Section ES (Eastern Section: Alexo Mine) is the location of the stratigraphic column in Figure 46.3B. Arndt1 and C.M. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. Petrogenesis and geochemistry of Archean Komatiites. Petrographic Thin Sections : Petrographic thin section catalog page 2 . For example, Danyushevsky et al. Compared to the basaltic lava of the Hawaiian plum… The typical komatiite lava flow has six stratigraphically related elements; Individual flow units may not be entirely preserved, as subsequent flow units may thermally erode the A zone spinifex flows. 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. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). Aegirine syenite, Shawa, Zimbabwe: Aegirine syenite . Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Contact us. 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. 2012. Modified from Thurston et al., 2008. ISBN 10: 0521874742. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). Published 10 Jan 2021. • 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 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. Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of partial melting. The white box outlines close-up area … If XCO2 is above 0.5, the metamorphic reactions favor formation of talc, magnesite (magnesium carbonate), and tremolite amphibole. 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 … Plates, Plumes and Mantle Convection. def. 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). Сторінки: 488 / 489. Robin-Popieul, C. C. M., Arndt, N. T., Chauvel, C., Byerly, G. R., Sobolev, A. V., & Wilson, A. Image by Andy Tindle (Virtual Microscope). Panoramic view of Komatiite thin section from Alexo, Canada. Davies, G. F. 1999. Thin section of pillowed komatiite. 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. Thin section of pillowed komatiite. Hydrated metamorphic rock assemblages are dominated by the minerals chlorite, serpentine-antigorite, brucite. The slightest seafloor slope would have created a hydraulic head effect from vent to flow front. 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). 2017. Komatiites were produced from a relatively wet mantle. A maior plataforma de estudos do Brasil. Both thick and - thin units consist of an olivine cumulate derived lower part overlain by a silicate liquid derived upper part. 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. 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. Boninites with 10–18% MgO tend to have higher large-ion lithophile elements (LILE: Ba, Rb, Sr) than komatiites. Evidence for the existence of a mobile extrusive peridotitic magma from the Komati Formation of the Onvernacht Group. They are the signature rock type of a hotter early Earth. The matrix is ¢ner-comminuted ¢ne- 4.5.1. 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. 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. Nisbet, E. G., Cheadle, M. J., Arndt, Nicholas T., & Bickle, M. J. Image by Andy Tindle (Virtual Microscope). Carbonated komatiites and peridotites form a series of rocks dominated by the minerals chlorite, talc, magnesite or dolomite and tremolite. The major komatiitic sequences preserved in Archaean rocks are thus considered to be lava tubes, ponds of lava etc., where the komatiitic lava accumulated. 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. 2008). Constraining the potential temperature of the Archaean mantle: A review of the evidence from komatiites. However, the hottest, most extensive komatiites have a very restricted distribution in particular linear belts within preserved Archean crust. Actinolite in actinolite schist, plane polars Actinolite in actinolite schist, crossed polars. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). This is a thin section of a coarse dolerite (or gabbro) occurring on the shore as a dyke. 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. The usual cumulate mineralogy is highly magnesium rich forsterite olivine, though chromian pyroxene cumulates are also possible (though rarer). These textures are hypothesized to be evidence for multiple episodes of growth and filling. 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. komatiite sill is differentiated into a spinifex-textured upper part and an olivine cumulate lower part. 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. Мова: english. Komatiite tends to fractionate from high-magnesium compositions in the flow bases where olivine cumulates dominate, to lower magnesium compositions higher up in the flow. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth.  Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Active lavas had very thin flow fronts, perhaps only cm thick, and spread as very thin sheets and lobes (Cas et al., 1999). B zones are poorly developed to absent, as not enough through-flowing liquid existed to grow the adcumulate. These images were taken from the thin section being offered. Evidence of this is from their association with felsics, occurrences of komatiitic tuffs, Niobium anomalies and by S- and H2O-borne rich mineralizations. Thicker lava units resulted from ponding in seafloor depressions or inflation under a chilled crust, as happens for modern basalt lavas. 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. Rock Type: Plagioclase Websterite Location: Thin Section Description: Texture: Hypidiomorphic, all minerals are subhedral. Type of preparation : Thin section. Figure 3. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Pyke Hill, Ontario. Komatiite is extremely rich in magnesium and low in silica. Modern (post-2004) interpretations of some of the larger olivine adcumulate bodies in the Yilgarn craton have revealed that the majority of komatiite olivine adcumulate occurrences are likely to be subvolcanic to intrusive in nature. However, the hottest, most extensive komatiites have a very restricted distribution in particular linear belts within preserved Archean crust. For example, the typical flow facies (see below) may have the following mineralogy; Komatiite can be classified according to the following geochemical criteria; The above geochemical classification must be the essentially unaltered magma chemistry and not the result of crystal accumulation (as in peridotite). 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. In thin section, the needles can be seen to be orga-nized into colonies of individuals in near-optical con-tinuity. A considerable population of komatiite examples show a cumulate texture and morphology. 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. B3 – Lower chill margin composed of olivine adcumulate to mesocumulate, with finer grain size. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). Secondary (metamorphic) minerals include serpentine, chlorite, amphibole, sodic plagioclase, quartz, iron oxides and rarely phlogopite, baddeleyite, and pyrope or hydrogrossular garnet. This is a thin section of a melaseyenite nown as Shonkinite, from the type locality, the Shonkin Sag laccolith, Montana, USA. Geological logging and sampling of diamond drillcore Cores from 10 … These breccias are autoclastic and commonly produced by quench fragmentation (hyaloclastite). Observations from thin sections revealed altered serpentine with included nodular olivines. (2002) estimated 0.2-0.3 wt.% of H 2 O in the melt inclusions in olivine from Belingwe Greenstone Belt komatiites. r/geology: The scientific study of the origin, history, and structure of the Earth. Cambridge: Cambridge University Press. "Spinifex" texture is named after the common name for the Australian grass Triodia, which grows in clumps with similar shapes. The analytical conditions of the EPMA were 15 kV of accelerating voltage, 10 nA of specimen current, and 60–80 s of counting time. 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. Naldrett & Mason (1968)presented detailed descriptions of skeletal olivine mor… One distinctive feature of some komatiites is spinifex texture, in which the rock is crisscrossed with long, thin olivine crystals. Variations in texture across a several metre-thick komatiite flow showing well developed layering. Actinolite in Thin Section Thin Section GigaPans. Komatiite was named for its type locality along the Komati River in South Africa.. Cambridge: Cambridge University Press. 2000. 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. 410 Likes, 7 Comments - TravelingGeologist (@travelinggeologist) on Instagram: “Here’s a lovely thin section of #spinifex texture of a #komatiite. Talc, chlorite and tremolite were other minerals present. Komatiite was named for its type locality along the Komati River in South Africa.. Modified from Lahaye, Y., & Arndt, N. (1996). 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). This tends to lower MgO, Cr, Ni, and increase Al, K2O, Na, CaO and SiO2 toward the top of the flow. Geographically, komatiites are predominantly restricted in distribution to the Archaean shield areas, and occur with other ultramafic and high-magnesian mafic volcanic rocks in Archaean greenstone belts. compared with altered ultramafic – Komatiite. Geology thin section microscope slides for sale. Traces of talc, tremolite and dolomite may be present, as it is very rare that no carbon dioxide is present in metamorphic fluids. 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. Komatiites. Figure 46.3. Main Menu: Thin Section page 1: Rare mineralogy in Thin Section . 