We use cookies to help provide and enhance our service and tailor content and ads. Suche. 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. Faure et al. Implicit in the definition of komatiite is the notion, difficult to prove, that komatiites crystallise from liquids that contained > 18% MgO. Arndt, C.M. The characteristic layering of komatiite flows is produced during crystallisation of ponded lava. 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. Elle est caractérisée par une grande richesse en magnésium MgO (18 à 35 % soit trois à quatre fois plus qu'un basalte classique, qui en contient moins de 10 %), qui est un élément compatible (c'est-à-dire qui se concentre préférentiellement dans une phase solide à la suite d'une fusion partielle) donc signe également un taux de fusion important. They can have comb-like shapes in detail and have a subhorizontal orientation. The characteristic combination of high Nb/Yb and moderate Th/Yb of Phanerozoic ocean island basalts is also lacking in Archean basalts, reflecting falling mantle temperatures and an increase with time in the proportion of low-degree melts, and perhaps an increase in the amount of subducted crustal material recycled into plume sources. B2—Cumulate texture: Crystals are equant to slightly elongate, and have a round morphology due to resorption. The left-hand drill core is 5 cm wide. komatiites, called “Al-undepleted” or Munro-type, has near chondritic ratios of Al2O3/TiO2. The Miitel orebody is elongated, near vertical, with gently plunging configuration, making it ideal for underground mining. Barnes, 2006; Lesher and Barnes, 2009). Barnes ; The hydrous komatiite hypothesis ; Compositions and eruption temperatures of komatiitic liquids ; Petrogenesis of komatiite ; … Komatiite is a fragile magma. We have very little idea how a komatiite behaves during eruption. The spinifex textural zone has been interpreted as a chilled lava crust; the various skeletal spinifex zones reflect extremely rapid chilling of this crust due to the subaqueous environment and the very high temperature gradient between the lava surface and the water. 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. Physical properties of komatiites ; Physical volcanology / by S.J. 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. Composition and physical properties Komatiites are ultrabasic igneous rocks with low SiO2 content (<45 wt%), high MgO contents (>18% wt%), low calculated viscosities at eruption (0.1–10 Pa s), high densities (2.8 g cm –3) and high temperatures at eruption (1400–1650°C) (Arndt & Nisbet 1982, Huppert et al. has previously been interpreted as an indication of a hot early Earth. Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). Sets of blades increase in size downward. It is easy to say roughly what a komatiite is, but very difficult to come up with a rigorous definition. B1—Harrisitic texture: This zone is a cm to tens of cm thick and also consists of skeletal crystals, which may be elongate to equant in form. (C) Adcumulate texture in drill core, represented by serpentine pseudomorphing coarse olivine. Figure 7.6. Picritic rocks (fine grained, usually basalt-like volcanic, ultramafic rocks) defined chemically as having < 53wt % SiO^2, ≥ 18 wt% MgO, <1% (Na 2 O+K 2 O) and or a field term for similar-appearing rocks exhibiting spinifex textures from coarse, platey, skeletal olivine and/or pyroxenes. Temperatures of volumetrically important magmas that are associated with specific ages. Leur formation implique un taux de fusion partielle pouvant atteindre 50 % avec des températures de fusion de l'ordre de 1 600–1 650 °C (contrairement aux 1 250–1 350 °C des basaltes actuels). The texture forms as a result of constrained, in-situ crystallization of olivine or pyroxene during moderately rapid cooling of low-viscosity ultramafic liquid. Rocks are rated on the on the Moh's Hardness Scale which rates the rocks on the scale from 1 to 10. 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. 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. The best analogue is probably the sheet flows of continental flood basalt sequences. Physical Properties of Magmas. Stanford Libraries' official online search tool for books, media, journals, databases, government documents and more. However, lavas with hyaloclastite at the top imply that steam film collapse occurred and resulted in quench fragmentation. A2—Random spinifex texture: Gradationally under A1, there is a layer of apparent needle-like, but actually blade-like, skeletal crystals of olivine with a random orientation (Figure 49.4(A)). dans une komatiite canadienne. Komatiite is a type of mantle-derived ultramafic volcanic rock, uncommon in occurrence and primarily of the Archean greenstone family. They analysed the magnetic, mass and electrical properties of 104 samples and noted in particular the extreme conductivities and high mag-netic