Aureole
a zone or halo of contact metamorphism found in the country rock surrounding an igneous intrusion
Contact metamorphism
changes in rock caused by the heat from a nearby magma body
Gneissic texture
a texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance
Index mineral
a mineral that is a good indicator of the metamorphic environment in which it formed; used to distinguish different zones of regional metamorphism
Migmatite
a rock exhibiting both igneous and metamorphic rock characteristics; such rocks may form when light-colored silicate minerals melt and they crystallize, while the dark silicate minerals remain solid
Regional metamorphism
metamorphism associated with large-scale mountain building
Metamorphism
the changes in mineral composition and texture of a rock subjected to high temperatures and pressures within earth
Slaty cleavage
a type of foliation that is characteristic of slates, in which there is a parallel arrangement of fine-grained metamorphic minerals
Burial metamorphism
low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata
Differential stress
forces that are unequal in different directions
Hydrothermal metamorphism
the hot, watery solution that escapes from a mass of magma during the latter stages of crystallization; such solutions may alter the surrounding country rock and are frequently the source of significant ore deposits
Nonfoliated texture
metamorphic rocks that do not exhibit foliation
Rock cleavage
the tendency of rocks to split along parallel, closely spaced surfaces; these surfaces are often highly inclined to the bedding planes in the rock
Cataclastic metamorphism
results from the crushing and shearing of rock during tectonic movement; generally along fault planes; might produce sheared, highly deformed rocks called mylonites
Confining pressure
stress that is applied uniformly in all directions
Foliation
a term for a linear arrangement of textural features often exhibited by metamorphic rocks
Impact metamorphism
metamorphism that occurs when meteorites strike earth's surface
Metasomatism
substantial chemical changes due to active fluids
Parent rock
the rock from which a metamorphic rock formed
Metamorphic facies
a group of associated minerals that are used to establish the pressures and temperatures at which rocks undergo metamorphism
What are the agents of metamorphism?
heat
pressure
chemically active fluids
What is the difference between differential stress and confining pressure? Which of these two stresses is most likely to produce foliation in a metamorphic rock?
differential stress - forces are unequal in different directions
confining pressure - squeezes rock equally in all directions
differential stress is most likely to produce foliation in a metamorphic rock
Describe hydrothermal metamorphism. What types of reactions occur? Where does hydrothermal metamorphism occur?
occurs along mid-ocean ridges where heated seawater percolates through hot, fractured basalt
crustal rocks on continents can react with invading, hot fluids associated with igneous intrusions
What metamorphic rock is a typical product of hydrothermal metamorphism?
talc and other clay minerals
Describe contact metamorphism. Where does it occur?
occurs at high temperatures, adjacent to magma chambers; restricted to a small area round the margins of a magmatic intrusion
What type of geothermal gradient is associated with contact metamorphism?
geothermal gradients are high
What is a contact metamorphic aureole?
the area surrounding the intrusion where the contact metamorphism effects are present
What are the differences between burial and regional metamorphism? Which is more extensive? Where does each type occur? Describe the stresses associated with burial versus regional metamorphism.
burial - sedimentary rocks are buried even deeper
regional - when temp. and pressures increase beyond range of burial metamorphism; occurs under places with high temp and ressure over large areas
regional is more extensive
What is cataclastic metamorphism? Where does it occur? What is the difference between a fault breccia and mylonite?
results form the crushing and shearing of rock during tectonic movement
occurs along fault planes
Describe how foliation is produced in a metamorphic rock (3 mechanisms).
1. preferred mineral orientation - perpendicular to stress
2. alternating mineral bands - compositional layers (light and dark)
3. mineral flattening - grains elongate and flatten
Name two common platy minerals that produce foliation in metamorphic rocks. Can non-platy minerals exhibit foliation (think metaconglomerate)?
chlorite and mica
yes
In what tectonic environment do blueschists and eclogites form?
progressive metamorphism of basalt
blueschist - very high pressures, relatively low temperatures
eclogites - extremely high pressures, moderate-high temperatures
Identify the parent rock for each of the following metamorphic rocks: slate, quartzite, marble, greenstone, and anthracite.
slate ---> shale
quartzite ---> sandstone
marble ---> limestone
greenstone ---> basalt
anthracite ---> bituminous coal
Rank the following metamorphic rocks in order of increasing grade of metamorphism: schist, granulite, phyllite, slate, gneiss.
slate
phyllite
schist
gneiss
granulite
What are migmatites? How do migmatites form? Do they represent low or high temperatures?
forms at temperatures exceeding 700 degrees C where gneiss partially melts
felsic minerals melt, mafic minerals remain solid
silica-rich liquid invades partially melted rock
softened rock contorts and deforms
What are index minerals? How are index minerals used in mapping metamorphic terrain?
good indicators of the metamorphic conditions under which they were formed (only present for short amount of time)
Know how the different types of metamorphism are related to plate tectonics (see Fig. 8.29 in your textbook). In terms of tectonic environments, where would you find each of the following metamorphic conditions: high-temperature/low-pressure, high-tempera
high-temp/low-pressure --->
high-temp/high-pressure --->
low-temp/high-pressure --->
hydrothermal metamorphism --->