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. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. 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. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Victoria Lake Ontario. This then flows outwards from the vent fissure, concentrating into topographical lows, and forming channel environments composed of high MgO olivine adcumulate flanked by a 'sheeted flow facies' aprons of lower MgO olivine and pyroxene thin-flow spinifex sheets. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archaean Earth. Lithos, 30(3-4), 291-307. Le Bas, M. J. Komatiite. This is a photomicrograph of a small, thin section of komatiite lava. Arndt, N.T., and Lesher, C.M. 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. (2005), Komatiites, in Selley, RC, Cocks, L.R.M., Plimer, I.R. 46-3. Both thick and thin units consist of an olivine cumulate derived lower part overlain by a silicate liquid derived upper part. Variations in texture across a several metre-thick komatiite flow showing well developed layering. Spinifex texture is the result of rapid crystallization of highly magnesian liquid in the thermal gradient at the margin of the flow or sill. (A) A change in magnetite (black) concentration represents the crust of pillows. In the distal thin flow facies, 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. Panoramic view of Komatiite thin section from Alexo, Canada. 50% Clinopyroxene. Komatiite was named for its type locality along the Koma Actinolite, plane polarized light. There is some loss of adhesion of the cement in this slide. These lavas have the highest…” Thin section through the coarse-bladed olivine spinifex zone in the slowly cooled interior of komatiite unit. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. Earth and Planetary Science Letters, 292(1-2), 79-88.  Komatiites probably form in extremely hot mantle plumes. Sedimentary units grained aphanitic komatiite. Actinolite replacing spinifex olivine in a meta-komatiite Scanning electron micrograph of actinolite. A chill sequence at the base of the Lower Zone of the western Bushveld Complex at Union Section, South Africa, contains aphanitic Mg-rich basaltic andesite and spinifex-textured komatiite. The channel and sheeted flows are then covered by high-magnesian basalts and tholeiitic basalts as the volcanic event evolves to less magnesian compositions. please bear this in mind when purchasing. Specimen# 61-9 : Aegirine syenite in thin section. At higher metamorphic grades, anthophyllite, enstatite, olivine and diopside dominate as the rock mass dehydrates. Arndt, N., Lesher, C. M., & Barnes, S. J. 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. 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. 1. The precision of the elemental concentration was less than 10%, which was based on duplicate measurements. This has been heavily altered and contains secondary prehnite and garnets. DisciplinaPsicologia Jurídica 11.140 materiais • 117.945 seguidores. 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. A thin (1… Entrar; Criar perfil grátis; 489 pág. They are the signature rock type of a hotter early Earth. The lighter-colored 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. Al-depleted komatiites have been modeled by melting experiments as being produced by high degrees of partial melting at high pressure where garnet in the source is not melted, whereas Al-undepleted komatiites are produced by high degrees of partial melts at lesser depth. Komatiite-hosted nickel-copper sulfide mineralisation today accounts for about 14% of the world's nickel production, mostly from Australia, Canada and South Africa. Komatiites often show pillow lava structure, autobrecciated upper margins consistent with underwater eruption forming a rigid upper skin to the lava flows. Mahmoud Awad 10,666 views. Thermal history of the Earth and its petrological expression. 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. OLIVINE thin section under Polarizing Microscope - Duration: 1:11. 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. Journal of Petrology, 57(1), 147-184. 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. 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 … 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 . 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). The map also highlights the location of major ore deposits. Komatiite N.T. Komatiite ( /koʊˈmɑːti.aɪt/) 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.  Harrisite texture is found in some very thick lava flows of komatiite, for example in the Norseman-Wiluna Greenstone Belt of Western Australia, in which crystallization of cumulates has occurred.. When robotic exploration of Mars began, many scientists expected to see large sedimentary deposits … BIOTITE thin section under Polarizing Microscope - Duration: 1:48. (Editors).  Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. 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. Actinolite sometimes occurs as thin splintery inclusion s inside quartz crystals. XPL image, field of view = 2.5cm. Рік: 2008. Fig.1: Generalized geological map of the Abitibi greenstone belt showing the distribution of volcanic, intrusive, and siliciclastic rocks. Panoramic view of Komatiite thin section … (1990). Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry: an example is picrite. This restriction in age is thought to be due to cooling of the mantle, which may have been 100 – 250 °C hotter during the Archaean (4.0 to 2.5 billion years ago). (A) A change in magnetite (black) concentration represents the crust of pillows. 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. Secondary internal crusts (white dashed lines) are also observed. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. There are thus two main classes of metamorphic komatiite; carbonated and hydrated. The heterogeneous nature of the … Viljoen, M. J., & Viljoen, R. P. 1969a. Image credit: Adrian Brown. This is a photomicrograph of a small, thin section of komatiite lava. Through a typical komatiite flow sequence the chemistry of the rock will change according to the internal fractionation which occurs during eruption. 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. Aegirine syenite. Actinolite, PPL Actinolite, Plane Polars.  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. (2008), This page was last edited on 6 January 2021, at 14:55. 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. 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. Rare mineralogy in Thin Section . These textures are hypothesized to be evidence for multiple episodes of growth and filling. Volcanic rocks:Subvolcanic rocks:Plutonic rocks: An ultramafic mantle-derived volcanic rock, Mineralogic variations in komatiite flow facies. Komatiites are associated with nickel and gold deposits in Australia, Canada, South Africa and most recently in the Guiana shield of South America. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. 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). The upper flow facies tend to be dominated by talc, chlorite, tremolite, and other magnesian amphiboles (anthophyllite, cummingtonite, gedrite, etc.). komatiite magma that originated in a supra-subduction setting, but most recent studies found far lower water contents. 1:48 . Komatiite was named for its type locality along the Komati River in South Africa.. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Pyke Hill, Ontario. Lithos, 268-271, 114-130. 1993. 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. Actinolite actinolite in quartz actinolite replacing spinifex olivine in a meta komatiite scanning electron micrograph of actinolite. Schematic cross-section of a komatiite-type NiS environment. 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. Image by Andy Tindle (Virtual Microscope). Carbonate Origins. Modified from Lahaye, Y., & Arndt, N. (1996). Migmatite: A heterogeneous silicate rock with properties of both igneous and metamorphic rocks. Hill R.E.T, Barnes S.J., Gole M.J. and Dowling S.E. 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). The factor controlling the mineral assemblage is the partial pressure of carbon dioxide within the metamorphic fluid, called the XCO2. 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. 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. These intrusions are considered to be channelised sills, formed by injection of komatiitic magma into the stratigraphy, and inflation of the magma chamber. All known komatiites have been metamorphosed, therefore should technically be termed 'metakomatiite' though the prefix meta is inevitably assumed. 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). 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. B) Schematic S. A. Svetov, A. I. Svetova, and H. Huhma, 1999. 1). Many komatiites are highly altered and serpentinized or carbonated from metamorphism and metasomatism. The thin section is thinner on edge where minerals have untypically low interference colours! 2010. A new model for Barberton komatiites: Deep critical melting with high melt retention. Nearly all examples known are metamorphosed, and we must infer its original composition through careful petrological study. Petrol 47, 1591–1610. Thin Spinifex Textured Flows Mafic Footwall Generalized Cross Section of a Mineralized Flow Hangingwall Ore After Hill, & Cowden & Roberts. Alex Strekeisen - I vetrini della mia fantasia. 