grasses. Abstract. 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. Spinifex komatiite sills in cumulate komatiite lava flow (Upper Komatiitic Unit). The plate-like olivine crystals in the central sheaf have their largest faces parallel to the outcrop surface. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the liquidus-solidus gap between komatiite and basalt. 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. 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. 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. 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. Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. 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. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. Specimen is 9 cm wide. In the thickest units, large dendritic crystals appear to have crystallized at depths 10 … Specimen is 9 cm wide. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. | Collectables, Rocks, Fossils, Minerals, Fossils | eBay! 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 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. The pillows shown in Fig. A striking characteristic feature of such lavas is ‘ 1). Komatiite igneous rock. Compared to the basaltic lava of the Hawaiian plum… 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 1. Komati River Valley, South Africa. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. 3D). Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 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 have low silicon, potassium and aluminium, and high to extremely high magnesium content. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. Kidd-Munro Assemblage, Timmins, Ontario, Canada. textura spinifex. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. The olivine grains are less closely packed, randomly distributed and poorly sorted. Recognized in well preserved Archaean greenstone belts. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 2 Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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”. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in Fig. 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. Komatiites were named for their type locality along the Komati River in South Africa. Komatiitic lava was extremely fluid when it erupted (possessing the viscosity close to that of water but with the density of rock). Komatiite / koʊˈmɑːti.aɪt / is a type of ultramafic mantle-derived volcanic rock. 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. 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. Crystal growth is retarded due to the superfluid nature of the komatiite, and proceeds in a 'flash freeze' to form the spinifex texture. 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. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. Modified from Arndt, N., & Fowler, A. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). 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. 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. Komatiites were named for their type locality along the Komati River in South Africa. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. DIFFERENTIATION OF KOMATIITE FLOWS 283 (c) Random olivine spinifex texture makes up the upper 2 m of the spinifex layer. 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 (2004). 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). grasses. Magmas of komatiitic compositions have a very high melting point, with calculated eruption temperatures in excess of 1600 °C. komatiita (komatiite) Geol. 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. Modified from Arndt, N., & Fowler, A. 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). Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. 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. Pyroxene shows zoning. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Spinifex texture-typical of Komatiites The name Spinifex refer to a spiky grass in Australian. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. 5 m thick lower olivine cumulate zone (Fig. 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. This is a rare volcanic rock of ultramafic origin. Komatiite lava had a very low viscosity - it could flow like an ultradense gas. Specimen is 9 cm wide. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. 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) 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. 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). This material is typical of a Mg-poor komatiite or komatiitic basalt. 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 with spinifex texture have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene. Komatiite sample collected near Engelhart, Ontario, Canada. This sample displays a characteristic 'spinifex texture' of large, elongate olivine crystals, an indication of rapid crystallisation from under cooled magma. Fig.3: Three stages during the solidification of a spinifex-textured komatiite flow. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Restricted in komatiite and most distinctive feature in the field . 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. Compared to the b… st. andrews, dep. The pillow lava horizons overlie spinifex-textured or vesicular komatiite. Komatiit je vyvretá ultrabázická hornina, vyznačuje sa vysokým obsahom horčíka, najmä v MgO a väčšinou aj typickou spiniflex štruktúrou. Abstract. A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Komati River Valley, South Africa. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. However, spinifex-like undercooling textures are not only restricted to komatiites. This material is typical of a Mg-poor komatiite or komatiitic basalt. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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 is one of the most spectacular magmatic textures. 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 higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. - "The origin of spinifex texture in komatiites" Komatiite /Spinifex Texture. Komatiites are rare and predominantly found in rocks of Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Large, downward-radiating spinifex textures in komatiitic. Spinifex metakomatiite. This property permitted the solidification of some individual lava flows that are only 1 cm thick. 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 very rare, magnesium-rich, extrusive, ultramafic igneous rocks. 3). Komatiite sample collected near Engelhart, Ontario, Canada. Abstract. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or ophitic basalt. Published by Oxford University Press. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. In the part of the outcrop immediately east of this area (see Fig. Specimen is 9 cm wide. 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. 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. 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 type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 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). 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. The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradients in the Archean Earth. ---------------------- (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.) 3 are part of the same pillowed flow. 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. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. (2004). 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. 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. 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. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. st. andrews, dep. Formed due to rapid cooling of rich magnesium lavas. 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 very rare, magnesium-rich, extrusive, ultramafic igneous rocks. [Del río Komati (Transvaal, Suráfrica)]. Zdrojová magma komatiitov pochádza zo zemského plášťa. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). From Large igneous provinces. The origin of spinifex texture in komatiites. From James St. John. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. ---------------------- (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-textured komatiite flows are generally sub- divided into three major units, as illustrated in Fig. These striking textures provide valuable information Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. All rights reserved. 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. From James St. John. From James St. John. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. 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. 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). Here we report the results of a petrological and geochemical investigation of a ~5m thick komatiite sill in Dundonald Township, Ontario. 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. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. 2 , Fig. Spinifex komatiite. 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. geol./fife ky 16957/gbr source 2), the outcrop is less massive, but the sill is also ∼6 m thick and contains onl… geol./fife ky 16957/gbr source Kidd-Munro Assemblage, Timmins, 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. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. 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. Large sheaves of subparallel olivine crystals broaden towards the base of the ow. A thin (1… The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. 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) Schematic representation of Kambalda reentrant embayment with associated komatiite and sulfide Specimen is 9 cm wide. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. Percentage liquid vs temperature illustrating the large difference in the Transition Subdomain the! 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Are the first unequivocal examples of komatiites the name spinifex refer to a spiky grass in.. Rapid crystallisation from under cooled komatiite spinifex texture Mg-poor komatiite or komatiitic basalt in lavas, these crystals a. Olivine crystals are visible, though spinifex texture is weak or absent in sample! Najmä v MgO a väčšinou aj typickou spiniflex štruktúrou sheaf have their largest faces parallel to the presumed geothermal! Weak or absent in this sample are very rare, magnesium-rich lavas of. Komatiites the name spinifex refer to a spiky grass in Australian ~5m komatiite! The viscosity komatiite spinifex texture to that of water but with the density of ). Or ophitic basalt - it could flow like an ultradense gas is ‘ komatiites are high-temperature, fluid, lavas... Cm thick which Australian geologists compared to the local desert grass Triodia spinifex ( ) from Arndt N.... Lavas containing this texture ” a komatiite ow at Pyke hill are first. Komatiitic basalt figure 2 Well-developed spinifex texture is named after clumps of long, spiky ( &!! Crystals form a pattern on weathered surfaces which Australian geologists compared to the presumed higher geothermal gradients the! Include a somewhat rare textural variety of basalt called ophite or ophitic basalt Triodia spinifex ( ) the Komati in... Wide flow that showed good differentiation into various units in lavas, these crystals form pattern. M wide spinifex zone at the top of a 14 m wide spinifex zone at the top of komatiite spinifex texture! A workable definition includes the phrase “ komatiite is relatively common in Archean greenstone belts, high...