Plate Tectonics

Inner Core

solid, mainly iron and some nickel (3 mil x pressure than surface)

Outer Core

liquid, mainly iron and some nickel

Mantle

rock shell comprised of mafic minerals

Crust

• mainly igneous rocks

• thin layer of sedimentary rocks

Discontinuity

surface where seismic waves change velocity

Mohorovicic Discontinuity

density of earth’s materials difference between the mantle and the crust

Continental Crust

• 30-70 km thick

• more felsic rocks (granite)

• lower density

Oceanic Crust

• 5-10 km thick

• more mafic rocks (basalt)

• higher density

Isostasy

the continental crust has a lower density than the mantle, so it floats on top of it (ice in water)

Upper Mantle

• continental and oceanic crust

• lithosphere

• asthenosphere

Lithosphere

brittle and strong (more likely to break under stress)

Asthenosphere

relatively weak (more likely to flow under stress)

History of Plate Tectonics 1.

1600, Dutch cartographer notices continents fit together

History of Plate Tectonics 2.

1900’s, Theory of continental drift by Alfred Wegener

Evidence of Continental Drift

• mountain ranges share rock types

• glaciers left scratches on rocks

• coal left behind from plant matter

History of Plate Tectonics 3.

1929, Arthur Holmes proposed convective currents in asthenosphere could cause continents to move

History of Plate Tectonics 4.

ocean floor mapping showed mid-ocean ridges combined with evidence of sea-floor spreading

History of Plate Tectonics 5.

1950s-60s, magnetic strips and rocks of equal age on either side of mid-ocean ridges

History of Plate Tectonics 6.

changes in the earths magnetic field leads to pole reversal

Modern Concepts of Plate Movement

• lithosphere is made of plates floating on asthenosphere

• 7 major plates

Rate of Plate Movement

a few centimeters per year

Evidence of Plate Movement

• all ocean crust in less than 200 my old

• continental crust is up to 3.5 by old

Types of Plate Boundaries

• divergent

• convergent

• transform

Divergent Plate Boundary

magma rises from mantle moving plates away from each other

Convergent Plate Boundary (Oceanic-Continetal)

the lower density continental lithosphere overrides higher density oceanic lithosphere

Convergent Plate Boundary (Continental-Continental)

when 2 continents meet, thus pushing up the lithosphere creating mountains

Thrust Fault

break in rock from stress, displacement occurs along break, causing mountain building

Folding

crust compressed without breaking, it bends

Anticline

upwarped crust

Syncline

downwarped crust

Transform Plate Boundary

near mid-ocean ridges at a right angle