st. andrews, dep. The type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 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. Restricted in komatiite and most distinctive feature in the field . Basaltic lavas normally have eruption temperatures of about 1100 to 1250 °C. Large, downward-radiating spinifex textures in komatiitic. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 3 are part of the same pillowed flow. Komatiitic lava would have behaved as a superfluid when erupted; it would have behaved as fluidly as water. 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. From Large igneous provinces. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. Komatiite sample collected from the Abitibi greenstone belt near Englehart, Ontario, Canada. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Swirling spinifex texture in metakomatiite in the Precambrian of Ontario, Canada. 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 igneous rock. Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE 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. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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. The spinifex texture is the result of rapid crystallization of a supercooled liquid. 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 are rare and predominantly found in rocks of 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 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. [Del río Komati (Transvaal, Suráfrica)]. 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 Sampling location The source material for OKUM was collected at Serpentine Mountain in McArthur Township, 25 km south of Timmins, NE Ontario, Canada. Schematic representation of Kambalda reentrant embayment with associated komatiite and sulfide 2 , Fig. A thin (1… The higher melting temperatures required to produce komatiite have been attributed to the presumed higher geothermal gradientsin the Archean Earth. Formed due to rapid cooling of rich magnesium lavas. 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. ---------------------- Komatiites are very rare, magnesium-rich, extrusive, ultramafic igneous rocks. 1). 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. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. This material is typical of a Mg-poor komatiite or komatiitic basalt. 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. Komati River Valley, South Africa. geol./fife ky 16957/gbr source [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. 3D). Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. In lavas, these crystals form a pattern on weathered surfaces which Australian geologists compared to the local desert grass Triodia spinifex (). The olivine grains are less closely packed, randomly distributed and poorly sorted. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. textura spinifex. Komatiites were named for their type locality along the Komati River in South Africa. 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. Primary (magmatic) mineral species also encountered in komatiites include olivine, the pyroxenes augite, pigeonite and bronzite, plagioclase, chromite, ilmenite and rarely pargasitic amphibole. 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. 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). Basaltic lavasnormally have eruption temperatures of about 1100 °C to 1250°C. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. 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 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. st. andrews, dep. From James St. John. Komatiite sample collected near Engelhart, Ontario, Canada. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Modified from Arndt, N., & Fowler, A. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. 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