Victoria's complex and fascinating origins and geology

see also:

• a brief history of the World
• Australian history up to 1900
• Prehistoric times
• evolution
• How Australia evolved in geological terms and evolution
• geology and geography of Melbourne
• GeoVic magnetic and gravity imagery

• for much of the ancient geologic periods, most of Victoria was under the ocean - until Tasmania came crashing into it and uplifted the region creating mountain ranges and many fault lines, many of which became filled with gold rich quartz due to countless earthquakes causing piezoelectric effects in quartz veins and allowing the gold to precipitate out of the supersaturated fluids in the faults.
• this period was also characterised by many volcanos
• then something even bigger happened - perhaps a massive asteroid hit east Antarctica and caused it to move away from southern Australia creating a rift valley which would become Bass Strait as a massive swamp land which would result in the formation of the gas and oil fields
• much more recently a new period of volcanism would dramatically change central and western Victoria
  • the gold rich rivers became covered in lava - creating the gold fields “deep leads”
  • Hanging Rock and Camel's Hump volcanoes result in the viscous magma blocking vents to form mamelons 6-7 mya
• the Port Phillip district sinks and eventually becomes flooded
• sea levels rise cutting off the land bridge to Tasmania and forming Bass Strait as it is today

• ~1600mya, Tasmania (“Vandieland”) gradually forms in a sea channel between Arizona and East Antarctica near the North Pole from sedimentation from rivers draining those two regions
• ~1400mya, a tectonic rift event occurred between the land mass that would be Tasmania and Arizona forming a sea between Tasmania and Arizona and an increasing separation on Nth America and Antarctica leaving a part of Tasmania attached to Arizona and another part of Tasmania attached to East Antarctica
• ~1000mya, volcanic arc under King Island which is part of Vandieland and which may have been rifted apart into a V shape as part of the formation of the Port Phillip Sunklands
• Tasmania and east Antarctica as well as Australia slowly migrate south

• c1300-1230mya - the Rodinia supercontinent was assembled
• 1300-1100 Mya - tectonic activity led to the assembly of Proterozoic Australia from collision of the 3 main cratons as an early component of the supercontinent of Rodinia.
  • Australia was well north of the equator and adjacent Eastern Antarctica, India, South China and Laurentia
• 850-800mya a rift developed between the continental masses of present-day Australia, East Antarctica, India and the Congo and Kalahari cratons on one side and later Laurentia, Baltica, Amazonia and the West African and Rio de la Plata cratons on the other.
• 870-500 mya Adelaide Rift Complex of sedimentary deposits begin to form
  • 830mya - rifting to the east formed the “Adelaide Geosyncline”
• 825–550mya Rodinia broke up in four stages
  • 18,000km long x 1600km wide Terra Australis Orogen forms along the south coast of what will be Gondwana stretching from coast of Sth America, east Antarctica and along the east coast of Australia
• 560mya - Mt William in central Victoria forms from an undersea volcano producing Victoria's oldest rocks - greenstone which was used by Aborigines for tools
• 550mya volcanic activity laid down rock in southern Gippsland in Victoria (eg. around Cape Liptrap)

• Victoria was still largely under the ocean just north of the Equator
• 570-530mya, Australia and East Antarctica merge with the remaining Gondwana in the Kuunga Orogeny
  • Tasmania and east Antarctica collide with south moving southern Australia as the Tasmania and east Antarctica craton gets sandwiched between Australian craton and Indian / Kalahari craton in the final stages of forming Gondwana
    • Tasmanian crust “Selwyn Block” pushes up into central Victoria. South-eastern part of NSW becomes wrapped around it causing a massive curved orocline while the oceanic crust, the Tabberabbera Zone pushes towards the surface and westwards and may be the geodynamic driver for this
      • today the Selwyn Block is covered by the Melbourne Zone of new volcanics and sedimentation but it is exposed in a few areas - Cape Liptrap, Theile Igneous Complex Dolodrook east of Licola, and a small area just SW of Geelong.
