Types of Metamorphism Contact (Dokanak) Metamorphism It takes place when a body of magma alters the surrounding country rock. At shallow depths, intruding magma raises the temperature of the surrounding rock, causing thermal alteration. Furthermore, the release of hot fluids into the country rock during intrusion can aid in the formation of new minerals. An aureole (hale) is the area of metamorphism surrounding an intrusion. It varies in width depending on the size, temperature and composition of the intruding magma as well as the mineralogy of the surrounding country rock.

Metamorphic aureoles Many contact metamorphic rocks also crisscrossed with veins and dikes from nearby intrusions and may be altered by high-temperature fluids that dissolved and carried away some rock constituents in solution while precipitating others that originated within magma. This process is called as metasomatism (metazomatizma) and it differs from ordinary metamorphism in that the bulk composition of the rock changes. For example, metasomatic alteration of contact aureoles in limestone has produced some valuable tungsten ore deposits in which the tungstate ion replaces the carbonate ion in calcite.

Metasomatism Dynamic Metamorphism (Dinamik Metamorfizma) Significant dynamic metamorphism, or pressure-dominated recrystallization, associated with fault zones in shallow crust where rocks are subjected to concentrated high levels of differential pressure. The metamorphic rocks that result from pure dynamic metamorphism are called mylonites (milonit), and typically they are restricted to narrow zones adjacent to faults. Another rock type is seen in these region is cataclasite (kataklasit). is Mylonite

Cataclasite (Kataklasit) Regional Metamorphism (Blgesel metamorfizma) It occurs over a large area and is usually caused by tremendous temperatures, pressures and deformation all occurring together within the deeper portion of the crust. Regional metamorphism is most obvious along convergent plate boundaries where rocks are intensely deformed and recrystallized during convergence and subduction. Geologists recognize low, medium, and high grade regional metamorphism based on index minerals (indeks mineraller) that form at specific pressure-temperature conditions. Beginning with a clay-rich parent rock such as shale and tracking its subjection to ever more intense pressure and heat illustrates the sequence of index minerals formed by low-to high-grade regional metamorphism. For example, chlorite (klorit) forms under low-grade conditions, staurolite (stavrolit) and kyanite (kyanit) under intermediate-grade, and sillimanite (sillimanit) under high-grade conditions.