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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.
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]
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.
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.
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.
Post-collisional magmatism is a result of decompression melting associated with isostatic rebound and possible extensional collapse of the thickened crust formed during the collision. [3] Slab detachment has also been proposed as a cause of late to post-collisional magmatism.
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 ...
This suggests that decompression melting may contribute, as this, too, is expected to increase with lithospheric thickness. The significant increase in magmatism during the last 2 million years indicates a major increase in melt availability, implying that either a larger reservoir of pre-existing melt or an exceptionally fusible source region ...