Metamorphic rocks

Metamorphism is a process that causes changes in texture, mineralogy or both occurring in the underlying rocks by diagenesis and weathering limit and upper limit is the melting (fusion). The process of change in texture that is not accompanied by changes mineraloginya there are 2 kinds, namely: Cataclastic and recrystallization. Cataclastic is the process of destruction on the rocks, while recrystallization is the process of rearrangement of the crystal lattice and relationships in the grain through the migration of ions and lattice deformation, without the destruction of the granules. Neocristalisasi is the process of forming new minerals that are not on the previous metamorphic rocks. A similar process occurs also during the process of diagenesis. So metamorphism same may be said with diagenesis, but only includes the processes that occur in the earth's surface (low p and t).

Metamorphic rocks are rocks with textures and minerals that illustrates cataclastik, recrystallization or neokristalisasi in response to different conditions of formation of these rocks and processes between diagenesis and anatexis. Batua common origin of these metamorphic from igneous, sedimentary, and metamorphic rocks themselves but to a lesser degree. Metamofisme, may also occur at temperatures and pressures higher than 200oC and 300 MPa. Rocks are exposed to the process of metamorphism may be located at a depth far from the earth's surface as it occurs in a subduction zone or collision. The upper limit of metamorphism occurs in pressure and temperature phase where the rocks did not experience melting or smelting. If you have experienced melting then it can no longer referred to as metamorphism.
Factors Affecting the metamorphism

Metamorphism occurred because some minerals stable only under certain conditions of pressure and temperature. When there is change in pressure and temperature, chemical reaction occurs that causes the minerals in rocks changed to achieve stability at a certain pressure and temperature.

The Factors Affecting metamorphism:

·         Geothermal Temperature Gradients along. Temperature can also increase associated with igneous intrusions.

·         Pressure increases with increasing, then, both pressure and temperature will vary in each depth. Pressure is defined as the force generated from all directions. There are several types of stress, called hydrostatic stress, or uniform stress. If stress is not the same from all directions, the stress is called differential stress.

o   If there are current or differential stress during metamorphism, will affect the texture of the rocks are formed.

o   Rounded grains can be aligned in the direction of maximum stress.
 minerals that crystallize or grow in the field of differential stress can have a better orientation. In particular, the silicate minerals (micas : Muscovite and biotite, chlorite, talc, and serpentine).

Silica-Gazette Gazette will grow with the sheets oriented perpendicular to the direction of maximum sharpness (maximum stress). The orientation of the sheets of silica can cause rupture of rocks along the parallel sheet. Such a structure is called foliasi.

·         Fluid Phase - Any space between the grains of minerals in rocks potentially containing fluid. Most of the fluid H2O, but can also contain dissolved minerals. Fluid phase is important because the chemical reaction involving one turn into solid minerals other solid minerals can be accelerated by the destruction of ions are transported by the fluid itself. Along with the increasing pressure of metamorphism, pore spaces in which the liquid will be reduced.

·         Time - Chemical reactions in metamorphism, during recrystallization, and formation of new minerals is running very slow. Through laboratory experiments it is said that the process of metamorphism with a longer time, will produce large grained minerals. Thus the coarse grained metamorphic rocks have been through a long phase of metamorphism. Experiments stating that the time involved is millions of years.

This type of metamorphism

1)      Based on the area and volume

·         local metamorphism is metamorphism in rocks of relatively small volume (less than 100 km ²)

·         regional metamorphism is metamorphism that occurs in a relatively large volume of rock (thousands of cubic kilometers)

2)      Based on the agent metamorfismenya

·         contact metamorphism, metamorphism with the main agent is the temperature that occurs due to igneous intrusions on the cooler shallow rocks are common on local scales. This contact is called contact aurele.

·         dynamic metamorphism is metamorphism that occurs due to deviatoric stress. This type occurs in fault zones and areas affected by meteoric jadtuah. This type occurs in a fairly wide area.

·         static metamorphism is metamorphism that occurs due to lithostatik which occurred at a depth of the relatively deep, as in the fore arc basin and trough.

·         dinamotermal metamorphism, metamorphism merupakam the most common and occur akabat combination of pressure and temperature.

Classification of metamorphic rocks (Based on its chemical composition)

This classification is in the review of the chemical elements contained in the metamorphic rock that would characterize his native rock. Based on the chemical composition of metamorphic rocks are divided into 5 groups, namely:

·         Calcic metamorphic rock is a metamorphic rock derived from rocks that are Classical (Al-rich element), generally composed of mudstone and shale. Example: batusabak and Phyllite.

·         Quartz Feldsphatic Rock is a metamorphic rock derived from rocks rich in quartz and feldspar elements. Example: Gneiss

·         Calcareous metamorphic Rocka dalah metamorphic rocks derived from limestone and dolomite. Example: Marble

·         Basic metamorphic rock is a metamorphic rock derived from alkaline igneous rocks, semibasa and medium enterprises, as well as tuffs and sedimentary rocks that are napalan with the content of the element K, Al, Fe, Mg.

·         Magnesia is a metamorphic rock metamorphic rock derived from Mg-rich rocks. Example: serpentit, schists.

Structure and texture of metamorphic rocks

The structure is a form of handspecimen or the larger rocks. Structure based on its scale textures dibedakand ari Diman is a form of microscopic textures sidudun by size, shape, orientation, and egg relationship. In metamorphic rocks occur because the process of deformation structures.

Textures in metamorphic rocks:

1.      texture foliasi, namely the parallel orientation of the minerals that show the bedding and the appearance of straightness. Examples of this texture, namely:

·         slaty texture, very fine grains (<0.1 mm), straightness on the orientation planardan subplanar, fractions are pages. Examples of rock is slate.

·         Texture phylitic, very fine grained to fine (<0.5 mm), the rock sample is phylite.

·         Texture schistose, fine-grained to very coarse (> 1 mm), examples of rock is schist.

·         gneissose texture, fine to very coarse grained, showing bedding because of differences in mineralogy.

·         Texture foliasi porphyroblastik, very fine grained to very coarse with a large crystal size (porphyroblastik) embedded in a matrix of fine-sized berfoliasi

·         mylonite texture.

2.      Texture diablastik, texture characterized by the absence of alignment buturan, oriented radially to the random texture example of this is:

·         Texture sheaf, which shows the texture of the grains which berdabang.

·         Texture spherolublastik, namely granular texture which shows the radial group.

·         Texture fibroblastic, texture diablastik of similar size

3.      Texture Grano blastik

·         Texture homogranular, is showing the texture of the grain size is nearly equal.

·         Texture heterogranular, a texture that shows non-uniform grain size.

·         Texture heterogranoblastik, a texture which is characterized by the same mineral kumpulam taapi with diverse sizes.

·         Texture nodularblastik texture, a texture that has nodular composed of small mineral with one or two minerals in the matrix that has a different composition.