Metamorphic Rocks 2 Flashcards
Describe marble
Medium grained Crystalline Granoblastic White Caco3
What is formed in the aureole of shale?
Inner- hornfels
Outer- spotted shale
What is formed in the aureole of limestone?
Inner- marble
Outer- sugar marble
describe hornfels
Medium grained Porphyroblasts Dark cordierite White andelucite Crystalline
Describe slate
Slaty cleavage Low grade Foliated chlorite Quartz Fine grained Dark grey Crystalline
Define metamorphism
Change in mineral content and texture
Why does metamorphism occur?
Due to a change in temperature and pressure
What temperature does metamorphism start?
150 degrees
What are the three types of metamorphism?
Contact metamorphism- low pressure & high temperature
Regional metamorphism- high temperature & high pressure
Dynamic metamorphism- low temperature & high pressure
What are the sources of heat for metamorphism?
Internal heat from the mantle
Heat from a magma intrusion
What are the sources of pressure for metamorphism?
Lithostatic pressure from overlying rocks
Lateral pressure from horizontal movement of plates
What 4 factors determine the nature of metamorphic change?
Temperature and pressure
Original composition of the rock
Presence of pore fluid
Time
Process and facies of shale?
Diagenesis
No facies
Process and facies of slate?
Low grade metamorphism at an accretionary prism
Zeolite
Process and facies of Phyllite?
Medium grade metamorphism in the upper section of the lower cc
Greenschist
Process and facies of schist?
Medium grade metamorphism in the upper section of the lower cc
Greenschist
Process and facies of gneiss?
High grade metamorphism in the lower section of the lower cc
Granulite/ amphibole
Process and facies of migmatite?
High grade metamorphism in the lower section of the lower cc
Granulite
Process and facies of granite?
Partial melting
No facies
Index minerals in order of increasing heat?
Chlorite Biotite Muscovite Garnet Kyanite Siliminite Alkali Feldspar
What is prograde metamorphism?
Changes that occur as a result of increasing heat and pressure
What is retrograde metamorphism?
Changes that occurs as a result of decreasing heat and pressure
What is the process of basalt to blueschist?
Plagioclase+ pyroxene+ OH = amphibole
Olivine+ OH = chlorite
What is the process of blueschist to granulite?
Amphibole-OH = pyroxene + plagioclase
Chlorite- OH = garnet
What is the process of granulite to amphibolite?
Pyroxene= amphibole
Plagioclase= plagioclase
Garnet= garnet + quartz
Order of mineral inclusions rocks
Basalt
Blueschist
Granulite
Amphibole
What type of metamorphism forms kyanite?
Regional
What type of metamorphism forms sillimanite?
Regional
What type of metamorphism forms andelucite?
Contact
What type of metamorphism forms the index minerals?
Regional
What rock forms the index minerals?
Shale
Describe slate
Contains chlorite, quartz, clay
Partially crystalline
Fine grained
Salty cleavage
Describe spotted slate
Contains chiastolite andelucite, chlorite, quartz
Partially crystalline
Porphyroblasts
Slaty cleavage
Describe hornfels
Contains cordierite, andelucite and quartz
Crystalline
Medium grained
Porphyroblasts
What is granoblastic?
Formed by metamorphic crystallisation under low pressure conditions
What is porphyroblastic?
Porphyroblast is formed by the metamorphic recrystallisation of biotite into garnet
What is mylonite?
Formed by the shearing of hot plastic or non competent rock
