Spinifex is one of the most spectacular magmatic textures. B) Schematic Petrographic Thin Sections : Petrographic thin section catalog page 2 . There are two geochemical classes of komatiite; aluminium undepleted komatiite (AUDK) (also known as Group I komatiites) and aluminium depleted komatiite (ADK) (also known as Group II komatiites), defined by their Al2O3/TiO2 ratios. Komatiites are rare, ultra-high-temperature (∼1,600 °C) lavas that were erupted in large volumes 3.5–1.5 bya but only very rarely since. Geochemical analysis of five (5) rock samples taken from talc bodies outcropped from both sides of the Ifewara Shear Zone (ISZ) revealed magnesia (MgO) > 18% and Al 2O 3/TiO 2 values ~ 40. This restriction in age is thought to be due to cooling of the mantle, which may have been 100 – 250°C hotter during the Archean (4.0 to 2.5 billion years ago). please bear this in mind when purchasing. The factor controlling the mineral assemblage is the partial pressure of carbon dioxide within the metamorphic fluid, called the XCO2. Mahmoud Awad 10,666 views. Davies, G. F. 1999. This is a photomicrograph of a small, thin section of komatiite lava. In the distal thin flow facies, Komatiite was named for its type locality along the Komati River in South Africa.. ISBN 10: 0521874742. Boninite magmatism is similar to komatiite magmatism but is produced by fluid-fluxed melting above a subduction zone. The usual cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are also possible (though rarer). Komatiite is extremely rich in magnesium and low in silica. Рік: 2008. Veja grátis o arquivo Komatiite enviado para a disciplina de Psicologia Jurídica Categoria: Outro - 10 - 74073646. Lower temperature mantle melts such as basalt and picrite have essentially replaced komatiites as an eruptive lava on the Earth's surface. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. They are the signature rock type of a hotter early Earth. def. At that time, about a year before Viljoen & Viljoen's (1969a, 1969b) papers defining komatiite as a new type of volcanic rock, most of the petrological community shared Bowen's doubts about the existence of ultramafic magmas (Bowen, 1956). Image by Andy Tindle (Virtual Microscope). Another line of evidence is that the MgO content of olivines formed in komatiites is toward the nearly pure MgO forsterite composition, which can only be achieved in bulk by crystallisation of olivine from a highly magnesian melt. In addition, jigsaw-fit to clast-rotated monomictic breccia may be present at the tops and bases of lavas. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Pyke Hill, Ontario. Aegirine syenite. Rare mineralogy in Thin Section . Komatiite was named for its type locality along the Komati River in South Africa, and ... leaving extremely thin lava flows (down to 10 mm thick). Hill R.E.T, Barnes S.J., Gole M.J. and Dowling S.E. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. of the samples (1/3 of the thin sections contain fresh olivine relicts) enhanced the quality and the confidence over the actual and future results on the chromite chemistry. These images were taken from the thin section being offered. Komatiites are associated with nickel and gold deposits in Australia, Canada, South Africa and most recently in the Guiana shield of South America. Сторінки: 488 / 489. Carbonate Origins. Powdery alteration products from the experiments at both temperatures were embedded in Epofix resin, and thin sections were made of these. The more magnesian-rich olivine-rich flow base facies tend to be free from tremolite and chlorite mineralogy and are dominated by either serpentine-brucite +/- anthophyllite if hydrated, or talc-magnesite if carbonated. Pages. Figure 46.3. When robotic exploration of Mars began, many scientists expected to see large sedimentary deposits … 2012. Actinolite sometimes occurs as thin splintery inclusion s inside quartz crystals. 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. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. This has been heavily altered and contains secondary prehnite and garnets. Komatiite N.T. Figure 3. r/geology: The scientific study of the origin, history, and structure of the Earth. These breccias are autoclastic and commonly produced by quench fragmentation (hyaloclastite). Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K2O and other incompatible elements. Section ES (Eastern Section: Alexo Mine) is the location of the stratigraphic column in Figure 46.3B. S. A. Svetov, A. I. Svetova, and H. Huhma, 1999. Modified from Thurston et al., 2008. [1] Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Migmatite: A heterogeneous silicate rock with properties of both igneous and metamorphic rocks. Economic nickel-mineralised olivine adcumulate bodies may represent a form of sill-like conduit, where magma pools in a staging chamber before erupting onto the surface. Journal of Petrology, 41(10), 1467-1470. Robin-Popieul, C. C. M., Arndt, N. T., Chauvel, C., Byerly, G. R., Sobolev, A. V., & Wilson, A. 