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Partial melting is the phenomenon that occurs when a rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them. Partial melting is an important part of the formation of all igneous rocks and some metamorphic rocks (e.g., migmatites), as evidenced by a multitude of geochemical, geophysical and petrological studies.
Extension and Decompression Melting - Decompression melting occurs mainly in extensional regimes, where the crust thins, allowing the mantle to upwell to an area of lower pressure where the melting point of the minerals is lower. The formation of pull-apart basins along strike-slip faults causes decompression melting.
Melting that is caused by a drop in pressure is referred to as decompression melting. [8] Decompression melting can occur in thickened portions of the Earth's crust and may be the result of a variety of processes, including erosion, tectonic denudation, and lithospheric thinning. [8]
Decompression melting occurs because of a decrease in pressure. [66] It is the most important mechanism for producing magma from the upper mantle. [67] The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water.
Decompression melting occurs because of a decrease in pressure. [40] The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level.
Many continental rift zones are associated with magmatism due to upwelling of the asthenosphere as the lithosphere is thinned, which leads to decompression melting. [6] The magmatism is often bimodal in character as the mantle-derived basaltic magmas cause partial melting of the continental 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 ...
The presence of pre-existing melt means that magmatism can occur even in areas where lithospheric extension is modest such as the Cameroon and Pitcairn-Gambier volcanic lines. [ 20 ] The rate of magma formation from decompression of the asthenosphere depends on how high the asthenosphere can rise, which in turn depends on the thickness of the ...