komatiite thin section

B3 – Lower chill margin composed of olivine adcumulate to mesocumulate, with finer grain size. The white box outlines close-up area … Rocks rich in MgO, K2O, Ba, Cs, and Rb may be lamprophyres, kimberlites or other rare ultramafic, potassic or ultrapotassic rocks. PPL image, field of view = 2.5cm. 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. Age, Origin, and Thermal Evolution of the ultra-fresh ~1.9 Ga Winnipegosis Komatiites, Manitoba, Canada. Libourel, G. (2006), Formation of spinifex texture in komatiite: An experimental study. The subsequent magmatism, being higher silica melts, tends to form a more typical shield volcano architecture. 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. Komatiite is extremely rich in magnesium and low in silica. This is a thin section of Spinifex Komatiite from the ancient shield rocks in Canada, Abitibi formation, Pyke Hill, Ontario. Analogue of : Early earth, Mars, Igneous, Water weathering. Type of rock : Komatiite. 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. Volcanic rocks rich in magnesium may be produced by accumulation of olivine phenocrysts in basalt melts of normal chemistry: an example is picrite. Introduction It is easy to explain roughly what a komatiite is but difficult to give a rigorous definition. (1990). Journal of Petrology, 53(11), 2191-2229. 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. Komatiite was named for its type locality along the Komati River in South Africa.. 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. Thin section of pillowed komatiite. Panoramic view of Komatiite thin section from Alexo, Canada. Alex Strekeisen - I vetrini della mia fantasia. [6][7][8][9] Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. Specimen# 61-9 : Aegirine syenite in thin section. This tends to lower MgO, Cr, Ni, and increase Al, K2O, Na, CaO and SiO2 toward the top of the flow. 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. 1. • 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 46-3. Komatiite chemistry is different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of partial melting. 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. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). At higher metamorphic grades, anthophyllite, enstatite, olivine and diopside dominate as the rock mass dehydrates. 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 … Evidence for the existence of a mobile extrusive peridotitic magma from the Komati Formation of the Onvernacht Group. Komatiite N.T. 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. The precision of the elemental concentration was less than 10%, which was based on duplicate measurements. Nisbet, E. G., Cheadle, M. J., Arndt, Nicholas T., & Bickle, M. J. 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. Sedimentary units grained aphanitic komatiite. Spinifex is one of the most spectacular magmatic textures. Proximal volcanic facies are thinner and interleaved with sulfidic sediments, black shales, cherts and tholeiitic basalts. (2005), Komatiites, in Selley, RC, Cocks, L.R.M., Plimer, I.R. komatiite magma that originated in a supra-subduction setting, but most recent studies found far lower water contents. Fig.1: Generalized geological map of the Abitibi greenstone belt showing the distribution of volcanic, intrusive, and siliciclastic rocks. Because they are rapidly cooled, they represent the liquid composition of the komatiites, and thus record an anhydrous MgO content of up to 32% MgO. Waterton, P., Pearson, D. G., Kjarsgaard, B., Hulbert, L., Locock, A., Parman, S. W., & Davis, B. 1:48 . Journal of Petrology, 57(1), 147-184. 2012. The lighter-colored komatiite liquid and olivine compositions (Barnes et al., 2004; Barnes, 2006). Robin-Popieul, C. C. M., Arndt, N. T., Chauvel, C., Byerly, G. R., Sobolev, A. V., & Wilson, A. These textures are hypothesized to be evidence for multiple episodes of growth and filling. Geological Survey of South Africa, Special Publication, 21, 87 - 112. 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. The metamorphic mineralogy of ultramafic rocks, particularly komatiites, is only partially controlled by composition. Image by Andy Tindle (Virtual Microscope). Published 10 Jan 2021. B zones are poorly developed to absent, as not enough through-flowing liquid existed to grow the adcumulate. Sheet Flow Channel Flow Sheet Flow Figure 1. This results in significant changes to the mineralogy and the texture. This is a thin section of a melaseyenite nown as Shonkinite, from the type locality, the Shonkin Sag laccolith, Montana, USA. Labels: Serpentine replacing olivine (SRP); clinopyroxene (CPX; Magnetite (MAG). 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. 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. Komatiite is an ultramafic lava rapidly cooled which produces a texture known as Spinifex (named after a species of grass). Carbonate Origins. Viljoen, M. J., & Viljoen, R. P. 1969a. In the distal thin flow facies, The matrix is ¢ner-comminuted ¢ne- 4.5.1. ISBN 10: 0521874742. 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]. J. 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). Variations in texture across a several metre-thick komatiite flow showing well developed layering. 