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56-636: The Yilgarn Craton is a large craton that constitutes a major part of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts . Zircon grains in the Jack Hills , Narryer Terrane have been dated at ~4.27 Ga , with one detrital zircon dated as old as 4.4 Ga. The Murchison Province of the craton contains the Yarrabubba impact structure , at over 2 billion years old it

112-400: A rising plume of molten material from the deep mantle. This would have built up a thick layer of depleted mantle underneath the cratons. A third model suggests that successive slabs of subducting oceanic lithosphere became lodged beneath a proto-craton, underplating the craton with chemically depleted rock. A fourth theory presented in a 2015 publication suggests that the origin of

168-549: A considerable Tertiary and younger sedimentary veneer of palaeochannel deposits derived from prolonged erosion, sedimentation and redeposition of older cover sequences and regolith as well as the Archaean basement itself. Recognised Tertiary cover sequences include the Bremer Basin , Officer Basin and others. The Yilgarn craton is believed to have remained at or above sea level for a considerable length of time. Some of

224-399: A fluid and/or metal source, or simply reflect a favourable pathway. The greater Kambalda district hosts a world-class nickel-sulfide mining district with a total pre-mining resource of 2 megatons (Mt) of nickel metal. Approximately 1.1 Mt of nickel metal has been produced since 1967, at an average rate of 35,000 tons of nickel per year. The Kambalda Dome is located in the south-central part of

280-762: A late phase that resulted in deposition and deformation of the Diemals Formation. Subsequent orogeny (ca. 2680–2655 Ma) resulted in shear zones and arcuate structures. The lithostratigraphy of the Marda–Diemals greenstone belt are similar to the northern Murchison Terrane, but has older greenstones and deformation events than the southern Eastern Goldfields Terrane. This indicates that the Eastern Goldfields Terrane may have accreted to an older Murchison–Southern Cross granite–greenstone nucleus. The Archaean Norseman-Wiluna Greenstone Belt in

336-666: A middle Proterozoic mobile belt which leads east to the Musgrave Block . The Gascoyne complex and other metamorphic belts of this age including reactivation of the Yarlarweelor Gneiss and Narryer Gneiss Terrane , indicate prolonged multi-phased strike-slip movement (relative to the Yilgarn Craton margin) from the late Archaean through to neoproterozoic and even into the Palaeozoic. The Yilgarn Craton

392-790: A significant pulse of greenhouse gases, as the age broadly overlaps with the youngest glacial deposits. The Southern Cross Province lies in the central area of the Yilgarn craton. The Marda–Diemals greenstone belt in the Southern Cross Terrane can be divided into three layers: the lower greenstone belt (ca. 3.0 Ga) characterized by mafic volcanic rock and banded iron formation, a felsic-intermediate volcanism layer, and an upper sedimentary layer (ca. 2.73 Ga) of calc-alkaline volcanic (Marda Complex) and clastic sedimentary rocks ( Diemals Formation ). East–West orogeny (ca. 2730–2680 Ma) occurred in two stages; an earlier folding phase and

448-457: A solid residue very close in composition to Archean lithospheric mantle, but continental shields do not contain enough komatiite to match the expected depletion. Either much of the komatiite never reached the surface, or other processes aided craton root formation. There are many competing hypotheses of how cratons have been formed. Jordan's model suggests that further cratonization was a result of repeated continental collisions. The thickening of

504-1310: A term for mountain or orogenic belts . Later Hans Stille shortened the former term to Kraton , from which craton derives. Examples of cratons are the Dharwar Craton in India, North China Craton , the East European Craton , the Amazonian Craton in South America, the Kaapvaal Craton in South Africa, the North American Craton (also called the Laurentia Craton), and the Gawler Craton in South Australia. Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice

560-503: Is a series of polydeformed high-grade early Archaean metamorphic belts, composed predominantly of feldspathic leucocratic granulite gneisses, which represent some of the oldest crustal fragments on Earth. The Western Gneiss Terrane is distinct from the remainder of the Yilgarn Craton in that the latter has a predominance of metavolcanic rocks, both felsic and mafic , whereas the former consists of high-grade metasediments and gneisses of unknown protolith . The Western Gneiss Terrane

616-411: Is bounded on the east-southeast by the ~1,300 Ma Albany-Fraser Orogen , composed primarily of amphibolite to greenschist facies sedimentary protolith gneisses, migmatites and granites. The Albany-Fraser Orogen displays both subduction-related and prolonged strike-slip tectonic structures and is intimately interconnected with the other Proterozoic basins and mobile belts of Australia. The Yilgarn Craton

