Metamorphic Rocks, Deformation, and Earthquakes Overview

Foliation

Parallel alignment of mineral grains in metamorphic rocks due to directed pressure

Metamorphic grade

Intensity of metamorphism, ranging from low (slight changes) to high (significant recrystallization)

Contact metamorphism

Changes in rock due to heat from nearby magma intrusion

Recrystallization

Process where minerals grow or change shape and size during metamorphism

Index minerals

Specific minerals that form only under certain temperature/pressure conditions, used to determine metamorphic grade

Metamorphic rocks

Form when existing rocks (protoliths) are subjected to changes in temperature, pressure, and/or chemical conditions without melting completely.

Increased temperature

A type of thermal metamorphism that contributes to the formation of metamorphic rocks.

Increased pressure

A type of dynamic metamorphism that contributes to the formation of metamorphic rocks.

Introduction of chemically active fluids

A process known as metasomatism that contributes to the formation of metamorphic rocks.

Textural changes

Grain size increases, minerals align, foliation develops during metamorphism.

Mineralogical changes

New minerals form as old ones become unstable during metamorphism.

Chemical changes

Elements may be added or removed when fluids are present during metamorphism.

Low-grade metamorphism

Slight changes from original rock (e.g., shale → slate).

Medium-grade metamorphism

Significant mineral recrystallization (e.g., slate → schist).

High-grade metamorphism

Complete recrystallization (e.g., schist → gneiss).

Importance of metamorphic grade

Helps geologists understand the tectonic history and depth of burial of the rock.

Slate

Fine-grained, splits into sheets.

Phyllite

Silky sheen, more crystalline than slate.

Schist

Visible mica flakes, strong foliation.

Gneiss

Banded appearance, coarse-grained.

Marble

Recrystallized calcite, non-foliated.

Quartzite

Recrystallized quartz, non-foliated.

Regional metamorphism

Occurs over large areas in mountain-building zones at convergent plate boundaries.

Dynamic metamorphism

Occurs along fault zones due to shearing forces, common at transform boundaries.

Hydrothermal metamorphism

Occurs where hot fluids circulate, common at mid-ocean ridges.

Burial metamorphism

Occurs due to deep burial in sedimentary basins.

Confining stress

Equal pressure from all directions.

Differential stress

Unequal pressure, causing shape change.

Compression

Squeezing forces that push rocks together.

Tension

Pulling forces that stretch rocks apart.

Shear

Forces that cause rocks to slide past each other.

Fault

Fracture along which rocks have moved relative to each other.

Footwall

Rock mass below the fault plane.

Hanging Wall

Rock mass above the fault plane.

Normal fault

Hanging wall moves down.

Reverse/Thrust fault

Hanging wall moves up.

Strike-slip fault

Horizontal movement.

Anticline

Upward-arching fold (oldest rocks in center).

Syncline

Downward-arching fold (youngest rocks in center).

Epicenter

Point on Earth's surface directly above where an earthquake originates.

Focus/Hypocenter

Actual point below ground where earthquake rupture begins.

P wave (Primary)

Compression/expansion (push-pull) wave that is the fastest and travels through solids, liquids, and gases.

S wave (Secondary)

Side-to-side shaking wave that is slower than P waves and only travels through solids.

Body waves

Waves (P and S) that travel through Earth's interior.

Surface waves

Waves that travel along Earth's surface, slower but more destructive than body waves.

Richter scale

Measures magnitude (energy released) on a logarithmic scale.

Mercalli scale

Measures intensity (observed effects) using Roman numerals I-XII.

Ground shaking

A hazard caused by the movement of the ground during an earthquake.

Landslides

Hazard involving the downward movement of rock and soil, often triggered by earthquakes.

Liquefaction

A phenomenon where soil behaves like liquid, often occurring during an earthquake.

Fires

Hazard that can occur as a result of ruptured gas lines or electrical failures during an earthquake.

Tsunamis

Large ocean waves formed by the displacement of water, typically due to underwater earthquakes.

Tsunami formation

Occurs when seafloor displacement displaces a large volume of water, creating waves that travel across oceans.

Common causes of tsunamis

Include underwater earthquakes (most common), underwater landslides, volcanic eruptions, and meteorite impacts (rare).

Tsunami wave height

As tsunami waves approach shore, they slow down and grow taller, sometimes reaching heights of 30+ meters.

Plate tectonics

The unifying theory that connects all three major topics in this unit.

Convergent boundaries

Where plates collide, creating compression.

Divergent boundaries

Where plates separate, creating tension.

Transform boundaries

Where plates slide past each other, creating shear stress.

Reverse/thrust faults

Faults that occur at convergent boundaries due to compression.

Normal faults

Faults that occur at divergent boundaries due to tension.

Strike-slip faults

Faults that occur at transform boundaries due to shear stress.

Folding of rock layers

A result of compression at convergent boundaries.

Earthquakes along subduction zones

Earthquakes that occur at convergent boundaries.

Rift valleys

Geological features formed at divergent boundaries due to tension.

Contact metamorphism near magma intrusions

Metamorphism that occurs due to the heat from magma.

Shallow earthquakes

Earthquakes that occur at divergent boundaries.

Dynamic metamorphism along fault zones

Metamorphism that occurs due to shear stress in fault zones.

Frequent earthquakes

Common occurrences at transform boundaries, such as the San Andreas Fault.

Tectonic stress

The stress that leads to deformation in geological processes.

Deformation

The change in shape or volume of rocks due to tectonic stress.

Faults/Folds

Structures that result from deformation.

Surface effects

Consequences of earthquakes, including tsunamis and landslides.

Resulting rock type

The type of rock that forms as a result of metamorphic processes.

Himalayan Mountains

An example of continental-continental collision creating compression and earthquakes.

Mid-Atlantic Ridge

An example of a divergent boundary with tension and volcanic activity.

San Andreas Fault

An example of a transform boundary with shear stress and frequent earthquakes.