• 550-470mya Delamerian Orogen in south-eastern Sth Aust forms the Flinders Ranges etc and outlines the Tasman Line which is the Pre-Cambrian margin of eastern Australia
• 538.8-251.9mya Paleozoic era
  • 538.8-485.4mya Cambrian period
    • 522-500mya: Stavely Arc and the Moyston Fault from Mildura, through just west of Stawell and to Mortlake marked the eastern border of Gondwana, giving it a similar geological environment at the time to the copper-rich Andes in South America.
      • eastern two thirds of Victoria is an oceanic floor that commences to be uplifted east of the Moyston Fault Line by a subducting Pacific plate creating a volcanic arc 525-511mya - the Stavely Volcanic Arc stretching from Victoria to the closely connected Antarctica and now sits between Ballarat and the Grampians - the final burst of volcanic activity from these arcs c500mya are what generally push up mineral rich magma to the surface such as gold - hence the Golden Triangle in western Victoria was formed (gold deposits in the eastern Victorian fields was formed separately)
      • Andean-type subduction under the Gondwana craton akin to what happened to form the Andes results in shallow water cooler Stavely volcanics to the east of the Grampians (which are likely to have Volcanic Hosted Massive Sulphide deposits in the marine chimney vents and deeper porphyry mineralisation below the volcanoes between the subduction plate and the Gondwana plate) as demonstrated by the finding of paired metamorphic complexes with hotter magma type partially melted rocks to the west of the Grampians in the Glenelg zone. Magnetic and seismic studies show 19 bands of volcanic arcs in this region which originated from 3 or 4 belts, most now buried by younger basin rocks.
      • the volcanic arc was shut down c500mya with a final release of pressure which should result in mineral rich porphyry deposits and granite and formed the 4 belts of volcanic and intrusive rocks
  • 500mya: 1st Ice Age occurred
  • 485.4-443.8mya Ordovician period
    • deepwater sedimentation of the St Arnaud and Castlemaine Group turbidites (incl. shales and slates which may contain graptolites), which are now emplaced in the Stawell and Bendigo Zones followed by deposition of the Sunbury Group in the Melbourne Zone, Bendoc Group and formation of the Molong Arc
    • shallow marine limestone and mudstone deposition Melbourne Zone, Tabberabbera zone eastern central Victoria until c405mya
  • 450-340mya Lachlan Orogen or Lachlan Fold Belt (LFB) forms over south-eastern Australia including Victoria and extending into Tasmania
    • in Victoria, the western limit of this is the Stawell-Ararat Fault
    • Late Ordovician to Early Silurian Benambran Orogeny impacts the Lachlan Fold Belt (also led to the formation of the Wagga-Omeo Zone)
  • 443.8-419.2mya Silurian period
    • 445.2 and 443.8mya - Hirnantian glaciation stage, Ordovician-Silurian extinction event killed 85% of species - may have been triggered by a massive asteroid impact in Deniliquin, NSW causing a 520km wide impact crater, although this may have occurred as early as 514mya
    • 440mya oceans over western Victoria retreated eastwards and Grampians strata is laid down on top of the Stavely Arc
    • granite intrusions as well as gold-bearing quartz reefs formed from hot salty fluids in New South Wales and Victoria
      • there is a lot of gold in the core of the earth (enough to coat the earth's surface 0.5m thick in gold) and some of this gains access to the mantle as colloidal gold or as gold salts via super-heated fluids through fractures in rock
      • repeated minor earthquakes result in immediate deposition of quartz and gold from pressurised supersaturated silica and minerals in water within the fault lines - a magnitude 2 earthquake results in 130-fold reduction in pressure while a magnitude 6 event could reduce pressures by 13,000 fold - each event laying down more gold-laden quartz reefs and a fault line could have hundreds of magnitude 2 events per year
      • the gold appears to precipitate out of solution onto quartz crystal attracted to other deposits of gold on the quartz - this process appears to be due to piezoelectricity generated in the quartz by the pressure waves of the earthquake at 20Hz, repetitive precipitation of the gold then results in localised deposits and even large nuggets of gold to form
    • the Lachlan Orogen / Lachlan Fold Belt (LBF) of southeastern Australia had a varied paleogeography with deep marine, shallow marine, subaerial environments and widespread igneous activity reflecting an extensional backarc setting. This changed to a compressional–extensional regime in the Devonian associated with episodic compressional events, including the Bindian, Tabberabberan and Kanimblan orogenies.
