Metamorphic consists of two Greek words ‘meta’ means change and ‘morphe’ mean form, hence metamorphic means change of form.
When tectonic forces, pressures, stress, or temperature change the mineralogy and texture of the igneous or sedimentary rock, the newly formed rock is called metamorphic. Metamorphic rocks are Crestline and hard rock.
How is a metamorphic rock formed?
The metamorphism is the process by which metamorphic rock is formed. Due to metamorphism, mineralogy and texture of preexisting rock are altered in response to changing environmental conditions. such environmental conditions are temperature, pressure, fluid, and mechanical stress.
The metamorphism process starts at about 150 degrees Celsius temperature. the temperature increases with depth in the crust due to the geothermal gradient. the geothermal gradient is the measurement of temperature with depth. the geothermal gradient varies with a place to place in crust.
pressure and mechanical stress
pressure and stress are other factors affecting metamorphism. the pressure on rock increase with depth. During metamorphism, the pressure experienced by rock is due to the weight of the overlayed rock.
the stress is due to the pressure that changes the shape of the rock. rock can be squeezed more strongly in one direction that shows unequal stress in all directions, called differential stress. so, differential stress in the rock leads to metamorphism.
the sedimentary and igneous rocks have cracks and pores. these rock pores are filled with a watery fluid, in which some amount of dissolved CO2, Cacl2, and NaCl. during high pressure and temperature fluids composition also change. during metamorphism, fluid speeds up chemical reactions by.
As a result of metamorphism, new textures and mineral assemblage are formed. the metamorphic process can complete in two ways:
1. mechanical deformation: preexisting rock is deformed due to heat, pressure, temperature, and especially differential stress.
2. chemical recrystallization: where new mineral assemblage form due to temperature and pressure changes. in recrystallization, losses of H2O and CO2 occurs as the rock is heated and squeezed.
Types of metamorphism
metamorphism depends on the relative effect of mechanical and chemical changes. the three types of metamorphism occur are contact metamorphism, regional metamorphism, and dynamic metamorphism.
1. Contact metamorphism
in the shallow depth of crust where temperature rise due to magma intrudes. Due to high temperature, chemical reaction and recrystallization begin in the surrounding cooler rocks. this process results in contact metamorphism where new mineral assemblage is formed.
in the type of metamorphism, foliation is minimal. Foliation is the layer of the sheet-structure minerals. the foliation is thin as of the sheet. this type of metamorphism occurs where often magma intruse.
2. Dynamic metamorphism
the dynamic metamorphism is not common. when two rock slides, the heat is generated. as a result, mechanical deformation begins to start. this type of metamorphism called dynamic metamorphism.
3. Burial metamorphism
this type of metamorphism occurs due to deep burial of rock in sedimentary basins. due to burial, pressure increased and burial metamorphism occurs. the chemical recrystallization starts and water speed up the chemical reaction. in the burial metamorphism, little deformation occurs and that results in a lack of foliation.
4. Regional metamorphism.
It is the most common metamorphism and occurs in the mountain range. this type of metamorphism occurs at the subduction zone where continental plates collide. due to this, mechanical deformation and recrystallization occur which results in regional metamorphism.
the mountain such as the Himalaya and the alps are formed by plate collision and composed of regional metamorphic rock.
4. Hydrothermal metamorphism.
these types of metamorphism occur near the surface of the earth where the intense activity of hot water changes the mineralogy of preexisted rock. the hot water more intensely reacts with minerals.
metamorphic rocks are formed by the process called metamorphism. metamorphism is the changes in mineralogy and textures of preexisted rock (sedimentary or igneous rock) due to conditions such as high temperature, pressure, mechanical stress, tectonic plate movement, and fluids. Metamorphism complete by either mechanical deformation or chemical recrystallization or both.