Australia: The Land Where Time Began
Australian Tectonic and Metallogenic Evolution - A Summery Pt.2
2,200-1700 Ma - The amalgamation of Nuna
Between 2215-1950 Ma a series of tectonic events occurred that led to the amalgamation of the Yilgarn Craton with the Pilbara Craton, the processes affecting the Capricorn Orogeny and amalgamated the West Australian Element (Cawood & Tyler, 2004), one of the earliest blocks of Nuna. The North Australian Element had mostly been formed before 1840 Ma as a result of the amalgamation of the Tanami-Tennant-Isa Province with the combined Kimberley-Pine Creek Province about 1840 Ma from the west, and from the east the Numil-Abingdon Seismic Province before 1850 Ma, and from the south, the Aileron Province before 1840 Ma. (Sheppard et al., 1999; Tyler & Sheppard, 2006; Goleby et al., 2009; Korsch et al., 2012). At about 1865 Ma turbiditic rocks of the Warramunga Formation (Compston, 1995) and the Stubbins Formation (Bagas et al., 2008), may have formed that were associated with convergence to the north of the Aileron Province, along the southern edge of the North Australian Element.
In the Gawler Province, that forms the core of the South Australian Element, the northern and eastern sections grew, at least partly, as the result of subduction from the east, possibly having originally being part of the North Australian Element (Payne et al., 2009). According to the authors1 this interpretation is consistent with studies (Payne et al., 2009) indicating the provenance of sediments from the northern and eastern Gawler Province is consistent with a source that is in the Isa Province, but not with the core of the Gawler Province that is of Archaean age.
Most of the North Australian Element and the West Australian Element had been assembled by about 1840 Ma, though it is possible the North Australian Element and the South Australian Element had been intermittently amalgamated since about 2500 Ma (Payne et al., 2009), 2 and possibly 3 elements from the Archaean-Palaeoproterozoic had assembled into the proto-Australian continent between 1810-1750 Ma. Along the southern margin of the North Australian Element north- to northeast-directed subduction began at about 1810 Ma that resulted in the convergence between the North Australian Element and the West Australian Element and the Archaean core of the Gawler Province. The first to dock with the North Australian Element was the West Australian Element at about 1790-1780 Ma during the Yapungku-Capricorn Orogeny (Bagas, 2004). Following this collision the north-directed subduction continued beneath the North Australian Element, and according to the authors1, this probably occurred with a sinistral strike-slip fault that developed along the margin of the southeast of the West Australian Element. During the Kimban-Nimrod-Strangways Orogeny between 1740-1690 Ma (Betts et al., 2008) the convergence period ended when the Gawler Province's Archaean core accreted onto the combined North Australian Element and West Australian Element.
Along the southern margin of the North Australian Element emplacement of sodic granites and mineral deposit formation occurred that is characteristic of convergent margins providing support for this interpretation. Along this margin there are 2 discrete belts of sodic granites. In the southern part of the magmatic belt from 1815-1795 Ma, that is west-northwest-trending, in the Tanami-Tennant-Isa Province there is an older belt. Along the southern margin of the Aileron Province associated with granites, dated to 1790-1750 Ma, (calc-alkalaine-tonalite (CAT)) suite of Zhao and McCulloch (1995). Lode gold deposits from 1810-1795 Ma (Cross et al., 2005) and volcanic-hosted massive sulphide from 1810-1765 Ma (Hussey et al., 2005), the formation of which is typical for convergent margins, developed in the southern part of the North Australian Element. The authors1 suggest it is likely Laurentia and the east of the proto-Australian continent were linked until 1690 Ma, at least (Betts & Giles, 2006).
1700-1300 Ma- Nuna breakup
Nuna soon began breaking up, though this process was complicated with Laurentia rifting to the east of proto-Australia, but a backarc basin system developed along the southern margin of Australia in the Proterozoic, as subduction stepped to the south (Scott et al., 2000; Giles et al., 2002; Betts et al., 2003). The emplacement between 1710-1685 Ma of layered mafic-ultramafic intrusions within the southern section of the Aileron Province (Claoué-Long & Hoatson, 2005) is the earliest evidence of extensional processes. Extension along the eastern margin of Australia in the Proterozoic, beginning about 1690 Ma (Betts et al., 2003; Gibson et al., 2008), is suggested by the development of turbidite-filled basins and tholeiitic mafic rock emplacement along the eastern margins of the South Australian Element in the Curnamona Province and the North Australian Element (Willis et al., 1983; Beardsmore et al., 1988 ). The Calvert and Isa Superbasins were produced by this extension (Southgate et al., 2000), which together with the Curnamona Province, that is related, host the Australian Proterozoic zinc belt. The separation of proto-Australia from Laurentia (Betts et al., 2003) was the ultimate result, the final separation occurring to the east of the Numil-Kowanyama-Abington Province in Queensland.