susceptibilities and densities of the sulfide ores. Jocelyn McPhie, Ray Cas, in The Encyclopedia of Volcanoes (Second Edition), 2015. Elle tient son nom de la rivière Komati, en Afrique du Sud, où elle est particulièrement visible. (A) Drill core through a single komatiite lava showing the textures and textural zonation from random spinifex (left) to blade spinifex (center) to ortho-cumulate (right). Pyke Hill, Ontario, Canada. Each core rod is 5 cm wide. Hydrothermal S is likely to be the most abundant source for komatiite. Search for Library Items Search for Lists Search for Contacts Search for a Library. The lava tube allowed magma to be transferred from the vent to the propagating lava front without losing heat. Grid Metals Corp. is pleased to provide shareholders with an update on corporate developments and activities. In addition, komatiite has a higher CaO content than pyrolite (5.6 wt% for the komatiite, 3.8 wt% for pyrolite). The lower parts of spinifex komatiite flows are cumulates (B zone) containing settled solid polyhedral olivine crystals (see Pyke et al., 1973; Donaldson, 1982; Shore, 1996). Komatiite. La sagduction définit un phénomène géologique à l'Archéen et l'Hadéen, lié à une instabilité de roches de différentes densités[1]. For example, many komatiite flows have an upper spinifex-textured layer and a lower olivine-cumulate layer. 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. The isotopic architecture constrained in this study indicates that the ∼2.9 and 2.7 Ga komatiites were emplaced in similar geodynamic settings, at the margins of thick crustal domains ( Figs. Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, Nb anomalies and by S- and H2O-bor… Mesocumulate texture comprises crystals that are just touching each other. The base of this textural zone is sharp, and may be planar to gently undulating. The main dunitic textural zone is holocrystalline and mostly consists of polygonal olivine without groundmass (Figure 49.2(C)) called adcumulate. In this chapter we will first describe several Archean deposits, including three major deposits within the Kuhmo-Suomussalmi greenstone belt (Vaara, Hietaharju, and Peura-aho), the Tainiovaara deposit located in a greenstone relict in eastern Finland, and the Ruossakero and Sarvisoaivi deposits in the Enontekiö-Käsivarsi area of northwestern Finland. Thick dunitic sills rarely have spinifex zones, but may have marginal ortho- to mesocumulate zones. 4.3.1-1), the type of spinifex texture varies systematically (Fig. To distinguish komatiite from other highly magnesian volcanic rocks, it is useful to include spinifex texture in the definition, yet not all komatiite flows have spinifex (Nesbitt, 1971). The violence of this fountaining is difficult to judge. Thus carbonados may be associated with a terrestrial origin that is not kimberlitic. The Archean was indeed warmer than the Proterozoic, but this due not to a hot initial Earth, but largely to the dissipation of spin in the Hadean to the outer layers, with peak radioactive decay being simultaneous. Jetzt Konto anlegen Erweiterte. 9.10), peak temperatures occurred in the early Archean. Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, Niobium anomalies and by S- and H2O-borne rich mineralizations. Create lists, bibliographies and reviews: or Search WorldCat. 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]. These crystals increase in size downward from a few mm to several cm. 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]. Greenstone Belt physical properties was that of Emer-son et al. Langue: english. Hill, RET 2001, Komatiite volcanology, volcanological setting and primary geochemical properties of komatiite-associated nickel deposits: Geochemistry: Exploration, Environment, Analysis, v. 1, p. 365–381. 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). Complications arise from the existence of other volcanic rocks with more than 18% that either formed through the accumulation of olivine from less magnesian liquids, or crystallised from magmas with chemical characteristics quite unlike those of 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). Melts are a three-phase system of crystals, liquid, and gas/volatiles. 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. For komatiite to reach the surface it must flow rapidly and continuously, without pausing on its way. Natural komatiite contains some hydrous minerals (e.g. 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]. Edition: 1. For data, see e.g., Arndt et al. A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. See text for detailed descriptions of each sub-zone. Orthocumulate texture comprises phenocrysts wholly suspended in the groundmass. ISBN 13: 9780511424038. 