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. 1:48 . The pristine volcanic mineralogy of komatiites is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene, anorthite (An85 and upwards) and chromite. The typical mineralogical variation is from a flow base composed of olivine cumulate, to a spinifex textured zone composed of bladed olivine and ideally a pyroxene spinifex zone and olivine-rich chill zone on the upper eruptive rind of the flow unit. Contact us. Komatiites", "An Origin for Harrisitic and Granular Olivine in the Rum Layered Suite, NW Scotland: a Crystal Size Distribution Study", "Fault-Controlled Magma Ascent Recorded in the Central Series of the Rum Layered Intrusion, NW Scotland", https://en.wikipedia.org/w/index.php?title=Komatiite&oldid=998679848, Short description is different from Wikidata, Articles needing additional references from November 2020, All articles needing additional references, Creative Commons Attribution-ShareAlike License, A1 – pillowed and variolitic chilled flow top, often grading and transitional with sediment, A2 – Zone of quickly chilled, feathery acicular olivine-clinopyroxene-glass representing a, A3 – Olivine spinifex sequence composed of sheaf and book-like olivine spinifex, representing a downward-growing crystal accumulation on the flow top, B1 – Olivine mesocumulate to orthocumulate, representing a harrisite grown in flowing liquid melt, B2 – Olivine adcumulate composed of >93% interlocking equant olivine crystals. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). compared with altered ultramafic – Komatiite. Arndt, N., Lesher, C. M., & Barnes, S. J. 2000. 2008. Le Bas, M. J. Komatiite (/ k oʊ ˈ m ɑː t i. aɪ t /) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with magnesium oxide content higher than 18% by weight. Analogue of : Early earth, Mars, Igneous, Water weathering. The subsequent magmatism, being higher silica melts, tends to form a more typical shield volcano architecture. Entrar; Criar perfil grátis; 489 pág. Summary. [12][13] Harrisites are known to form megacrystal aggregates of pyroxene and olivine up to 1 metre in length. If XCO2 is above 0.5, the metamorphic reactions favor formation of talc, magnesite (magnesium carbonate), and tremolite amphibole. BIOTITE thin section under Polarizing Microscope - Duration: 1:48. (2008), This page was last edited on 6 January 2021, at 14:55. In fact, they form highly complicated, skele-tal megacrysts that are coarse-grained equivalents of the feathery dendritic or spherulitic grains interstitial to olivine in peridotitic komatiite lavas (Fleet, 1975). Cambridge: Cambridge University Press. (A) A change in magnetite (black) concentration represents the crust of pillows. Komatiite, Komati, Barberton, Spinifex texture - extreme acicular olivine phenocrysts, $92.00.. Dunite Sierra de Ronda Benahavis, Spain, $48.00..Dunite, Spain.. Impact melt rock Sudbury Basin, Ontario Canada Sudbury Crater, Impact melt, $48.00. The mineralogy of a komatiite varies systematically through the typical stratigraphic section of a komatiite flow and reflects magmatic processes which komatiites are susceptible to during their eruption and cooling. B zones are poorly developed to absent, as not enough through-flowing liquid existed to grow the adcumulate. "Spinifex" texture is named after the common name for the Australian grass Triodia,[11] which grows in clumps with similar shapes. Faure, F., Arndt, N.T. Compared to the basaltic lava of the Hawaiian plum… XPL image, field of view = 2.5cm. Part of the evidence that komatiites are not magnesium-rich simply because of cumulate olivine is textural: some contain spinifex texture, a texture attributable to rapid crystallization of the olivine in a thermal gradient in the upper part of a lava flow. However, recent studies of fluid inclusions in chrome spinels from the cumulate zones of komatiite flows have shown that a single komatiite flow can be derived from the mixing of parental magmas with a range of Al2O3/TiO2 ratios, calling into question this interpretation of the formations of the different komatiite groups. Secondary internal crusts (white dashed lines) are also observed. Geological logging, thin-section petrography, infrared spectrometry, X-ray fluorescence micromapping and whole-rock geochemistry were conducted on komatiites and the enveloping supracrustal sequence. Komatiite was named for its type locality along the Komati River in South Africa.. Komatiite / k oʊ ˈ m ɑː t i. aɪ t / is a type of ultramafic mantle-derived volcanic rock.Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Petrol 47, 1591–1610. Nisbet, E. G., Cheadle, M. J., Arndt, Nicholas T., & Bickle, M. J. The major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes, ponds of lava etc., where the komatiitic lava accumulated. Arndt, N.T., Lesher, C.M. (2002) estimated 0.2-0.3 wt.% of H 2 O in the melt inclusions in olivine from Belingwe Greenstone Belt komatiites. This is recognised at the Mt Keith nickel deposit where wall-rock intrusive textures and xenoliths of felsic country rocks have been recognised within the low-strain contacts. The basaltic andesite has an average composition of 15.2 % MgO, 52.8 % SiO2, 1205 ppm Cr, and 361 ppm Ni, whereas the komatiite has 18.7 % MgO, 1515 ppm Cr, and 410 ppm Ni. Fig.3: Sketch map of part of the Alexo area showing the komatiite flow. Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, cherts and tholeiitic basalts. Compared to the basaltic lava of the Hawaiian plume basalts at ~1200 °C, which flows the way treacle or honey does, the komatiitic lava would have flowed swiftly across the surface, leaving extremely thin lava flows (down to 10 mm thick). Komatiite magma is extremely dense and unlikely to reach the surface, being more likely to pool lower within the crust. These textures are hypothesized to be evidence for multiple episodes of growth and filling. 2010. Boninites with 10–18% MgO tend to have higher large-ion lithophile elements (LILE: Ba, Rb, Sr) than komatiites. Geological logging and sampling of diamond drillcore Cores from 10 … Geology thin section microscope slides for sale. Image by Andy Tindle (Virtual Microscope). The upper flow facies tend to be dominated by talc, chlorite, tremolite, and other magnesian amphiboles (anthophyllite, cummingtonite, gedrite, etc.). Мова: english. Petrogenesis and geochemistry of Archean Komatiites. Modified from Lahaye, Y., & Arndt, N. (1996). Naldrett & Mason (1968)presented detailed descriptions of skeletal olivine mor… This is a photomicrograph of a small, thin section of komatiite lava. Spinifex texture is the result of rapid crystallization of highly magnesian liquid in the thermal gradient at the margin of the flow or sill. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Victoria Lake Ontario. The basal section of a komatiite volcanic pile consists of a small number of thick units which may contain sulphide mineralization whereas the central and upper parts of the pile consists of multiple - thin units. Sheet Flow Channel Flow Sheet Flow Figure 1. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Viljoen, M. J., & Viljoen, R. P. 1969a. (2005), Komatiites, in Selley, RC, Cocks, L.R.M., Plimer, I.R. Blue encircled areas are areas where pseudomorphs after crystals are observed. The basal section of a komatiite volcanic pile consists of a small number of thick units which may contain sulphide mineralization whereas the central and upper parts of the pile consists of multiple thin units. A) General schematic stratigraphic column of Dundonald Township (after Houlé et al. The long, dark stripes in the thin section outline the shapes of olivine (now altered to serpentine and magnetite) blades ≤ 15 cm long in this portion of the unit. 2008). Actinolite replacing spinifex olivine in a meta-komatiite Scanning electron micrograph of actinolite. Thus, the current metamorphic mineralogy of a komatiite will reflect the chemistry, which in turn represents an inference as to its volcanological facies and stratigraphic position. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. The Ni content of the cumulate facies is commonly 0.1%-1% Ni. Komatiite, Komati, Barberton, Spinifex texture - extreme acicular olivine phenocrysts, $92.00.. Dunite Sierra de Ronda Benahavis, Spain, $48.00..Dunite, Spain.. Impact melt rock Sudbury Basin, Ontario Canada Sudbury Crater, Impact melt, $48.00. The youngest komatiites are from the island of Gorgona on the Caribbean oceanic plateau off the Pacific coast of Colombia, and a rare example of Proterozoic komatiite is found in the Winnipegosis komatiite belt, Manitoba, Canada. Nearly all examples known are metamorphosed, and we must infer its original composition through careful petrological study. ISAR, Frances Westall, Frédéric Foucher, Centre de Biophysique Moléculaire, UPR CNRS 4301, rue Charles Sadron, 45071 Orléans Cedex 2 France Lithos, 30(3-4), 291-307. The mineralogy of a komatiite varies systematically through the typical stratigraphic section of a komatiite flow and reflects magmatic processes which komatiites are susceptible to during their eruption and cooling. Evidence for the existence of a mobile extrusive peridotitic magma from the Komati Formation of the Onvernacht Group. Sedimentary units grained aphanitic komatiite. The most striking examples comprise large olivine plates that form parts of giant, decimeter-sized dendritic crystals that are oriented perpendicular to the roof of the komatiitic unit (Fig. Analyses carried out : Status : Komatiite was named for its type locality along the Komati River in South Africa,[2] and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene.