METAMORPHIC ROCKS Flashcards
1
Q
isochemical
A
no chemicals are added or removed (except H²O and CO²)
2
Q
Contact metamorphism
A
- an isochemical change due to heat
- usually at >200°C
3
Q
Granoblastic texture
A
- sedimentary rocks are granular
- heat welds the grains together
4
Q
Grade
A
higher grade = bigger crystals as more weld together
- low - 200 - 300°C
- medium - 300 - 500°C
- high - 500°C - melting point
5
Q
Contact metamorphism- sandstone (orthoquartzite) and limestone
A
Sandstone –> metaquartzite
Limestone –> marble
- low - granoblastic texture equal size to original grains
- medium - granoblastic texture bigger than original grain size
- high - same as medium + sedimentary structures are destroyed
6
Q
Contact metamorphism - clay minerals
A
- Sedimentary rocks made from clay minerals are chemically complex.
- They contain a range of elements so can form a range of rocks
- shale / mudstone / clay
low grade
- spotted rock
- spots of biotite mica grow
medium grade
- andalucite “slate”
- adalusite crystals grow (porphyroblast)
high grade
- hornfels
- silimanite crystals grow + sedimentary structures are destroyed
7
Q
Metamorphic aureole width
A
angle of side of intrusion
- affects outcrop width of aureole
- steep = narrow outcrop
Other reasons:
- volume of intrusion - bigger intrusion = bigger aureole
- magma temperature - hotter = bigger aureole
- magma composition - mafic = hotter
- country rock composition - water transfers heat so aureole is wider
8
Q
Regional metamorphism
A
- an isochemical change involving heat and pressure
- > 200°C and >200MPa
9
Q
Regional metamorphism - clay minerals
A
- rocks rich in clay minerals develop foliations
Low grade
- slate
- “slaty cleavage”
Medium
- schist
- garnets of shiny mica
High
- gneiss
- gneissos banding / segregated light + dark minerals