    • The Lachlan Orogen includes Cambrian to Carboniferous rocks in central and eastern NSW west of the Sydney Basin and extending southwards into Victoria and northeastern Tasmania
      • The western boundary of the Lachlan Orogen in western Victoria is generally taken along the Moyston Fault, although the Grampians Supergroup west of the Moyston Fault has characteristics of the Lachlan Orogen including probable Silurian to Early Devonian sedimentation and deformation.¹⁾
    • The Grampians Group may possibly have been deformed in the Silurian to Early Devonian associated with either the Benambran Orogeny or the Bindian Orogeny
  • 444-435mya, phase 1 Benambran Orogeny in Wagga-Omeo zone, Bega, Murda Syncline, and ? in eastern Tasmania
  • 435-427mya, phase 2 Benambran Orogeny in Tabberabbera zone, western Victorian highlands east of Moyston fault
  • 423-419mya Silurian sedimentary deposits carry gold across much of Victoria's gold fields Ballarat - Bendigo and including under Melbourne - the Silurian Melbourne Formation (these were deposited in deep water in contrast to Devonian sediments which deposited in shallow waters and were later largely covered by volcanic flows laying down basalt in the past 5 million years)
  • 419.2-358.9mya Devonian period
    • 425-415mya rivers lay down the 7km thick sandstone sediments which were later tilted and are now the peaks of the Grampians
    • Middle Devonian Tabberabberan Orogeny affected the entire LFB and terminated the precratonic stage of its development
  • 415mya The Baragwanathia Flora, some of the world's earliest vascular plants, found only in the Yea Beds of Victoria, Australia, occurs in two strata separated by 1,700 m (5,600 ft) or 30 Ma; the upper assemblage is more diverse and includes Baragwanathia, the first primitive herbaceous lycopod to evolve from the zosterophylls.
  • 411-386mya, the granites of Melville Caves and adjacent regions in NW Vic form
  • 405mya, Grampians form with has 1st tilting, twisting and folding which included the upper sedimentation sandstone layers and the older Stavely volcanics layer
  • 405-385mya, Tabberabberan Orogeny eastern part of the Melbourne Zone
  • 400-385mya, Bulla Granites of the western part of the Melbourne Zone form
  • 400mya, Grampians tilting and folding ceases
  • 400mya, Buchan Rift develops in eastern Victoria
  • 400mya:
    • Victoria still mainly undersea apart from western Victoria
      • warm, harsh, unforgiving landscape; oxygen levels were lower than today and ultraviolet radiation higher
      • there was very little soil and there were very few plants affecting the flow of rivers, rivers didn’t meander as much and tended to flood out onto the plains and push everything with them
      • some fungi were massive, such as Prototaxites towering metres above anything else.
      • the earliest forms of vascular plants trying to gain a foothold on land while non-vascular plants were moss-like - Taungurungia garrattii (a Yea fossil which presumably arrived there from floods from the west of Victoria where it would have grown and then was uplifted with the rest of Victoria) is an early example of this, that grew to about 20cm high - the only other plant that would have been bigger in Victoria was the lycopod Baragwanathi that grew up to 2.7 metres high and was the only plant at the time with what we would recognize as leaves - microphylls, which were narrow and strap-like with one central vein
      • most plants from this period fall under three categories—rhyniophytes, lycophytes, and zosterophylls; zosterophylls being further divided into two groups.
