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11 – magma chamber. A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upwards. [1]
It is worth reiterating that magma chambers are not usually static single entities. The typical magma chamber is formed from a series of injections of melt and magma, and most are also subject to some form of partial melt extraction. Granite magmas are generally much more viscous than mafic magmas and are usually more homogeneous in composition ...
While cooling, the magma evolves in composition because different minerals crystallize from the melt. 1: olivine crystallizes; 2: olivine and pyroxene crystallize; 3: pyroxene and plagioclase crystallize; 4: plagioclase crystallizes. At the bottom of the magma reservoir, a cumulate rock forms.
Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt , andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite ...
This is an idealization, and such processes as magma convection (where cooled magma next to the contact sinks to the bottom of the magma chamber and hotter magma takes its place) can alter the cooling process, reducing the thickness of chilled margins while hastening cooling of the intrusion as a whole. [43]
The fractures take the form of a set of concentric cones dipping at a relatively shallow angle into the magma chamber. [3] [13] When the caldera is subsequently emptied by explosive volcanic activity, the roof of the magma chamber collapses as a plug of rock surrounded by a ring fracture. Magma rising into the ring fracture produces a ring dike.
Here, inflation is a possible mechanism to continue the growth of intrusion. If, at this point, the surface area of the magma is large enough to generate a magma force that can overcome the lithostatic load of the overlying layer, vertical inflation can take place. [28] The vertical inflation of magma chambers creates laccoliths. [28]
At the bottom of the magma reservoir, a cumulate rock forms. Cumulate rocks are the typical product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, although they are possible on the roofs if anorthite plagioclase is able to float free of a denser mafic ...