komatiite physical properties

Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, Niobium anomalies and by S- and H2O-borne rich mineralizations. Magma = liquid + crystals + volatiles +Xenos. Volcanic rocks contain high MgO and display olivine–chromite cumulate texture. The width varies between 2 and 10 m. The total postproduction reserves and resources at Miitel Mine stand at 629,000 tonnes (∼693,000 tons) garaging 3.1% Ni [19,500 tonnes (∼21,500 tons) of nickel metal] as of June 2015. Also shown are the dry melting temperature for 3.5 Ga ADK from Barberton and 2.7 Ga AUK from the Belingwe greenstone belts (Nisbet et al. Other articles where Komatiite is discussed: Africa: General considerations: The rock type komatiite is particularly diagnostic of those volcanic sequences and is almost exclusively restricted to the Archean Eon. Ce phénomène explique la tectonique verticale au milieu de plaque tectonique à l'Archéen et l'Hadéen ou il n'existe pas d'épaississant crustal comme on peut l'observer aujourd'hui conduisant à une tectonique verticale[1]. The Dachine komatiite of French Guiana contains single diamonds of over 500 μm in size, which are predominantly resorbed octahedrons and cubes with typical surface characteristics indicative of a deep origin. Pages: 488 / 489. Les masses basaltiques ayant une densité trop faible pour initier une sagduction, seules les komatiites, avec une densité de 3,3 permettent d'initier le phénomène[1]. However, lavas with hyaloclastite at the top imply that steam film collapse occurred and resulted in quench fragmentation. Preservation of substantial volumes of gneisses by ~2.9 Ga, shortly after the bulk of komatiite production, cooroborates the timeing of stabilization and radial cooling of the outer layers. Stephen J. Barnes, Nicholas T. Arndt, in Earth's Oldest Rocks (Second Edition), 2019. 7.6). 2 – 6 ). The primary liquid is assumed to have had 28% MgO, and at this value, Barberton‐type komatiite has about 25 ppm Zr, and Munro‐type komatiite has about 15 ppm Zr. It is far hotter than surrounding rocks, especially when it passes through the lithosphere, and it has a strong capacity to interact with them. Année: 2008. However, when komatiite traverses or erupts onto a granitic substrate, as in the Kambalda area in Western Australia, the high density of mantle rocks lower in the liquid column must counterbalance the low density of the granites. mi). l'évolution de la chimie du manteau conduisant à la disparition de mise en place de komatiites vers -2,5 Ga, et l'épaississement des plaques lithosphériques qui a augmenté durant l’Archéen. The Widgiemooltha dome structure is a large regional anticline dome with surface coverage of 450 sq. A proportion of these are komatiite-derived, but the prevalent basalt type throughout the Archean is a characteristic plagioclase-saturated low-MgO tholeiite with rare earth element patterns that are nearly flat or slightly depleted in light elements (light rare earth element [LREE]). Komatiite-hosted Ni-Cu-PGE deposits are found both in Archean and Paleoproterozoic greenstone belts in Finland (Fig. (1999) for the Rocky’s Reward deposit at Leinster. La plupart sont vieilles de plus de deux milliards d'années et on ne connaît en raison de leur âge que des komatiites métamorphisées (en toute rigueur des métakomatiites). Affleurements et répartitions dans le temps, Les komatiites à l'origine de la sagduction, Roches volcaniques (classification chimique), https://fr.wikipedia.org/w/index.php?title=Komatiite&oldid=176664978, Portail:Sciences de la Terre et de l'Univers/Articles liés, licence Creative Commons attribution, partage dans les mêmes conditions, comment citer les auteurs et mentionner la licence. Orthocumulate texture comprises phenocrysts wholly suspended in the groundmass. For komatiite to reach the surface it must flow rapidly and continuously, without pausing on its way. We use cookies to help provide and enhance our service and tailor content and ads. Anne M. Hofmeister, in Heat Transport and Energetics of the Earth and Rocky Planets, 2020. Mt Keith mine, Western Australia. These small pulses of lava may never have moved far from the feeder channel before ponding and crystallising beneath a thin elastic crust. Within the upper parts of komatiite flows (Fig. Island, Colombia (Echeverria 1980), and a fourth type, Ti-rich komatiite occurs in the Baltic. ISBN 10: 0521874742. Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, Nb anomalies and by S- and H2O-bor… Faure et al. (1977). These breccias are autoclastic and commonly produced by quench fragmentation (hyaloclastite). … Create lists, bibliographies and reviews: or Search WorldCat. A viscosity of 1–2 Pascal-seconds was estimated for dry komatiite containing 28% MgO, which compares with 500–1000 Pascal-seconds for typical basalts. The Archean komatiite-hosted nickel–copper–PGE sulfide deposits are located within the Eastern Goldfields Superterrane of the Yilgarn Craton in Western Australia. Each core rod is 5 cm wide. Texture spinifex d'une komatiite au microscope. The cooling rate indicates an average loss of heat from the upper mantle of ~3.8 TW, which is compatible with our estimate of today's radioactive power as 1.5 TW (Section 9.2.5). km (174 sq. Implicit in the definition of komatiite is the notion, difficult to prove, that komatiites crystallise from liquids that contained > 18% MgO. Sur Terre, les komatiites sont très rares et essentiellement limités aux roches d'âge archéen. of komatiite-associated Ni—Cu—PGE deposits (Chapter 10). komatiites, called “Al-undepleted” or Munro-type, has near chondritic ratios of Al2O3/TiO2. From magma temperatures (Fig. Envoyer vers Kindle ou courriel . These crystals increase in size downward from a few mm to several cm. Fichier: PDF, 16,57 MB. Stanford Libraries' official online search tool for books, media, journals, databases, government documents and more. Komatiites have low silicon , potassium and aluminium , and high to extremely high magnesium content. The heterogeneous nature of komatiite magmatism at ∼2.9 and 2.7 Ga is consistent with the impingement of a mantle plume onto lithosphere of variable thickness (Figs. For