chloriteepidote

Chloriteepidote is a term used in metamorphic petrology to describe a rock or mineral assemblage in which chlorite and epidote are the dominant minerals. It is not a single mineral, but rather an association that is most often found in greenschist- to lower amphibolite-facies rocks. The chlorite component typically belongs to the chlorite group minerals (such as clinochlore or chamosite), which form as hydrated phyllosilicates, while epidote refers to epidote-group minerals, including epidote itself and related species like zoisite that can occur with epidote under certain conditions.

Formation and occurrence

Chloriteepidote assemblages form during regional metamorphism or hydrothermal alteration when rocks experience hydration, heat, and chemically reactive fluids. They are commonly reported in pelitic (clay-rich) and intermediate to mafic rocks, where chlorite remains stable at relatively low temperatures and epidote becomes stable with increasing calcium, aluminum, and silica content. The two minerals are often accompanied by other minerals such as quartz, calcite, plagioclase, and minor minerals that reflect the prevailing pressure-temperature and fluid conditions.

Interpretation and significance

In metamorphic geology, the chloriteepidote assemblage serves as a qualitative indicator of metamorphic grade and fluid activity. Its presence suggests greenschist to lower amphibolite facies conditions and is useful for inferring physicochemical evolution during metamorphism, including hydration history and possible retrogression.

See also

Chlorite-bearing rocks, Epidote-bearing rocks, Greenschist facies, Amphibolite facies.

Note: The term refers to an assemblage rather than a distinct mineral species.

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