Introduction To Earth Science - UIOWA Exam 2

Agents of Metamorphism

1. Heat

2. Pressure

3. Fluids

All commonly occur together

Geothermal Gradient

The rate at which temperature increases with depth.

(20°C to 30°C per km) deepest drilled hole,12.3 km, 245°C (473°F).

Metamorphic Grade

The intensity of heat and pressure that a rock has experienced during metamorphism.

Low: low temp and pressures

Intermediate: higher temp and pressure

High: very high temp and pressure

Protolith

The original rock from which a metamorphic rock forms. AKA the "parent rock"

Changes during metamorphism include..

Texture, reorientation, recrystallization, creation of new minerals

Reorientation

Realignment of minerals in a rock due to directed pressure (stress). Common in foliated metamorphic rocks.

Recrystallization

Minerals in a rock change size, shape, or arrangement without altering chemical composition. Results in fewer but larger grains.

Porphyroblastic Texture

Large grains (porphyroblasts) surrounded by fine-grained matrix of other minerals.

(Like chocolate chips in cookie dough)

Foliation Texture

Any planar arrangement of mineral grains or structural features within a rock. Minerals are aligned in parallel layers or bands due to the directed pressure.

Slate

Very fine-grained rock. Excellent rock cleavage, smooth dull surface. Generated from low grade metamorphism of shale or mudstone.

Schist

Medium to coarse grained rock. Platy materials (mainly micas) predominate. Describes the rock texture and adds mineral name to indicate the composition.

Gneiss

High grade metamorphic rock, medium to coarse grained with a light/dark banded appearance. Parent rock = Schist, granite, volcanic

Migmatite

Transition from high grade metamorphic to igneous rock.

Light bands = igneous melt

Dark bands = metamorphic

Marble

Non foliated metamorphic rock. Parent rock = limestone or dolostone

Quartzite

Non foliated metamorphic rock. Parent rock = quartz-rich sandstone. Quartz grains fused together.

Index Minerals

Specific minerals in metamorphic rocks that indicate the temperature and pressure conditions (metamorphic grade) under which the rock formed. Mostly found in medium to high grade metamorphic rocks.

Common Index Minerals include...

Chlorite, muscovite, garnet, biotite, sillimanite

Metamorphic Zones

Shows how metamorphic conditions change gradually across a region. Each zone is named after the first appearing index mineral.

Contact Metamorphism

Caused by heat from a nearby magma or lava intrusion. Pressure is usually low. Affecting the rocks immediately around the intrusion. Rocks often become non-foliated. Rocks "baked" by nearby magma like cookies in the oven.

Common rocks:

Limestone --> Marble

Sandstone --> Quartzite

Shale --> Hornfels

Regional Metamorphism

Caused by high pressure and heat over large areas, usually from mountain building (tectonic collision). Pressure is high and directional, causing foliation. The scale is extensive.

Common rocks:

Shale --> Slate --> Phyllite --> Schist --> Gneiss

Basalt --> Amphibolite

Hydrothermal Metamorphism

Chemical alteration as hot, ion-rich fluids (hydrothermal solutions) circulate through fissures and cracks that develop in the rock. Almost widespread along mid-ocean ridge system.

Impact Metamorphism

Meteorites hit Earth at high speed. Example: Graphite in rock shocked to diamond (more dense). Similar to smashing a cookie with a hammer.

Fault Zone Metamorphism

When rocks are deformed and altered along a fault, due to intense pressure, shear stress, and frictional heating during fault movement.

Burial Metamorphism

When rocks are slowly buried under thick layers of sediment, causing increased pressure and temperature over time. (Low P + Low T)

Alfred Wegner

German meteorologist and geophysicist who proposed continental drift, suggesting all continents were once joined in Pangaea. Evidence: matching coastlines, fossils, rock formations, and paleoclimate data. Early ideas led to plate tectonics.

