Plate Tectonics

Plate Tectonics

movement of plates & forces acting on them

What explains the distribution of volcanoes, earthquakes, mountain chains, rock assemblages, and seafloor structures?

plate tectonics

Continental Drift

large scale movement of continents across the earth

Proposed by Alfred Wagner

Evidence: jig-saw puzzle fit of continents, similar rocks & rock ages across oceans, similar fossils across oceans, distribution of climatic belts

continental drift

Seafloor Spreading

creation of oceanic crust & movement of existing crust across Earth’s surface from MOR’s (mid ocean ridges)

Proposed by Harry Hess

MOR’s first mapped by Marie Tharp

seafloor spreading

Magnetic Anomaly

parallel bands of alternating high & low magnetic intensity on the seafloor

fe-rich minerals in basalt seafloor align to magnetic north during crystallization

evidence for magnetic field reversal (north pole points to Antartica)

mirror image of field reversals on either side of MOR

magnetic anomaly

Lithosphere is broken into ___ (plates) of different sizes and shapes

pieces

Plate Boundaries

breaks between plates

Plates are moving __ each other (exert lots of ___ on adjacent plates)

past; pressure

What are plate boundaries are marked by?

earthquakes/fault lines

Plates can be composed of what?

continental and/or oceanic crust

Active Margin

a continental margin that is also a plate boundary, typically with tectonic activity like earthquakes, volcanoes, and mountain building

West Coast of South America

active margin

Passive Margin

a continental margin that is not a plate boundary, with little tectonic activity; typically features broad continental shelves

East Coast of North America

passive margin

Plates move apart by sea-floor spreading or rifting

divergent plates

T/F: divergent plate boundaries create a new lithosphere and increase plate area

true

T/F: divergent plate boundaries create a new atmosphere and decrease plate area

false

Specific types of divergent plate crustal interaction?

continent-continent, oceanic-oceanic

Ocean-Ocean Plate Sepreration

ex: mid ocean ridge; major geological features: mid ocean ridge, rift valleys, shallow earthquakes

Continent-Continent Plate Seperation

ex: east african rift; rift valleys, volcanoes, shallow earthquakes

What is a Rift Valley?

a lowland region that forms where tectonic plates are moving apart

• plates come together

• one plate recycled (subducted or crumpled)

convergent plate boundaries

What is subduction?

the process by which one tectonic plate moves beneath another and sinks into the mantle due to gravitational forces

Plate area __ at convergent boundaries

decreases

Specific types of convergent plate crustal interaction?

oceanic-oceanic, oceanic-continental, continental-continental