Theory of Plate Theory of Plate Tectonics – an Tectonics – an

overviewoverview

Geo 100N Geo 100N

Spring 2005Spring 2005

Plate Tectonics -OverviewPlate Tectonics -Overview

1.1. The Lithosphere and CrustThe Lithosphere and Crust

2.2. Basic Concepts of Plate TectonicsBasic Concepts of Plate Tectonics

3.3. Plate Movements and BoundariesPlate Movements and Boundaries

4.4. SummarySummary

Inside the EarthInside the Earth

USGS

The LithosphereThe Lithosphere

http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part1.html

Basic Concepts of Plate Basic Concepts of Plate TectonicsTectonics

The Earth’s surface is covered by The Earth’s surface is covered by about 12 lithospheric platesabout 12 lithospheric plates

USGS

The plates move slowly (a few The plates move slowly (a few cm/year).cm/year).

USGS

Most Most endogenicendogenic geological activity geological activity occurs at or near plate boundaries.occurs at or near plate boundaries.

Mt St Helens, 1980

Endogenic = process that originates within the Earth’s interior

Plate interiors are relatively quiet Plate interiors are relatively quiet geologicallygeologically

Plate Movements and Plate Movements and BoundariesBoundaries

Divergent boundariesDivergent boundaries

Plates move apartPlates move apart

Volcanic activity is always presentVolcanic activity is always present

Earthquakes are shallowEarthquakes are shallow

Two types of boundaries:Two types of boundaries:1.1. OceanicOceanic

2.2. ContinentalContinental

Oceanic Divergent BoundaryOceanic Divergent Boundary Sea-floor spreading of oceanic lithosphere Sea-floor spreading of oceanic lithosphere examples: Mid Atlantic Ridge, East Pacific examples: Mid Atlantic Ridge, East Pacific

RidgeRidge

USGS

Sea-floor spreading of oceanic Sea-floor spreading of oceanic lithospherelithosphere

USGS, Digital elevation model

Mid Atlantic Rift at IcelandMid Atlantic Rift at Iceland

Þingvellir (Thingvellir), Iceland

Continental Divergent BoundaryContinental Divergent Boundary

Continental rifting Continental rifting

Eventually, oceanic crust is formed and Eventually, oceanic crust is formed and divergence becomes oceanic typedivergence becomes oceanic type

Modern Example: East AfricaModern Example: East Africa

East African Rift ZoneEast African Rift Zone

Oldoinyo Lengai, Kenya

Convergent boundariesConvergent boundaries

Plates move toward each otherPlates move toward each other

Volcanic activity commonVolcanic activity common

Deep, medium, and shallow Deep, medium, and shallow earthquakes earthquakes

Three types of Convergent BoundariesThree types of Convergent Boundaries1.1. Ocean-oceanOcean-ocean

2.2. Ocean-continentOcean-continent

3.3. Continent-continentContinent-continent

Ocean-ocean convergenceOcean-ocean convergence

SubductionSubduction – one oceanic plate subducts – one oceanic plate subducts (dives) beneath the other(dives) beneath the other

Volcanic island arcVolcanic island arc is formed is formed Example: Aleutian Islands Example: Aleutian Islands

Aleutian Islands, AlaskaAleutian Islands, Alaska

Kanaga

Ocean-continent convergenceOcean-continent convergence

During ocean-continent convergence, During ocean-continent convergence, oceanic lithosphere oceanic lithosphere alwaysalways subducts subducts beneath continental lithosphere beneath continental lithosphere

Continental volcanic arcContinental volcanic arc formed formedExample: Andes mountains Example: Andes mountains

Continent-continent convergence Continent-continent convergence

Subduction does not occur (continental crust Subduction does not occur (continental crust is is too buoyanttoo buoyant to be subducted) to be subducted)

Mountain building occurs without volcanismMountain building occurs without volcanism

Example: Himalayas, AlpsExample: Himalayas, Alps

India-Asia CollisionIndia-Asia Collision

Collision of India Collision of India with Eurasian plate with Eurasian plate caused uplift of the caused uplift of the Himalaya, the Himalaya, the highest mountains highest mountains on Earth.on Earth.

Transform boundariesTransform boundaries

Plates slide past Plates slide past each othereach other

Little or no volcanic Little or no volcanic activityactivity

Shallow earthquakesShallow earthquakes

Example: oceanic Example: oceanic transform faults; transform faults; San Andreas FaultSan Andreas Fault

San Andreas FaultSan Andreas Fault

Pacific plate is Pacific plate is moving NW moving NW relative to the relative to the North American North American PlatePlate

As plates move, As plates move, transform fault transform fault slips, and slips, and earthquakes occurearthquakes occur

Summary Summary

1.1. Earth’s surface is covered by about Earth’s surface is covered by about 12 lithospheric plates. 12 lithospheric plates.

2.2. The plates move slowly (2.5-15 The plates move slowly (2.5-15 cm/year). cm/year).

3.3. Most volcanism and earthquake Most volcanism and earthquake activity occurs at or near plate activity occurs at or near plate boundaries. boundaries.

4.4. Plate interiors are relatively quiet Plate interiors are relatively quiet geologically (some exceptions). geologically (some exceptions).

Geo 100- Useful InformationGeo 100- Useful Information

Course Homepage:Course Homepage: http://mercury.atmos.albany.edu/geo100/

For SKN, email your name to instructor For SKN, email your name to instructor atat

arnason@albany.eduarnason@albany.edu