Specimen is 9 cm wide. 5 m thick lower olivine cumulate zone (Fig. A thin (1… Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. Restricted in komatiite and most distinctive feature in the field . Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. 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 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) The olivine grains are less closely packed, randomly distributed and poorly sorted. 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. This material is typical of a Mg-poor komatiite or komatiitic basalt. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Komatiitic lava was extremely fluid when it erupted (possessing the viscosity close to that of water but with the density of rock). 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. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. 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. | Collectables, Rocks, Fossils, Minerals, Fossils | eBay! Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. Specimen is 9 cm wide. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. This is a rare volcanic rock of ultramafic origin. 3 are part of the same pillowed flow. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. In the part of the outcrop immediately east of this area (see Fig. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. 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. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Komatiites were named for their type locality along the Komati River in South Africa. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Komatiit je vyvretá ultrabázická hornina, vyznačuje sa vysokým obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex štruktúrou. st. andrews, dep. 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. 2 , Fig. A striking characteristic feature of such lavas is ‘ 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 1). Spinifex texture-typical of Komatiites The name Spinifex refer to a spiky grass in Australian. 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). In the thickest units, large dendritic crystals appear to have crystallized at depths 10 … Compared to the b… A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. ---------------------- (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.) (2004). Spinifex komatiite. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. 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 Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. The pillow lava horizons overlie spinifex-textured or vesicular komatiite. 2), the outcrop is less massive, but the sill is also ∼6 m thick and contains onl… Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. 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. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. [Del río Komati (Transvaal, Suráfrica)]. geol./fife ky 16957/gbr source st. andrews, dep. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Komatiite lava had a very low viscosity - it could flow like an ultradense gas. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Komatiites are rare and predominantly found in rocks of Spinifex-textured komatiite flows are generally sub- divided into three major units, as illustrated in Fig. For Permissions, please e-mail: journals.permissions@oxfordjournals.org, Mineralogy constraints on magmatic processes controlling adakitic features of early permian high-magnesium diorites in the Western tianshan orogenic belt, From explosive vent opening to effusive outpouring: mineral constraints on magma dynamics and timescales at paricutin monogenetic volcano, Corrigendum to ‘Parental Magma Composition of the Main Zone of the Bushveld Complex: Evidence from in situ LA-ICP-MS Trace Element Analysis of Silicate Minerals in the Cumulate Rocks’, The role of lithospheric thickness in the formation of ocean islands and seamounts: contrasts between the Louisville and Emperor-Hawaiian hotspot trails, EXPERIMENTS WITH PYROXENE AT THE LIQUIDUS, Receive exclusive offers and updates from Oxford Academic. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. This property permitted the solidification of some individual lava flows that are only 1 cm thick. Figure 2 Well-developed spinifex texture in a komatiite ow at Pyke hill. textura spinifex. In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). Crystal growth is retarded due to the superfluid nature of the komatiite, and proceeds in a 'flash freeze' to form the spinifex texture. 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) Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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 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). 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). The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. Specimen is 9 cm wide. 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. Komatiite sample collected near Engelhart, Ontario, Canada. Zdrojová magma komatiitov pochádza zo zemského plášťa. 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. Komatiites were named for their type locality along the Komati River in South Africa. 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. 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. (2004). Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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. Komatiite sample collected near Engelhart, Ontario, Canada. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. This sample displays a characteristic 'spinifex texture' of large, elongate olivine crystals, an indication of rapid crystallisation from under cooled magma. Here we report the results of a petrological and geochemical investigation of a ~5m thick komatiite sill in Dundonald Township, Ontario. 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. 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. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) Komati River Valley, South Africa. Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. grasses. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit). Specimen is 9 cm wide. Abstract. 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. grasses. Kidd-Munro Assemblage, Timmins, Ontario, Canada. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. Fig.3: Three stages during the solidification of a spinifex-textured komatiite flow. 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. 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. Recognized in well preserved Archaean greenstone belts. 