Lecture THREE Types of Metamorphism Types of metamorphism

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Lecture THREE Types of Metamorphism

Lecture THREE Types of Metamorphism

Types of metamorphism On the basis of (i) Geological setting, and (ii) agents of

Types of metamorphism On the basis of (i) Geological setting, and (ii) agents of metamorphism, the type of metamorphism includes: - Regional extent (over a wide area) - Orogenic metamorphism (T, P, active fluids) - Ocean floor metamorphism (T) - Subduction zone metamorphism (HP/LT) - Burial metamohism (LT/LP) - Local extent (local area) - Contact or thermal metamorphism (T) - Cataclastic or shear zone metamorphism (P) - Hydrothermal metamorphism (active fluids) - Impact or shock metamorphism (extreme P-T)

A 1: Orogenic metamorphism (Regional or dynamothermal metamorphism) _Features of metamorphism : orogenic -

A 1: Orogenic metamorphism (Regional or dynamothermal metamorphism) _Features of metamorphism : orogenic - Where? : Restricted to orogenic belts and extent over distance of hundreds to southlands Kms, e. g. East-African orogen - The agents of metamorphism: include T, P & active chemical solution -Time duration is long (million or tens of millions years) - The yielded rocks suffered deformation and recrystallization, and exhibit penetrative fabric with preferred orientation of mineral grains. They could suffered phases of crystallization and deformation - At higher P-T conditions, partial to complete melting may accompanied and both migmatites and granites may associates, or granulite could be develop.

m i g m a ti te s

m i g m a ti te s

A 2: Ocean-floor metamorphism _Features of metamorhism : ocean-floor - where? : Restricted to

A 2: Ocean-floor metamorphism _Features of metamorhism : ocean-floor - where? : Restricted to transformation of the oceanic crust at the vicinity of mid-ocean ridge - Occur in the upper part of the oceanic crust, typically in sheeted dykes - The agents of metamorphism include T & sea water percolation - The yielded rocks are mostly basic (sheated dykes) in composition, with no penetrative fabric (non-foliated texture)

A 3: Subduction zone metamorphism _Features of subduction zone metamorphism : where? : At

A 3: Subduction zone metamorphism _Features of subduction zone metamorphism : where? : At convergence plate margins, where subduction of cold oceanic lithosphere and overlying sediments against an adjacent continental or oceanic plate. - - The agents of metamorphism include higher pressure, low temperature conditions - The yielded rocks contain high pressure mineral assemblage such glucophane, and kyanite should formed -To preserve such environment , the rock requires rapid uplift

A 4: Burial metamorphism _Features metamorhism : of burial - Where? : in subsidence

A 4: Burial metamorphism _Features metamorhism : of burial - Where? : in subsidence basins, where sediments and interlayered volcanics suffered low temperature regional metamorphism - Agent of metamorphism include low temperature-low pressure conditions due to burial affect without any influence of orogenesis or magmatic intrusions. - The yielded rocks lack schistosity and the original fabrics are largely preserved. So, the yielded rocks are distinguished only in thin section - In Extensional regime, Diatathermal metamorphism is used

B 1: Contact or thermal metamorphism _Features of Contact or thermal metamorphism : -

B 1: Contact or thermal metamorphism _Features of Contact or thermal metamorphism : - Where ? : At vicinity of contacts with intrusive or extrusive igneous rock bodies -Agent of metamorphism is the higher temperature resulted from heat emanating from the magma, and sometimes by deformation connecting with the emplacement of the igneous bodies. - The zone of the contact metamorphism is known as contact aureole, various from meter to few kms. -The width of the zone depend up on: 1 - volume of the magmatic bodies 2 - nature of the magmatic bodies (basaltic or granitic composition) 3 - The intrusion depth of magmatic bodies.

B 1: Contact or thermal metamorphism, cont. 4 - Type of country rocks (Shale,

B 1: Contact or thermal metamorphism, cont. 4 - Type of country rocks (Shale, limestones or igneous rocks) 5 - structures of the country rocks (cracks and fissures) - Duration of metamorphism is short time (up to hundred years) - The yielded rocks are generally fine grained and lack schistosity (hornfels) - In case of higher temperature influence, Pyrometamorphism, is used. - Migmatites could produced in such conditions.

B 2 - Cataclastic or shear zone metamorphism _Features of cataclastic or shear zone

B 2 - Cataclastic or shear zone metamorphism _Features of cataclastic or shear zone metamorphism : - where? : Restricted to the vicinity of faults of overthrusts in the upper crust level (brittle deformation) -Agents of metamorphism is pressure in form of mechanical forces. -The yielded rocks suffered crushing, granulation and pulverization (reducing in grain size). - The yielded rocks are non-foliated and braccia-like, cataclasite, ultramylonite to pseudotachylite. mylonite,

B 2 - Cataclastic or shear zone metamorphism

B 2 - Cataclastic or shear zone metamorphism

B 3 - Hydrothermal metamorphism _Features of metamorphism : hydrothermal - where? : Localized

B 3 - Hydrothermal metamorphism _Features of metamorphism : hydrothermal - where? : Localized at interaction of hot, largely aqueous fluids (from igneous source) with country rocks. - Similar to regional ocean-floor metamorphism - the aqueous hydrothermal fluids usually transported via fractures and shear zones at some distance either near or far from their source - The yielded rocks are mineralogically and chemically changed than the protolith and ore deposits are occasionally originated -If the gases instead the aqueous fluids, Pneumatolytic metamorphism, is used

B 4 - Impact or shock metamorphism _Features of impact metamorphism : - Where?

B 4 - Impact or shock metamorphism _Features of impact metamorphism : - Where? : Impact of fall meteorites with different size on the Earth’s crust. - This impact yielded shock waves with extreme higher P-T conditions, up to 1000 kbar and 5000 °C - Duration time is very short, microsecond. - The impacted rocks were vaporized, but in less condition, they melted to produce vesicular glass containing coesite and stishovite, as well as minute diamond

Metamorphism and plate tectonic 1 - Divergent plate margin: -Ocean floor metamorphism (HT/LP &

Metamorphism and plate tectonic 1 - Divergent plate margin: -Ocean floor metamorphism (HT/LP & seawater fluids) - Diatathermal metamorphism (HT/LP) - Contact metamorphism (HT/LP) - Hydrothermal metamorphism (Hydrothermal fluids)

Metamorphism and plate tectonic 2 - Convergent plate metamorphism -Orogenic condition (various P-T) -

Metamorphism and plate tectonic 2 - Convergent plate metamorphism -Orogenic condition (various P-T) - Cataclastic and Subduction zone metamorphism (LT/HP) 3 - Transform plate boundaries - Cataclastic or Subduction zone metamorphism (LT/HP)