komatiite spinifex texture

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

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