  • Victoria experiences a very high level of volcanism which may have been further increased after the Woodleigh crater impact event in WA and the volcanism alone could have been responsible for the Devonian extinction event
    • 374mya: Cerberean Caldera supervolcano forms the Marysville Igneous Complex within the Lake Eildon Nat Park and last eruption 365mya with 27km caldera diameter which then collapsed 1-2km into the earth
    • Acheron caldera (same magma chamber as Cerberean)
    • Mt Macedon erupts
    • Mt Dandenong erupts
    • massive volcanoes in western Victoria near Rocklands forming the:
      • Moralla gemfields of geodes and smoky quartz due to unique slowly erupting rhyolitic lava now covered in 2-6m of sediment
      • various ignimbrite layers
  • From the middle Devonian period to the beginning of the Cretaceous period (a span of some 250 million years), most of Victoria was no longer covered by ocean and several thousand metres of sediments were eroded away to form a nearly level plain and which exposed granite formed in the Middle Devonian period.
  • 365mya: the You Yangs batholith magma chamber very slowly cooled and solidifies deep under the sea which then receded and eroded the overlying sedimentary material to form the granite which is the exposed residual You Yangs
  • 358.9-298.9mya Carboniferous period
    • Pangaea supercontinent formed with Australia being close to the south pole
    • 350-320mya: the middle crust began to melt and magma rose up to just below the surface forming the large Islington Granite intrusion in Werribee Gorge
    • 330mya: north-south Temperance Reef of gold/quartz deposited under Nth Ballarat (at depth of 300m present day Ballarat but southern end abruptly disappeared and has not been found)
      • horst and graben event presumably moved the southern end deeper in a depression which then became buried by sediment from erosion of Black Hill horst section and then also later by volcanic activity which would suggest the reef is at ~180m depth under Ballarat East
    • 318mya Kanimblan Orogeny was the terminal event for the LFB and converted the LFB into a neocraton
      • Uplift and deformation occurred in a 1,000 km long belt extending from Tasmania to Cape York. However the original width was 2,000 to 3,000 km wide, with the excess size absorbed by folding and thrust faulting. This formed the Great Dividing Range.
  • 298.9-251.9mya Permian period
    • The Permian Bacchus Marsh Formation outcrops around Werribee Gorge (as well as Lake Eppalock). This formation represents the movement of a glacier from a S-SW direction across the region, with up to at least eight distinct advances (source). At this time the Australian portion of Gondwana lay near the South Pole and had a glacial climate which extended into the Triassic and Cretaceous.
    • The most common Permian deposit type around Werribee Gorge is a tillite or diamictite
• 252-66mya Mesozoic era
  • 251.9-201.4mya Triassic period
  • 201.4-145mya Jurassic period
  • 145-66mya Cretaceous period
    • 110mya, Australia's 1st mammals evolved including the 1st monotremes (ancestors of the platypus)
    • Victoria's southern coast (especially around Inverloch) has areas of early Cretaceous period layers of siltstone and sandstone as well as conglomerate exposed which contains dinosaur fossils as well as early amphibians and mammals from 105-120mya when Victoria was located at latitude 70-75deg South and the climate was cool temperate similar to current day Tasmania uplands. Vulcanism dated to 99.9mya extruded igneous rock over some areas. The swampy backwaters were to form the coal seams as well as the oil and gas deposits in the region.
    • 100mya 1st of two dynamic uplift events caused by convection in the Earth's mantle to form the present structure of the Snowy Mountains, 2nd was 50mya;
    • 85mya: New Zealand, New Caledonia and the rest of the now submerged continent of Zealandia begin to separate from Australia forming the Tasman Sea
    • 80mya: initial uplift of Victorian Alps
    • 85-65 Ma, Tasmania was still connected to Antarctica by the stretched crust of the South Tasman Rise. Climate was hot and humid. Australia was separated from Antarctica by 100km. Bass Strait was then the Bassian Plain - a rift valley of river flood plains, swamps and lakes.