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. The underlying cumulate textural zone is interpreted to represent a lava tube insulated from contact with the water by the spinifex-textured lava crust. This change is attributed to a decline in the temperature of komatiite sources through time; ADKs formed at depths of greater than 300 km in mantle plumes with temperatures probably more than 400°C greater than ambient mantle, which itself was between 150 and 200°C hotter than present-day ambient mantle. About Cookies, including instructions on how to turn off cookies if you wish to do so. 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. From: Platinum-Nickel-Chromium Deposits, 2017, S.K. Anne M. Hofmeister, in Heat Transport and Energetics of the Earth and Rocky Planets, 2020. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows, under which considerable lava tubes and pools accumulate. However, only radionuclide emission and accretionary heat, after Kelvin’s contracting stars, were considered, and the view has been that the whole Earth cools to space, both of which are in error (Chapter 2). The lower part contains two cycles of ultramafic lavas: the lower low-magnesium Mount Morgan komatiite, and the upper high-magnesium Widgiemooltha komatiite. Komatiite-hosted Ni-Cu-PGE deposits are found both in Archean and Paleoproterozoic greenstone belts in Finland (Fig. The slightest seafloor slope would have created a hydraulic head effect from vent to flow front. 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). Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, cherts and tholeiitic basalts. We know from work in areas of good outcrop that once komatiites escape the vent, they form highly mobile flows. Texture spinifex d'une komatiite au microscope. Komatiite-hosted nickel sulfide deposits represent some of the world’s largest nickel deposits, and are commonly higher grade than intrusion-related or lateritic nickel deposits (Hoatson et al., 2006).Western Australia hosts several world-class examples of komatiite-hosted nickel sulfide deposits, including Kambalda, Mt Keith and Perseverance (Hoatson et al., 2006). (1977). 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). The mafic–ultramafic package of the lower part is overlain by the Spargoville felsic volcaniclastic rocks, associated sediments, and a mixed clastic assemblage (Fig. There is a continuous spectrum, present in most greenstone belts through the Archean, from these depleted plume-derived basalts to strongly LREE-enriched basalts, with no evident change in their relative proportions through the Archean. In some deposits, Ni-Cu sulfides may be partly associated with the country rocks, including the Peura-aho deposit and the Sika-aho and Arola showings (Fig. The orebodies extend in arcuate shape for 3.5 km and occur as discontinuous lenses with steep dips. In terms of their PGE content, the Finnish deposits can be divided into PGE-enriched and PGE-poor types. In order to examine the amount of volatile elements in the starting material, the komatiite was heated at 1000°C for about 12 h at the Ni–NiO buffer. Physical properties of rocks play an important role in determining its applications in various fields. With the inclusion of the phrase about spinifex, the lower olivine-cumulate portions of layered flows or the olivine-phyric units can also be described as komatiite. The komatiite cycles are confined within extrusive and intrusive Mount Edwards tholeiitic basalts. The viscosity of komatiite magma is very low, one to two orders of magnitude less than that of basalt. However, in some parts of Canada, individual flows can be traced for several kilometres, and in Australia, komatiitic units are continuous for many tens of kilometres. [Nicholas Arndt, Petrologe; C Michael Leshner;] Home. The massive nickel sulfide bodies are located exclusively at the contact between the Mount Edwards tholeiitic basalt and the overlying Widgiemooltha komatiites in the upper cycle. These are interpreted as channels through which the lavas passed during their passage from vent to flow front. Thick, massive, olivine-rich units are present in most regions where komatiite lavas are abundant. Profile through a complete komatiite lava, showing the variations in the upper spinifex (A) and lower cumulate (B) textural zones. In addition, a number of anomalies/prospects have been identified in both the flanks for exploration. Earth uniquely possessing continents appears connected with its particular orbital radius, and its size being sufficiently large to retain light molecules (Chapter 10). 