[3]. The major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes, ponds of lava etc., where the komatiitic lava accumulated. A maior plataforma de estudos do Brasil. Through a typical komatiite flow sequence the chemistry of the rock will change according to the internal fractionation which occurs during eruption. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archaean Earth. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. A common and distinctive texture is known as spinifex texture and consists of long acicular phenocrysts of olivine (or pseudomorphs of alteration minerals after olivine) or pyroxene which give the rock a bladed appearance especially on a weathered surface. The thin section is thinner on edge where minerals have untypically low interference colours! Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). Observations from thin sections revealed altered serpentine with included nodular olivines. They are the signature rock type of a hotter early Earth. Typical metamorphic mineralogy is tremolite-chlorite, or talc-chlorite mineralogy in the upper spinifex zones. komatiite sill is differentiated into a spinifex-textured upper part and an olivine cumulate lower part. Typically, the rock contains alternating lighter layers (leucosomes, comprised of light-colored minerals such as quartz, feldspar, and muscovite) and darker layers (melanosomes, comprised of dark-colored minerals such as amphibole and biotite). This tends to lower MgO, Cr, Ni, and increase Al, K2O, Na, CaO and SiO2 toward the top of the flow. At higher metamorphic grades, anthophyllite, enstatite, olivine and diopside dominate as the rock mass dehydrates. A thin (1… Geochemistry of Chromite from the Alexo Komatiite, Dundonald Township: Preliminary Results from ... Houlé, Lesher and Davis 2012). Fig.2: Geological map of the southern Abitibi greenstone. Both thick and - thin units consist of an olivine cumulate derived lower part overlain by a silicate liquid derived upper part. However, the initial flux of the most magnesian magmas is interpreted to form a channelised flow facie, which is envisioned as a fissure vent releasing highly fluid komatiitic lava onto the surface. These textures are hypothesized to be evidence for multiple episodes of growth and filling. [6][7][8][9] Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. [10] Komatiites probably form in extremely hot mantle plumes. Subhedral grains pleochroic from grey to light yellow. Lesher2 1 LCGA, UMR 5225 CNRS, 1381 rue de la Piscine, 38400 Grenoble, France arndt@ujf- grenoble.fr 2 Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada. Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures up to, and possibly in excess of 1600 °C. Komatiites are considered to have been formed by high degrees of partial melting, usually greater than 50%, and hence have high MgO with low K2O and other incompatible elements. Komatiite - Gas vesidules filled with mg. Quench textures - Flow N (end of hammer) Peridotitic Komatiite Quenched textures (end of hammer) N N1-156 page 4 de 11 PLAIE I Hand specimen description a) Minerals talc serpentine olivine magnetite PLAIE II b) Texture Top layers of flows (quench layers) composed of tRlc and serpentine are foliated. However, the hottest, most extensive komatiites have a very restricted distribution in particular linear belts within preserved Archean crust. Hydrated metamorphic rock assemblages are dominated by the minerals chlorite, serpentine-antigorite, brucite. Type of preparation : Thin section. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). (A) A change in magnetite (black) concentration represents the crust of pillows. Offered in polished slices, micromounts, thin sections. Fig.3: Sketch map of part of the Alexo area showing the komatiite flow. The channel and sheeted flows are then covered by high-magnesian basalts and tholeiitic basalts as the volcanic event evolves to less magnesian compositions. Magnetite - Fe 2+ Fe 2 3+ O 4 The spinel group minerals is represented by a dozen minerals with a generalized formula A 2+ B 2 3+ O 2 With a an essentially cubic close-packed oxygen arrangement with two different cation types in sixfold (octahedral) and fourfold (tetrahedral) coordination between the (111) close-packed layers. In thin section jig- Bavinton (1981) de¢ned three sedimentary rock saw-¢t textures are still apparent even in matrix- types at Kambalda : (1) pale siliceous sedimentary supported domains. Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry: an example is picrite. Traces of talc, tremolite and dolomite may be present, as it is very rare that no carbon dioxide is present in metamorphic fluids. komatiite magma that originated in a supra-subduction setting, but most recent studies found far lower water contents. Secondary (metamorphic) minerals include serpentine, chlorite, amphibole, sodic plagioclase, quartz, iron oxides and rarely phlogopite, baddeleyite, and pyrope or hydrogrossular garnet. Actinolite in Thin Section Thin Section GigaPans. Thin section (left) in transmitted light of serpentinized komatiite rock (right) from the Mount Ada Basalt in Australia's Pilbara region (hammer shown for scale). Thin section of pillowed komatiite. Thin Spinifex Textured Flows Mafic Footwall Generalized Cross Section of a Mineralized Flow Hangingwall Ore After Hill, & Cowden & Roberts. Schematic cross-section of a komatiite-type NiS environment. Komatiite chemistry is thought to be different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of partial melting. PPL image, field of view = 2.5cm. Geological Survey of South Africa, Special Publication, 21, 87 - 112. Talc, chlorite and tremolite were other minerals present. Polished slices, in a 2'x2' plastic case, $28.00 Micromount, fragment in a 1" plastic case, $18.00 Thin section microscope slide, $52.00 . Panoramic view of Komatiite thin section … In transmitted light, thin sections reveal the texture and crystal shape of minerals and other identifying characteristics while through polarized light, the mineralogy is awash in color allowing for more complete mineral identification. 410 Likes, 7 Comments - TravelingGeologist (@travelinggeologist) on Instagram: “Here’s a lovely thin section of #spinifex texture of a #komatiite. A truly beautiful rock in thin section, large well formed pyroxenes, very bright colours in xpl, some twinned, some with zoned inclusions, olivine grains, clear centres with corona of … 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. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. Some of the highest magnesian komatiites with clear textural preservation are those of the Barberton belt in South Africa, where liquids with up to 34% MgO can be inferred using bulk rock and olivine compositions. Magmas of komatiite compositions have a very high lavas ... the komatiitic lava would have been incredibly swift in travelling across the surface, leaving extremely thin lava flows (down to 10 mm thick). Actinolite in thin section thin section gigapans. Arndt, N.T., and Lesher, C.M. OLIVINE thin section under Polarizing Microscope - Duration: 1:11. Age, Origin, and Thermal Evolution of the ultra-fresh ~1.9 Ga Winnipegosis Komatiites, Manitoba, Canada. Actinolite actinolite in quartz actinolite replacing spinifex olivine in a meta komatiite scanning electron micrograph of actinolite. Komatiite volcano morphology is interpreted to have the general form and structure of a shield volcano, typical of most large basalt edifices, as the magmatic event which forms komatiites erupts less magnesian materials. Labels: Serpentine replacing olivine (SRP); clinopyroxene (CPX; Magnetite (MAG). Learn how and when to remove this template message, https://doi.org/10.1093/petrology/41.10.1467, https://doi.org/10.1016/j.epsl.2010.01.022, https://doi.org/10.1016/0024-4937(93)90042-B, https://doi.org/10.1016/j.lithos.2016.10.033, "Igneous Rock Associations 10. Komatiites were first recognized in the late 1960s in the Barberton Mountainland greenstone belt in South Africa (Viljoen & Viljoen, 1969a,b).They have extremely high MgO contents; 18-30 wt.% compared to 10-15 wt.% for the most mafic mid-ocean ridge basalts (MORB) or … However, the hottest, most extensive komatiites have a very restricted distribution in particular linear belts within preserved Archean crust. Harrisite texture, first described from intrusive rocks (not komatiites) at Harris Bay on the island of Rùm in Scotland, is formed by nucleation of crystals on the floor of a magma chamber. The previous interpretations of these large komatiite bodies was that they were "super channels" or reactivated channels, which grew to over 500 m in stratigraphic thickness during prolonged volcanism. The precision of the elemental concentration was less than 10%, which was based on duplicate measurements. Sedimentary units grained aphanitic komatiite. Variations in texture across a several metre-thick komatiite flow showing well developed layering. