Partial melting

[1] The parameters that influence partial melting include the composition of the source rock, the pressure and temperature of the environment, and the availability of water or other fluids.

[2] With a few exceptions (e.g., Yellowstone[3]), conduction of heat is considered a mechanism too slow and inefficient to partially melt large bodies of rock.

Magmatic and hydrothermal ore deposits, such as chromite, Ni-Cu sulfides, rare-metal pegmatites, kimberlites, volcanic-hosted massive sulfide deposits are some examples of valuable natural resources closely related to the conditions of the origin, migration and emplacement of partial melts.

The extent to which partial melting occurs depends on the balance between temperature and pressure, with both having a strong influence on the process.

Furthermore, some consider that volatiles control the stability of minerals and the chemical reactions that happen during partial melting,[10] while others assign a more subordinate role to these components.

In continental rifts, where the lithosphere is colder and more rigid, decompression melting occurs when material from the hot and more plastic asthenosphere is transported to lower pressures.

In this case, when water, oceanic crustal material and metamorphosed mantle rocks are added into the system, minerals can be melted at lower temperatures.

In this event, if sufficient heat is released, it can cause the melting of the surrounding rocks and the creation of felsic magma.

A rock with composition C B starts to melt when its temperature is T A and reaches the solidus curve, the temperature below which all the substance is solid. The newly formed liquid phase has an initial composition of C L at T A . As the temperature increases towards T B , the partial melting of the solid phase leads to changes in composition from C B to C S (blue line). As the liquid phase increases, its composition gets closer to the rock’s original composition C B (red line). When the temperature reaches T B , the whole solid phase has melted, characterizing the substance being above the liquidus curve. [ 5 ] [ 6 ]
Diagram showing the physical processes inside the Earth that lead to the generation of magma. The plots above show the rate at which the temperature (red line) and the solidus (green line) change based on depth and tectonic setting (A to D). [ 12 ]
A close-up showing a mid-ocean ridge with a magma reservoir below. Hot and less dense mantle rocks rise to lower pressure zones leading to decompression melting. [ 13 ]
At 4,800 m above sea level , Klyuchevskoi is located in Kamchatka , Russia and is a product of flux melting on a subduction zone . [ 14 ]