Intro to Geology: Chapter 7

Compression

stress that squeezes rock until it folds or breaks

Foliation

the arrangement of leaflike layers in a rock

Metamorphic Aureole

the distinct belt of metamorphic rock that forms around an igneous intrusion

Metamorphic Grade

the intensity of metamorphism that formed a rock; the maxmimum temperature and pressure attained during metamorphism

Metamorphic Foliation

the layering of any rock that has been altered by intense heat and/or pressure; usually beneath surface; more resistant than parent rock

Preferred Orientation

the metamorphic texture that exists where platy grains lie parallel to one another and/or elongate grains align in the same direction

Metamorphic Texture

the nature of metamorphic rocks in which ways the grains in the rock have grown in place and interlock; slate, phyllite, schist, gneiss

Protolith

the original rock from which a metamorphic rock formed

Exhumation

the process (involving uplift and erosion) that returns deeply buried rocks to the surface

Metamorphism

the process in which one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure

Mylonite

the resulting rock from dynamic metamorphism; has a foliation that parallels the fault

Metaconglomerate

weakly foliated; coarse grained; stretched pebbles with preferred orientation; from quartz-rich conglomerate

Metamorphic Zone

The region between two metamorphic isograds, typically named after an index mineral found within the region

Contact (Thermal) Metamorphism

a change in the texture, structure, or chemical composition of a rock due to contact with magma

Slate

a fine-grained metamorphic rock that can be split into thin layers

Phyllite

a fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica

Shear

a form of stress that pushes a rock in two opposite horizontal directions

Shield

a large, relatively flat expanse of ancient metamorphic rock within the stable continental interior

Metamorphic Mineral

a mineral formed by solid-state transitions under metamorphic conditions

Metamorphic Rock

a type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions

Gneiss

banded metamorphic rock that contains mostly elongated and granular, as opposed to platy, minerals; composed of quartz, potassium feldspar and sodium felspar; light and dark bands.

Metasomatism

change in composition by interaction with fluids

Hydrothermal Metamorphism

chemical alterations that occur as hot, ion-rich water circulates through fractures in rock

Hornfels

fine-grained, unfoliated metamorphic rock whose parent rock is either shale or basalt; contact metamorphism

Metamorphic Facies

groupings of metamorphic rocks of various mineral compositions formed under different grades of metamorphism from different parent rocks

Quartzite

hard metamorphic rock consisting essentially of interlocking quartz crystals

Isograd

line connecting points of similar conditions during geological metamorphism

Marble

metamorphic rock that is non-foliated, coarse, crystalline rock whose parent is usually limestone; primarily calcite

Schist

metamorphic, foliated, medium to coarse grained texture, looks scaly or flaky, parent rock is phyllite

Thermal Metamorphism

metamorphism caused by heat conducted into country rock from an igneous intrusion

Regional Metamorphism

metamorphism caused by high pressures and temperatures that extend over large regions, as happens where plates collide

Burial Metamorphism

metamorphism due to the increase in temperature and pressure in a rock when it has been buried to a depth of several kilometers

Dynamothermal Metamorphism

metamorphism that involves heat, pressure, and shearing

Dynamic Metamorphism

metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure

Shock Metamorphism

metamorphism that occurs when minerals are subjected to the high pressures and temperatures of shock waves generated when a meteorite collides with Earth

Migmatite

mixed igneous and metamorphic rock; forms when metamorphic rock partially melts