Please enable JavaScript.
Coggle requires JavaScript to display documents.
A2 Metamorphic Rocks (Progressive regional metamorphism (process:…
A2 Metamorphic Rocks
Progressive regional metamorphism
process: diagnesis
rock: shale
process: low grade regional metamorphism
rock: slate
facies: zeolite
process: medium grade regional metamorphism
rock: phyllite
facies: greenschist
process: high grade regional metamorphism
rock: gneiss
facies: granulite/amphibolite
process: high grade regional metamorphism
rock: migmatite
facies: granulite
process: partial melting
rock: granite
Types of metamorphism
CONTACT- low pressure and high temperatures caused by the flow of magma from a magma intrusion
REGIONAL- high temperatures and high pressures that occur deep within the crust during plate collisions
DYNAMIC- low temperature and high pressures that occur along major fault zones
sources of heat
internal heat from the mantle
heat from a magma intrusion
sources of pressure
lithostatic pressure caused by the weight of the rock
lateral pressure created by horizontal movement of plates
Pressure- Temperature- Time paths
A) burial by subduction
B) Prograde Metamorphism- changes that occur as a result of increasing heat and pressure
C) Retrograde Metamorphism- changes that occur as a result of decreasing heat and pressure
D) uplift due to plate collision
A) Basalt (plagioclase, pyroxene, olivine)
B) Blueschist (amphibole, chlorite)
C) Granulite (pyroxene, plagioclase, garnet)
D) Amphibolite (amphibole, plagioclase, garnet, quartz)
Stability Fields
phase diagram for the stability fields of kyanite, sillimanite and andalucite which are polymorphs (same chemical formula but different structures)
Regional Metamorphism of Shale
composed of quartz, calcite and various clay crystals
Index minerals in increasing heat
chlorite
biotite
muscovite
garnet
kyanite
sillimanite
alkali feldspar
Slate
minerals: chlorite, quartz and clay
texture: partially crystalline, fine grained, slaty cleavage
Spotted Shale
minerals: chiastolite, andalucite, quartz
texture: partially crystalline, porphyroblasts, slaty cleavage
Hornfels
minerals: cordierite, andalucite, quartz
texture: crystalline, medium grained, porphyroblasts
Granoblastic
formed by the metamorphic crystallisation under low pressure conditions
Porphyroblastic
formed by the metamorphic recrystallisation of biotite into garnet
mylonite
formed by the shearing of hot 'plastic' or non competent rock
METAMORPHISM- a change in the mineral content and texture that takes place in a rock in response to changing temperature and pressure
Occurs when the temperatures exceed 150 degrees at an approximate depth of 6km
The upper limit varies from 600 to 1000 degrees
