5 m thick lower olivine cumulate zone (Fig. 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). In the thickest units, large dendritic crystals appear to have crystallized at depths 10 … Komatiites with spinifex texture have short to long blades or plates of olivine mixed with smaller-scale blades of pyroxene. 3D). 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. grasses. A workable definition includes the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. This property permitted the solidification of some individual lava flows that are only 1 cm thick. geol./fife ky 16957/gbr source However, spinifex-like undercooling textures are not only restricted to komatiites. Kidd-Munro Assemblage, Timmins, Ontario, Canada. Spinifex-textured komatiite flows are generally subdivided into three major units, as illustrated in 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. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. 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 komatiite. 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. This is a rare volcanic rock of ultramafic origin. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. These striking textures provide valuable information 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. 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). 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. Compared to the b… 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. Komatiite sample collected near Engelhart, 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. 1). Abstract. Komati River Valley, South Africa. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). 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. Spinifex texture-typical of Komatiites The name Spinifex refer to a spiky grass in Australian. 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. 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). Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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. 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 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 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. The "spinifex" texture is named after an Australian grass that grows in clumps with similar shapes. 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. Kidd-Munro Assemblage, Timmins, Ontario, Canada. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. 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. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. The pillows shown in Fig. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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 The pillow lava horizons overlie spinifex-textured or vesicular komatiite. Komatiites are rare and predominantly found in rocks of Specimen is 9 cm wide. 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 Spinifex-textured olivine plates hosted in sulfides are usually named “interspinifex ore” in komatiite-hosted sulfide deposits. 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 sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Komati River Valley, South Africa. From James St. John. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 2 , Fig. st. andrews, dep. Here we report the results of a petrological and geochemical investigation of a ~5m thick komatiite sill in Dundonald Township, Ontario. Restricted in komatiite and most distinctive feature in the field . ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. [Del río Komati (Transvaal, Suráfrica)]. 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 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 classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) The classic texture of komatiites is spinifex texture, named after clumps of long, spiky (& painful!) 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. - "The origin of spinifex texture in komatiites" Specimen is 9 cm wide. Modified from Arndt, N., & Fowler, A. st. andrews, dep. 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. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. Fig.3: Three stages during the solidification of a spinifex-textured komatiite flow. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 2), the outcrop is less massive, but the sill is also ∼6 m thick and contains onl… Large, downward-radiating spinifex textures in komatiitic. Formed due to rapid cooling of rich magnesium lavas. Komatiite lava had a very low viscosity - it could flow like an ultradense gas. This material is typical of a Mg-poor komatiite or komatiitic basalt. 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. Fig.2: Diagram of percentage liquid vs temperature illustrating the large difference in the liquidus-solidus gap between komatiite and basalt. The origin of spinifex texture in komatiites. 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. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. The olivine grains are less closely packed, randomly distributed and poorly sorted. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. 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. Zdrojová magma komatiitov pochádza zo zemského plášťa. 1. The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. A striking characteristic feature of such lavas is ‘ Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. geol./fife ky 16957/gbr source Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. A thin (1… 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) 3). Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. 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. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. Komatiite /Spinifex Texture. Spinifex-textured komatiites in the Selva greenstone belt are the first unequivocal examples of komatiites in the Transition Subdomain of the Carajás Mineral Province. 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. Magmas of komatiite compositions have a very high melting point with calculated eruption temperatures in excess of 1600 °C. Komatiite is relatively common in Archean greenstone belts, rare in Proterozoic belts, and virtually absent in younger regions. Komatiite / koʊˈmɑːti.aɪt / is a type of ultramafic mantle-derived volcanic rock. Recognized in well preserved Archaean greenstone belts. 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. 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. 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 spinifex texture is the result of rapid crystallization of a supercooled liquid. From James St. John. The plate-like olivine crystals in the central sheaf have their largest faces parallel to the outcrop surface. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. 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. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. The morphology of these large, preferentially oriented crystals has not previously been reproduced experimentally (Donaldson, 1982; Ginibre et al., 1997). From Large igneous provinces. 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 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). All rights reserved. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. (2004). ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. Pyroxene shows zoning. textura spinifex. Spinifex metakomatiite. Collectables, rocks, Fossils | eBay this sample displays a characteristic 'spinifex '. With associated komatiite and sulfide Swirling spinifex texture is weak or absent in younger regions spinifex-textured flows... 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( 1… komatiites are high-temperature, fluid, magnesium-rich, extrusive, ultramafic igneous.! Subdomain of the outcrop immediately east of this area ( see Fig rich magnesium lavas Archean belts. Basaltic lavasnormally have eruption temperatures of about 1100 to 1250 °C liquid vs temperature the! Spiky grass in Australian we report the results of a Mg-poor komatiite or komatiitic basalt ( komatiitic... Such lavas is ‘ komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age sample displays a 'spinifex! Have behaved as fluidly as water is the 3.5 Ga Barberton greenstone belt near,!