AS metamorphic Flashcards
Contact metamorphism
localised/smaller area
heat predominant diving force
takes place in rocks (country rock) intruded by magma
creates met areole
regional met
larger area 10-1000km2
predominant force = pressure
at C plate boundaries
likely foliation as pressure causes alignment
Dynamic met/ cataclasis
happens in fault zones
when rocks move fast each other quickly and suddenly
may be fairly old cold and brittle
crushed and ground into angular fragments and some recryst
foliation
texture found in met rocks formed by pref alignment of flat platy minerals e.g. clay
mid to high pressure and flat platy mins present to form
usually regional
unfoliated usually contact met and low pressure
foliated rocks and formation
all reg met and parent rock shale
slate- shale to slate
phyllite - slate to phyllite
schist- phyllite to schist
gneiss - schist to gneiss
Non foliated rocks and parents
Marble (contact or reg) - limestone to marble
Metaquartzite (contact or reg)-sandstone to meta
spotted rock (contact only)- shale to spotted
marble summary
parent- limestone
colour-white
texture- granoblastic ( same grain size, increases with grade)
min comp- calcite
type- contact or reg
metaquartzite summary
parent- quartz
colour-white/grey
texture- granoblastic ( same grain size, increases with grade)
min comp- quartz
type- contact or reg
spotted rock summary
parent- shale
colour-grey/purple/green or black
texture- fine grained, partly developed slatey cleavage
min comp- clay and micas
type- contact
slate summary
parent- shale
colour-grey/green/purple/black
texture- slatey cleavage
min comp- clay and muscovite and chlorite
type- low grade reg
Phyllite summary
parent- shale
colour-green/grey
texture- wavey foliation ,fine grain
min comp- clay and muscovite
type- low grade reg
schist summary
parent- shale
colour-silvery sheen
texture- schistosity, med grain
min comp- muscovite and biotite, quartz and GARNET
type- med reg
Gneiss summary
parent- shale
colour-light and black bands
texture- gneissose banding, coarse grained
min comp- biotite, feldspar, sillimanite and kyanite
type- high grade reg
index minerals
chlorite (low), muscovite and biotite, garnet (med), staurolite ,sillimanite and kyanite(high)
diagram of diff temps and pressures for diff grades
SEE IN BOOKLET
diagenesis- 200 (pressure) to 200 (temp)
not found on earth - 200-1000 pressure, 0-200 temp
contact met- 0-200 pressure and 200-800 temp
igneous- 200-1000 pressure and 600-1000 temp
low grade- up to 600 pressure and 300 temp
med grade- up to 900 pressure and 500 temp
high grade- 900 - +1000 pressure and 500-800 temp
metamorphic areole
igneous intrusions cause country rock to metamorphose and recrystalise due to heat
George Barrow
first to recognise and map zones of progressive met
discovered met zonation in highlands (Barrovian zones)
in diff grades of met diff minerals found - index mins
Chlorite-biotite-garnet-staurolite-sillimanite-kyanite
slatey cleavage
splits into thin sheets along cleavage planes
(fine low grade and must contain flat platy mins)
schistosity
happens when alignment of flat platy minerals 90 degrees to max pressure
often find garnet porphyroblasts
Gneissose banding
light and dark minerals separate into distinct bands
mica rich layer= foliated
pale layer = granoblastic
porphyroblastic
larger crystals surrounded by smaller matrix
e.g. garnet mica schist
granoblastic
unfoliated formed by heat, randomly orientated equidimensional crystals
crenulation cleavage
2 or more stresses cause multiple foliations going against each other giving wavey appearance