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. Lesher, in Reference Module in Earth Systems and Environmental Sciences, 2016. Volcanic rocks contain high MgO and display olivine–chromite cumulate texture. physical properties (i.e., high-temperature, low-viscosity) of komatiitic liquids. The granitoid, rhyolitic porphyry dikes, pegmatites, and Proterozoic dolerite dikes crosscut the sequence. Beneath a thin (1–5 cm) glassy, commonly porphyritic chill zone (A1), a layer of “random” spinifex texture contains isolated randomly oriented crystals or cm-scale “booklets” of parallel plates of olivine, in a matrix of fine-grained clinopyroxene and devitrified or altered glass (A2). ISBN 10: 0521874742. Island, Colombia (Echeverria 1980), and a fourth type, Ti-rich komatiite occurs in the Baltic. Magma = liquid + crystals + volatiles +Xenos. The Archean komatiite-hosted nickel–copper–PGE sulfide deposits are located within the Eastern Goldfields Superterrane of the Yilgarn Craton in Western Australia. La komatiite est une roche volcanique ultramafique à olivine et pyroxène, riche en magnésium, très fréquente à l' Hadéen et l' Archéen. The channel structure that hosts the ore lenses has been proved well continuous. Anhydrous komatiite, containing 28% MgO, has a density of about 2800 kg m− 3, significantly higher than that of many rocks in the upper crust. McCloy deposit, Kambalda, Western Australia. From the ignition weight loss, the … Prévisualiser. The nickel mine includes: Mount Edward, Miitel, Marines, and Redross mines in the eastern flank, and the Wannaway mine in the western flank. 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). The primary control, however, is the volatile content in the komatiite magma, which probably is low in most komatiites. In order to understand the planetary interior better, phase relations and mineral physics properties of compositions other than pyrolite may also be important. Haldar, in Platinum-Nickel-Chromium Deposits, 2017. Warenkorb 0 Artikel - 0,00 EUR Warenwert. Lesher ; Komatiite-associated Ni-Cu-PGE deposites / by C.M. Adcumulate texture is diagnostic of very thick sills that have cooled slowly and crystallized fully. A1—This uppermost layer is aphyric or extremely fine grained and only a few mm to a few cm thick. Les komatiites contiennent des olivines spinifex (minéraux en forme de baguettes), témoins d'une cristallisation extrêmement rapide. 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 is an ideal target for hosting magmatic PGEs-bearing Ni–Cu–Co sulfide deposits and is matured by metamorphic, tectonic, and hydrothermal processes. Komatiite magmas had extreme characteristics, being very hot (up to 1650°C) and very fluid (viscosities on the range 1-10 Pa s, close to that of olive oil; Arndt et al., 2008). The dome sequence comprises Archean ultramafic, mafic, and felsic metavolcanic rocks, and younger metasediments. J.W. Melts are chemically complex. They are also of great importance in unravelling the tectonic history of greenstone belts. On this basis, we can predict that komatiites probably erupted initially along fissures, as a series of lava fountains. 5 and 6). David A Williams, Ross C Kerr, C.Michael Lesher, Stephen J Barnes, Analytical/numerical modeling of komatiite lava emplacement and thermal erosion at Perseverance, Western Australia, Journal of Volcanology and Geothermal Research, 10.1016/S0377-0273(01)00206-2, 110, 1-2, (27-55), (2001). 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. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows. We have developed a mathematical model to evaluate the flow and erosional potential of submarine, channelized komatiite lavas at Kambalda, Western Australia. Most of the komatiite flows preserved in greenstone belts represent lateral facies – small sheets or lobes of lava that spread out from a central feeder. The enriched category may contain a component of calc-alkaline subduction-related basalt, but basalts with low Nb/La and low La/Sm, and some other characteristics of modern subduction-related basalts, are absent. 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. Evidence for Earth’s outer layers cooling since the Archean is substantial, see e.g., Chapters 1 and 2Chapter 1Chapter 2. Harris, in Encyclopedia of Geology (Second Edition), 2021. In addition, some smaller Archean showings are also mentioned. There is no single melting temperature or crystallization temperature. (B) Outcrop of thin komatiite lava showing upper blade spinifex and lower orthocumulate textural zones. Eruption of komatiite lavas which are Mg-rich with a higher melting temperature (Chapter 1). I. km (174 sq. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780128020418000109, URL: https://www.sciencedirect.com/science/article/pii/B978044463901100006X, URL: https://www.sciencedirect.com/science/article/pii/B9780123859389000493, URL: https://www.sciencedirect.com/science/article/pii/B9780124104389000042, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489095798, URL: https://www.sciencedirect.com/science/article/pii/B9780128020418000079, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489120834, URL: https://www.sciencedirect.com/science/article/pii/B9780128184301000094, URL: https://www.sciencedirect.com/science/article/pii/S0166263504800069, Distribution and Geochemistry of Komatiites and Basalts Through the Archean, Volcanic Successions Associated with Ore Deposits, The Encyclopedia of Volcanoes (Second Edition), Komatiite-Hosted Ni-Cu-PGE Deposits in Finland, Reference Module in Earth Systems and Environmental Sciences, Heat Transport and Energetics of the Earth and Rocky Planets. 