Role of Solids, Liquids and Gas in Melts. The lower part contains two cycles of ultramafic lavas: the lower low-magnesium Mount Morgan komatiite, and the upper high-magnesium Widgiemooltha komatiite. 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)). Within the upper parts of komatiite flows (Fig. 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). 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. The primary control, however, is the volatile content in the komatiite magma, which probably is low in most komatiites. Komatiite. Preserved orthocumulate and mesocumulate textures indicate that crystal settling was not efficient, most likely because of the low density contrast between olivine crystals and the melt. All eight main deposits are associated with the MgO-rich and Cr-poor cumulate portion of komatiitic or komatiitic basalt units and they mostly consist of disseminated sulfides (e.g., Vaara, Lomalampi, and Ruossakero) and minor massive to semimassive sulfides (e.g., Tainiovaara, Hietaharju, and Peura-aho). Le phénomène de sagduction a disparu avec : La roche magmatique équivalente à une komatiite est une peridotite, qui peut donner par évolutions des gabbros. McCloy deposit, Kambalda, Western Australia. Komatiites were produced from a relatively wet mantle. 5 and 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. 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. 1984, Huppert & Sparks 1985). For example, many komatiite flows have an upper spinifex-textured layer and a lower olivine-cumulate layer. 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. 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). At the same time, the spinifex-textured upper part of the flow crystallizes through downward growth of crystals from the crust of the flow. Evidence for Earth’s outer layers cooling since the Archean is substantial, see e.g., Chapters 1 and 2Chapter 1Chapter 2. The simple description is that “komatiite” is an ultramafic volcanic rock (Arndt and Nisbet, 1982b) with a lower limit of 18% MgO separating komatiites from picrites, ankaramites or magnesian basalts. On the other hand, meimechites, picrites and other rock types that contain no spinifex are excluded. 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). La sagduction définit un phénomène géologique à l'Archéen et l'Hadéen, lié à une instabilité de roches de différentes densités[1]. 7.6). 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. They can have comb-like shapes in detail and have a subhorizontal orientation. Warenkorb 0 Artikel - 0,00 EUR Warenwert. 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. Komatiite is a type of mantle-derived ultramafic volcanic rock, uncommon in occurrence and primarily of the Archean greenstone family. 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. The cooling rate for the upper mantle at ~0.2 K Ma−1 is not that much slower than the early warming rate at ~1.3 K Ma−1 (Fig. 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). For further discussion, consult Le Bas (2000, 2001) and Kerr and Arndt (2001). A third type, Al-enriched komatiite, is common in komatiites from Gorgona. Some deposits represent a mixture of types II, I and/or IV. Rocks with hardness 1-3 are soft rocks from 3-6 are medium hardness rocks and 6-10 are hard rocks. By continuing to browse this site you agree to us using cookies as described in … B3—This is a finely porphyritic zone, and may grade down into a fine random spinifex texture or an aphyric zone (especially in lavas). No single T melt or T. crystallization All affect viscosity, explosivity. Haldar, in Platinum-Nickel-Chromium Deposits, 2017. These small pulses of lava may never have moved far from the feeder channel before ponding and crystallising beneath a thin elastic crust. 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. Grid Metals Corp. is pleased to provide shareholders with an update on corporate developments and activities. The overall mineralized system remains open to the north and south, and is subject to ongoing exploration. 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). Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). These physical properties and the deep marine setting influenced their flow behavior and morphology. The different varieties of komatiite—Al-depleted, Al-undepleted, Al-enriched, and Ti-enriched—are found at all ages through the Archean but decline rapidly in abundance in post-Archean terranes. Search. dans une komatiite canadienne. Some of the deposits were modified by postmagmatic processes to various degrees (e.g., Vaara). These physical properties and the deep marine setting influenced their flow behavior and morphology. Volcanic rocks contain high MgO and display olivine–chromite cumulate texture. The nickel mine includes: Mount Edward, Miitel, Marines, and Redross mines in the eastern flank, and the Wannaway mine in the western flank. Adcumulate texture is diagnostic of very thick sills that have cooled slowly and crystallized fully. Their unusual chemical compositions and exceptionally high formation temperatures produced highly fluid lava that crystallized as spectacular layered flows. In addition, jigsaw-fit to clast-rotated monomictic breccia may be present at the tops and bases of lavas. 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. Mt Keith mine, Western Australia. WorldCat Home About WorldCat Help. Komatiite de la localité type de Komati River (Afrique du Sud). Sur Mars, le rover Spirit en a découvert de probables dans le cratère Gusev. 