Metamorphic petrology - L2 Flashcards
What characteristics are used to classify metamorphic rocks?
Texture
Fabric
Composition
How are metamorphic rocks commonly named?
have a prefix-type modifier and then name to show textural or mineralogical aspect
How can the fabric of metamorphic rocks be described?
foliated / weakly foliated / non-foliated
What forms can foliations be found in?
cleavage
schistosity- preferred orientation of elongated or platy grains
banding
What are the protolith for magmatic and sedimentary?
Magmatic- Ortho
Sedimentary- Para
How can mineral content be used to identify metamorphic rocks?
based on the prevailing mineral
What factors can be used to for classifying metamorphic rocks?
Fabric
Protolith
Mineral content
Geological setting/ nature of metamorphism
Metamorphic grade
Metamorphic facies
What is foliation?
any planar fabric element, generally formed by platy minerals
What rocks show examples of foliation?
Mica
Chlorite
What are rocks with foliation also called?
S-tectonites
What is lineation?
any linear fabric element generally formed by elongated minerals
What rocks show examples of lineation?
Pyroxenes
Amphibole
Tourmaline
What can rocks with lineation also be called?
L-tectonites
What are S-L tectonites?
Rocks with both foliation and lineation
What does pressure do to minerals undergoing metamorphism?
rotates and realigns
What texture is produced by foliation?
lepidoblastic
What is lepidoblastic texture like?
metamorphic texture in which platy or tabular minerals are aligned to produce a planar fabric
Where does lineation typically occur?
shear zones- minerals realign parallel to shear sense
What texture is defined by lineation?
nematoblastic texture
What is a nematoblastic texture like?
almost looks like a bunch of straws tied together facing same direction
What is slaty cleavage?
property of a rock to split along a regular set of sub-parallel planes
What is slaty cleavage yielded by?
preferred alignment of phyllosilicates (i.e., chlorite, mica, etc.) due to tectonic stress
What texture is produced from slaty cleavage?
Aphanitic texture (small crystals cant be seen by eye)
What texture will rocks with a slaty texture have?
lepidoblastic
What are the characteristics of slate?
Compact,
very fine-grained,
well-developed cleavage
What are the characteristics of Phyllite?
Coarser grain with a shiny cleavage made by fine phyllo-silicates
May have both foliation and lineation
What is schistosity?
preferred orientation of mineral grains or grain aggregates produced by metamorphic processes
What will the grain size from schistosity be?
coarse grained enough to see with the unaided eye
What will the fabric of schistosity be?
planar but lineation’s may be present
What is a schist?
metamorphic rock exhibiting a schistosity
What is a gneiss?
metamorphic rock displaying gneissose structure
What is a gneissose structure?
coarse grained with layering composed of alternating felsic (white) and mafic (darker) mineral layers
What are typical non-foliated rocks created by?
contact metamorphism
What are Granofels?
general term for metamorphic rock with granoblastic texture
What is a granoblastic texture like?
equidimensional, anhedral grains with no preferred orientation
What is a hornfel?
type of granofels that is typically very fine-grained and compact, and occurs in contact aureoles
How is a granoblastic texture formed?
equidimensional grains with straight edged frequently forming a triple junction at 120°
What is a Porphyroblastic texture?
metamorphic rocks that have one or more metamorphic minerals that grew much larger than the others.
What is each individual crystal in porphyroblastic texture called?
porphyroblast
What is an augen gneiss?
a gneiss with an augen texture
What is an augen texture?
large eye-shaped grains derived from sheared pre-existing large crystals
What are the individual grains in an augen gneiss called?
auge
What is a metamorphic facie?
a range of P-T conditions over which a mineral assemblage is stable
(P-T or pressure temp)
