Geology Mod 8

Aureole

A zone of altered rock around an igneous intrusion caused by heat from the intrusion during CONTACT METAMORPHISM

Burial Metamorphism

Low-grade metamorphism THAT OCCURS as SEDIMENTS ARE BURIED DEEP IN SEDIMENTARY BASINS. Caused by CONFINING PRESSURE and low temperatures.

Confining Pressure

Equal pressure applied in all directions due to burial; COMPACTS rocks but doesn’t cause foliation

Contact Metamorphism

Occurs when rocks are heated by nearby magma. Happens at shallow depths with LOW PRESSURE and HIGH TEMPERATURES

Differential Stress

Unequal pressure from different directions; causes deformation and produces foliation in rocks.

Foliation

Layered or banded appearance in metamorphic rocks due to alignment of minerals under differential stress

Gneissic Texture

Coarse foliation with light and dark mineral banding, characteristic of high-grade metamorphism

Hydrothermal Metamorphism

Alteration by hot, chemically active fluids; common near mid-ocean ridges. Produces rocks like greenstone

Impact metamorphism

Caused by meteorite impacts; produces high-pressure minerals and breccias

Index Mineral

Mineral that forms under specific temperature and pressure, used to estimate metamorphic grade

Metamorphism

Transformation of a rock by heat, pressure, and/or chemically active fluids

Metasomatism

Chemical change in a rock during metamorphism due to fluid introduction, which adds or removes elements

Migmatite

A rock that’s part metamorphic, part igneous due to partial melting under extreme temperatures

Nonfoliated Texture

Metamorphic rocks with no visible alignment of minerals’ often composed of equiangular crystals

Parent Rock

The original rock that undergoes metamorphism

Regional Metamorphism

Widespread metamorphism associated with mountain-building, occuring at convergent plate boundaries

Rock Cleavage

The tendency of a rock to split along flat planes; typically seen in low-grade metamorphic rocks

Schistosity

Foliation in schist formed by parallel alignment of platy minerals

Slaty Cleavage

Very fine foliation in slate, allowing it to split into thin sheets

Cataclastic Metamorphism

Occurs along fault zones, where rocks are crushed and fragmented by mechanical deformation

Metamorphic Facies

A set of metamorphic mineral assemblages formed under similar pressure and temperature conditions.