Metamorphic Moron Flashcards
Metamorphic Structures
Temp, pressure, and directional stress affect rocks during metamorphism
Temperature
Controls which minerals are present
Directional Pressure
stress and strain are responsible for most textural changes
Foliation
layer appearance, result of directed pressure from large-scale/regional deformation events i.e mountain building
Non-foliated
rocks without abundant platy or elongate mineral will not develop foliation nor rocks that don;t experience directed pressure = contact metamorphism
From low-T to high-T, there are two types of major progressive changes in any metamorphic rock:
- Increase in crystal size with increasing metamorphic grade
- Progressive and predictable change in mineralogy with increasing metamorphic grade
Index minerals
define the sequence of mineral zones marked by the first appearance of mineral in a sequence of each zone from low-T to high-T. Higher-grade = higher up in sequence of minerals
Barrovian Sequence
Chlorite -> Biotite/Muscovite -> Garnet -> Kyanite
from low to high grade
Porphyroblasts
When metamorphic minerals occur as large crystals within a finer-grained matrix = porphyroblastic texture
Slate
Clean and flat breakage along closely spaced planes from the parallel arrangement of tiny tiny tiny crystals of clay and mica. Egg-shell type shine.
Phyllite
Very closely spaced crystals and glossy appearance due to parallel arrangement of mica crystals. Shinier than slate due to larger reflective mica crystals
Schist
Parallel arrangement of mica crystals large enough to see with the naked eye.
Gneiss
Discrete layers of different mineral content = banded appearance, dark bonds usually composed of hornblende and/or biotite, light bands = quartz and feldspars