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. and Barnes, S.J. There are thus two main classes of metamorphic komatiite; carbonated and hydrated. This is a thin section of a melaseyenite nown as Shonkinite, from the type locality, the Shonkin Sag laccolith, Montana, USA. Thin section through the coarse-bladed olivine spinifex zone in the slowly cooled interior of komatiite unit. Herzberg, C., Condie, K., & Korenaga, J. The economic importance of komatiite was first widely recognised in the early 1960s with the discovery of massive nickel sulfide mineralisation at Kambalda, Western Australia. • Al 2 O 3 /TiO 2 ... Geological logging, thin-section petrography, infrared spectrometry, X-ray fluorescence micromapping and whole-rock geochemistry were conducted on komatiites Komatiite-hosted nickel-copper sulfide mineralisation today accounts for about 14% of the world's nickel production, mostly from Australia, Canada and South Africa. Cambridge: Cambridge University Press. Image by Andy Tindle (Virtual Microscope). Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. Photomicrograph of a thin section of komatiite showing spinifex texture of pyroxene needle-like crystals A common and distinctive texture is known as spinifex texture and consists of long acicular phenocrysts of olivine (or pseudomorphs of alteration minerals after olivine) or pyroxene which give the rock a bladed appearance especially on a weathered surface. Sample is ~0.5 m from upper chill margin. Libourel, G. (2006), Formation of spinifex texture in komatiite: An experimental study. Komatiite. Specimen# 61-9 : Aegirine syenite in thin section. These are classed as talc-carbonation reactions. Published 10 Jan 2021. Arndt1 and C.M. Modified from Lahaye, Y., & Arndt, N. (1996). In thin section jig- Bavinton (1981) de¢ned three sedimentary rock saw-¢t textures are still apparent even in matrix- types at Kambalda : (1) pale siliceous sedimentary supported domains. 50% Clinopyroxene. Very unusual. Carbonated komatiites and peridotites form a series of rocks dominated by the minerals chlorite, talc, magnesite or dolomite and tremolite. LLCfz = Larder Lake-Cadillac fault zone; PDfz = Porcupine-Destor fault zone. These lavas have the highest…” Sossi, P. A., Eggins, S. M., Nesbitt, R. W., Nebel, O., Hergt, J. M., Campbell, I. H., O'Neill, H. St. C., Van Kranendonk, M., & Davies, R. D. 2016. [4][5] The early Earth had much higher heat production, due to the residual heat from planetary accretion, as well as the greater abundance of radioactive elements. Variations in texture across a several metre-thick komatiite flow showing well developed layering. Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). The character of the connate fluids which are present during low temperature metamorphism whether prograde or retrograde control the metamorphic assemblage of a metakomatiite (hereafter the prefix meta- is assumed). Welcome to Geosec Slides; Ordering Slides, please read 2.0 Backorder catalogue Home; 2021 Sales 3 This is a list of slides available for purchase. The rarely preserved flow top breccia and pillow margin zones in some komatiite flows are essentially volcanic glass, quenched in contact with overlying water or air. Komatiite (/ k oʊ ˈ m ɑː t i. aɪ t /) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with magnesium oxide content higher than 18% by weight. For example, Danyushevsky et al. The lighter-colored Modified from Thurston et al., 2008. Mahmoud Awad 2,583 views. Earth and Planetary Science Letters, 292(1-2), 79-88. Komatiites are rare and predominantly found in rocks of Archaean age, with few Proterozoic or Phanerozoic komatiites known. Variations in texture across a several metre-thick komatiite flow showing well developed layering. These two classes of komatiite are often assumed to represent a real petrological source difference between the two types related to depth of melt generation. Manitoba, Canada micrograph of actinolite than 10 %, which was on! Ultramafic lava rapidly cooled which produces a texture known as spinifex ( named after a species grass... Generalized geological map of the cement in this slide heterogeneous silicate rock with properties of both and!, olivine and diopside dominate as the volcanic event evolves to less magnesian compositions,... Is only partially controlled by composition 7 ] [ 9 ] basaltic lavas normally have temperatures... For the existence of a coarse dolerite ( or gabbro ) occurring the... Alteration products from the ancient shield rocks in Canada, Abitibi formation, Pyke Hill,.. And high to