereas the base of the asthenosphere lies at a depth of about 700 kilometers (430 mi). The LVZ also has a high seismic attenuation (seismic waves moving through the asthenosphere lose energy) and significant anisotropy (shear waves polarized vertically have a lower velocity than shear waves polarized horizontally). The discovery of

2880-408: The mantle moves in a ductile fashion. The asthenosphere is where the mantle rock most closely approaches its melting point, and a small amount of melt is likely to present in this layer. Seismic waves pass relatively slowly through the asthenosphere compared to the overlying lithospheric mantle. Thus, it has been called the low-velocity zone (LVZ), although the two are not strictly the same;

2940-444: The north-east of the main depocentre. Deposition occurred only after a major marine transgression event during the late Neoproterozoic after the Sturtian Glaciation. The Stansbury Basin is one of the two known Cambrian basins of the Adelaide Superbasin. It is exposed in the south of the superbasin, extending from Kangaroo Island and the Mount Lofty Ranges toward Victoria underneath the Murray Basin. The true eastward extent of this basin

3000-443: The oceanic mantle , the transition from the lithosphere to the asthenosphere (the LAB) is shallower than for the continental mantle (about 60 km in some old oceanic regions) with a sharp and large velocity drop (5–10%). At the mid-ocean ridges , the LAB rises to within a few kilometers of the ocean floor. The upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of

3060-414: The rock) contributes to its mechanical weakness. More extensive decompression melting of the asthenosphere takes place where it wells upwards, and this is the most important source of magma on Earth. It is the source of mid-ocean ridge basalt (MORB) and of some magmas that erupt above subduction zones or in regions of continental rifting . The asthenosphere is a part of the upper mantle just below

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3120-407: The strata, and resulted in the creation of a major mountain range, the eroded stumps of which can today be seen as the Mount Lofty and Flinders Ranges. Not all of the basin experienced tectonic activity; the deposits on the Stuart Shelf and Coombalarnie Platform to the north-west and north-east remained undisturbed (and still do today). Accompanying this folding and faulting were several intrusions :

3180-420: The supercontinent Rodinia. Deposition continued through to the Delamerian Orogeny c. 514–490 Ma at which time deposition in the Adelaide Superbasin stopped and the rocks were folded and deformed. Initially, deposition occurred from gradual subsidence of peneplained cratonic lithosphere before developing into a rift basin. After about 725 Ma, deposition continued in a mostly passive margin setting along

3240-466: The surface. Granites cover 61000 km. There are 875 lithological units of granite. There are 100 volcanic units derived from the same magma as the granites. The basement of the belt is Cambrian 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

3300-402: The top of the sedimentary sequence marked by a major basin-wide disconformity separating it from the Cambrian Arrowie and Stansbury Basins. The Torrens Hinge Zone is a transitional area between the relatively undeformed platform deposits of the Stuart Shelf and the deformed rocks of the central Adelaide Rift Complex. It runs along the western margin of the primary rift basin. The Stuart Shelf

3360-440: The viscosity is dependent both on temperature and strain rate reliably produce an oceanic asthenosphere, suggesting that strain-rate weakening is a significant contributing mechanism, and explaining the particularly weak asthenosphere below the Pacific plate. Decompression melting of asthenospheric rock creeping towards the surface is the most important source of magma on Earth. Most of this erupts at mid-ocean ridges to form

3420-584: The west and thin-skinned in the east. Sites within the Lachlan Fold Belt have been associated with economically significant production of gold, copper, silver, lead, zinc and tin. There remains potential for further mineral discoveries. Delamerian Orogeny The Adelaide Superbasin (previously known as the Adelaide Geosyncline and Adelaide Rift Complex ) is a major Neoproterozoic to middle Cambrian geological province in central and south-east South Australia , western New South Wales , and western Victoria . The Adelaide Superbasin consists of

3480-447: 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

3540-414: The western edge of the Palaeo-Pacific Ocean, with renewed rifting during the Ediacaran to the east (present day) of the main depocentres until being terminated by the Delamerian Orogeny. The most abundant rock types indicate a transition from evaporitic depositional environments through to proximal marine, glacial and marine depositional environments . The thickest parts of the stratigraphy reach

3600-404: 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

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