REPORTERS: ♥IVAN FRITZ ESGUERRA♥ ^__^ ♥PRINCESS DANIELLE MATAS♥

METAMORPHISM  Metamorphism (“meta” means change and “morph” means form) is a change that occurs in rocks involving a recrystallization of minerals and crystallization of new minerals.

Agents of metamorphism : 1. Heat - Minerals expand so that ions are separated from one another, stretching and weakening the bond and enable freed ions to migrate through the rock to form the seeds of metamorphic minerals. 2. Pressure - compresses the rocks and minerals, forcing their ions closer together rearranged into more compact mineral structure. Two types of pressure: Two types of pressure: A. Lithostatic pressure (“lithos” meaning rock and “status” meaning position) A. Lithostatic pressure (“lithos” meaning rock and “status” meaning position) - is the pressure exerted on a rock as it is burried deeper and deeper in the earth and is of equal intensity in all directions. B. Direct pressure - greater pressure in some directions and can therefore deform and flatten rocks.

a. Lithostatic pressure b. Directed pressure A. B.

3. Chemically active fluids -the solutions of active fluids change the composition of a rock and form new minerals during metamorphism. A.HEAT B. PRESSUREC. ACTIVE FLUIDS NA+ THE AGENTS OF METAMORPHISM:

Regional metamorphism:  Regional or Barrovian metamorphism covers large areas of continental crust typically associated with mountain ranges, particularly subduction zones or the roots of previously eroded mountains. Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event. continental crusteroded orogenic eventcontinental crusteroded orogenic event

Contact metamorphism  Rocks can also be heated by intruding magmas, and the increase in their temperature can cause them to become metamorphosed. Because magmas often rise to very shallow levels in the crust (and of course often erupt), they carry their heat into low pressure environments. This heat is conducted into the rocks the magmas intrude.  Consequently, contact metamorphic rocks are found adjacent to plutonic rocks. The metamorphic grade is highest at the contact and lessens with increasing distance from the contact. Thin bands of contact metamorphic rocks are sometimes formed beneath lava flows.  Consequently, contact metamorphic rocks are found adjacent to plutonic rocks. The metamorphic grade is highest at the contact and lessens with increasing distance from the contact. Thin bands of contact metamorphic rocks are sometimes formed beneath lava flows.

Blueschist metamorphism  occurs under conditions of low temperatures and a range of pressures. It seems that conditions of low T and high P exist only in special places. The high pressures required to produce some of the characteristic mineral assemblages found in blueschists imply that the metamorphism occurs deep in the Earth where temperatures normally are also high.

The two lines shown on the figure set the P-T boundary of the conditions of regional metamorphism. Where the temperature is low, the pressure is low; where the temperature is high, the pressure is high. The terms low grade, intermediate grade, and high grade metamorphism refers to these P-T conditions. At the highest grades of regional metamorphism, rocks can begin to melt in the presence of sufficient water.

FOLIATION  Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the typical sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. fabricrocksmetamorphicorogenic beltsmudrocksslatephyllite schistgneissfabricrocksmetamorphicorogenic beltsmudrocksslatephyllite schistgneiss

GNEISS,a foliated metamorphic rock

Three common types of foliation are: GNEISS  a compositional banding that is manifested by alternating bands of different minerals, such as light color bands rich in feldspars and quartz and dark bands rich in biotite or amphiboles. Rocks possessing this type of foliation have the name

Gneiss is a typical rock type formed by regional metamorphism, in which a sedimentary or igneous rock has been deeply buried and subjected to high temperatures and pressures. Nearly all traces of the original structures (including fossils) and fabric (such as layering and ripple marks) are wiped out as the minerals migrate and recrystallize. The streaks are composed of minerals, like hornblende

SCHIST  Rocks possessing a foliation resulting from the parallel alignment of flat minerals such as mica. The planes of this alignment are perpendicular to the principle compressional stress during the deformation.

Schist is formed by regional metamorphism and has schistose fabric—it has coarse mineral grains and is fissile, splitting in thin layers

SLATE  an incipient plane of weakness along which a rock easily breaks to yield flat, smooth (in the absence of other complications) surfaces. These are planes in which microscopic size mica grains crystallize during metamorphism. This type of foliation also forms perpendicular to the principle compressional stress.

SLATE

REGIONAL FLOW DIAGRAM FOR METAMORPHISM OF PELITIC ROCKS SHALE CONTACT MYLONITE GRANOFELS DYNAMIC COMPACTION AND REORIENTATION SLATE Micas and chlorite form PHYLLITE Grains recrystallize, coarsen Porphyroblasts form SCHIST GNEISS GRANOFELS NOLAYERINGNOLAYERING MICADESTROYEDMICADESTROYED LAYERINGLAYERING

FLOW DIAGRAM METAMORPHISM FOR MAFIC ROCKS DYNAMIC CONTACT BASALT REGIONAL Hydration reactions GREENSCHIST ALBITE,EPIDOTE, CHLORITE,ACTINOLITE Dehydration reactions begin AMPHIBOLITE HORNBLENDE, PLAGIOCLASE,GARNET GREENSTONE MYLONITE ALBITE,EPIDOTE, CHLORITE,ACTINOLITE AMPHIBOLITE HORNBLENDE, PLAGIOCLASE,GARNET MAFIC GNEISS Plagioclase, pyroxenes, garnet PYROXENE GRANOFELS Plagioclase, pyroxenes, garnet LAYERINGLAYERING COMPLETE DEHYDRATION NOLAYERINGNOLAYERING

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