E&E 151 S Introductory Geology: Chapter 7 (Metamorphism) Definitive Study

Metamorphism

Changes in mineral assemblage, texture, or chemical composition that occur in pre-existing rocks beneath Earth's surface exclusively in the solid state without melting.

Parent Rock (Protolith)

The original, pre-existing rock prior to metamorphic alteration.

Metamorphic Grade

A measure of the relative intensity of temperature and pressure conditions, ranging from low-grade to high-grade.

Prograde Metamorphism

The progressive recrystallization of a rock into higher-grade metamorphic rocks as temperature and pressure increase during deep burial.

Retrograde Metamorphism

Recrystallization under decreasing temperature and pressure conditions during uplift, which typically requires the addition of water.

Migmatite

A mixed igneous and metamorphic rock formed at ultra-high temperatures where partial melting begins, producing light-colored granitic layers.

Geothermal Gradient

The rate at which temperature naturally increases with depth beneath Earth's surface.

Polymorphs

Minerals sharing identical chemical compositions that crystallize into different crystal structures depending on temperature and pressure conditions.

Confining Pressure (Lithostatic Pressure)

Equal pressure applied in all directions from overlying rock burial, reducing pore space and compressing mineral grains.

Differential Stress

Unequal tectonic forces applied to a rock from different directions.

Compressive Stress

Differential stress that squeezes rock into flattened or oblong shapes.

Shearing

Differential stress that causes rock units to slide parallel to one another across a plane.

Metasomatism

Metamorphism accompanied by the net addition or removal of chemical ions brought in by circulating hydrothermal fluids.

Contact Metamorphism (Thermal Metamorphism)

Metamorphism driven predominantly by high temperatures adjacent to intruding magma bodies (plutons) at low pressures.

Regional Metamorphism

Metamorphism occurring across vast areas associated with mountain-building belts and convergent plate margins under high pressure and differential stress.

Hydrothermal Metamorphism / Seafloor Metamorphism

Chemical alteration caused by hot, ion-rich water circulating through rock fractures, especially prominent along mid-ocean ridges.

Dynamic Metamorphism

Metamorphism restricted to fault zones where extreme shearing crushes and pulverizes rock.

Mylonite

A dense, fine-grained rock formed from pulverized material within fault zones during dynamic metamorphism.

Shock Metamorphism

Sudden, extreme pressure increases resulting from meteorite impacts.

Coesite and Stishovite

Ultra-high-pressure silica polymorphs produced during shock metamorphism.

Tektites

Small, streamlined glass droplets formed when impact-melted rock is thrown into the atmosphere and solidifies in flight.

Index Minerals

Key minerals with restricted pressure-temperature stability fields (such as andalusite, kyanite, and sillimanite) that serve as indicators of metamorphic intensity.

Metamorphic Facies

Groups of metamorphic rocks characterized by distinct mineral assemblages that reflect specific pressure-temperature environmental conditions.

Zeolite & Prehnite-Pumpellyite Facies

Low-grade metamorphic facies formed under low temperatures and low-to-moderate pressures.

Greenschist Facies

Low-to-medium grade regional metamorphic facies characterized by green minerals like chlorite, actinolite, and epidote.

Amphibolite Facies

Medium-to-high grade regional metamorphic facies dominated by hornblende and plagioclase feldspar.

Granulite Facies

High-grade metamorphic facies characterized by high temperatures and high pressures.

Blueschist Facies

High-pressure, low-temperature metamorphic facies characteristic of subduction zones, containing the blue amphibole glaucophane.

Eclogite Facies

Very high-pressure metamorphic facies formed deep within subduction zones.

Hornfels Facies

High-temperature, low-pressure metamorphic facies typical of contact metamorphism around igneous intrusions.