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672-568: Is considered to be peak granulite facies, but the majority has preserved peak amphibolite facies assemblages. In total, the Western Gneiss Terrane sub-blocks represent an earlier substrate upon which the majority of the Yilgarn Craton's about 2.70 to 2.55 Ga greenstone metavolcanic belts have been deposited and into which the voluminous Archaean trondhjemite-tonalite-granodiorite suite and trondhjemite - tonalite - diorite suite granites were emplaced. The Murchison Province

728-409: Is considered to have been produced during Caenozoic to Palaeocene tropical conditions, as evidenced by mottled duricrust which records fossilised tree roots, some over 60 million years old. Previous weathering events have been recorded in magnetically remnant ferruginous laterite of a Jurassic age, at about 180 Ma. The regolith of the Yilgarn impacts directly on the flora and fauna, as some of

784-685: Is continuing in several areas around Ravensthorpe, Balagundi, in the Yandall Belt, and the Duketon Belt, where large felsic volcanic packages are known to exist. The Yilgarn Craton may host up to 60% of the world's recoverable rare-earth elements , primarily in the Mount Weld Carbonatite . Smaller carbonatite occurrences at Ponton, near Laverton, and regionally within the eastern granite-gneiss and greenstone belts, may also prove economic. Craton The term craton

840-486: Is currently recovered from several areas in the Yilgarn Craton, although it is a much smaller set of mines than those in the Pilbara Craton . Iron ore is mined at Koolyanobbing, north of Kalgoorlie from hematite weathered banded iron formation , at Mount Gibson, Weld Range and Jack Hills in the Western Gneiss Terrane from hematite banded iron formation to produce direct-shipping ore. The Karara Iron Ore Project

896-714: Is exposed along the western half of the northern margin of the Yilgarn Craton as the Narryer Gneiss Terrane , a composite of heavily polydeformed feldspathic metagranite and metasedimentary amphibolite -grade gneisses and migmatites , dated at greater than 3.3 Ga and up to 3.8 Ga in age, flanked by the Murgoo Gneiss Terrane (2.95 Ga), as well as sheets of 2.75 Ga to 2.6 Ga granite, obducted ophiolite sheets (the Trillbar Complex) and some 2.4 Ga to 2.0 Ga Proterozoic gneiss belts. On

952-541: Is exposed in the western and northern third of the Yilgarn Craton. The Province is bounded by major transcrustal structures which separate it from the surrounding tectonic provinces of the craton and the Western Gneiss Belt. The Murchison Province Stratigraphy, after Watkins (1990), is divided into six basic structural-stratigraphic components - two greenstone belt metavolcanic-metasedimentary sequences and four suites of granitoids. The structural framework in

1008-674: Is partially covered by onlapping sedimentary basins of Palaeozoic and Phanerozoic age in the east and north-east, including the Canning Basin . It is bounded on the western edge by the Darling Scarp and Darling Fault which separate the Yilgarn Craton from the Perth Basin to the west, and is covered by several remnant sedimentary basins of Jurassic age such as the Collie Sub-Basin. The Yilgarn Craton also has

1064-452: Is strongly influenced by the inclusion of moisture. Craton peridotite moisture content is unusually low, which leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium and iron. Peridotites are important for understanding the deep composition and origin of cratons because peridotite nodules are pieces of mantle rock modified by partial melting. Harzburgite peridotites represent

1120-528: Is the oldest dated meteorite impact crater . The Yilgarn Craton appears to have been assembled between ~2.94 and 2.63 Ga by the accretion of a multitude of formerly present blocks or terranes of existing continental crust , most of which formed between 3.2 Ga and 2.8 Ga. This accretion event is recorded by widespread granite and granodiorite intrusions, which comprise over 70% of the Yilgarn craton; voluminous tholeiitic basalt and komatiite volcanism ; regional metamorphism and deformation as well as

1176-578: Is the only operational magnetite mine in the Yilgarn Craton, however, other magnetite iron ore deposits are being investigated as a source of magnetite ore in the Albany-Fraser Complex, where a large deposit is being proposed at Southdown. The Jack Hills, Weld Range and Mount Gibson banded iron formations, as well as banded iron formations around Yalgoo , are also considered potential sources of magnetite iron ore, although no operations are as yet running on this type of ore. Further away from