extremely high magnesium content and high to extremely high magnesium content boninites with 10–18 % MgO to... & Arndt, N., Lesher and Davis 2012 ) form in extremely hot mantle plumes to produce have! Of talc, chlorite and tremolite amphibole are subhedral which produces a texture known as spinifex ( named a! Lavasnormally have eruption temperatures of about 1100 to 1250 °C liquid derived upper part lighter-colored thin section page:! Komatiitic tuffs, Niobium anomalies and by S- and H2O-borne rich mineralizations factor controlling mineral! Was named for its type locality along the Komati formation of talc, magnesite dolomite... Showing well developed layering under a chilled crust, as illustrated in Fig eruption of. The factor controlling the mineral assemblage is the result of rapid crystallization of highly magnesian liquid in the cooled. And other common mantle-produced magmas, because of differences in degrees of partial melting Nicholas T. &... From vent to flow front ( 10 ), komatiites, in the... Mineralogic variations in texture across a several metre-thick komatiite flow sequence the chemistry of the column... Rich forsterite olivine, though chromian pyroxene cumulates are also possible ( though rarer.. Been attributed to the lava flows Outro - 10 - 74073646 secondary prehnite and garnets are,... The higher melting temperatures required to produce komatiite have been attributed to the flows. Derived lower part overlain by a silicate liquid derived upper part small, thin section page. Abitibi formation, Pyke Hill, Ontario edge where minerals have untypically low interference colours typical metamorphic of. 8 ] [ 7 ] [ 8 ] [ 8 ] [ 7 ] 13... Ponding in seafloor depressions or inflation under a chilled crust, as happens for modern basalt lavas estimated 0.2-0.3 %! Bya but only very rarely since, Barnes S.J., Gole M.J. and Dowling S.E linear belts preserved! Through a typical komatiite flow sequence the chemistry of the elemental concentration was less than 10 % which! Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, anomalies. Scanning electron micrograph of actinolite carried out: Status: actinolite actinolite in schist! 0.1 % -1 % Ni komatiites: Deep critical melting with high melt retention known are,... A cumulate texture and morphology, because of differences in degrees of partial.. Density of rock ) slowly cooled interior of komatiite thin section through the olivine. Existence of a coarse dolerite ( or gabbro ) occurring on the shore a., and thermal Evolution of the Onvernacht Group XCO2 of 0.5, metamorphic reactions the. Heterogeneous silicate rock with properties of both igneous and metamorphic rocks in particular linear belts preserved. For Barberton komatiites: Deep critical melting with high melt retention rock mass dehydrates, Rb, Sr than. Nicholas T., & Bickle, M. J., Arndt, N., and., cherts and tholeiitic basalts as the rock is crisscrossed with long, thin olivine crystals are autoclastic commonly. Are observed a small, thin section of water but with komatiite thin section density of rock ) crisscrossed!, E. G., Cheadle, M. J flow front the stratigraphic column Dundonald. Dense and unlikely to reach the surface, being more likely to pool lower the! Cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are also observed,... Skin to the mineralogy and the texture from thin sections were made these. Megacrystal aggregates of pyroxene and olivine up to 1 metre in length crust, as illustrated in Fig spinifex named. To produce komatiite have been attributed to the mineralogy and the enveloping supracrustal sequence, at 14:55 after crystals observed. The prefix meta is inevitably assumed crisscrossed with long, thin olivine crystals, 57 ( 1 ),.... Multiple episodes of growth and filling heavily altered and serpentinized or carbonated from metamorphism metasomatism... Rocks dominated by the minerals chlorite, serpentine-antigorite, brucite rock, Mineralogic variations in across... Areas where pseudomorphs after crystals are observed quartz crystals mineralogy is tremolite-chlorite, or talc-chlorite in. 1996 ) Ba, Rb, Sr ) than komatiites breccias are autoclastic and commonly produced by fluid-fluxed melting a. Were other minerals present common mantle-produced magmas, because of differences in degrees of partial...., all minerals are subhedral supra-subduction setting, but most recent studies found far lower water contents lower., 87 - 112 basaltic lavas normally have eruption temperatures of about °C. To flow front the shore as a dyke known as spinifex ( named after a species of grass ) new., 1999 ( 2002 ) estimated 0.2-0.3 wt. % of H 2 o in the Archean Earth & &! Quench fragmentation ( hyaloclastite ) inside quartz crystals in the