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komatiita (komatiite) Geol. Spinifex texture-typical of Komatiites The name Spinifex refer to a spiky grass in Australian. Here we report the results of a petrological and geochemical investigation of a ~5m thick komatiite sill in Dundonald Township, Ontario. Kidd-Munro Assemblage, Timmins, Ontario, Canada. Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. st. andrews, dep. Outcrops of spinifex-textured komatiites, located ∼1.5 km to the south of the Carajás ridge, were discovered during regional exploration for Ni-Cu-(PGE) sulfide deposits by VALE. 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 lava had a very low viscosity - it could flow like an ultradense gas. From James St. John. To distinguish komatiite from other highly magnesian volcanic rocks, it is useful to include spinifex texture in the definition, yet not all komatiite flows have spinifex (Nesbitt, 1971). Komati River Valley, South Africa. 1). Komatiite lava from the type locality in the Komati Valley, Barberton Mountainland, South Africa, showing the distinctive "spinifex texture" formed by dendritic plates of olivine (scale shown by a hammer on the right edge of photo) Fig.3: Three stages during the solidification of a spinifex-textured komatiite flow. Crystal growth is retarded due to the superfluid nature of the komatiite, and proceeds in a 'flash freeze' to form the spinifex texture. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or ophitic basalt. 5 m thick lower olivine cumulate zone (Fig. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. Published by Oxford University Press. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Recognized in well preserved Archaean greenstone belts. grasses. Modified from Arndt, N., & Fowler, A. 1. From James St. John. 2 Roca volcánica ultramáfica, formada a partir de magmas de alta temperatura y elevado contenido en MgO (del 18 al 32%) y caracterizada por la presencia en ella de unas texturas esqueléticas llamadas spinifex.V. Specimen is 9 cm wide. This is a rare volcanic rock of ultramafic origin. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Abstract. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene. Komatiite igneous rock. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) [Del río Komati (Transvaal, Suráfrica)]. Komatiitic lava was extremely fluid when it erupted (possessing the viscosity close to that of water but with the density of rock). The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. I i l Spinifex texture komatiite blllbl Platy-spinifex komatiite • Cumulate texture komatiite I Basalt •l Pillow Basalt • • Massive sulfides Matrix sulfides Interflow sediment "Silicate domes" Basalt Flow Top Ocelli Localities Figure 1. Komatiite sample collected near Engelhart, Ontario, Canada. Komatiite 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. The distinctive spinifex texture is formed by skeletal, platy, or acicular crystals of olivine, orthopyroxene, or clinopyroxene, or their pseudomorphs in ultramafic and mafic lavas or silicate-rich furnace slag. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Specimen is 9 cm wide. Komatiite /Spinifex Texture. 3D). Ophitic texture is defined inconsistently, but it is an important variety of basalt texture where pyroxene (or occasionally olivine) forms larger crystals and typically contains numerous crystals of plagioclase (right). geol./fife ky 16957/gbr source Komatiite lava from the type locality in the Komati Valley, Barberton Mountainland, South Africa, showing the distinctive "spinifex texture" formed by dendritic plates of olivine (scale shown by a hammer on the right edge of photo) Petrography and mineralogy, Growth forms and composition of chromian spinel in MORB magma: diffusion-controlled crystallization of chromian spinel, Morphology and composition of spinel in Pu'u ‘O’o lava (1996–1998), Kilauea volcano, Hawaii, Journal of Volcanology and Geothermal Research, The origin of spinifex texture in komatiites, Komatiites II: experimental and theoretical investigations of post-emplacement cooling and crystallization, © The Author 2006. Although komatiite has been defined as an ultramafic volcanic rock characterised by spinifex texture, there is a growing recognition that similar textures form in high-level dykes and sills. Large, downward-radiating spinifex textures in komatiitic. textura spinifex. Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. However, spinifex-like undercooling textures are not only restricted to komatiites. Komatiites were named for their type locality along the Komati River in South Africa. 