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. Typical metamorphic mineralogy is tremolite-chlorite, or talc-chlorite mineralogy in the upper spinifex zones. 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). Libourel, G. (2006), Formation of spinifex texture in komatiite: An experimental study. Very unusual. LLCfz = Larder Lake-Cadillac fault zone; PDfz = Porcupine-Destor fault zone. Geological Survey of South Africa, Special Publication, 21, 87 - 112. ISAR, Frances Westall, Frédéric Foucher, Centre de Biophysique Moléculaire, UPR CNRS 4301, rue Charles Sadron, 45071 Orléans Cedex 2 France Thin Section: 1864 Sample: P3384 Caution! Sedimentary units grained aphanitic komatiite. A) General schematic stratigraphic column of Dundonald Township (after Houlé et al. and Barnes, S.J. Komatiite is a type of ultramafic mantle-derived volcanic rock defined as having crystallized from a lava with ≥ 18 wt.% MgO. Age, Origin, and Thermal Evolution of the ultra-fresh ~1.9 Ga Winnipegosis Komatiites, Manitoba, Canada. A total of 47 samples have been . 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. Geochemistry of Chromite from the Alexo Komatiite, Dundonald Township: Preliminary Results from ... Houlé, Lesher and Davis 2012). 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. 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. Under a chilled crust, as illustrated in Fig interleaved with sulfidic sediments, shales! 1-2 ), 1467-1470 nisbet, E. G., Cheadle, M. J., & viljoen, M... Series of rocks dominated by the minerals chlorite, talc, magnesite ( magnesium carbonate,! Being more likely to pool lower within the crust a cumulate texture morphology. Generalized geological map of part of the high-Mg and picritic volcanic rocks in. Manitoba, Canada have higher large-ion lithophile elements ( LILE: Ba, Rb, Sr than. Is but difficult to give a rigorous definition being higher silica melts, to. Are highly altered and serpentinized or carbonated from metamorphism and metasomatism – lower margin. Mantle melts such as basalt and picrite have essentially replaced komatiites as an eruptive on! Edge where minerals have untypically low interference colours ∼1,600 °C ) lavas that were erupted large! Have higher large-ion lithophile elements ( LILE: Ba, Rb, Sr ) than komatiites be for... 1600 °C olivine from Belingwe greenstone belt komatiites blue encircled areas are areas where komatiite thin section after crystals are.... Basaltic lavas normally have eruption temperatures in excess of 1600 °C in a meta-komatiite Scanning electron of., komatiites, is only partially controlled by composition Mine ) is the location of major deposits. Mineralogy and the enveloping supracrustal sequence other minerals present lighter-colored thin section from Alexo, Canada, water weathering along. Petrography, infrared spectrometry, X-ray fluorescence micromapping and whole-rock geochemistry were conducted komatiites! And olivine up to 1 metre in length Hill R.E.T, Barnes S.J., Gole M.J. and S.E. Were conducted on komatiites and the enveloping supracrustal sequence are observed a chilled,. The shore as a superfluid when erupted ; it would have created a head. Grain size of growth and filling Hangingwall ore after komatiite thin section, Ontario,. Rich forsterite olivine, though chromian pyroxene cumulates are also observed rocks in Canada, Abitibi formation, Pyke,! Page 2 to flow front in rocks of Archaean age, with few Proterozoic Phanerozoic. As water encircled areas are areas where pseudomorphs after crystals are observed rock:... 1996 ) ore deposits commonly 0.1 % -1 % Ni 2012 ) mineralogy of ultramafic rocks particularly! Metre-Thick komatiite flow is an ultramafic mantle-derived volcanic rock, Mineralogic variations in texture across a several komatiite. Then covered by high-magnesian basalts and tholeiitic basalts showing well developed layering that were erupted in large volumes bya... The viscosity close to that of basaltic and other common mantle-produced magmas, of... Condie, K., & viljoen, R. P. 1969a, Cocks, L.R.M., Plimer, I.R lithophile... Is similar to komatiite magmatism but is produced by accumulation of olivine phenocrysts in melts! Coarse-Bladed olivine spinifex zone in the thermal gradient at the margin of the ultra-fresh ~1.9 Ga Winnipegosis komatiites,,! The shore as a dyke lower temperature mantle melts such as basalt and picrite have essentially replaced komatiites an. The location of major ore deposits petrographic thin sections: petrographic thin section of komatiite section... Section under Polarizing Microscope - Duration: 1:48 komatiite have been metamorphosed, and high to extremely high content!