Pilbara Craton

The Pilbara Craton is an old and stable part of the continental lithosphere located in Pilbara, Western Australia.

The Pilbara Craton is one of only two pristine Archaean 3.6-2.7 Ga (billion years ago) crusts identified on the Earth, along with the Kaapvaal Craton in South Africa. Both locations may have once been part of the Vaalbara Supercontinent or the continent of Ur.

In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton.[1][2]

The earliest direct evidence of life on Earth may be fossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.[3][4]

IBRA 6.1 Pilbara
Australia map. Pilbara Region is coloured in red.

See also

References

  1. ^ Staff (9 May 2017). "Oldest evidence of life on land found in 3.48-billion-year-old Australian rocks". Phys.org. Retrieved 13 May 2017.
  2. ^ Djokic, Tara; Van Kranendonk, Martin J.; Campbell, Kathleen A.; Walter, Malcolm R.; Ward, Colin R. (9 May 2017). "Earliest signs of life on land preserved in ca. 3.5 Ga hot spring deposits". Nature Communications. 8: 15263. doi:10.1038/ncomms15263. PMC 5436104. PMID 28486437. Retrieved 13 May 2017.
  3. ^ Tyrell, Kelly April (18 December 2017). "Oldest fossils ever found show life on Earth began before 3.5 billion years ago". University of Wisconsin-Madison. Retrieved 27 December 2017.
  4. ^ Schopf, J. William; Kitajima, Kouki; Spicuzza, Michael J.; Kudryavtsev, Anatolly B.; Valley, John W. (2017). "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions". PNAS. 115 (1): 53–58. doi:10.1073/pnas.1718063115. PMC 5776830. PMID 29255053. Retrieved 27 December 2017.

Bibliography

  • Kato, Y.; Nakamura, K. (2003). "Origin and global tectonic significance of Early Archean cherts from the Marble Bar greenstone belt, Pilbara Craton, Western Australia". Precambrian Research. 125 (3–4): 191–243. doi:10.1016/S0301-9268(03)00043-3.
  • Oliver, N. H. S.; Cawood, P.A (2001). "Early tectonic dewatering and brecciation on the overturned sequence at Marble Bar, Pilbara Craton, Western Australia: dome-related or not?". Precambrian Research. 105 (1): 1–15. doi:10.1016/S0301-9268(00)00098-X.
  • Terabayashi, M.; Masada, Y.; Ozawa, H. (2003). "Archean ocean-floor metamorphism in the North Pole area, Pilbara Craton, Western Australia". Precambrian Research. 127 (1–3): 167–180. doi:10.1016/S0301-9268(03)00186-4.
  • Zegers, E.; de Wit, M. J.; Dann, J.; White, S. H. (1998). "Vaalbara, Earth's oldest assembled continent? A combined structural, geochronological, and palaeomagnetic test". Terra Nova. 10 (5): 250–259. CiteSeerX 10.1.1.566.6728. doi:10.1046/j.1365-3121.1998.00199.x.

External links

Australian Shield

The Australian Shield, also called the Western Australian Shield or Western Plateau, occupies more than half of the continent of Australia. The word shield is used because it refers to ancient, molten rock which has cooled and solidified. The Australian Shield has a characteristic depth of 4.5 km and an estimated age of 2.8 to 3.5 billion years. In places younger sedimentary rock covers the shield's Precambrian surface.

Chichester Range

The Chichester Range is a range in the Pilbara region of Western Australia.

The range rises abruptly from the coastal plain and is composed of rolling hills, escarpments, jagged peaks, gorges and winding tree-lined watercourses.The range is best described as an escarpment with a height of 350 metres (1,150 ft) forming a tableland behind that slope gently to the South until it runs into the Hamersley Range. The steep escarpment is defined by a jumble of weathered basalts and granophyresThe highest point of the Chichester Range is Mount Herbert with a height of 367 metres (1,204 ft), the peak takes about 45 minutes to climb and a car park is at the base of the peak. The peak is also on the route of the Chichester Range Camel trail, a tourist attraction that is operated on the range that finishes at Python's Pool. The range is part of the Millstream-Chichester National Park, along with Millstream station that is one of the few permanent watercourses in the area.

Geologically the range is made up of a mixture sandstone, igneous rocks, and mineralised banded iron formation, being part of the Pilbara Craton.

The area was named by the explorer Francis Thomas Gregory in 1861 after the Parliamentary Under-Secretary of State for the Colonies Chichester Fortescue.The traditional owners of the area are the Bailgu or Palyku peoples, who speak the Yinjibarndi language

The range is the basis of two major river basins; the Fortescue Basin and the Port Hedland coast Basin.

The Port Hedland Coast Basin is the catchment area for many rivers including the Harding River, Sherlock River, Yule River and Shaw River.