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1232-553: Is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons are composed of two layers: a continental shield , in which the basement rock crops out at the surface, and a platform which overlays the shield in some areas with sedimentary rock . The word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen , referring to stable continental platforms, and orogen as

1288-647: The Baltic Shield had been eroded into a subdued terrain already during the Late Mesoproterozoic when the rapakivi granites intruded. Calc-silicate A calc–silicate rock is a rock produced by metasomatic alteration of existing rocks in which calcium silicate minerals such as diopside and wollastonite are produced. Calc–silicate skarn or hornfels occur within impure limestone or dolomite strata adjacent to an intruding igneous rock . This rock -related article

1344-489: The Yarrabubba crater , which is the oldest dated meteorite impact crater , at 2229 ± 5 Ma . The crater is heavily eroded and no surface expression remains of the original structure. The primary trace is an elliptical aero- magnetic anomaly , measuring approximately 20 km by 11 km, as well as the presence of shock-recrystallised minerals. This impact may have ended the Huronian glaciation by climate forcing with

1400-406: The "cratonic regime". It involves processes of pediplanation and etchplanation that lead to the formation of flattish surfaces known as peneplains . While the process of etchplanation is associated to humid climate and pediplanation with arid and semi-arid climate, shifting climate over geological time leads to the formation of so-called polygenetic peneplains of mixed origin. Another result of

1456-481: The Archaean Norseman-Wiluna greenstone belt in the southeastern Yilgarn Craton. Kambalda type komatiitic nickel ore deposits are the primary source of nickel metal within the Yilgarn Craton. Copper, lead and zinc are currently mined from Golden Grove and the newly developed Jaguar zinc mine . Minor amounts of copper have been recovered from several copper-bearing gold deposits such as those in

1512-674: The Eastern Goldfield Province contains most of Australia's lode gold deposits, including the famous Kalgoorlie Golden Mile containing the Super Pit . These gold deposits are generally of large tonnage and are confined to the volcanic-intrusive-sedimentary sequences of the greenstone belts and not the granites. There is a pattern of gold distribution along the Archean Boulder-Lefroy shear zone. Extrusive komatiites (ultramafic volcanic rocks) occur along

1568-573: The Gullewa Greenstone Belt, at Burtville south of Laverton, at Granny Smith and elsewhere. The desert area encircling Kalgoorlie, with an area of 500,000 square kilometres, is theorised to host a 100 million tonne copper-zinc deposit. The geology of several volcanic belts in the Yilgarn Craton are strikingly similar to the world's great base-metal mines at Kidd Creek in Northern Ontario , Canada . Exploration for copper

1624-730: The Jimperding Gneiss Complex range in age from 3267 ± 30 Ma to 3341 ± 100 Ma, with metamorphic overgrowth dated at 3180 Ma. On the southwest of the Yilgarn Craton the Balingup Gneiss Complex is situated inboard from the Early Proterozoic Leeuwin Complex of metamorphic rocks. The Balingup Complex consists primarily of metasedimentary paragneiss, granite orthogneiss, with minor layers of calc-silicate , ultramafic and ortho-amphibolite gneiss. The metamorphic grade

1680-514: The Norseman-Wiluna Greenstone Belt. A change from volcanic-dominated to plutonic-dominated magmatism occurred in the Norseman-Wiluna Greenstone Belt approximately 2685–2675 Ma. Voluminous high-Ca granite intrusions occurred 2670–2655 Ma. Much of the gold was deposited between 2650–2630 Ma, with much of this associated with strike-slip reactivation of earlier faults (normal and reverse). An earlier gold event 2660-2655 Ma

1736-633: The Southern Cross and the greenschist metamorphic Murchison Provinces). Some greenstone belts and granites are as old as 3.1-2.9 Ga, and some are younger, at ~2.75-2.65 Ga. The craton is one of the distinct physiographic provinces of the West Australian Shield physiographic division, which comprises the Stirling-Mount Barren Block, Darling Hills, and Recherche Shelf sections. The Western Gneiss Terrane

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1792-528: The Yilgarn regolith is the oldest in the world, recording weathering events as early as the Cretaceous Period. This has been created by the generally subtropical latitudes and conditions of the Yilgarn craton, with minimal to no glaciation and generally flat topographical relief resulting in comparatively minor erosion. The regolith is extremely deeply weathered, in some areas completely converted to saprolite up to 100 metres below surface. This

