metamorphism and metamorphic rocks -...

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Metamorphism and Metamorphic RocksMetamorphic rocks (from the Greek meta, “change” and morpho,“shape”) constitute the third major group of rocks. They result from thetransformation of other rocks by metamorphic processes that usuallyoccur beneath Earth’s surface. During metamorphism, rocks aresubjected to sufficient heat, pressure and fluid activity to change theirmineral composition, texture or both, thus forming new rock.Agents of MetamorphismHeat, Pressure, Fluid activityHeat is an important agent of metamorphism becouse it increases therate of chemical rections that may produce minerals different from thosein the original rock.The heat may come from intrusive magmas or result from deep burial inthe crust. The temperature increases with depth and that Earth’sgeothermal gradient averages about 25oC/km. The rocks are alsosubjected to increasing temperature and pressure along subduction zone.

Prof.Dr.Kadir Dirik Lecture Notes

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Pressure when rocks are burried, they are subjected to increasinglygreater lithostatic pressure. This results from the weight of overlyingrocks and is applied equally in all directions

C. Gillen, Metamorphic Geology, Figure 4.4,


3Prof.Dr.Kadir Dirik Ders Notları

(a) (b)

Rocks may also experience differential pressure (directed pressure).


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Fluid Activity. In almost every region of metamorphism, water and carbondioxide are present in varying amounts along mineral grains boundaries orin the pore spaces of rocks.These fluids, which may contain ions in solution, enhance metamorphismby increasing the rate of chemical reactions. eg.

2Mg2SiO4 + 2H2O → Mg3Si2O5(OH)4 + MgOOlivine Sea Water Serpentine Carried away in solution

TYPES OF METAMORPHISM1. Contact Metamorphism (Dokanak-Kontakt Metamorfizması)2. Hydrothermal Metamorphism (Hidrotermal Metamorfizma)3. Dynamic metamorphism (Dinamik Metamorfizma)4. Regional Metamorphism (Bölgesel Metamorfizma) 5. Burial Metamorphism (Gömülme)


5Prof.Dr.Kadir Dirik Lecture Notes

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Metamorfik hale (metamorphic aurole) tipik olarak magmatik sokulumuçevreler. Bu idealleştirilmiş granit batolitiyle ilişkili olan çevresindeki metamorfikhale, sokulum kütlesinden uzaklaştıkça sıcaklığın düştüğünü yansıtan üç mineraltopluluğu kuşağını içerir. Batolitin yanındaki iç kuşakta andaluzit-kordiyerithornfels oluşur. Bu kuşağı, içinde bir miktar biyotitin geliştiği yaygın yenidenkristallenmeli bir ara kuşak ile sokulumdan en uzakta benekli kayraklarla ayırtedilen dış kuşak bulunur.

(Monroe&Wicander, 2005)


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Dynamic metamorphism is associated with fault zone where rocks aresubjected to high differential pressure.


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Milonitin içindegelişmiş ultramilonit: Kuvars-feldispat ve biyotiten oluşan iritaneli bir kayaç.

Kataklasit


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Certain minerals form only within specific temperature and pressureranges. Such minerals are named as index minerals.

(Monroe&Wicander, 2005)


Prof.Dr.Kadir Dirik Ders Notları 10Prof.Dr.Kadir Dirik Lecture Notes


CLASSIFICATION OF METAMORPHIC ROCKSFoliated Metamorphic RocksRocks subjected to heat and differential pressure during metamorphismtypically have minerals arranged in a parallel fashion, giving them a foliatedtexture.


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Non foliated Metamorphic Rocks


Prof.Dr.Kadir Dirik Ders Notları 17Prof.Dr.Kadir Dirik Lecture Notes


METAMORPHISM AND NATURAL RESOURCESMarble and slateTalc for talcum powderGraphite for pencils and dry lubricantsGarnet and corundum used for abrasives or gemstoneAndalusite, kyanite, sillimanite for manufacturing high-temperature porcelains

Ore-deposit Major-mineral Formula Use


metamorphism and metamorphic rocks -...

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