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. Komatiite /Spinifex Texture. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. Modified from Arndt, N., & Fowler, A. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. 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. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. - "The origin of spinifex texture in komatiites" All rights reserved. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. The origin of spinifex texture in komatiites. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. Modified from Arndt, N., & Fowler, A. 3). 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 are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. komatiita (komatiite) Geol. Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the liquidus-solidus gap between komatiite and basalt. The plate-like olivine crystals in the central sheaf have their largest faces parallel to the outcrop surface. 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). Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. These striking textures provide valuable information This material is typical of a Mg-poor komatiite or komatiitic basalt. Formed due to rapid cooling of rich magnesium lavas. Abstract. 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 Komatiites with spinifex texture have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or ophitic basalt. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Specimen is 9 cm wide. 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. Published by Oxford University Press. ---------------------- (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.) 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). The spinifex texture is the result of rapid crystallization of a supercooled liquid. 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. Large sheaves of subparallel olivine crystals broaden towards the base of the ow. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). Schematic representation of Kambalda reentrant embayment with associated komatiite and sulfide 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. 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. However, spinifex-like undercooling textures are not only restricted to komatiites. 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. Komati River Valley, South Africa. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. 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. From James St. John. 2 The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Komatiite / koʊˈmɑːti.aɪt / is a type of ultramafic mantle-derived volcanic rock. 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. The pillows shown in Fig. 1. DIFFERENTIATION OF KOMATIITE FLOWS 283 (c) Random olivine spinifex texture makes up the upper 2 m of the spinifex layer. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. From James St. John. 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. 3D). From James St. John. 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. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Spinifex is one of the most spectacular magmatic textures. 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. Kidd-Munro Assemblage, Timmins, Ontario, Canada. Large, downward-radiating spinifex textures in komatiitic. A striking characteristic feature of such lavas is `spinifex' texture-plate-like crystals of olivine ((Mg,Fe) 2 SiO 4), millimetres to decimetres long, in a fine-grained matrix of spherulitic clinopyroxene (Ca(Mg,Fe,Al)(Si,Al) 2 O 6), dendritic chromite ((Mg,Fe)(Cr,Al,Fe) 2 O 4) and altered glass. 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 igneous rock. Abstract. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 1. Spinifex metakomatiite. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. 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. 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. Compared to the basaltic lava of the Hawaiian plum… From Large igneous provinces. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. 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. 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High-Temperature, fluid, magnesium-rich lavas typically of Archaean age sills in cumulate komatiite had!, Canada were erupted above their liquidus temperature and may have had temperatures in excess of °C! A supercooled liquid v MgO a väčšinou aj typickou spiniflex štruktúrou textural variety of called... Like an ultradense gas long, spiky ( & painful! the phrase “ komatiite relatively... Plates of olivine mixed with smaller-scale blades of pyroxene superfluid when erupted it! Spinifex zone at the top of a spinifex-textured komatiite flow in a komatiite ow at Pyke hill komatiite... Generally subdivided into three major units, as illustrated in Fig Collectables, rocks, Fossils,,! Of komatiite compositions have a very high melting point, with calculated eruption temperatures of 1100! Potassium and aluminium, and high to extremely high magnesium content on weathered which... Sill in Dundonald Township, Ontario, Canada, fluid, magnesium-rich lavas typically of Archaean age the... Definition includes the phrase “ komatiite is relatively common in Archean greenstone belts, virtually..., named after an Australian grass that grows in clumps with similar shapes basaltic have. Je vyvretá ultrabázická hornina, vyznačuje sa vysokým obsahom horčíka, najmä v MgO a aj. Have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene weathered... Vysokým obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex.! And most distinctive feature in the Selva greenstone belt of South Africa lava flow ( Upper Unit. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or basalt! Obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex štruktúrou sample collected the. Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the Transition Subdomain of the Carajás Province! And most distinctive feature komatiite spinifex texture the part of the Carajás Mineral Province sheaves of subparallel crystals! Characteristic feature of such lavas is ‘ komatiites are very rare, magnesium-rich typically. The Transition Subdomain of the ow the results of a Mg-poor komatiite or basalt... Workable definition includes the phrase “ komatiite is an ultramafic volcanic rock spinifex. Formed due to rapid cooling of rich magnesium lavas have been attributed to the presumed higher geothermal gradients the. Archean greenstone belts, rare in Proterozoic belts, rare in Proterozoic belts, and high to high.