Geological Eons and Metamorphic Processes

Hadean Eon

Earliest eon; unstable atmosphere and early oceans.

Archean Eon

Earth cools; first evidence of life appears.

Proterozoic Eon

Half of Earth's history; significant oxygenation occurs.

Phanerozoic Eon

Current eon; diverse life forms and geological events.

Paleozoic Era

Early era with four continents and Appalachian formation.

Ediacaran Fauna

Soft-bodied multicellular invertebrates from Proterozoic.

Trace Fossils

Indirect evidence of life; includes footprints and burrows.

Permineralization

Minerals fill spaces in organic tissues post-burial.

Metamorphic Rock

Rock altered by heat, pressure, or fluids.

Agents of Metamorphism

Heat, pressure, and hydrothermal fluids alter rocks.

Neocrystallization

New minerals form from original protolith components.

Foliated Texture

Planar fabric alignment in metamorphic rocks.

Parent Rock

Original rock composition determines metamorphic outcomes.

Contact Metamorphism

Heat from magma alters surrounding host rock.

Dynamic Metamorphism

Shearing forces in fault zones alter rock structure.

Regional Metamorphism

Occurs during mountain formation; high temperature and pressure.

Hydrothermal Metamorphism

Hot, ion-rich water alters rocks at mid-ocean ridges.

Subduction Metamorphism

Low temperature increase; high pressure forms blueschist.

Shock Metamorphism

High pressure and temperature from meteor impacts.

Carbonization

Plant matter leaves a carbon film after decay.

Molds and Casts

Cavity left by dissolved organism; filled by sediment.

Polymorph

Same chemical composition, different structural forms.

Migmatites

Partially melted gneiss; both igneous and metamorphic.

Metaconglomerate

Metamorphic rock with flattened gravel clasts.

Intensity of Metamorphism

Progression from shale to gneiss through heat/pressure.

Common Foliated Rocks

Includes slate, phyllite, schist, and gneiss.

Nonfoliated Rock

Rock without layered texture; example: hornfels.

Exhumation

The return of rocks to the surface.

Metamorphic minerals

Minerals formed based on protolith composition.

Index minerals

Minerals indicating specific metamorphic conditions.

Barrovian zones

Zones defined by specific index minerals.

Isograd

First appearance of metamorphic index minerals.

Facies

Groups of metamorphic rocks under similar conditions.

Blueschist facies

Formed in low temperature/pressure subduction zones.

Eclogite facies

Stable under normal geothermal conditions.

Greenschist facies

Common in medium pressure metamorphic rocks.

Hornfels facies

Formed under low pressure conditions.

Zeolite facies

Low-grade metamorphic rocks with limited recrystallization.

Latitude

Angular distance from the equator.

Longitude

Angular distance east or west of the meridian.

Mercator projection

Cylindrical map projection, distorts areas.

Stress

Force applied per unit area.

Strain

Physical change due to applied stress.

Deformation

Change in rocks from tectonic forces.

Tensional forces

Forces acting at divergent boundaries.

Compressional forces

Forces acting at convergent boundaries.

Shear forces

Forces acting at transform boundaries.

Elastic deformation

Temporary change that recovers after stress.

Brittle deformation

Permanent change resulting in fractures.

Ductile deformation

Permanent change resulting in bending.

Anticline

Archlike fold with oldest rocks at core.

Syncline

Troughlike fold with youngest rocks at core.

Earthquake

Sudden slip along a fault.

Hypocenter

Location of fault movement underground.

Epicenter

Point on surface directly above hypocenter.

Elastic rebound theory

Stress builds until rocks slip and release.

Seismic waves

Energy waves traveling through Earth's interior.

Richter scale

Measures earthquake size based on amplitude.

Moment magnitude scale

Measures total energy released by an earthquake.

Modified Mercalli intensity

Measures earthquake impact on structures.

Liquefaction

Soil loses strength during shaking, causing collapse.

Tsunami

Long waves generated by underwater displacement.

Foreshocks

Smaller earthquakes preceding a larger one.

Aftershock

Smaller earthquakes following a major event.

shear stress

Moves one part of the mineral sideways relative to another part. (As if you have a ball of dough and apply pressure to the top of it)

Metasomatism

the process by which a rock's overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements

Foliation

Layering formed as a consequence of the alignment of mineral grains, or of compositional banding in a metamorphic rock.

Thermal or contact metamorphism

Hot Magma rises from the great depth beneath the earth's surface and intrudes into a cooler rock at a more shallow depth

Burial Metamorphism

A sediment becomes progressively buried deeper in a sedimentary basin

dynamic metamorphism

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

dynamo thermal metamorphism (Regional Metamorphism)

Metamorphism that involves heat, pressure, and shearing.

shock metamorphism

the changes that can occur in a rock due to the passage of a shock wave, generally resulting from a meteorite impact

exhumation

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