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Basalt (UK: / ˈ b æ s ɔː l t,-əl t /; [1] US: / b ə ˈ s ɔː l t, ˈ b eɪ s ɔː l t /) [2] is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon.
Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet 's mantle or crust.
Decompression melting in upwelling asthenosphere likely begins at a depth as great as 100 to 150 kilometers (60 to 90 mi), where the small amounts of volatiles in the mantle rock (about 100 ppm of water and 60 ppm of carbon dioxide) assist in melting not more than about 0.1% of the rock. At a depth of about 70 kilometers (40 mi), dry melting ...
Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts. [1][2] It is typically dark in color (brown, black or purplish-red), and basaltic or andesitic in composition. Scoria has relatively low density, as it is riddled ...
Plumes are postulated to rise through the mantle and begin to partially melt on reaching shallow depths in the asthenosphere by decompression melting. This would create large volumes of magma. The plume hypothesis postulates that this melt rises to the surface and erupts to form "hot spots".
Igneous textures are used by geologists in determining the mode of origin of igneous rocks and are used in rock classification. The six main types of textures are phaneritic, aphanitic, porphyritic, glassy, pyroclastic, and pegmatitic. Aphanitic (a = not, phaner = visible) rocks, in contrast to phaneritic rocks, typically form from lava which ...
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within crust and mantle of a rocky planetary body, such as the Earth. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation. [1]
The resultant molten rock rose through the Earth's crust over the span of 100 Ma, forming several plutons, or a chain of volcanoes if the magma reached the surface. Most of the granitic rocks formed between 105 and 85 Ma, during the Cretaceous , with pluton formation ending around about 70 Ma.