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). Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 3). Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. This sample displays a characteristic 'spinifex texture' of large, elongate olivine crystals, an indication of rapid crystallisation from under cooled magma. Komatiites with spinifex texture have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene. 1. Zdrojová magma komatiitov pochádza zo zemského plášťa. Komatiite sample collected near Engelhart, Ontario, Canada. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. komatiite An extrusive igneous rock of peridotite composition, dominated by essential magnesium olivine accompanied by lesser amounts of aluminous clinopyroxene and chromite, and found as lava flows and shallow sills within Archaean and Proterozoic rock successions. Specimen is 9 cm wide. The origin of spinifex texture in komatiites. komatiite An extrusive igneous rock of peridotite composition, dominated by essential magnesium olivine accompanied by lesser amounts of aluminous clinopyroxene and chromite, and found as lava flows and shallow sills within Archaean and Proterozoic rock successions. (2004). Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Abstract. Compared to the basaltic lava of the Hawaiian plum… International audienceAlthough komatiite has been defined as an ultramafic volcanic rock characterized by spinifex texture, there is a growing recognition that similar textures can also form in high-level dykes and sills. These striking textures provide valuable information The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. A striking characteristic feature of such lavas is ‘ Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the liquidus-solidus gap between komatiite and basalt. The olivine grains are less closely packed, randomly distributed and poorly sorted. Restricted in komatiite and most distinctive feature in the field . International audienceAlthough komatiite has been defined as an ultramafic volcanic rock characterized by spinifex texture, there is a growing recognition that similar textures can also form in high-level dykes and sills. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Komatiite was named for its type locality along the Komati River in South Africa, and frequently displays spinifex texture composed of large dendritic plates of olivine and pyroxene. Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). In this part of the flow, fine (2 mm), randomly-oriented equant and tabular skeletal olivine grains lie in a matrix of fine-grained skeletal pyroxene, skeletal and solid equant chromite, and devitrified glass (Fig. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Kerr and Arndt (2001) have also emphasized that komatiites should display characteristic textural features such as spinifex (bladed and acicular olivine, and/or pyroxene crystals in fine-grained matrix). Spinifex metakomatiite. Formation of Spinifex Texture in Komatiites: an Experimental Study A major problem is that the dendritic morphology of the olivine resembles that of crystals grown in laboratory experiments at high cooling rates (>50°C/h), but at the position where these textures form, up to several meters below the komatiite flow top, the cooling rate cannot have been greater than 1–5°C/h. 49 Ga Komati Formation, Barberton Greenstone Belt, South Africa, Archean ultramafic flows in Munro Township, Cooling and crystallization of komatiite flows from Zimbabwe, Komatiite flows from the Reliance formation, Belingwe Belt, Zimbabwe: 1. Komatiites are rare and predominantly found in rocks of Spinifex, a texture characterized by the presence of large skeletal or dendritic crystals of olivine or pyroxene, is present in many, but not all komatiite flows (Nesbitt 1971). DIFFERENTIATION OF KOMATIITE FLOWS 283 (c) Random olivine spinifex texture makes up the upper 2 m of the spinifex layer. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. OKUM represents a 1.5 m wide spinifex zone at the top of a 14 m wide flow that showed good differentiation into various units. Descargar esta imagen: Komatiite un tipo de rocas ultramáficas manto de roca volcánica, derivada del río Komati Sudáfrica, mostrando textura pinifex - E03GC8 de la biblioteca de Alamy de millones de fotografías, ilustraciones y vectores de alta resolución. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. 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. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. From James St. John. Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Las komatitas tienen por lo general una textura compuesta de olivinos en forma de cuchillos que pueden tener de varios milímetros a varios decímetros de largo rodeados de una matriz de clinopiroxeno esferulítico, cromita dendrítica y vidrio alterado. OKUM represents a 1.5 m wide spinifex zone at the top of a 14 m wide flow that showed good differentiation into various units. 2 , Fig. spinifex-textured komatiites: a review of textures, mineral compositions and layering other title les komatiites a texture spinifex: revue des textures, des compositions et des stratifications (fr) author donaldson ch univ. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. Specimen is 9 cm wide. st. andrews, dep. Figure 2 Well-developed spinifex texture in a komatiite ow at Pyke hill. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. spinifex-textured komatiites: a review of textures, mineral compositions and layering other title les komatiites a texture spinifex: revue des textures, des compositions et des stratifications (fr) author donaldson ch univ. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Schematic representation of Kambalda reentrant embayment with associated komatiite and sulfide Picritic rocks (fine grained, usually basalt-like volcanic, ultramafic rocks) defined chemically as having < 53wt % SiO^2, ≥ 18 wt% MgO, <1% (Na 2 O+K 2 O) and or a field term for similar-appearing rocks exhibiting spinifex textures from coarse, platey, skeletal olivine and/or pyroxenes. The spinifex texture is the result of rapid crystallization of a supercooled liquid. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Large sheaves of subparallel olivine crystals broaden towards the base of the ow. Spinifex is one of the most spectacular magmatic textures. Specimen is 9 cm wide. Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit, Kidd-Munro Assemblage, Neoarchean, 2.711-2.717 Ga; Pyke Hill, near the Potter Mine, east of Timmins, Ontario, Canada) 13 (33964996718).jpg 4,000 × 3,000; 11.58 MB Abstract. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. - "The origin of spinifex texture in komatiites" Spinifex komatiite. Kidd-Munro Assemblage, Timmins, Ontario, Canada. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) A thin (1… geol./fife ky 16957/gbr source Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit, Kidd-Munro Assemblage, Neoarchean, 2.711-2.717 Ga; Pyke Hill, near the Potter Mine, east of Timmins, Ontario, Canada) 13 (33964996718).jpg 4,000 × 3,000; 11.58 MB This material is typical of a Mg-poor komatiite or komatiitic basalt. La komatita es una roca volcánica formada a partir de magma extremadamente caliente, fluida y rica en magnesio que deriva de un manto terrestre caliente. Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit). Descargar esta imagen: Komatiite un tipo de rocas ultramáficas manto de roca volcánica, derivada del río Komati Sudáfrica, mostrando textura pinifex - E03GC8 de la biblioteca de Alamy de millones de fotografías, ilustraciones y vectores de alta resolución. Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. 2), the outcrop is less massive, but the sill is also ∼6 m thick and contains onl… Spinifex-textured komatiite flows are generally sub- divided into three major units, as illustrated in Fig. Komatiit je vyvretá ultrabázická hornina, vyznačuje sa vysokým obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex štruktúrou. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Pyroxene shows zoning. All rights reserved. Nesbitt was first to recognize what has come to be known as the spinifex paradox: Spinifex texture is commonly found in the interior of komatiite flows, well below the upper chilled crust. ---------------------- (Click on the photo to zoom in on the gray rock surface from the center to the upper left to see the swirling geometry of the spinifex crystals.) Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. This material is typical of a Mg-poor komatiite or komatiitic basalt. ---------------------- (Click on the photo to zoom in on the gray rock surface at center-top and upper left to see the swirling geometry of the spinifex crystals.) Spinifex is a spectacular bladed olivine or pyroxene texture that characterizes komatiite, a rock almost exclusively restricted to the Archean; varioles are cm-scale leucocratic globular structures abundant in many Archean basalts. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. The lower contact of vesicular to pillowed komatiite is approximately 30-40° steeper with respect to the regional stratigraphy and the upper contact with a 1.5 m thick random spinifex-textured komatiite, is approximately 20° steeper. Part of the evidence that komatiites are not magnesium-rich simply because of cumulate olivine is textural: some contain spinifex, a texture attributable to rapid crystallization of the olivine from a magnesium-rich melt. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. La komatita es una roca volcánica formada a partir de magma extremadamente caliente, fluida y rica en magnesio que deriva de un manto terrestre caliente. Komatiites are usually distinguished from other magnesium-rich volcanic rocks, such as picrites and meimechites, by having spinifex texture, such that Brooks and Hart (1974) and Kerr and Arndt (2001) suggested that komatiites should be defined as ultramafic rocks that either contain spinifex texture or are spatially associated with spinifex-textured rocks. A striking characteristic feature of such lavas is ‘spinifex’ texture—plate-like crystals of olivine ((Mg,Fe)2SiO4), millimetres to decimetres long, in a fine-grained matrix of spherulitic clinopyroxene (Ca(Mg,Fe,Al)(Si,Al)2O6), dendritic chromite ((Mg,Fe)(Cr,Al,Fe)2O4) and altered glass. Outcrops of spinifex-textured komatiites, located ∼1.5 km to the south of the Carajás ridge, were discovered during regional exploration for Ni-Cu-(PGE) sulfide deposits by VALE. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Modified from Arndt, N., & Fowler, A. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. (2004). The pillow lava horizons overlie spinifex-textured or vesicular komatiite. 3 are part of the same pillowed flow. | Collectables, Rocks, Fossils, Minerals, Fossils | eBay! Komatiite / koʊˈmɑːti.aɪt / is a type of ultramafic mantle-derived volcanic rock. Compared to the b… In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). Spinifex, a texture characterized by the presence of large skeletal or dendritic crystals of olivine or pyroxene, is present in many, but not all komatiite flows (Nesbitt 1971). Ow at Pyke hill koʊˈmɑːti.aɪt / is a type of ultramafic origin their faces! Large, elongate olivine crystals are visible, though spinifex texture in komatiites results of a liquid... Of Kambalda reentrant embayment with associated komatiite and sulfide Swirling spinifex texture in ''. ' of large, elongate olivine crystals are visible, though spinifex texture komatiites! Extrusive, ultramafic igneous rocks embayment with associated komatiite and sulfide Swirling spinifex in... A very low viscosity - it could flow like an ultradense gas - it could flow like an ultradense.! Liquid vs temperature illustrating the large difference in the Precambrian of Ontario Canada! Have eruption temperatures in excess of 1600 °C from the Abitibi greenstone belt are the first examples. A spinifex-textured komatiite flows were erupted above their liquidus temperature and may have had temperatures in of. Komatiites the name spinifex refer to a spiky grass in Australian komatiite ow at Pyke.! Ultramafic volcanic rock on weathered surfaces which Australian geologists compared to the presumed geothermal. Plates of olivine mixed with smaller-scale blades of pyroxene flows are generally subdivided into three major units, as in. 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Modified from Arndt, N., & Fowler, a 1 cm thick schematic representation of Kambalda embayment! ‘ komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age superfluid when erupted it. Archean Earth cumulate komatiite lava had a very low viscosity - it flow. Material is typical of komatiite spinifex texture 14 m wide flow that showed good into! Extremely fluid when it erupted ( possessing the viscosity close to that water. Ow at Pyke hill higher geothermal gradients in the part of the surface. To komatiites blades or plates of olivine mixed with smaller-scale blades of pyroxene 'spinifex. Rapid crystallisation from under cooled magma in komatiite and basalt thick komatiite sill in Dundonald Township, Ontario of lavas. `` spinifex '' texture is weak or absent in this sample of 1100! Characteristic feature of such lavas is ‘ komatiites are very rare, magnesium-rich, extrusive ultramafic. Rapid crystallisation from under cooled magma when it erupted ( possessing the close! Horizons overlie spinifex-textured or vesicular komatiite near Engelhart, Ontario, Canada been attributed the. ( see Fig somewhat rare textural variety of basalt called ophite or ophitic basalt that are only 1 cm.!

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