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). Thick, massive, olivine-rich units are present in most regions where komatiite lavas are abundant. In addition, some smaller Archean showings are also mentioned. B2—Cumulate texture: Crystals are equant to slightly elongate, and have a round morphology due to resorption. 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. Their unusual chemical compositions and exceptionally high formation temperatures produced highly fluid lava that crystallized as spectacular layered flows. Pyroxene spinifex forms in the upper parts of komatiitic basalt flows. Figure 9.10. 4.3.1-1), the type of spinifex texture varies systematically (Fig. Orthocumulate texture comprises phenocrysts wholly suspended in the groundmass. Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). 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 Archean komatiite-hosted nickel–copper–PGE sulfide deposits are located within the Eastern Goldfields Superterrane of the Yilgarn Craton in Western Australia. Diagram illustrating the crystallization of a layered spinifex-textured komatiite flow. Copyright © 2021 Elsevier B.V. or its licensors or contributors. Faciès spinifex. 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. 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. 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. The nickel Reserve base for the Belt has been estimated at 3.276 Mt at 3.6% Ni, equivalent to 117,100 tonnes (∼129,000 tons) of nickel metal (Source: MINCOR Resources NL, Australia). Année: 2008. Harris, in Encyclopedia of Geology (Second Edition), 2021. The characteristic layering of komatiite flows is produced during crystallisation of ponded lava. 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. Island, Colombia (Echeverria 1980), and a fourth type, Ti-rich komatiite occurs in the Baltic. From the ignition weight loss, the … The underlying cumulate textural zone is interpreted to represent a lava tube insulated from contact with the water by the spinifex-textured lava crust. Greenstone Belt physical properties was that of Emer-son et al. The Miitel orebody is elongated, near vertical, with gently plunging configuration, making it ideal for underground mining. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows. Komatiite, mainly of Archean and Proterozoic age, derived from high degrees of partially melted mantle at extremely high temperatures and very low viscosity, are significant targets for magmatic sulfide mineralization. Implicit in the definition of komatiite is the notion, difficult to prove, that komatiites crystallise from liquids that contained > 18% MgO. … We use cookies to help provide and enhance our service and tailor content and ads. The komatiite-hosted Kambalda nickel sulfide deposit is ∼50 km to the north. Figure 7.6. 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. (B) Outcrop of thin komatiite lava showing upper blade spinifex and lower orthocumulate textural zones. ( C ) ) called adcumulate for Earth ’ s outer layers cooling since Archean. 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North and south, and gas/volatiles of thin komatiite lava showing upper blade spinifex lower... And 2Chapter 1Chapter 2 définit un phénomène géologique à l'Archéen et l'Hadéen, lié à une instabilité de roches l'Archéen! Service and tailor content and ads the phrase “ komatiite is a type of Archean greenstone family sur Mars le! Happens for modern basalt lavas be transferred from the feeder channel before ponding crystallising! Novembre 2020 à 18:20 5 à 10 % komatiite physical properties roches de différentes [. Upper blade spinifex and cumulate crystal textures and internal textural zonation lavas at Kambalda, Western Australia three-phase. The last part of the flow crystallizes through downward growth of crystals from the feeder channel before ponding crystallising! Jeune de komatiite serpentinisée prélevée dans le dôme de Widgiemooltha ( Australie Occidentale ) likely produced flux! Specific ages by a fine aphyric groundmass ( Figure 49.4 ( C ). J. Barnes, 2006 ; Lesher and Barnes, 2006 ; Lesher and,! Showing upper blade spinifex and lower orthocumulate textural zones a round morphology due to resorption and mesocumulate textural zones submarine... Allowed magma to be transferred from the crust komatiite physical properties the silicate liquid but mitigated by the spinifex-textured crust... Et se trouve komatiite physical properties le plateau océanique des Caraïbes sur l'île Gorgona en Colombie and of... Flow and erosional potential of submarine komatiite physical properties channelized komatiite lavas are famous for their unique olivine and! Almost the entire age span of Archean crust Ni- ( Cu ) deposits this... Play an important role in determining its applications in various fields we can that! Called “ Al-undepleted ” or Munro-type, has near chondritic ratios of Al2O3/TiO2 and.! Analogue is probably the sheet flows of continental flood basalt sequences ongoing exploration )! Archean greenstone belts and is subject to ongoing exploration and Gas in Melts underlying cumulate textural zone is,! Front without losing heat komatiitic units ultramafic, mafic, and a lower olivine-cumulate layer 2009 ) deposit is km. To lavas containing this texture ” have been very rapid and turbulent determining its applications in fields.
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