Week 4: Metamorphic rocks Flashcards
Describe the agents of metamorphism.
Heat - Breaks and reforms bonds to recrystallise new stable minerals.
Pressure - Causes minerals with platy or elongated shapes to rotate and align and recrystallize.
Hydrothermal fluid - Accelerates chemical reactions.
Say how the agents of metamorphism occur.
Heat - Due to the geothermal gradient as well as magmatic intrusions and compression/friction of the crust.
Pressure - Vertical loading (depth) and differential stress (normal compression & tension and shear).
Hydrothermal fluid - Hot water with dissolved ions and volatiles found in groundwater, released from magma or as a product of metamorphic reactions.
State how these rocks relate to one another.
Temperature, pressure, differential stress, foliation, hydrothermal fluids.
Describe the formation of this foliated texture: Rock or slaty cleavage.
Closely spaced planar surfaces along which rocks split.
Describe the formation of this foliated texture: Schistosity.
Platy minerals are discernible with the unaided eye and exhibit a planar or layered structure. Rocks having this texture are referred to as schist.
Describe the formation of this foliated texture: Gneissic foliation or banding.
During higher grades of metamorphism, ion migration results in the segregation of minerals. Gneissic rocks exhibit a distinctive banded appearance.
Know and differentiate between the types of metamorphic rocks according to both texture and composition.
TEXTURE:
Foliated naming based on texture.
- [Slate, phyllite, schist, gneiss, migmatite]
Non-foliated to weakly foliated naming based on composition.
- [Marble, Quartzite, Amphibolite, Hornfels]
What does the textural term granoblastic refer to and how do you identify it?
Isotropic texture. Mosaic of equigranular crystals.
What does the textural term porphyroblastic refer to and how do you identify it?
Isotropic texture but larger crystals. Large grains, called porphyroblasts, surrounded by a fine-grained matrix of other minerals.
What is metamorphism?
The transformation of a rock, in its solid state, to adapt to new conditions.
What is Hydrothermal alteration called?
Metasomatism.
What is the name and importance of the parent rock?
Protolith.
The most nb part of the parent rock is its mineral composition.
What are the types of metamorphism?
5 kinds.
Contact metamorphism - From a rise in temperature when magma invades a host rock. Forms bands around the pluton which range from highly altered to slightly altered.
Regional metamorphism - Occurs over a large area. From tremendous T, & P within the deep crust along convergent boundaries. (Mountain forming). Index minerals only form at specific Temperatures.
Hydrothermal metamorphism - Chemical alteration caused when hot, ion-rich fluids circulate through rocks. Common along mid-ocean ridges and
divergent plate boundaries.
Burial metamorphism - Caused by increasing P from sedimentary layers above.
Shock/Impact metamorphism - The compressional shock wave from an asteroid/comet.
