Metamorphism and types
rock cycle
- rocks that are buried in the geosphere and are affected by: pressure, differential stress and temperature
- creates new minerals from recrystallization
1. contact,
2. dynamic,
3. regional
they combine to deform and recrystalize rocks without melting
meta= beyond
solid state stress
- stress is not uniform in all directions.
- can be divided into
1. * mean stress (acts to change volume)
2. differential stress (acts to change shape). - The force concentration varies with direction in a state of stress.
Fabric
-alignment of minerals
-this develops if the rock changes shape in response to DIFFERENTIAL STRESS
State of stress “equation”
pressure/mean stress + differential stress = state of stress
-pressure can vary in all directions
Temperature and in what way does it form meta rocks
- Temperature increases with depth inside the Earth.
- Increasing temperature weakens rocks, encourages recrystallization, and transforms
- the hot magma transfers heat to nearby rocks to cool down and produces new minerals as a result
-this is the only way for magma to cool
Rocks named by fabric
metamorphic rock types
slate, schist, gneiss
-diff stress
Rocks based on composition
metamorphic rock types
Quartzite, marble, greenstone
mean stress
acts to change volume
differential stress
acts to change shape
Geothermal gradient
- the rate at which temperature increases with depth.
contact metamorphism
- due to heat from nearby magma
- new high temp minerals
- increases grain size
- little fabric
- ex is hornfels
regional metamorphism
- high temperature and pressure with differential stress
- occurs at the interior of mountian belts
- strong fabric from deformation caused by diff stress
- past tectonic events
dynamic metamorphism
- rocks flow in solid state from response to diff stress
- strong fabric
- reduces grain size
- ex mylonite, conglomerate
slate
- fine grained
- formed at low temp
- strong fabric - colour variation and bedding in mudstone
- regional metamorphism
schist
- course grained
*mica minerals - formed at high temperature
- strong fabric orientation
- regional metamorphism
gneiss
- banded
- forms at high temp
- grains visible
rocks with no fabric
- quartzite
- marble
- greenstone
- they are all stable
quartzite grains and parent rock
*metamorphosed sandstone
* interlocking quartz grains
* stable
marble
- mainly carbonates
- metamorphosed limestone
- course interlocking calcite crystals
greenstone
- metamorphosed mafic volcanic rock - basalt
- high temps
- ferro-magnesium silicates- olivine
rock cycle summary
- describes the processes of partial melting, magma formation, weathering, erosion, sedimentation and metamorphism
*subduction as a process returning crust to the mantle
subduction
returns crust to the mantel
rock cycle process
magma cools to make igneous rock, erosion and weathering = transport of material- deposited as a sediment - undergoes diagenesis+lithification= sed rock - rocks may be buried then subject to heat press and deformation= metamorphic rock - if hot enough partial melting may produce magma.
* if metamorphic rock isnt returned to mantle it skips straight to weathering
* igneous can skip to metamorphism
partial melting
- brings magma to the crust from uplift
- or at high temps of metamorphism
