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Examples of volatiles within magma include water, carbon dioxide, and halogen gases. [1] High pressures allow these volatiles to stay relatively stable within solution. [1] However, over time, as the magmatic pressure decreases, volatiles will rise out of solution in the gaseous phase, further decreasing the magmatic pressure. [1]
Gas is thus important in a volcano system because it generates explosive eruptions. [2] Magma in the mantle and lower crust has a high volatile content. Water and carbon dioxide are not the only volatiles that volcanoes release; other volatiles include hydrogen sulfide and sulfur dioxide. Sulfur dioxide is common in basaltic and rhyolite rocks.
As magma ascends towards the surface, the ambient pressure decreases, which decreases the solubility of the dissolved volatiles. Once the solubility decreases below the volatile concentration, the volatiles will tend to come out of solution within the magma (exsolve) and form a separate gas phase (the magma is super-saturated in volatiles).
Such magmas, and those derived from them, build up island arcs such as those in the Pacific Ring of Fire. [70] These magmas form rocks of the calc-alkaline series, an important part of the continental crust. [71] With low density and viscosity, hydrous magmas are highly buoyant and will move upwards in Earth's mantle. [72]
Melt inclusions can be used to determine the composition, compositional evolution and volatile components [14] of magmas that existed in the history of magma systems. This is because melt inclusions act as a tiny pressure vessel that isolates and preserves the ambient melt surrounding the crystal before they are modified by later processes ...
Where hotspots are developed beneath the continents the products are different, as the mantle-derived magmas cause melting of the continental crust, forming granitic magmas that reach the surface as rhyolites. The Yellowstone hotspot is an example of continental hotspot magmatism, which also displays time-progressive shifts in magmatic activity.
Magma mixing is the process by which two magmas meet, comingle, and form a magma of a composition somewhere between the two end-member magmas. Magma mixing is a common process in volcanic magma chambers, which are open-system chambers where magmas enter the chamber, [ 10 ] undergo some form of assimilation, fractional crystallisation and ...
Then as the magma crystallizes, volatiles such as water, carbon dioxide and sulfur dioxide increase in concentration in the liquid phase of the magma. [1] Eventually, at a very late stage of crystallization, the volatile concentration becomes so great that a separate hydrothermal fluid phase separated from the silicate magma. [1]