1848-612: The coast, deposits of banded iron formation at Wiluna and Laverton are also under investigation, although infrastructure is considered too poor to render these deposits economic. The Yilgarn Craton is host to around 4% of the world's economically demonstrably recoverable reserves (EDR) of gold. Major gold deposits occur at Kalgoorlie, Kambalda, Mount Magnet, Boddington, Laverton and Wiluna, and are hosted in greenstone belts. These form linear belts of mafic, ultramafic and felsic volcanics, intercalated with sedimentary sequences, and have been deformed and metamorphosed. The mode of occurrence of

1904-502: The craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years. Rock fragments ( xenoliths ) carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites . These inclusions have densities consistent with craton composition and are composed of mantle material residual from high degrees of partial melt. Peridotite

1960-465: The cratons is similar to crustal plateaus observed on Venus, which may have been created by large asteroid impacts. In this model, large impacts on the Earth's early lithosphere penetrated deep into the mantle and created enormous lava ponds. The paper suggests these lava ponds cooled to form the craton's root. The chemistry of xenoliths and seismic tomography both favor the two accretional models over

2016-399: The crust associated with these collisions may have been balanced by craton root thickening according to the principle of isostacy . Jordan likens this model to "kneading" of the cratons, allowing low density material to move up and higher density to move down, creating stable cratonic roots as deep as 400 km (250 mi). A second model suggests that the surface crust was thickened by

2072-481: The crystalline residues after extraction of melts of compositions like basalt and komatiite . The process by which cratons were formed is called cratonization . There is much about this process that remains uncertain, with very little consensus in the scientific community. However, the first cratonic landmasses likely formed during the Archean eon. This is indicated by the age of diamonds , which originate in

2128-426: The depleted "lid" formed by the first layer. The impact origin model does not require plumes or accretion; this model is, however, not incompatible with either. All these proposed mechanisms rely on buoyant, viscous material separating from a denser residue due to mantle flow, and it is possible that more than one mechanism contributed to craton root formation. The long-term erosion of cratons has been labelled

2184-658: The emplacement of the vast majority of the craton's endowment in gold mineralisation. These accretion events occurred in several phases, probably by accretion of continental fragments separated by pauses in subduction , with renewed activity occurring episodically. The craton is primarily composed of approximately 2.8 billion year old (~2.8 Ga) granite-gneiss metamorphic terrain (the Southwestern Province and Western Gneiss Belt), and three granite- greenstone terrains (the North-East Goldfields,

2240-504: The gold mineralisation tends to be small- to medium-sized structurally controlled lodes, shears, and quartz veins. A key feature beneath many of the region's gold deposits are granite-cored domes at a range of scales. These provided an architecture that focussed fluid metals into the upper crust's depositional sites. Signatures of the mantle are found in many large deposits, including melts from metasomatised mantle wedge as well as lamprophyres. Debate continues whether these mantle rocks were

2296-471: The late Archean, accompanied by voluminous mafic magmatism. However, melt extraction alone cannot explain all the properties of craton roots. Jordan notes in his paper that this mechanism could be effective for constructing craton roots only down to a depth of 200 kilometers (120 mi). The great depths of craton roots required further explanation. The 30 to 40 percent partial melting of mantle rock at 4 to 10 GPa pressure produces komatiite magma and

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2352-468: The longevity of cratons is that they may alternate between periods of high and low relative sea levels . High relative sea level leads to increased oceanicity, while the opposite leads to increased inland conditions . Many cratons have had subdued topographies since Precambrian times. For example, the Yilgarn Craton of Western Australia was flattish already by Middle Proterozoic times and

2408-416: The northeastern Yilgarn craton was largely shaped by transpression that led to the development of folds, reverse faults, sinistral strike-slip movement on NNW-trending regional shear zones, followed by regional folding and shortening. The later occurred in overlapping tectonic processes. The first deformation event is poorly understood but appears to have involved N-S thrusting. The Murchison Province contains

2464-420: The plume model. However, other geochemical evidence favors mantle plumes. Tomography shows two layers in the craton roots beneath North America. One is found at depths shallower than 150 km (93 mi) and may be Archean, while the second is found at depths from 180 to 240 km (110 to 150 mi) and may be younger. The second layer may be a less depleted thermal boundary layer that stagnated against

