Geology of Victoria
Encyclopedia
Victoria is an Australia
n state, situated at the southern end of the Great Dividing Range
. The Great Dividing Range stretches along the east coast of the continent and terminates near the Victorian city of Ballarat
west of the capital Melbourne, though the nearby Grampians
may be considered to be the final part of the range. The highest mountains in Victoria (just under 2000 m) are the Victorian Alps, located in the northeast of the state.
There was an area of extensive volcanism
in central and southwestern Victoria, where there are numerous extinct volcano
es and volcanic lakes. The Western Victorian Volcanic Plains are the third largest in the world after the Deccan in western India
, and the Snake River
Plateau in Idaho
, United States
. The most recent volcanic activity was at Mt Eccles, which last erupted a few thousand years ago. Large basalt
ic lava flows are present on the western side of Melbourne and in the southwest of the state. Central and western Victoria comprise world-class vein-hosted gold deposits, hosted mostly in the extensive Ordovician
turbidite
s. The southeast of the state has enormous brown coal
fields.
The low flat northwest of the state that borders the Murray River
was once the bed of an ancient sea and the land is much afflicted with salinity
. Saline drainage from Victorian land is one of the sources of the salinity problem in the Murray-Darling River system. Commercial salt
evaporation is undertaken near Swan Hill
.
Neoproterozoic
This period is covered by the recent Geological Survey of Victoria publication The Tasman Fold Belt System in Victoria. The sequence of events associated with the building of southeastern Australia reveals that mineralization and magmatic processes are intimately linked with the tectonic
development of the region. The history is dominated by east-west compression of predominantly oceanic sedimentary
and igneous rock
s and their resultant fold
ing, faulting and uplift
. Recently, it has become increasingly apparent that major north-south movements have also been involved in constructing eastern Australia.
The Palaeozoic basement is traversed by thrust fault
s more or less parallel to the north-south structural grain. The largest faults separate rocks with different ages and structural histories, and subdivide Victoria into three main structural rankings consisting of twofold belts (Delamerian and Lachlan), two terranes in the Lachlan Fold Belt
(Whitelaw and Benambra), and ten structural zones (Glenelg, Grampians-Stavely, Stawell, Bendigo, Melbourne, Tabberabbera, Omeo, Deddick, Kuark, Mallacoota).
rocks and was deformed in the Late Cambrian Delamerian Orogeny
whereas the Lachlan Fold Belt contains mainly Cambrian-Devonian
rocks with the main deformations occurring in the late Ordovician
to early Carboniferous interval. The first regional deformation to affect the Lachlan Fold Belt was the Benambran Orogeny, about 450 MYA, after the Delamerian Orogeny. Granite
s comprise 20% of the total exposed area of the Lachlan Fold Belt and fall within an age range of 440 to 350 MYA. Volcanics associated with the granites are also widespread and cover an additional 5%. Blocks of older crust
consisting of Neoproterozoic-Cambrian rocks, such as the Selwyn Block in central Victoria, were deformed during the late Cambrian Tyennan Orogeny prior to being incorporated into the Lachlan Fold Belt.
divides the Lachlan Fold Belt into two terranes, the Whitelaw Terrane to the west and the Benambra Terrane to the east. The main difference between these is that orogen-parallel (north-south) transport was more prevalent in the Benambra Terrane, whereas convergent east-west transport orthogonal to the orogen was dominant in the Whitelaw Terrane.
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 state, situated at the southern end of 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...
. The Great Dividing Range stretches along the east coast of the continent and terminates near the Victorian city of Ballarat
Ballarat, Victoria
Ballarat is a city in the state of Victoria, Australia, approximately west-north-west of the state capital Melbourne situated on the lower plains of the Great Dividing Range and the Yarrowee River catchment. It is the largest inland centre and third most populous city in the state and the fifth...
west of the capital Melbourne, though the nearby Grampians
Grampians National Park
The Grampians National Park is a national park in Victoria, Australia, 235 kilometres west of Melbourne. The Park was listed on the Australian National Heritage List on 15 December 2006 for its outstanding natural beauty and being one of the richest indigenous rock art sites in south-eastern...
may be considered to be the final part of the range. The highest mountains in Victoria (just under 2000 m) are the Victorian Alps, located in the northeast of the state.
There was an area of extensive volcanism
Volcanism
Volcanism 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....
in central and southwestern Victoria, where there are numerous extinct volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es and volcanic lakes. The Western Victorian Volcanic Plains are the third largest in the world after the Deccan in western India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, and the Snake River
Snake River
The Snake is a major river of the greater Pacific Northwest in the United States. At long, it is the largest tributary of the Columbia River, the largest North American river that empties into the Pacific Ocean...