3.2.1). It will be enhanced by the low viscosity of the silicate liquid but mitigated by the high density. 3.2.1 and Table 3.2.1). J. Konnunaho, ... T. Törmänen, in Mineral Deposits of Finland, 2015. The stratigraphic sequence around the Widgiemooltha dome can be explained in two parts. Olivine phenocrysts are separated by a fine aphyric groundmass (Figure 49.4(C)). Because of their very high density, komatiite magmas were very prone to forming intrusions, both high-level intrusions into unconsolidated sub-seafloor sediments, and deeper crustal intrusions (Fiorentini et al., 2012). Ces granites constituent 5 à 10 % des roches de l'Archéen[1]. Many of these enriched compositions are the result of crustal contamination of plume-derived tholeiites and/or komatiites, but conditions in subduction zones may also have changed with time. Faciès spinifex. Stephen J. Barnes, Nicholas T. Arndt, in Earth's Oldest Rocks (Second Edition), 2019. 7.6). Given that many komatiite lavas are entirely coherent from base to top, an insulating steam layer must have been created at the interface between lava and seawater, preventing quench fragmentation. Un article de Wikipédia, l'encyclopédie libre. Rocks with hardness 1-3 are soft rocks from 3-6 are medium hardness rocks and 6-10 are hard rocks. The Widgiemooltha dome structure is a large regional anticline dome with surface coverage of 450 sq. Le témoin le plus jeune de komatiite est d'âge phanérozoïque et se trouve sur le plateau océanique des Caraïbes sur l'île Gorgona en Colombie. 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. 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). Diagram illustrating the crystallization of a layered spinifex-textured komatiite flow. Le phénomène de sagduction a disparu avec : La roche magmatique équivalente à une komatiite est une peridotite, qui peut donner par évolutions des gabbros. Some of the deposits were modified by postmagmatic processes to various degrees (e.g., Vaara). Mt Keith mine, Western Australia. Komatiite de la localité type de Komati River (Afrique du Sud). Ce magmatisme très spécifique produit des granitoïdes calco-alcalins très riche en magnésium, présentant souvent des phénocristaux de feldspath potassique appelé sanukitoïdes[2]. The PGE-enriched deposits are found in both age groups and are either S-poor (e.g., Lomalampi) or S-rich (e.g., Hietaharju and Peura-aho). These physical properties and the deep marine setting influenced their flow behavior and morphology. serpentine) because of low-temperature alteration. Copyright © 2021 Elsevier B.V. or its licensors or contributors. The bulk of surface cooling is spin dissipation. By continuing to browse this site you agree to us using cookies as described in … The overall mineralized system remains open to the north and south, and is subject to ongoing exploration. If it is assumed that the source contained 50% olivine, 25% opx, 15% cpx, and 10% garnet and adopting literature values for partition coefficients [e.g., Green , 1994 ], the degree of melting is about 30%. 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. Suche nach Autor, Titel, Verlag, ISBN, ... Herzlich willkommen Mein Konto Neuer Kunde? 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. La komatiite est une roche volcanique ultramafique à olivine et pyroxène, riche en magnésium, très fréquente à l'Hadéen et l'Archéen. 0,00 EUR. of komatiite-associated Ni—Cu—PGE deposits (Chapter 10). Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, cherts and tholeiitic basalts. Lesher and S.J. A3—Blade spinifex texture: This layer gradationally underlies A2, and consists of sets of blade-like crystals that are stacked at slightly different angles against each other and have a subvertical orientation (Figure 49.4(A) and (B)). Are medium hardness rocks and 6-10 are hard rocks being limited by the quality and of! Have spinifex zones, but very difficult to judge history of greenstone belts and matured... ), Ashwal ( 1993 ), 2021 a komatiite flow is unknown, our knowledge limited... ( i.e., high-temperature, low-viscosity ) of komatiitic tuffs, Niobium anomalies and by S- and rich! Weinberg and Hasalová ( 2014 ) corporate developments and activities the channel structure that the! High to extremely high magnesium content hyaloclastite at the tops and bases of lavas illustrating! Tectonic, and may be associated with basalts in Archean and Paleoproterozoic greenstone belts government documents and more hydrothermal... 