Komatiite

Komatiite is an ultramafic volcanic rock with exceptionally high magnesium content, commonly marked by elongated olivine or pyroxene crystals forming spinifex textures. Most known komatiites formed during the Archean eon.

Ultramafic rock: A rock composed chiefly of minerals with little silica and abundant magnesium and iron. Komatiite is a volcanic member of this broad, magnesium-rich rock group.
Magma: Molten or partly molten rock beneath or at Earth’s surface, containing crystals and dissolved gases. Komatiite forms when unusually hot, magnesium-rich magma reaches the surface and cools.
Archean: The interval of geologic time from about 4.0 to 2.5 billion years ago. Most preserved komatiites date from this interval, when Earth’s mantle was hotter.
Mantle temperature: The thermal state of Earth’s mantle, inferred from geophysical and geochemical evidence. Komatiite compositions provide evidence that Archean mantle temperatures exceeded modern values.
Adiabatic decompression melting: Melting caused when rising mantle rock expands and cools without exchanging heat with its surroundings. Its contribution to komatiite generation depends on mantle temperature and the depth of melting.
Olivine: A magnesium- and iron-rich silicate mineral common in Earth’s mantle and many ultramafic rocks. Its elongated crystals commonly create komatiite’s characteristic spinifex texture.
Fractional crystallization: The evolution of magma as early-forming crystals separate from the remaining liquid. It can alter komatiite magma compositions and concentrate metals during cooling.
Mantle plume: A buoyant upwelling of unusually hot rock rising through Earth’s mantle. Plume-related melting is one proposed source of the high temperatures needed to make komatiite.
Nickel sulfide ore deposits: Concentrations of nickel-bearing sulfide minerals that can be mined as metal ores. Some komatiite flows host economically significant nickel sulfide deposits.
Komatiite petrogenesis: The set of processes by which komatiite magma is generated, modified, and emplaced. Competing source and melting models seek to explain komatiite compositions and eruption temperatures.

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