Metamorphism Flashcards
What are four major factors controlling metamorphic processes?
Temperature, Pressure, Pore fluid pressure, Time
Where does Earth’s internal heat come from?
Radioactive elements e.g. uranium and potassium
Define Heat Flow
The amount of heat flowing out at the Earth’s surface
What is the main type of pressure in the Earth’s crust?
Confining pressure
Pressure at Depth =
Depth x Density x Acceleration due to gravity
What are three places fluids can be found in?
Pore spaces between grains, Tiny cracks and fractures, Veins
What are two reasons pore fluids important in metamorphism?
They act as catalysts and accelerate metamorphic reactions, They act as solvents and so bring ions into contact with each other as they move
Define Differential Stress
The difference between the maximum and minimum principal stresses
What are the four main types of metamorphism?
Contact, Regional, Burial, Dynamic
What five metamorphic rocks come from shale?
Spotted rock, Hornfels, Slate, Gneiss, Schist
What metamorphic rock comes from sandstone?
Metaquartzite
What metamorphic rock comes from limestone?
Marble
What metamorphic rock comes from basalt?
Eclogite
Define Aluminosilicate
Very common group of minerals including kyanite, sillimanite and andalusite
What metamorphism is kyanite associated with?
Burial metamorphism (high pressure, low temperature)
What metamorphism is sillimanite associated with?
Regional metamorphism (high pressure, high temperature)
What metamorphism is andalusite associated with?
Contact metamorphism (low pressure, high temperature)
Define Polymorph
Share the same chemical formula of Al2Si2O5, but they have different chemical structures and therefore different physical properties
What three things does the textures in metamorphic rocks depend on?
Temperature and pressure conditions, Effect of tectonic stresses, Original texture of the rock
Define Granoblastic Crystals
Metamorphic rock with minerals of equal size
Define Porphyroblastic Texture
Large crystals set in a finer groundmass
Define Poikiloblastic Texture
Poikiloblasts are usually porphyroblasts with pieces of other minerals within them
Define Porphyroclastic Texture
Clasts set in a finer matrix, associated with dynamic metamorphism
Define Non-Foliated
Develop where there is an absence of stresses and consequently the minerals show no preferred orientation
Define Foliated
Show a preferred orientation of the minerals, usually in a direction at right angles to the maximum pressure
What are five factors controlling the extent of baking around an igneous intrusion?
Size and shape of the igneous body, Composition, Thermal conductivity of the country rock, Volatile content, Distance from igneous body
Define Pelites
Fine grained sedimentary parents like clays, shales and mudstones
How do pelites respond to increases in temperature?
Reactions take place quickly for clay minerals and micas due to their large surface area, making them sensitive to the effect of heat and new minerals grow as the temperature rises
Define Phyllites
Strongly cleaved rocks rich in platy minerals, particularly chlorite
Between what temperatures do phyllites form?
250-300 degrees C
What are the three types of porphyroblasts?
Post-tectonic, Syn-tectonic, Pre-tectonic
Define Post-Tectonic
Forms after the period of deformation
Define Syn-Tectonic
Forms during the period of deformation
Define Pre-Tectonic
Forms before the period of deformation
Define Burial Metamorphism
High pressure/low temperature regional metamorphism associated with convergent plate margins
Define Isograd
Areas which have had the same amount of metamorphism
Define Dynamic Metamorphism
They are of local significance only, restricted to narrow zones adjacent to faults and thrusts
Define Cataclasis
The grinding down of broken rock, producing elongated lens shaped porphyroblasts which tend to show a preferred orientation or lineation
What rock is the result of cataclasis?
Mylonite
Define Pressure-Temperature-Time Path
The set of all P-T conditions experienced by a rock during its metamorphic history
