Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. geol./fife ky 16957/gbr source The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. Modified from Arndt, N., & Fowler, A. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Spinifex komatiite. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. DIFFERENTIATION OF KOMATIITE FLOWS 283 (c) Random olivine spinifex texture makes up the upper 2 m of the spinifex layer. This is a rare volcanic rock of ultramafic origin. 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). Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. 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). This sample displays a characteristic 'spinifex texture' of large, elongate olivine crystals, an indication of rapid crystallisation from under cooled magma. Restricted in komatiite and most distinctive feature in the field . 2), the outcrop is less massive, but the sill is also ∼6 m thick and contains onl… Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. 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. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Kidd-Munro Assemblage, Timmins, Ontario, Canada. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Large, downward-radiating spinifex textures in komatiitic. Komatiites were named for their type locality along the Komati River in South Africa. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. 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. 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 Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the liquidus-solidus gap between komatiite and basalt. 3 are part of the same pillowed flow. 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 metakomatiite. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. In the thickest units, large dendritic crystals appear to have crystallized at depths 10 … The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 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. 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. 2 , Fig. 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. Figure 2 Well-developed spinifex texture in a komatiite ow at Pyke hill. Abstract. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or ophitic basalt. Pyroxene shows zoning. Komatiite sample collected near Engelhart, Ontario, Canada. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. 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. 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. st. andrews, dep. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. - "The origin of spinifex texture in komatiites" Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. From James St. John. 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. 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) 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. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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. 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). Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. The plate-like olivine crystals in the central sheaf have their largest faces parallel to the outcrop surface. From James St. John. 3). 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. 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 have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiites are rare and predominantly found in rocks of Here we report the results of a petrological and geochemical investigation of a ~5m thick komatiite sill in Dundonald Township, Ontario. 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. Komati River Valley, South Africa. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. 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. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Kidd-Munro Assemblage, Timmins, Ontario, Canada. [Del río Komati (Transvaal, Suráfrica)]. 1). 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 Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Recognized in well preserved Archaean greenstone belts. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Zdrojová magma komatiitov pochádza zo zemského plášťa. 2 A striking characteristic feature of such lavas is ‘ The pillow lava horizons overlie spinifex-textured or vesicular komatiite. 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. Abstract. st. andrews, dep. 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. Abstract. Compared to the basaltic lava of the Hawaiian plum… Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. This property permitted the solidification of some individual lava flows that are only 1 cm thick. Formed due to rapid cooling of rich magnesium lavas. 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 These striking textures provide valuable information Crystal growth is retarded due to the superfluid nature of the komatiite, and proceeds in a 'flash freeze' to form the spinifex texture. The olivine grains are less closely packed, randomly distributed and poorly sorted. Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit). 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. In the part of the outcrop immediately east of this area (see Fig. 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. From Large igneous provinces. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. Komatiites with spinifex texture have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. This material is typical of a Mg-poor komatiite or komatiitic basalt. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). A thin (1… In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) 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. 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). Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. 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. ---------------------- (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.) All rights reserved. Komatiit je vyvretá ultrabázická hornina, vyznačuje sa vysokým obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex štruktúrou. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Spinifex-textured komatiite flows are generally sub- divided into three major units, as illustrated in Fig. Komatiite /Spinifex Texture. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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). | Collectables, Rocks, Fossils, Minerals, Fossils | eBay! Komati River Valley, South Africa. Komatiites were named for their type locality along the Komati River in South Africa. Specimen is 9 cm wide. komatiita (komatiite) Geol. 1. grasses. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. 5 m thick lower olivine cumulate zone (Fig. (2004). 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. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Specimen is 9 cm wide. The spinifex texture is the result of rapid crystallization of a supercooled liquid. Komatiite igneous rock. This material is typical of a Mg-poor komatiite or komatiitic basalt. Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. 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. (2004). Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 3D). Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Specimen is 9 cm wide. 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). 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. ---------------------- (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 are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. 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. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Large sheaves of subparallel olivine crystals broaden towards the base of the ow. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. Fig.3: Three stages during the solidification of a spinifex-textured komatiite flow. 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. Specimen is 9 cm wide. Modified from Arndt, N., & Fowler, A. Komatiitic lava was extremely fluid when it erupted (possessing the viscosity close to that of water but with the density of rock). 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. 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 chemistry is thought to be different from that of basaltic and other common mantle-produced magmas, because of differences in degrees of partial melting. Compared to the b… A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. 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. The origin of spinifex texture in komatiites. Spinifex texture-typical of Komatiites The name Spinifex refer to a spiky grass in Australian. However, spinifex-like undercooling textures are not only restricted to komatiites. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. The pillows shown in Fig. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. 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. From James St. John. Published by Oxford University Press. A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. 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Broaden towards the base of the Carajás Mineral Province ‘ komatiites are high-temperature, fluid, magnesium-rich lavas of...

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