Metamorphism Flashcards
metamorphic rock
changes in solid rock when a rock is subjected to temperatures or pressures very different from where they formed
most important agent
HEAT
Chemically active fluids
RECRYSTALIZATION
Uniform Confining pressure
equal
DENSER
Directed pressure
DISTORTION
FOLIATION
• Directed pressure forms a layered or banded texture preferred orientation of platy minerals in a metamorphic rock;
SHEETS
foliation 3 factors
preferred orientation
mineral grains into a new orientation
- Changing the shape of equi- dimensional grains into elongate shapes aligned in the preferred orientation
- Re-crystallization of minerals to form new grains growing in direction of preferred orientation
CONTACT metamorphism
where rock minerals and texture are changed, mainly by heat, due to contact with magma.
REGIONAL meta
where rock minerals and texture are changed by heat and pressure over a wide area or region.
• Slate (low grade metamorphism)
Very fine-grained
• Originally mudrocks, and volcanic ash • Excellent, flat, rock cleavage (slaty) • Colour depends on specific minerals
• black contains organic material; • red contains iron oxide;
• green contains chlorite
Phyllite
Exhibits wavy rock cleavage
• Composed mainly of fine crystals of muscovite and/or chlorite
Schist Medium- to coarse-grained
Platy minerals dominate
• The term schist also describes the texture (strongly foliated texture
- Gneiss
* Medium- to coarse-grained
Banded appearance
• High-grade metamorphism
• Often composed of light feldspar-rich bands with layers of dark ferromagnesian minerals (called gneissic texture or gneissosity)
Order (slate- Gneiss)
increase depth and pressure
Slate
Phyllite
Schist
Gneiss
SUBDUCTION ZONE
Where two tectonic plates meet at a subduction zone, one bends and slides underneath the other,
HIGH PRESSURE LOW TEMP