    • 85-55mya: Tasman Rift Zone forms creating the Tasman Sea - New Zealand, New Caledonia and the rest of the now submerged continent of Zealandia begin to separate from Australia forming the Gippsland Basin, Tasman Rift Zone and the Tasman Sea - this halted 55mya ²⁾
  • 66mya Cretaceous–Paleogene extinction event

• 66mya - current Cenozoic era
• 66mya: Pentland Hills volcanic group active 66-33mya
• In the Early Cenozoic ~66mya, Australia was still connected to Antarctica c. 35–40° south of its current location and both continents were largely unglaciated.
• A rift between the two developed but remained an embayment until the Eocene-Oligocene boundary when the Circumpolar Current developed and the glaciation of Antarctica began.
• Australia was warm and wet during the Palaeocene and dominated by rainforest.
• 65mya, further drifting away from Antarctica results in three interconnected marine basins (Otway, Gippsland and Bass basins) forming along the southern edge of Victoria’s continental plate and significant marine sediments were laid down in shallow seas. Some parts of these basins now lie onshore but most are to be found beneath Bass Strait where commercial oil and gas reserves have been found within these sediments.
• 55mya, small marsupials migrate to Australia from Sth America via Antarctic
• 55mya: Tasman Rift Event ends and subduction events under NZ commence
  • ending of Tasman Rift Event is perhaps due to start of a subducting event under NZ which is ongoing and is now possibly pulling on Victoria as the southern island is subducting eastwards while to the north of NZ it is subducting westwards and Australia continue moves northwards
  • late Cretaceous and early Tertiary extensive volcanic lava flows down many valleys in South Gippsland (eg Warragul, Mirboo, Leongatha as well as on the southern Mornington Peninsula around Red Hill) - these generally started from east and moved westwards until they reached the fault line near Bacchus Marsh - after that time were the newer volcanics of Western Victoria
    • Thorpdale volcanic group active near Moe 66-5mya;
    • Carrajung volcanic group near Yarram 59-47.8mya
    • Karoonda Park volcanic group in the old Buchan rift Zone active 47.8-41mya and 33.9-28.1mya
    • Mornington volcanic group (including Phillip Island) active 47.8-41.2mya
    • Nunnett Plains volcanic group east of Omeo active 47.8-41mya
    • Mount Jim volcanic group NW of Dargo active 37.7-23mya
    • Neerim volcanic group north of Warragul active 33.9-16mya
    • Monbulk volcanic group 23-5.3mya
    • Murraduc basalt in Bellarine Peninsula
    • Tullamarine volcanic group
    • Greensborough basalt
    • Pentland volcanic group
• 40-30mya: the Tasman Gateway between Australia and Antarctica begins to open
• 40mya Southern Ocean reaches the northern and western end of the Grampians via Sth Australia - the sedimentation from the Grampians laid down the sea floor in this region which is now the Little Desert National Park
• 33mya: The opening of the Tasman Gateway at the Eocene-Oligocene boundary (33 Ma) resulted in abrupt cooling but the Oligocene became a period of high rainfall with swamps in southeast Australia.
• 28-20mya: Port Phillip sunklands form in Victoria from a mountainous past due to rift event and sea level rise flooding the area from the Otways, across Port Phillip Bay and to the north of Melbourne
• 23mya: the Antarctic Circumpolar Current (ACC) is established with the full opening of the Drake Passage and the deepening of the Tasman Gateway
• late Oligocene (c25mya?) to Middle Miocene (c10mya?): green to grey richly fossiliferous silt marine sediments known as the Fyansford Formation laid down on top of older volcanic basalts. These were in some places with calcareous lenses, or even limestone such as at Green Gully, near Keilor
• During the Miocene, a warm and humid climate developed with pockets of rainforests in central Australia, but before the end of the period, colder and drier climate severely reduced this rainforest.