2520-609: The post-Archaean events which have involved the Yilgarn Craton. The Yilgarn Craton is bound on the western side by the Perth Basin , of Jurassic age, and is separated from this basin by the Darling Fault . The Perth Basin is considered to be a rift fill basin formed on a passive margin. The Perth Basin is bound on the north by the Gascoyne Complex , Glengarry Basin and Yerrida Basin , which are all part of

2576-550: The roots of cratons, and which are almost always over 2 billion years and often over 3 billion years in age. Rock of Archean age makes up only 7% of the world's current cratons; even allowing for erosion and destruction of past formations, this suggests that only 5 to 40 percent of the present continental crust formed during the Archean. Cratonization likely was completed during the Proterozoic . Subsequent growth of continents

2632-460: The salt behind. The greenstone belts of the Yilgarn Craton include: The Yilgarn Craton is Australia's premier mineral province. It attracts more than half of Australia's minerals exploration expenditure, and produces two thirds of all gold and most of the nickel mined in Australia. The craton contains some 30% of the world's known gold reserves, about 20% of the world's nickel reserves, 80% of

2688-474: The soil is essentially fossilised. Much of the groundwater of the Yilgarn is hypersaline, with some being supersaturated in salt. This renders swathes of land barren, with significant salt lakes, and high saline water tables. The origin of this salt is thought to be from precipitation of sea salt carried over the Australian landmass for the past several dozen million years, and the high evaporation rate leaving

2744-515: The surrounding hotter, but more chemically dense, mantle. In addition to cooling the craton roots and lowering their chemical density, the extraction of magma also increased the viscosity and melting temperature of the craton roots and prevented mixing with the surrounding undepleted mantle. The resulting mantle roots have remained stable for billions of years. Jordan suggests that depletion occurred primarily in subduction zones and secondarily as flood basalts . This model of melt extraction from

2800-503: The typical 100 km (60 mi) thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere , and the low-velocity zone seen elsewhere at these depths is weak or absent beneath stable cratons. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy and a low intrinsic density. This low density offsets density increases from geothermal contraction and prevents

2856-455: The upper mantle has held up well with subsequent observations. The properties of mantle xenoliths confirm that the geothermal gradient is much lower beneath continents than oceans. The olivine of craton root xenoliths is extremely dry, which would give the roots a very high viscosity. Rhenium–osmium dating of xenoliths indicates that the oldest melting events took place in the early to middle Archean. Significant cratonization continued into

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2912-466: The western edge of the Yilgarn Craton, partially covered by Phanerozoic sedimentary basins and in faulted contact with the 2.7 Ga to 2.55 Ga Yilgarn tectonic domains, lies the Jimperding Gneiss Complex of 2.75 to 2.65 Ga age, composed primarily of micaceous quartzite , quartz-feldspar-biotite-garnet gneiss, andalusite and sillimanite schists , banded iron formation and other exotics, intruded by minor masses of porphyritic granite. Detrital zircons in

2968-594: The world's tantalum reserves, considerable iron ore , copper , zinc and minor lead reserves. The craton contains significant platinum , vanadium , hard-rock titanium and considerable iron ore resources. Mining is conducted mostly in the greenstone belts around mining centres such as Kalgoorlie , Kambalda , Norseman , Meekatharra and Wiluna , and minor centres such as Laverton , Leinster , Leonora and Southern Cross . Ore concentrates or finished product are transported by rail or road to Perth , Fremantle , Esperance , Albany or Geraldton . Iron ore

3024-444: Was associated with major extension (normal faulting and granite doming) resulting in the formation of late basins and the intrusion of mantle-derived magmas (syenites and Mafic-type granites/porphyries) and tight anticlockwise PTt paths. The Yilgarn Craton is bound on all sides by younger terranes of various ages, but predominantly of Proterozoic age. The boundaries between the various flanking terranes provide considerable evidence of

3080-473: Was by accretion at continental margins. The origin of the roots of cratons is still debated. However, the present understanding of cratonization began with the publication in 1978 of a paper by Thomas H. Jordan in Nature . Jordan proposes that cratons formed from a high degree of partial melting of the upper mantle, with 30 to 40 percent of the source rock entering the melt. Such a high degree of melting

3136-423: Was possible because of the high mantle temperatures of the Archean. The extraction of so much magma left behind a solid peridotite residue that was enriched in lightweight magnesium and thus lower in chemical density than undepleted mantle. This lower chemical density compensated for the effects of thermal contraction as the craton and its roots cooled, so that the physical density of the cratonic roots matched that of

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