Plateau in Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The most recent volcanic activity was at Mt Eccles, which last erupted a few thousand years ago. Large basalt
Basalt
Basalt 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...
ic lava flows are present on the western side of Melbourne and in the southwest of the state. Central and western Victoria comprise world-class vein-hosted gold deposits, hosted mostly in the extensive 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...
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. The southeast of the state has enormous brown 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...
fields.
The low flat northwest of the state that borders the Murray River
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
was once the bed of an ancient sea and the land is much afflicted with salinity
Salinity in Australia
Soil salinity and dryland salinity are two problems degrading the environment of Australia. Salinity is a concern in most states, but especially in the south-west of Western Australia....
. Saline drainage from Victorian land is one of the sources of the salinity problem in the Murray-Darling River system. Commercial salt
Halite
Halite , commonly known as rock salt, is the mineral form of sodium chloride . Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities...
evaporation is undertaken near Swan Hill
Swan Hill, Victoria
Swan Hill is a city in the northwest of Victoria, Australia. It is located on the Murray Valley Highway, on the south bank of the Murray River, downstream from the junction of the Loddon River. At the 2006 census, Swan Hill had a population of 9,684.-History:...
.
NeoproterozoicNeoproterozoicThe Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
to early CarboniferousCarboniferousThe 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"...
This period is covered by the recent Geological Survey of Victoria publication The Tasman Fold Belt System in Victoria. The sequence of events associated with the building of southeastern Australia reveals that mineralization and magmatic processes are intimately linked with the tectonicPlate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
development of the region. The history is dominated by east-west compression of predominantly oceanic sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
and igneous rock
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
s and their resultant fold
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
ing, faulting and uplift
Tectonic uplift
Tectonic uplift is a geological process most often caused by plate tectonics which increases elevation. The opposite of uplift is subsidence, which results in a decrease in elevation. Uplift may be orogenic or isostatic.-Orogenic uplift:...
. Recently, it has become increasingly apparent that major north-south movements have also been involved in constructing eastern Australia.
The Palaeozoic basement is traversed by thrust fault
Thrust fault
A 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...
s more or less parallel to the north-south structural grain. The largest faults separate rocks with different ages and structural histories, and subdivide Victoria into three main structural rankings consisting of twofold belts (Delamerian and Lachlan), two terranes in the Lachlan Fold Belt
Lachlan Fold Belt
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...
(Whitelaw and Benambra), and ten structural zones (Glenelg, Grampians-Stavely, Stawell, Bendigo, Melbourne, Tabberabbera, Omeo, Deddick, Kuark, Mallacoota).
Moyston Fault
The Moyston Fault is the most important fault as it forms the terrane boundary between the Delamerian and Lachlan fold belts. These twofold belts show important differences. The Delamerian Fold Belt is mainly composed of Neoproterozoic-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...
rocks and was deformed in the Late Cambrian Delamerian Orogeny
Orogeny
Orogeny 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...
whereas the Lachlan Fold Belt contains mainly Cambrian-Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
rocks with the main deformations occurring in the 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...
to early Carboniferous interval. The first regional deformation to affect the Lachlan Fold Belt was the Benambran Orogeny, about 450 MYA, after the Delamerian Orogeny. Granite
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...
s comprise 20% of the total exposed area of the Lachlan Fold Belt and fall within an age range of 440 to 350 MYA. Volcanics associated with the granites are also widespread and cover an additional 5%. Blocks of older crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
consisting of Neoproterozoic-Cambrian rocks, such as the Selwyn Block in central Victoria, were deformed during the late Cambrian Tyennan Orogeny prior to being incorporated into the Lachlan Fold Belt.
Baragwanath Transform
The second major structural break in Victoria is the Baragwanath Transform, which occurs along the eastern side of the Selwyn Block. This transform faultTransform fault
A transform fault or transform boundary, also known as conservative plate boundary since these faults neither create nor destroy lithosphere, is a type of fault whose relative motion is predominantly horizontal in either sinistral or dextral direction. Furthermore, transform faults end abruptly...
divides the Lachlan Fold Belt into two terranes, the Whitelaw Terrane to the west and the Benambra Terrane to the east. The main difference between these is that orogen-parallel (north-south) transport was more prevalent in the Benambra Terrane, whereas convergent east-west transport orthogonal to the orogen was dominant in the Whitelaw Terrane.
See also
- List of Victorian volcanoes
- Australian gold rushesAustralian gold rushesThe Australian gold rush started in 1851 when prospector Edward Hammond Hargraves claimed the discovery of payable gold near Bathurst, New South Wales, at a site Edward Hargraves called Ophir.Eight months later, gold was found in Victoria...