• A brief period of increased rainfall in the Pliocene was followed by drier climate which favoured grassland.
• Since then, the fluctuation between wet interglacial periods and dry glacial periods has developed into the present arid regime.
• Australia has thus experienced various climate changes over a 15-million-year period with a gradual decrease in precipitation.

• as NZ plate pushes towards NE Victoria over past 6 million years, there has been ongoing uplift of the Victorian Alps and continues to pull on SE Victoria and this could also have contributed to western Victoria's vulcanism in this era in addition to the magmatic hotspot
• 6-7mya Hanging Rock, Camel's Hump, The Jim Jim and Brock's Monument volcanic eruptions which would leave the unique mamelons we see today due to the viscous magma plugging the vents
• 2-5mya: volcanic eruptions in Victoria such as Mt Blackwood (c4mya) produce extensive laval sheets forming the Werribee and Keilor basalt plains
  • west-east running Yarrowee River in Ballarat forms after volcanic activity 4-7mya covered the old north-south running Deep Lead ancient rivers which had been uplifted as Black Hill by a Horst and Graben events due to the splitting of Antarctica from Australia and which then formed sedimentary deep leads such the under Bakery Hill reef then covered by basalt
• 2mya: Volcanoes to the north of Melbourne.
  • Lava flows erupted from Hayes Hill near Mernda, flowed down the ancestral Merri Creek and Darebin Creek valleys into the Yarra Valley at Fairfield and down that valley onto the Yarra delta as far as the present site of Spencer Street bridge. Yarra River became entrenched along the boundary between the these lava flows and the softer Silurian bedrock
• 1.5mya: Anakies in Victoria last eruption
• 1mya: last eruption of Mt Warrenheip near Ballarat with flow going NE? (older flow went Sth)
• sedimentation in the Murray and Otway Basins cover the older rocks in much of western Victoria
• 470,000yrs ago: Mt Franklin last eruption (near Daylesford, Vic)
• 100-150,000yrs ago: Mt Buninyong 1st erupts producing a steep scoria cone and the 6km Clarendon lave flow travelling SE. Later a lava lake formed on Mt Buninyong and resulted in the westward lava flow over what is now Buninyng
• 70,000yrs ago: modern course of the Murray River was carved when a series of earthquakes and aftershocks that went for years lifted the ground along the 80km Cadell fault line which stretches from Deniliquin through Echuca, to Rochester in northern Victoria. A series of six very large earthquakes events occurring every 5000-10000yrs formed the fault scar, which is up to 10 to 15 metres high at Mathoura resulting in the river being diverted from Mathoura to Echuca. This fault line is regarded as being dormant as no quakes have occurred in the past 20,000yrs, although it could be overdue for its 1 in 10,000yr magnitude quake.
• 35000yrs ago: earliest Aboriginal features in Tasmania
• 31000yrs ago, earliest Aboriginal features in Victoria - Keilor area near Melbourne
• 18000yrs ago: glaciation maximum resulted in the central basin of Bass Strait being enclosed by raised sills forming a large shallow lake
• 12,000yrs ago, Mt Buninyong has another major eruption destroying the previous scoria cone
• 11,650 yrs ago marked the end of the last glaciation event and the start of an interglacial period
  • sea levels rose resulting in the sills of the Bassian Basin being breached resulting in the formation of Bass Strait 8000 yrs ago which now has an average depth of 60m and Port Philip Bay filling with sea water instead of being just a depressed swamp land
• 5000 yrs ago - south coast Australia and SW coast of NZ hit by a 200m mega tsunami caused by comet impact into Indian Ocean - the Burckle Crater, depositing seismic chevrons and causing coastal scarring (and building the 600 foot high mountains in Madagascar)
• 4500 years ago last volcanic activity in Victoria was at Tower Hill near Warrnambool