Evidence of Continental Drift

Fit of continents: coastlines match like puzzle pieces

Fossils: same species on different continents (e.g., Mesosaurus)

Rocks & mountains: similar age/type across continents

Paleoclimate: glacial deposits in tropics, coal in cold regions

Pangea

A supercontinent that existed about 200-300 mya, where all of Earth's landmass was joined.

When did Pangea form?

During the late Paleozoic era

When did Pangea breakup?

During the Mesozoic era.

Gondwana

The large southern land mass that existed from the Cambrian (540 mya) to the Jurassic (138 mya). Present-day remnants are South America, Africa, India, Australia, and Antarctica.

Strike-Slip Fault

Type of fault where the movement is mainly horizontal. Caused by shear stress. E.g., San Andreas Fault

Dip-Slip Fault

Type of fault where the movement is mainly up and down. Includes normal and reverse faults.

Stress

A force applied to rock that changes its shape or position.

Types: Compression (push), Tension (pull), Shear (slide)

Strain

The change in shape or size of rock caused by stress.

Elastic Deformation

Temporary change, returns to original shape. Think of a rubber band bending.

Plastic Deformation

Permanent bending without breaking. Like bending clay.

Ductile Deformation

Low, permanent bending/stretching (deep underground). Similar to plastic deformation. ***FOLDING

Brittle Deformation

Rock breaks or fractures. Happens near the surface where it is cooler. ***FAULTS

Joints

Type of rock fracture with NO movement. Often caused by tension or cooling.

Faults

Type of rock fracture WITH movement. Caused by stress and movement of rocks sliding past each other.

Normal Fault

Caused by tension → hanging wall moves down

Reverse Fault

Caused by compression → hanging wall moves up

Thrust Fault

A low angle (less than ~45°) reverse fault. Common in mountain building.

Transform Fault

Rocks slide past each other horizontally due to shear stress. AKA Strike-slip

Hanging Wall

Rock above the fault

Footwall

Rock below the fault

Compression fault types

Reverse / Thrust

Extension fault types

Normal

Shear stress fault types

Transform / Strike-slip

Right-lateral

Opposite side moves right for a strike-slip fault

Left-lateral

Opposite side moves left for a strike-slip fault

Anticline

Rock layers fold upward into an arch shape. Oldest rocks in the center. Looks like an upside-down U (∩)

Syncline

Rock layers fold downward (bowl shape). Youngest rocks in the center. Looks like a Smile U shape (∪)

Fold Axis

Line connecting hinge points (max curvature) along the fold.

Fold Limb

The sides of the fold. Rock layers slope away from the hinge. Can be steep or gentle.

Fold Hinge

The point of maximum curvature in the fold. Where the fold bends the most. Often where stress is highest.

Axial Plane

An imaginary plane that connects all the lines of maximum curvature.

A Symmetrical Fold..

Has a vertical axial plane

An Asymmetrical Fold...

Has an axial plane from vertical to 45 degrees

An Overturned Fold...

Has an axial plane from 45 degrees to 0 degrees

Domes

Circular structures where older underlying material is forced upward. The material exposed in the center of domes is older than

the material exposed on the flanks of the dome.

Basins

Roughly circular depressions that gradually fill with younger and younger material. The material exposed in the center of basins is younger than the material exposed at the basin margins.

Folded Mountains

Formed by Compression that folds rock layers. Example: Himalayas

Fault-block Mountains

Formed by Tension faults; blocks tilt or drop. Example: Sierra Nevada

Volcanic Mountains

Formed by magma erupting and building up layers. Example: Mount Fuji

Dome Mountains

Formed by uplift of rock layers (usually magma pushes up but doesn't erupt). Example: Black Hills

Continental Shield

Ancient, stable crystalline rock forming the continental core.

Active Margins

A continent-ocean boundary where tectonic activity like earthquakes, volcanoes, and mountain building is common.

Passive Margins

A continent-ocean boundary that is not near a plate boundary, so it experiences little tectonic activity. Calm, no big movement.

