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Contact metamorphism occurs typically around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole, [44] the contact aureole, or simply the aureole. [45]
The breakdown of hydrous mineral phases typically occurs at depths greater than 10 km. [11] Each of these metamorphic facies is marked by the presence of a specific stable mineral assemblage, recording the metamorphic conditions undergone by the subducting slab. Transitions between facies cause hydrous minerals to dehydrate at certain pressure ...
Also called Indianite. A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments. anticline An arched fold in which the layers usually dip away from the fold axis. Contrast syncline. aphanic Having the ...
A contact can be formed during deposition, by the intrusion of magma, [2] or through faulting or other deformation of rock beds that brings distinct rock bodies into contact. [ 3 ] The geologic subdiscipline of stratigraphy is primarily concerned with depositional contacts, [ 4 ] while faults and shear zones are of particular interest in ...
Running water carries vast amounts of sediment in rivers back to the ocean and inland basins. The accumulated and buried sediments are converted back into rock. A less obvious role of water is in the metamorphism processes that occur in fresh seafloor volcanic rocks as seawater, sometimes heated, flows through the fractures and crevices in the ...
Mid-ocean ridges exhibit active volcanism and seismicity. [3] The oceanic crust is in a constant state of 'renewal' at the mid-ocean ridges by the processes of seafloor spreading and plate tectonics. New magma steadily emerges onto the ocean floor and intrudes into the existing ocean crust at and near rifts along the ridge axes. The rocks ...
Within the upper crust, which is the only part of the Earth's crust geologists can directly sample, metamorphic rock forms only from processes that can occur at shallow depth. These are contact (thermal) metamorphism, dynamic (cataclastic) metamorphism, hydrothermal metamorphism, and impact metamorphism.
In contact metamorphism (metamorphism caused by high temperatures at low pressure in the vicinity of an igneous intrusion) a local contact aureole of zones is formed around a heat source. In rocks in subduction zones , that are transported to great depths in relatively low temperatures, rare types of metamorphic zones can develop.