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Magmatism. Geological map showing the Gangdese batholith, which is a product of magmatic activity about 100 million years ago. Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production ...
Oceanic magmas likely result from partial melting of 3% to 15% of the source rock. [81] Some calk-alkaline granitoids may be produced by a high degree of partial melting, as much as 15% to 30%. [82] High-magnesium magmas, such as komatiite and picrite, may also be the products of a high degree of partial melting of mantle rock. [83]
Mechanism of formation. Bimodal volcanism is normally explained as a result of partial melting of the crust, creating granitic magmas, during the emplacement of large volumes of relatively hot basaltic magma from a mantle source. The two magma types then form separate magma chambers giving rise to periodic eruption of both types of lava. [7][8]
Granite often occurs as relatively small, less than 100 km 2 stock masses and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations, very coarse-grained pegmatite masses occur with granite. [18]
Rhyolite (/ ˈraɪ.əlaɪt / RY-ə-lyte) [1][2][3][4] is the most silica -rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase.
In essence, fractional crystallization is the removal of early formed crystals from an originally homogeneous magma (for example, by gravity settling) so that these crystals are prevented from further reaction with the residual melt. [3] The composition of the remaining melt becomes relatively depleted in some components and enriched in others ...
The plutons associated with the Sierra Nevada Batholith intruded into pre-existing rocks on the North American Continent. As the plutons intruded into these rocks, many were altered or metamorphosed. The "host rocks" include passive margin sequence units, deep water sediments, and shallow-water passive margin units.
The S-type Granya Granite shows the characteristic white feldspars, grey quartz, and black biotite, the highly reflective mineral is muscovite. The S-type Strathbogie Granite crops out in the Strathbogie Ranges of Australia. A hand sample from the Strathbogie Granite has a porphyritic texture with larger crystal of grey quartz, called ...