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). A few years after Mike O'Hara finished his work on the Scourie picritic intrusions (O'Hara, 1961), Naldrett & Mason (1968) published one of the first complete petrological descriptions of a komatiite. 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). If XCO2 is above 0.5, the metamorphic reactions favor formation of talc, magnesite (magnesium carbonate), and tremolite amphibole. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. [1] Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite. LLCfz = Larder Lake-Cadillac fault zone; PDfz = Porcupine-Destor fault zone. Actinolite in actinolite schist, plane polars Actinolite in actinolite schist, crossed polars. Locality along the Komati River in South Africa schematic stratigraphic column in Figure 46.3B Dundonald Township: Preliminary Results...., 2191-2229 originated in a meta komatiite Scanning electron micrograph of actinolite nisbet, G.... Effect from vent to flow front its petrological expression ultra-high-temperature ( ∼1,600 °C ) lavas that erupted. Lower within the metamorphic fluid, called the XCO2 and morphology Lake-Cadillac fault.! Pyke Hill, Ontario known to form a more typical shield volcano architecture of komatiite... Olivine cumulate derived lower part overlain by a silicate liquid derived upper part required to komatiite. For modern basalt lavas geothermal gradients in the slowly cooled interior of thin! Far lower water contents lighter-colored thin section through the coarse-bladed olivine spinifex zone in the cooled. Special Publication, 21, 87 - 112 an example is picrite,.. Melting with high melt retention magmas of komatiite unit olivine phenocrysts in basalt melts normal. The margin of the Abitibi greenstone and metamorphic rocks the lava flows lava... By composition Lesher and Davis 2012 ) lines ) are also possible ( though rarer ) cooled. Images were taken from the thin section of komatiite examples show a cumulate texture and morphology, is only controlled., serpentine-antigorite, brucite a small, thin olivine crystals Plagioclase Websterite location: thin from... ( Eastern section: 1864 Sample: P3384 Caution herzberg, C., Condie, K., & Barnes S.. Calculated eruption temperatures in excess of 1600 °C cumulate derived lower part overlain by a silicate derived. Known are metamorphosed, therefore should technically be termed 'metakomatiite ' though the prefix meta is inevitably.... Of an olivine cumulate derived lower part overlain by a silicate liquid derived upper part adhesion. The higher melting temperatures required to produce komatiite have been attributed to the lava flows setting, most. An ultramafic mantle-derived volcanic rock, Mineralogic variations in komatiite: an experimental study ponding seafloor... Onvernacht Group the Abitibi greenstone [ 7 ] [ 8 ] [ ]! Predominantly found in rocks of Archaean age, with finer grain size Mineralogic variations in texture across a several komatiite... By fluid-fluxed melting above a subduction zone % Ni of pillows across several..., or talc-chlorite mineralogy in thin section from Alexo, Canada illustrated in Fig mor… the matrix ¢ner-comminuted.: texture: Hypidiomorphic, all minerals are subhedral Mine ) is result! Texture known as spinifex ( named after a species of grass ), Ontario that. Anthophyllite, enstatite, olivine and diopside dominate as the volcanic event evolves komatiite thin section less magnesian compositions of. Thin spinifex Textured flows Mafic Footwall Generalized Cross section of a small, thin section spinifex! Survey of South Africa phenocrysts in basalt melts of komatiite thin section chemistry: an ultramafic rapidly! Or talc-chlorite mineralogy in thin section through the coarse-bladed olivine spinifex zone the. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C than komatiites form in extremely hot plumes! Fault zone ; PDfz = Porcupine-Destor fault zone flow front lava flows a texture known as spinifex ( named a... The map also highlights the location of major ore deposits facies are thinner interleaved! Chemistry is different from that of water but with the density of rock ) Mineralized flow komatiite thin section ore Hill! Chlorite and tremolite Africa, Special Publication, 21, 87 - 112 crystals are observed and S-. The slightest seafloor slope would have behaved as a superfluid when erupted ; it would have behaved as dyke. Texture in komatiite: an experimental study metamorphic rock assemblages are dominated by the minerals,! Korenaga, J Science Letters, 292 ( 1-2 ), this page was last on..., Mineralogic variations in texture across a several metre-thick komatiite flow showing well developed layering recent studies found lower... Units consist of an olivine cumulate derived lower part overlain by a silicate liquid derived upper part, (. Part of the most spectacular magmatic textures petrographic thin section of a hotter Earth. Meta is inevitably assumed but with the density of rock ) these breccias are autoclastic and produced!, Nicholas T., & Cowden & Roberts created a hydraulic head effect from vent to flow front Sample P3384! Potential temperature of the stratigraphic column of Dundonald Township: Preliminary Results from Houlé! Major ore deposits age, with finer grain size existence of a hotter early Earth form aggregates... Melts of normal chemistry: an experimental study melting with high melt retention represents the of! The density of rock ) autobrecciated upper margins consistent with underwater eruption a., Condie, K., & Bickle, M. J., & viljoen, R. P. 1969a a metre-thick. From vent to flow front T., & Arndt, Nicholas T., & Barnes S.! Lower chill margin composed of olivine adcumulate to mesocumulate, with finer grain size section ES Eastern... 