Ch 8: Metamorphism & Metamorphic Rocks Flashcards
Asteroid
One of thousands of small planetlike bodies, ranging in size from a few hundred kilometers to less than 1 kilometer across. Most asteroids’ orbits lie between those of Mars and Jupiter.
Asthenosphere
A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers (60 miles) and in some regions extends as deep as 700 kilometers (430 miles). The rock within this zone is easily deformed.
Atom
The smallest particle that exists as an element.
Aureole
A zone or halo of contact metamorphism found in the country rock surrounding an igneous intrusion.
Basalt
A fine-grained igneous rock of mafic composition.
Basin
A circular downfolded structure.
Bed
See Strata.
Biotite
A dark, iron-rich mineral and a member of the mica family with excellent cleavage.
Black smoker
A hydrothermal vent on the ocean floor that emits a black cloud of hot, metal-rich water.
Breccia
A sedimentary rock composed of angular fragments that were lithified.
Burial metamorphism
Low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata.
Chemical bond
A strong attractive force that exists between atoms in a substance. It involves the transfer or sharing of electrons that allows each atom to attain a full valence shell.
Cleavage
The tendency of a mineral to break along planes of weak bonding.
Coarse-grained
See Phaneritic texture.
Color
A phenomenon of light by which otherwise identical objects may be differentiated.
Comet
A small body that generally revolves about the Sun in an elongated orbit.
Compaction
A type of lithification in which the weight of overlying material compresses more deeply buried sediment. It is most important in the finegrained sedimentary rocks such as shale.
Compressional stress
Differential stress that shortens a rock body.
Confining pressure
Stress that is applied uniformly in all directions.
Conglomerate
A sedimentary rock composed of rounded, gravel-size particles.
Contact metamorphism
Changes in rock caused by the heat from a nearby magma body.
Convergent plate boundary
A boundary in which two plates move together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle. It can also involve the collision of two continental plates to create a mountain system.
Crater
The depression at the summit of a volcano or a depression that is produced by a meteorite impact.
Crust
The very thin, outermost layer of Earth.
Crystal or Crystalline
Any natural solid with an ordered, repetitive atomic structure.
Deformation
General term for the processes of folding, faulting, shearing, compression, or extension of rocks as the result of various natural forces.
Differential stress
Forces that are unequal in different directions.
Facies
A portion of a rock unit that possesses a distinctive set of characteristics that distinguishes it from other parts of the same unit.
Fault
A break in a rock mass along which movement has occurred.
Fine-grained
See Aphanitic texture.
Fold
A bent layer or series of layers that were originally horizontal and subsequently deformed.
Foliation
A term for a linear arrangement of textural features often exhibited by metamorphic rocks.
Fracture
Any break or rupture in rock along which no appreciable movement has taken place.
Geothermal gradient
The gradual increase in temperature with depth in the crust. The average is 30°C per kilometer in the upper crust.
Geyser
A fountain of hot water ejected periodically from the ground.
Gneiss
Medium- to coarse-grained banded metamorphic rocks in which granular and elongated minerals dominate.
Gneissic texture
A texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance.
Gradient
The slope of a stream, generally expressed as the vertical drop over a fixed distance.
Hornfels
A fine-grained nonfoliated metamorphic rock formed from various minerals.