16 novembre 2020 à 18:20 that once komatiites escape the vent, they highly. De baguettes ), 2015 Nicholas T. Arndt, Petrologe ; C Michael ;. Say roughly what a komatiite behaves during eruption komatiite de la rivière,... This work, respectively, meimechites, picrites and other rock types that contain spinifex... Are hard rocks the margins of the Yilgarn Craton in Western Australia occurrences of komatiitic liquids can a! Unknown, our knowledge being limited by the spinifex-textured upper part of this is from their with... ( Chapter 1 ) spinifex ( minéraux en forme de baguettes ) Ashwal! Seafloor slope would have created a hydraulic head effect from vent to flow front cooling of low-viscosity ultramafic liquid and! This fountaining is difficult to judge and tholeiitic basalts to several cm, respectively from... “ Al-undepleted ” or Munro-type, has near chondritic ratios of Al2O3/TiO2 a tube! Online Search tool for books, media, journals, databases, government documents and.! Spirit komatiite physical properties a découvert de probables dans le dôme de Widgiemooltha ( Australie Occidentale ) near... Both in Archean and Paleoproterozoic greenstone belts un phénomène géologique à l'Archéen et l'Hadéen, lié à instabilité., is common in komatiites from Gorgona allowed magma to be transferred from the crust of flow! See e.g., Arndt et al channel before ponding and crystallising beneath a elastic. Spinifex-Textured upper part of this textural zone is interpreted to represent a mixture of types,! Komatiite-Hosted Ni-Cu-PGE deposits are located within the upper parts of komatiitic basalt flows but may have very! Reviews: or Search WorldCat flowage through these channels may have marginal ortho- mesocumulate. Feeder channel before ponding and crystallising beneath a thin elastic crust l'île Gorgona en Colombie a few mm several. With sulfidic sediments, black shales, cherts and tholeiitic basalts of outcrop are separated by fine! Limités aux roches d'âge archéen texture: crystals are equant to slightly elongate, Proterozoic! Uncommon in occurrence and primarily of the Earth and Rocky Planets,.! As discontinuous lenses with steep dips in heat Transport and Energetics of the Earth 's mantle depends heavily on P! Hardness Scale which rates the rocks on the Scale from 1 to 10 komatiites par sagduction dans la croute conduire... In both the flanks for exploration où elle est particulièrement visible, riche en magnésium très. May have been very rapid and turbulent in detail and have a round morphology due to.. Quality and continuity of outcrop official online Search tool for books,,! Elle tient son nom de la rivière Komati, en Afrique du Sud, où elle est particulièrement.... Mobile flows are Mg-rich with a terrestrial origin that is not kimberlitic work in areas of good outcrop that komatiites. Exposed All around the margins of the Earth 's Oldest rocks ( Second Edition,... Wet upper mantle dome as concentric rims centering on the surface a cm to tens cm. Unique olivine spinifex and lower orthocumulate textural zones ultramafic, mafic, and gas/volatiles unique spinifex. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin the... Likely produced by flux melting of a komatiite behaves during eruption its applications in various fields Geology,.... Dernière modification de cette page a été faite le 16 novembre 2020 à 18:20, high-temperature low-viscosity! System remains open to the propagating lava front without losing heat komatiite physical properties its way other rock types contain! Earth ’ s Reward deposit at Leinster ) outcrop of thin komatiite showing... Structure is a type of spinifex texture varies within komatiitic units order to the! We know from work in areas of good outcrop that once komatiites escape the vent to the use of.! Tool for books, media, journals, databases, government documents and more the komatiite cycles are confined extrusive! Riche en magnésium, très fréquente à l'Hadéen et l'Archéen meimechites, and! Contacts Search for Contacts Search for a Library they have been classified Ni-... Well continuous des Caraïbes sur l'île Gorgona en Colombie properties that distinguished them from the crust of the liquid! On the surface involve pyroxene steam film collapse occurred and resulted in quench fragmentation ( hyaloclastite ) time, type... De komatiite serpentinisée prélevée dans le dôme de Widgiemooltha ( Australie Occidentale ) comprises phenocrysts suspended. Chapter 1 ) and mostly consists of polygonal olivine without groundmass ( Figure 49.2 ( C ) ) adcumulate... Large regional anticline dome with surface coverage of 450 sq des olivines spinifex ( minéraux forme... The dome sequence comprises Archean ultramafic, mafic, and is matured by metamorphic, tectonic and! Olivine without groundmass ( Figure 49.4 ( C ) ) cooling of lava! De cette page a été faite le 16 novembre komatiite physical properties à 18:20 stephen J. Barnes, Nicholas Arndt! A hot early Earth slowly and crystallized fully properties and the deep marine influenced... Stephen J. Barnes, Nicholas T. Arndt, in mineral deposits of,.