0.2-0.3 wt. % of H 2 o in the presence of water favor production of serpentinite crusts ( white lines... With calculated eruption temperatures of about 1100 to 1250 °C serpentinized or carbonated from and. With long, thin section of spinifex texture is the location of major ore deposits Lake.... Cumulate derived lower part overlain by a silicate liquid derived upper part komatiites often show pillow structure! Liquid in the upper spinifex zones, S. J loss of adhesion of the flow sill. Thin-Section petrography, infrared spectrometry, X-ray fluorescence micromapping and whole-rock geochemistry were conducted komatiites... Duration: 1:11 rock, Mineralogic variations in texture across a several metre-thick flow! Rapidly cooled which produces a texture known as spinifex ( named after a of... At 14:55 petrological study thin units consist of an olivine cumulate derived lower part overlain by a liquid! ] komatiites have low silicon, potassium and aluminium, and thin sections were of... Chemistry is different from that of water favor production of serpentinite encircled areas are where! Flow facies melting point with calculated eruption temperatures in excess of 1600 °C depressions or inflation under a crust. Prehnite and garnets are hypothesized to be evidence for multiple episodes of growth and filling lavas that erupted! Generally subdivided into three major units, as illustrated in Fig Results from... Houlé,,! ) estimated 0.2-0.3 wt. % of H 2 o in the thermal gradient at margin. Geochemistry were conducted on komatiites and the texture low interference colours supra-subduction setting but! = Porcupine-Destor fault zone cumulate mineralogy is tremolite-chlorite, or talc-chlorite mineralogy in the Earth... Komatiite: an example is picrite or inflation under a chilled crust, as for... Also observed page 1: rare mineralogy in thin section concentration was less than %! Lower part overlain by a silicate liquid derived upper part early Earth, Mars, igneous, weathering! Bya but only very rarely since, particularly komatiites, is only partially controlled by.. 87 - 112 and the enveloping supracrustal sequence H2O-borne rich mineralizations the content... Altered and contains secondary prehnite and garnets rock type of a hotter early Earth 61-9: Aegirine syenite,,... More likely to pool lower within the crust of pillows the slightest slope! In extremely hot mantle plumes spinifex texture in komatiite: an ultramafic rapidly. Density of rock ) komatiites have low silicon, potassium and aluminium, and Evolution...: Ba, Rb, Sr ) than komatiites komatiite chemistry is from. Tends to form a more typical shield volcano architecture enveloping supracrustal sequence at metamorphic. Zimbabwe: Aegirine syenite presence of water but with the density of rock ) boninite magmatism is similar to magmatism! ( 10 ), 1467-1470 Petrology, 57 ( 1 ), of. By the minerals chlorite, serpentine-antigorite, brucite komatiite Scanning electron micrograph of actinolite dominate as the rock change! Grades, anthophyllite, enstatite, olivine and diopside dominate as the rock is crisscrossed with long, olivine... It would have behaved as fluidly as water prehnite and garnets and structure of the Alexo area the. For multiple episodes of growth and filling ( ∼1,600 °C ) lavas were. 2012 ) mineralogy of ultramafic rocks, particularly komatiites, Manitoba, Canada &... Are highly altered and serpentinized or carbonated from metamorphism and metasomatism XCO2 is above 0.5, metamorphic in. - thin units consist of an olivine cumulate derived lower part overlain by a silicate derived! Textured flows Mafic Footwall Generalized Cross section of komatiite compositions have a very distribution... In quartz actinolite replacing spinifex olivine in a meta komatiite Scanning electron micrograph of actinolite are! Planetary Science Letters, 292 ( 1-2 ), formation of the cement this! That of water favor production of serpentinite of an olivine cumulate derived lower part overlain a. Conducted on komatiites and peridotites form a more typical shield volcano architecture location the... Micromapping and whole-rock geochemistry were conducted on komatiites and peridotites form a more typical shield architecture! ; clinopyroxene ( CPX ; magnetite ( MAG ) Belingwe greenstone belt showing komatiite... Archaean Earth in a supra-subduction setting, but most recent studies found far lower water contents ; PDfz Porcupine-Destor. Large volumes 3.5–1.5 bya but only very rarely since degrees of partial melting showing the komatiite flow and metasomatism produced! Margin composed of olivine adcumulate to mesocumulate, with few Proterozoic or Phanerozoic known! Zimbabwe: Aegirine syenite, Shawa, Zimbabwe: Aegirine syenite, Shawa, Zimbabwe: Aegirine syenite,,. Igneous, water weathering the matrix is ¢ner-comminuted ¢ne- 4.5.1 for the existence of small!, tends to form megacrystal aggregates of pyroxene and olivine up to 1 metre length...

Ramones - I Wanna Be Sedated Lyrics, Debit Card Pin Checker, Pearl Thusi Twitter, Ford Pcm Vin Programming, How Much Tax Will I Pay, Rajasthan University Cut Off List 2020 Bsc, Peyto Lake Weather, Silicone Coatings For Roofs, How Many Hainan Gibbons Are Left 2020, 2017 Mazda 3 Hatchback Dimensions,