komatiite to reach the surface and erupt, it must fill a continuous liquid column within rocks whose average density is greater than that of the komatiite itself. Diagram illustrating the crystallization of a layered spinifex-textured komatiite flow. Komatiite magmas were very high temperature magmas (1400–1650 °C), and had ultralow viscosities (0.1–10.0 Pa s) and very high density (2800 kg m-3) (Huppert and Sparks, 1985). serpentine) because of low-temperature alteration. Cette différence abouti à une enfoncement de l'unité plus dense à état solide (komatiites) dans une unité moins dense, fonctionnement inverse du phénomène de diapirisme[1]. Komatiite is a key reference for researchers and advanced students interested in petrology, Archaean geology, economic geology, and broader questions about the evolution of the Earth's crust and mantle. In komatiitic basalts, such textures can also involve pyroxene. The major deposits are situated on the eastern flank of the Widgiemooltha dome within the fault-bounded Coolgardie domain of the Kalgoorlie terrane (Vaillant et al., 2015b). The underlying layer of platy olivine spinifex has an organised structure wherein arrays of large bladed olivine crystals, possibly metres long, are oriented roughly perpendicular to the flow top (A3), forming sheaf-like structures that fan out from flow tops and serve as top indicators. From the ignition weight loss, the … It will be enhanced by the low viscosity of the silicate liquid but mitigated by the high density. The best analogue is probably the sheet flows of continental flood basalt sequences. Sur Mars, le rover Spirit en a découvert de probables dans le cratère Gusev. The silica rich gneisses were likely produced by flux melting of a wet upper mantle. These are interpreted as channels through which the lavas passed during their passage from vent to flow front. Polyhedral olivine grains, which were present before eruption or crystallized during flowage, settle to the base of the flow or crystallize in situ to form the lower cumulate layer (Figure 6). Jocelyn McPhie, Ray Cas, in The Encyclopedia of Volcanoes (Second Edition), 2015. Turbulence further suggests that komatiite flows were thermally mixed and homogeneous, and that there were no thermal or compositional heterogeneities or velocity variations across the width or the depth of the flows, which allows us to reduce the cooling model to one dimension. In addition, a number of anomalies/prospects have been identified in both the flanks for exploration. Flowage through these channels may have been very rapid and turbulent. Although these diamonds are not polycrystalline, their isotopic characteristics are very similar to those found for carbonados. MINCOR Resources NL, Australia, discovered the North Miitel orebody in 2002 and the South Miitel orebody in 2005, and has continued to extend these discoveries ever since. L'enfoncement de komatiites par sagduction dans la croute peut conduire à sa fusion et sa contamination par un magma de TTG[1]. The primary control, however, is the volatile content in the komatiite magma, which probably is low in most komatiites. B3—This is a finely porphyritic zone, and may grade down into a fine random spinifex texture or an aphyric zone (especially in lavas). Their carbon isotope values have a mode of − 24‰ and whilst most of the diamonds are Type II, (see color for a definition), a mode of − 28‰ has been determined for nitrogen isotopes (δ15N). The main dunitic textural zone is holocrystalline and mostly consists of polygonal olivine without groundmass (Figure 49.2(C)) called adcumulate. Al-depleted komatiites (ADKs) are prevalent in older Archean terranes, decline sharply in proportion to other komatiite types after about 2.7 Ga, and disappear altogether in the Proterozoic. Figure 6. Temperatures of volumetrically important magmas that are associated with specific ages. The left-hand drill core is 5 cm wide. Komatiite is also a relatively dense magma. Komatiites were produced from a relatively wet mantle. When it flows rapidly past crustal rocks, it is capable of thermally eroding and assimilating them; if it ponds in a crustal magma chamber, it will fractionally crystallise and lose its ultramafic character. Thick dunitic sills rarely have spinifex zones, but may have marginal ortho- to mesocumulate zones. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows. Les komatiites contiennent des olivines spinifex (minéraux en forme de baguettes), témoins d'une cristallisation extrêmement rapide. Role of Solids, Liquids and Gas in Melts. The dome sequence comprises Archean ultramafic, mafic, and felsic metavolcanic rocks, and younger metasediments. 4.3.3-2d). Sulfur saturation occurs when silicate magma exceeds its capacity to dissolve S and/or contaminated in excess by a large quantity of S to the magma from country rocks. Haldar, in Platinum-Nickel-Chromium Deposits, 2017. The komatiite-hosted Kambalda nickel sulfide deposit is ∼50 km to the north. Their unusual chemical compositions and exceptionally high formation temperatures produced highly fluid lava that crystallized as spectacular layered flows. On the other hand, meimechites, picrites and other rock types that contain no spinifex are excluded. Komatiite lavas would have been turbulent mostly near the vent, becoming laminar farther away (Cas et al., 1999), similar to carbonatite lavas at Oldoinyo Lengai volcano in Tanzania. 9.9). An example of the first type is a phenocryst-charged basaltic liquid (a picrite according to some definitions); an example of the second is meimechite (Arndt et al., 1995), a rare alkaline lava with unusual major and trace element composition. Hill, RET, Barnes, SJ, Gole, MJ and Dowling, SE 1995, The volcanology of komatiites as deduced from field relationships in the Norseman- Thin syn-depositional komatiite sills that were intruded into unconsolidated sediment may have all of the above zones as well as sediment-matrix komatiite breccia (peperite) along the contacts. Planar to gently undulating may also be important en Afrique du Sud, où elle est visible! 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komatiite physical properties 2021