Crenadactylus pilbarensis

Crenadactylus pilbarensis is a species of gecko found in the Pilbara region of Australia. They resemble other species of the genus Crenadactylus, tiny clawless Australian geckos found across a large area of the continent, but has persisted as an ancient lineage in a region of the northwest.

Dome (geology)

A dome is a feature in structural geology consisting of symmetrical anticlines that intersect each other at their respective apices. Intact, domes are distinct, rounded, spherical-to-ellipsoidal-shaped protrusions on the Earth's surface. However, a transect parallel to Earth's surface of a dome features concentric rings of strata. Consequently, if the top of a dome has been eroded flat, the resulting structure in plan view appears as a bullseye, with the youngest rock layers at the outside, and each ring growing progressively older moving inwards. These strata would have been horizontal at the time of deposition, then later deformed by the uplift associated with dome formation.

Eastern Pilbara Craton

The Eastern Pilbara Craton is the eastern portion of the Pilbara Craton located in Western Australia. This region contains variably metamorphosed mafic and ultramafic greenstone belt rocks, intrusive granitic dome structures, and volcanic sedimentary rocks. These greenstone belts worldwide are thought to be the remnants of ancient volcanic belts, and are subject to much debate in today's scientific community. Areas such as Isua and Barberton which have similar lithologies and ages as Pilbara have been argued to be subduction accretion arcs, while others suggest that they are the result of vertical tectonics. This debate is crucial to investigating when/how plate tectonics began on Earth. The Pilbara Craton along with the Kaapvaal Craton are the only remaining areas of the Earth with pristine 3.6–2.5 Ga crust. The extremely old and rare nature of this crustal region makes it a valuable resource in the understanding of the evolution of the Archean Earth.

Gascoyne Complex

The Gascoyne Complex is a terrane of Proterozoic granite and metamorphic rock in the central-western part of Western Australia. The complex outcrops at the exposed western end of the Capricorn Orogen, a 1,000 km-long arcuate belt of folded, faulted and metamorphosed rocks between two Archean cratons; the Pilbara craton to the north and the Yilgarn craton to the south. The Gascoyne Complex is thought to record the collision of these two different Archean continental fragments during the Capricorn Orogeny at 1830–1780 Ma.

The Gascoyne Complex is separated from the Yilgarn Craton to the south by a major fault, the Errabiddy Shear Zone. To the east and northeast rocks of the complex are overlain unconformably by fine-grained Mesoproterozoic sedimentary rocks of the Edmund Basin and Collier Basin (formerly known as the Bangemall Basin). Several inliers of granite within these sedimentary basins also belong to the Gascoyne Complex. To the west, the Gascoyne Complex is overlain unconformably by sedimentary rocks of the Phanerozoic Carnarvon Basin. To the north, schist of the Gascoyne Complex probably pass with decreasing intensity of metamorphism into metamorphosed sedimentary rocks of the upper Wyloo Group.

The Gascoyne Complex is divided into two parts, the 1840–1620 Ma northern and central Gascoyne Complex, and the 2005–1970 Ma Glenburgh Terrane in the southern Gascoyne Complex. The two are separated by a major east-southeast trending fault, the Chalba Shear Zone. Rocks of the Glenburgh Terrane do not outcrop at surface north of the Chalba Shear Zone, but it is unclear as to whether or not rocks of this terrane floor all or part of the central and northern Gascoyne Complex.

The Gascoyne Complex has been shaped by four orogenies, the most important and widespread of which were the 1830–1780 Ma Capricorn Orogeny and the 1680–1620 Ma Mangaroon Orogeny. Both of these orogenies were marked by extensive folding, faulting and metamorphism, and were accompanied by the intrusion of large volumes of granite referred to as supersuites. The effects of the oldest orogeny, the 2005–1960 Ma Glenburgh Orogeny, although known only from the southern end of the complex, reflect a period of substantial granite magmatism and intense deformation and metamorphism. The Neoproterozoic Edmundian Orogeny mainly consists of the reactivation of earlier formed faults in the Gascoyne Complex, along with folding and faulting of the overlying Edmund and Collier basins.

Geyserite

Geyserite is a form of opaline silica that is often found around hot springs and geysers. It is sometimes referred to as sinter. Botryoidal geyserite is known as fiorite.

In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite uncovered in the Pilbara Craton of Western Australia.

Kaapvaal Craton

The Kaapvaal Craton (centred on Limpopo Province in South Africa), along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.

List of shields and cratons

A craton is an ancient part of the Earth's continental crust which has been more or less stable since Precambrian times. Cratons whose ancient rocks are widely exposed at the surface, often with relatively subdued relief, are known as shields. If the ancient rocks are largely overlain by a cover of younger rocks then the 'hidden' craton may be referred to as a platform.

