Crystal growth is retarded due to the superfluid nature of the komatiite, and proceeds in a 'flash freeze' to form the spinifex texture. 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 type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. These striking textures provide valuable information st. andrews, dep. Spinifex is one of the most spectacular magmatic textures. 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. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. This sample displays a characteristic 'spinifex texture' of large, elongate olivine crystals, an indication of rapid crystallisation from under cooled magma. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. Komatiite sample collected from the Abitibi greenstone belt near Englehart, 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. 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!) This material is typical of a Mg-poor komatiite or komatiitic basalt. geol./fife ky 16957/gbr source Komati River Valley, South Africa. 1. From Large igneous provinces. textura spinifex. Komatiite ( /koʊˈmɑːti.aɪt/) is a type of ultramafic mantle-derived volcanic rock defined as having crystallised from a lava with ≥ 18 wt% MgO. 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). Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. Modified from Arndt, N., & Fowler, A. 1. In the part of the outcrop immediately east of this area (see Fig. Komatiite / koʊˈmɑːti.aɪt / is a type of ultramafic mantle-derived volcanic rock. 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. Bladed olivine crystals are visible, though spinifex texture is weak or absent in this sample. A workable definition of komatiite should include the phrase “komatiite is an ultramafic volcanic rock containing spinifex or related to lavas containing this texture”. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content. [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. Keweenaw rift rocks include a somewhat rare textural variety of basalt called ophite or ophitic basalt. Komatiites are high-temperature, fluid, magnesium-rich lavas typically of Archaean age. From James St. John. ---------------------- (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.) DIFFERENTIATION OF KOMATIITE FLOWS 283 (c) Random olivine spinifex texture makes up the upper 2 m of the spinifex layer. 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. 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 type area is the 3.5 Ga Barberton greenstone belt of South Africa where the rock type was first discovered. 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. Komatiites are rare and predominantly found in rocks of The plate-like olivine crystals in the central sheaf have their largest faces parallel to the outcrop surface. [1] [2] [3] La erupción de komatitas fue particularmente común en el Precámbrico, cuando el flujo de calor en la Tierra era mayor. Many komatiite flows were erupted above their liquidus temperature and may have had temperatures in excess of 1600°C. Is an ultramafic volcanic rock of ultramafic origin good differentiation into various units had temperatures in excess of 1600°C common. 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