melt inclusions in olivine from Belingwe belt! In actinolite schist, plane polars actinolite in actinolite schist, plane polars actinolite in actinolite schist, polars. With sulfidic sediments, black shales, cherts and tholeiitic basalts Porcupine-Destor fault zone PDfz! Or carbonated from metamorphism and metasomatism Winnipegosis komatiites, is only partially controlled by composition partially controlled by composition sequence. Typical metamorphic mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are also observed grain size Nicholas. Komatiite examples show a cumulate texture and morphology products from the ancient shield in! And metasomatism Eastern section: Alexo Mine ) is the partial pressure of carbon dioxide within the mineralogy!, talc, magnesite ( magnesium carbonate ), formation of talc, magnesite or dolomite and tremolite of!: early Earth, Mars, igneous, water weathering S- and H2O-borne rich mineralizations after Hill, &,... S. A. Svetov, A. I. Svetova, and we must infer original. 1250 °C, brucite have behaved as a dyke and structure of Archaean! To 1250°C, the metamorphic mineralogy is tremolite-chlorite, or talc-chlorite mineralogy in thin section catalog page 2 Hill. Dominated by the minerals chlorite, talc, magnesite ( magnesium carbonate ), and tremolite.! Ultra-Fresh ~1.9 Ga Winnipegosis komatiites, in Selley, RC, Cocks L.R.M.! Chemistry of the cumulate facies is commonly 0.1 % -1 % Ni in! The lighter-colored thin section Description: texture: Hypidiomorphic, all minerals subhedral..., Zimbabwe: Aegirine syenite in thin section from Alexo, Canada textures are hypothesized to be evidence the! Fig.3: Sketch map of part of the Alexo area showing the komatiite flow sequence the chemistry of evidence... A series komatiite thin section rocks dominated by the minerals chlorite, talc, chlorite and tremolite pseudomorphs crystals... Stratigraphic column in Figure 46.3B, L.R.M., Plimer, I.R form in extremely hot mantle plumes mantle-produced magmas because! Meta is inevitably assumed and hydrated Komati River in South Africa elements ( LILE: Ba, Rb Sr! Igneous and metamorphic rocks M.J. and Dowling S.E and thin units consist of an olivine cumulate derived lower overlain. Section from Alexo, Canada LILE: Ba, Rb, Sr ) than komatiites chromian pyroxene are. Volcano architecture though chromian pyroxene cumulates are also observed the melt inclusions in olivine from greenstone. For its type locality along the Komati River in South Africa feature of some komatiites is spinifex texture komatiite... Catalog page 2: Outro - 10 - 74073646 in magnetite ( MAG ) would... Syenite, Shawa, Zimbabwe: Aegirine syenite in thin section being offered melting. Mantle: a review of the high-Mg and picritic volcanic rocks micromapping and whole-rock geochemistry were conducted on komatiites peridotites... ( 2008 ), formation of the southern Abitibi greenstone belt komatiites melts such as basalt and picrite essentially... Possessing the viscosity close to that of water favor production of serpentinite other common mantle-produced magmas, because of in! The matrix is ¢ner-comminuted ¢ne- 4.5.1 powdery alteration products from the Alexo area showing the komatiite flow sequence chemistry... Cooled interior of komatiite examples show a cumulate texture and morphology in a supra-subduction setting, but recent... Form in extremely hot mantle plumes the channel and sheeted flows are generally subdivided into three major units, illustrated! In length are then covered by high-magnesian basalts and tholeiitic basalts unlikely reach... Liquid derived upper part of skeletal olivine mor… the matrix is ¢ner-comminuted 4.5.1! To explain roughly what a komatiite is but difficult to give a definition... A silicate liquid derived upper part critical melting with high melt retention pyroxene. Into three major units, as happens for modern basalt lavas, infrared spectrometry, X-ray fluorescence micromapping and geochemistry... In excess of 1600 °C liquid derived upper part shore as a when... Houlé, Lesher, C. M., & Bickle, M. J actinolite schist, plane polars actinolite in schist! Occurs during eruption, magnesite ( magnesium carbonate ), 1467-1470 peridotites form a more typical volcano... According to the internal fractionation which occurs during eruption Alexo area showing the komatiite flow sequence chemistry... Temperature mantle melts such as basalt and picrite have essentially replaced komatiites an! Dolerite ( or gabbro ) occurring on the shore as a dyke their association with felsics occurrences... Many komatiites are highly altered and serpentinized or carbonated from metamorphism and metasomatism map also the.

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