Felsic magmatic rocks and minor sedimentary rocks, now orthogneiss and paragneiss, were deposited as the oldest known rocks in the Warumpi Province, beginning at about 1690 Ma (Scrimgeour et al., 2005). It has also been inferred (Kirkland et al., 2011) that convergence and the development of backarc basins took place along the southeast margin of the West Australian Element from 1710-1665 Ma. Granitic rocks formed from 1690-1665 Ma that have arc-like geochemical signatures in the region (Eddy Suite; Kirkland et al., 2011) and the Warumpi Province (Argilke Suite; Cawood & Korsch, 2008) support the inference of north-dipping subduction.
The accretion of rocks of the Warumpi Province at about 1640 Ma resulted from the closure of the backarc basin system of the continental margin that began at about 1660 Ma through a series of north-dipping and south-dipping subduction systems (Scrimgeour et al., 2005), which was followed at about 1590 Ma by those of the Musgrave Province (Wade et al., 2006) and at about 1560 Ma by those of the Gawler Province (Korsch et al., 2011a). The authors1 suggest the Gawler Province is likely to have been the northern extension of the Mawson Continent, which also included the Terre Adélie Craton as well as large parts of the East Antarctic Shield, during this period (e.g., Boger, 2011), though it has been suggested (Swain et al., 2008) that at about 1610 Ma the Terre Adélie Craton accreted onto the Gawler Province following northeast-dipping subduction. It has been suggested (Giles et al., 2004) that the Mawson Continent, including the Gawler and Curnamona Provinces, must have rifted from proto-Australia, because during the assembly of Rodinia these elements converged again (Giles et al., 2004).
Episodic deformation was also involved through much of Proterozoic Australia during the period 1640-1500 Ma. At about 1640-1635 Ma the earliest deformational event system affected only the North Australian Element, involving north-south-directed contraction along the southern margin (Liebig Orogeny; Scrimgeour et al., 2005) and in the east (Riversleigh Inversion; Geological Survey of Queensland, 2011). Then accretion of the Warumpi Province (Scrimgeour et al., 2005) may have resulted in this event that is marked by a U-turn on the North Australian apparent polar wander path (Idnurn, 2000).
Contractional deformation affected the Isa (early phase of the Isan Orogeny; Geological Survey of Queensland, 2011), Aileron (early part of the Chewings Orogeny; Rubatto et .al., 2001) and Curnamona Provinces (Olarian Orogeny; Page et al., 2005) between 1605-1585 Ma. This event was a north-south to northwest-southeast directed crustal shortening event (Geological Survey of Queensland, 2011) that the authors1 suggest may relate to the accretion of the Musgrave Province.
High pressure metamorphism at this time similarly affected the northern part of the Gawler Province (Cutts et al., 2011), though the Archaean core of the province is mot known to have been affected by this deformation. In the Gawler Province the central part is characterised by the emplacement between 1595-1575 Ma of the Hiltaba Magmatic Province, including the Gawler Range Volcanics, that was felsic dominated, and the coeval Hiltaba Granite Suite. This magmatic event was interpreted as being the result of a migrating hot spot or plume (Betts et al., 2007), the timing of magmatism correlating to a shift from a contractional to an extensional environment (Skirrow, 2010). In the Aileron Province, largely a low-pressure high-temperature magmatic event, the Chewings Orogeny continued until 1560 Ma (Rubatto et al., 2001), has been suggested to possibly have resulted from backarc extension relating to convergence between the Gawler Province and the North Australian Element (Korsch et al.. 2011a).
Thermotectonic activity contracted mostly to eastern Proterozoic Australia after about 1570 Ma, though in the Gawler and Curnamona Provinces there remained some restricted activity. The Middle Isan Orogeny, from 1560-1540 Ma, and further east the Jana Orogeny, involving east-west contraction, may be related to convergence between Australia and Laurentia (Geological Survey of Queensland, 2011). Emplacement of the Williams Suite, that is anorgenic, and associated deformation, that occurred between 1545-1500 Ma, has been suggested to possibly relate to the movement of a hot spot (Betts et al., 2007).
During the formation and breakup of Nuna much of the mineral deposits in Australia, particularly iron and base metals, were formed. During amalgamation upgrading of iron ore deposits in the Hamersley Basin (about 2008 Ma; Miller et al.. 2005), and in the Pine Creek and Tanami provinces the formation of lode gold deposits (about 1810-1790 Ma; Compston & Matthai, 1994; Cross et al., 2005). During the breakup of Nuna the zinc-lead-silver deposits of the zinc belt from the Proterozoic of Australia (1690-1575 Ma; Betts et al., 2003; Leach et al., 2010) formed as Nuna was breaking up, and at Olympic Dam iron oxide-copper-gold deposits (about 1875 Ma; Skirrow et al., 2007) and Cloncurry Mineral Provinces (Mostly 1530-1500 Ma; Duncan et al., 2011) have been suggested to possibly relate to a hot spot or plume that was migrating (Betts et al., 2007. The timing of the formation of many deposits in the North Australian Element correspond to bends in the Australian apparent polar wander path (Idnurm, 2000). According to the authors1 these bends occur as a response to plate motion changes and/or plate reorganisation that is associated with tectonic processes on a large scale, such as occurred at 1640-1590 Ma. High heat-producing magmatism and felsic volcanism rock was generated abundantly during the Mesoproterozoic (Neumann et al., 2000). The crustal heat production of Australia at the present was contributed to by the resulting rocks, and the provide a thermal source for geothermal power and a uranium resource for nuclear power. The development of the oldest oil play in the world, though the quantities are uneconomic, occurred at this time, in the Upper Roper Group in the McArthur Basin, of Mesoproterozoic age, northwest of Mt Isa (Jackson et al., 1986).