Microbialite

Microbialite is a rock or benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of automicrite, or authigenic carbonate mud, and therefore it precipitates in situ instead of being transported and deposited. Been formed in situ, a microbialite can be seen as a type of boundstone where reef builders are microbes, and precipitation of carbonate is biotically induced instead of forming tests, shells or skeletons. Bacteria can precipitate carbonate both in shallow and in deep water (except for cyanobacyeria) and so microbialites can form regardless of the sun light.Microbialites were very important to the formation of Precambrian and Phanerozoic limestones in many different environments, marine and not. The best age for stromatolites was from 2800 Ma to 1000 Ma where stromatolites were the main constituents of carbonate platforms

Monzogranite

Monzogranites are biotite granite rocks that are considered to be the final fractionation product of magma. Monzogranites are characteristically felsic (SiO2 > 73%, and FeO + MgO + TiO2 < 2.4), weakly peraluminous (Al2O3/ (CaO + Na2O + K2O) = 0.98–1.11), and contain ilmenite, sphene, apatite and zircon as accessory minerals. Although the compositional range of the monzogranites is small, it defines a differentiation trend that is essentially controlled by biotite and plagioclase fractionation. (Fagiono, 2002). Monzogranites can be divided into two groups (magnesio-potassic monzogranite and ferro-potassic monzogranite) and are further categorized into rock types based on their macroscopic characteristics, melt characteristics, specific features, available isotopic data, and the locality in which they are found.

Otwayite

Otwayite, Ni2CO3(OH)2, is a hydrated nickel carbonate mineral. Otwayite is green, with a hardness of 4, a specific gravity of 3.4, and crystallises in the orthorhombic system.

Paleoarchean

The Paleoarchean (), also spelled Palaeoarchaean (formerly known as early Archean), is a geologic era within the Archaean Eon. It spans the period of time 3,600 to 3,200 million years ago—the era is defined chronometrically and is not referenced to a specific level of a rock section on Earth. The name derives from Greek "Palaios" ancient. The oldest ascertained life form of fossilized bacteria in microbial mats, 3,480 million years old, found in Western Australia, is from this era. The first supercontinent Vaalbara formed during this period.

During this era, a large asteroid, about 37 to 58 kilometres (23–36 mi) wide, collided with the Earth in the area of South Africa about 3.26 billion years ago, creating the features known as the Barberton greenstone belt.

Paleophycology

Paleophycology (also once known as paleoalgology) is the subdiscipline of paleobotany that deals with the study and identification of fossil algae and their evolutionary relationships and ecology.The field is very important in the science of paleolimnology as the algae leave many indicators of fossil ecosystems. Primary and most familiar are both fossil shells from diatoms and biogeochemical traces of algal pigments in lake sediments. These fossils are clues to changes in nutrient availability and ecology of lakes.

Some paleophycologists:

John P. Smol, a Canadian paleolimnologist

Stanley Awramik, an American Precambrian paleontologist

Bruno R. C. Granier, a French stratigrapher and micropaleontologist

Robert Riding, a British geologist and expert on calcareous algae and stromatolites

Vaalbara

Vaalbara was an Archean supercontinent consisting of the Kaapvaal Craton (now located in eastern South Africa) and the Pilbara Craton (now found in north-western Western Australia). E. S. Cheney derived the name from the last four letters of each craton's name. The two cratons consist of crust dating from 2.7 to 3.6 Gya, which would make Vaalbara one of Earth's earliest supercontinents.

Warrawoona Group

The Warrawoona Group is a geological unit in Western Australia containing putative fossils of cyanobacteria cells. Dated 3.465 Ga, these microstructures, found in archean chert, are considered to be the oldest known geological record of life on earth.

Western Plateau

The Western Plateau or sometimes referred as the Australian Shield, is Australia's largest drainage division and is composed predominantly of the remains of the ancient rock shield of Gondwana. It covers two thirds of the continent; 2,700,000 square kilometres of arid land including large parts of Western Australia, South Australia, and the Northern Territory. For comparison, it is roughly four times the size of, or the same size as the whole of continental Europe from Poland west to Portugal. It is Australia's largest drainage division.Rain rarely falls in this region and aside from a handful of permanent waterholes, surface water is absent at all times except after heavy rain. Most of the territory is flat sandy or stony desert with a sparse covering of shrubs or tussock grasses. Average rainfall varies from one area to another and is quoted at 100 to 350 mm per year (between 4 and 14 inches) but is highly unpredictable.

There are no permanent watercourses. The general trend is for run-off to flow inland, but there is insufficient rainfall to produce any marked drainage pattern.

Whim Creek Copper Mine

The Whim Creek Copper Mine is an operating copper oxide mine, located in the Pilbara region of Western Australia.

Yilgarn Craton

The Yilgarn Craton is a large craton that constitutes the bulk 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.

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