Orogeny / Orogenesis

Process that collectively produce a mountain belt; folding, faulting, magmatism, and metamorphism.

Terrane

Crustal fragment with a unique geologic history, added to a continent.

Physical Weathering

The breakdown of rock into smaller pieces without changing its chemical composition; caused by physical forces like temperature changes, pressure release, or abrasion.

Chemical Weathering

The breakdown of rock through chemical reactions that change the rock's minerals into new substances (such as through dissolution, oxidation, or hydrolysis).

Mechanical Weathering

Another term for physical weathering — rock is broken into smaller fragments without changing what it is made of.

Causes of Erosion

Water, wind, ice, gravity.

Dissolution

A type of chemical weathering where minerals in rock are dissolved by water or acidic solutions.

Hydrolysis

reaction of mineral with water.

Hydrogen ion attacks and replaces other ions.

Oxidation

Loss of an electron via chemical reaction (often due to exposure to oxygen)

Regolith

The layer of loose, unconsolidated material that sits on top of bedrock; rock and mineral fragments

Soil

The upper layer of the regolith that is capable of supporting plant life. It forms from weathered rock, organic material, water, and air.

Humus

The nutrient-rich, decomposed organic matter in soil.

Soil Formation

Breakdown of rock + organic matter → soil layers capable of supporting life. Key factors: Climate, Organisms, Relief, Parent material, Time (CLORPT)

Soil Horizons (Layers)

- O horizon: Topsoil - Loose and partly decayed organic matter

- A horizon: Topsoil - Mineral matter mixed with some humus

- E horizon: Light colored mineral particles; Zone of leaching

- B horizon: Subsoil - Accumulation of clay from above

- C horizon: Subsoil - Partially altered parent material

Turbidity Current

A fast-moving underwater flow of sediment-laden water that moves downslope along the seafloor due to gravity. Similar to a muddy avalanche under the sea.

Graded Bed

A layer of sediment in which particle sizes change gradually from bottom to top. Coarse particles at the bottom, finer particles at the top. Formed by sediment settling from water or air. Often deposited by turbidity currents or floods. Indicates decreasing energy of the transporting medium over time.

Deep-Sea Fan

A large, fan-shaped deposit of sediment on the ocean floor formed by turbidity currents flowing from the continental shelf into the deep ocean.

Alluvial Fan

A fan-shaped deposit of sediment formed where a stream or river flows out of a narrow valley onto a flat plain, losing energy and spreading out.

Relative Dating

Determining the order of events in rock layers, not exact age.

Numerical Dating

The process of determining the actual age of rocks, fossils, or geologic events in years. Usually uses radioactive decay of isotopes.

Principle of Superposition (Geologic Principle)

What ever is on top is younger than what's on bottom.

Principle of Original Horizontality (Geologic Principle)

Beds are originally deposited parallel to the horizon (i.e. horizontal)

Principle of Lateral Continuity (Geologic Principle)

Beds are deposited uniformly in lateral directions unless something is blocking them.

Principle of Cross Cutting Relationships (Geologic Principle)

Whatever is doing the cutting is younger than what gets cut.

Uniformitarianism

Processes on Earth today are the same as those that were operating in the past. The present is the key to the past

Included Fragments

Fragments inside a rock are older than the rock that holds them.

Biotic Succession

Because species evolve and go extinct over time, you can determine the relative age of a rock unit by its fossil content.

Biostratigraphy

Using fossils to determine the relative ages of rock layers.

Index Fossils

Fossils of organisms that lived for a short period of time, were widespread, and are used to identify and date rock layers. Examples: Trilobites, Ammonites, Brachiopods.

Stratigraphic Range

The vertical span of rock layers where a fossil species is found, from its first appearance to its last appearance. If a fossil appears in Layer B through Layer E, its stratigraphic range = B-E

Nonconformity

A contact between igneous or metamorphic rocks and sedimentary rocks. Indicates long time gap.