The Hamersley Basin iron ore deposits are unusual compared to other Australian ore deposits as they formed as the result of geological events that were between several hundreds of millions to billions of years apart, and occurring in geological environments that were quite different. Before the Great Oxidation Event (2450-2090 Ma; Farquhar et al., 2010) banded-iron formation proto-ore was deposited, then was upgraded by oxidised, basinal brines at about 2008 Ma (Müller et al., 2005), which oxidised the iron and removed the silica and carbonate. Phosphorus was then removed by palaeoweathering to leave high-grade direct shipping ore (Barley et al., 1999; Taylor et al., 2001).
1300-700 - Amalgamation and breakup of Rodinia
On a global scale, during the period between 1300-700 Ma the assembly and breakup of Rodinia, the second supercontinent occurred. Crustal reworking in the Albany-Fraser-Musgrave Belt and the formation, later, of the intracratonic Central Australian Basin System, characterised this period in Australia. The presence of important mineralising events during this period, though of different character to other times during the history of Australia, is indicated by new discoveries and more data from existing mineral deposits.
During the period 1300-700 Ma the earliest major event that affected Australia were a series of deformational events that overprinted the Albany-Fraser and Musgrave Orogens between 1345-1140 Ma (Myers et al., 1996; Smithies et al.. 2010; Kirkland et al., 2011). The authors1 suggest that these events probably relate to the collision of the combined West-North Australian Element with the Mawson Craton, which included the South Australian Element and the East Antarctic Shield (Boger, 2011). This collision, that was a prelude to the assembly of Rodinia, mainly assembled between 1100-980 Ma (Pisarevsky et al., 2003).
Before and during the assembly of Rodinia diverse mineral deposits formed, including deposits of diamond, REE and orthomagmatic Nickel-copper-PGE. Diamond and REE deposits, that are associated with alkalic rocks, include the Argyle diamond pipe, that has been dated to about 1178 Ma (Pidgeon et al., 1989), have been suggested to have resulted from an intracratonic plume event. Differences have been found between the formation of Rodinia and that of the earlier Kenorland and Nuna and later Pangaea-Gondwana supercontinents/supercratons, such as the lack of the volcanic-hosted massive sulphide and lode gold deposits that are characteristic of the assembly of the earlier and later supercontinents, in other parts of the world, as well as in Australia, which suggests there were important differences in the geodynamic processes involved between the formation of Rodinia compared with those associated with the assembly of the Nuna and Pangaea-Gondwana.
At about 850 Ma rifting began that led to the breakup of Rodinia, the final breakup occurring at about 750 Ma. The northwest trending Gairdner Large Igneous Province is one of the earliest manifestations of this process (Wingate et al., 1998), which intruded into both the North and South Australian Elements, and in the northwest extended into the Peterson Orogen (Hoatson et al., 2008). The authors1 suggest that the formation of some of the Central Australian Basin System is likely to have resulted from extension associated with the Breakup of Rodinia. Beginning at about 850 Ma (Walter et al., 1995), the development of this basin system extended to the Devonian, affected most of central Australia, including the Officer, Amadeus, Georgina and Yeneena Basins, as well as the Adelaide Rift System. The earliest known major salt deposits are included in these basins, that are in the Bitter Springs Formation in the Amadeus Basin, and there is also evidence of several periods of glaciation and the first flowering of multicellular life. The salinity of seawater has been lowered by the deposition of salt in such places as the Bitter Springs and subsequent salt deposits around the world since the Neoproterozoic (Knauth, 2005).
The formation of uranium and copper deposits in the Yeneena Basin and the Adelaide Rift System between 840-790 Ma (Huston et al., 2010) were related to the formation and/or inversion of basins. Australia has been placed next to the Kalahari Craton in some reconstructions (Pisarevsky et al., 2003), and the Kalahari Craton contains the highly productive Zambian Copper Belt (Shelley et al., 2005). The basin hosting this belt is of a similar age and has similar fill to parts of the Central Australian Basin System, and ore deposition ages overlap.
2200-1300 Ma - Nuna, amalgamation and break up
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading|