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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.
The formation of pull-apart basins along strike-slip faults causes decompression melting. Advection of melts and heat flux into the lower crust results in partial melting of crustal rock. [16] The buoyant magma rises due to its lower density and is able to exploit weaknesses such as fault planes, using strike-slips as conduits for motion. [4]
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.
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.
Rocks in the lower crust and the upper mantle are subject to partial melting. The rate of partial melting and the resultant silicate melt composition depend on temperature, pressure, flux addition (water, volatiles) and the source rock composition. [4] In oceanic crust, decompression melting of mantle materials forms basaltic magma.
When a plume head encounters the base of the lithosphere, it is expected to flatten out against this barrier and to undergo widespread decompression melting to form large volumes of basalt magma. It may then erupt onto the surface. Numerical modelling predicts that melting and eruption will take place over several million years. [16]
Near-isothermal decompression after the peak (Stage 1 retrograde metamorphism) [2] Further decompression and cooling at a slow rate (Stage 2 retrograde metamorphism) [ 2 ] One might expect that the rock reaches its peak metamorphism at the peak temperature and pressure at similar time, and near- isothermal decompression P-T-t path is observed ...
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.