Geology Unit 5: Plate Tectonics

Plate Techtonic Theory

1. Earth's crust is divided into sections called plates. 2. These plates 'float' on top of the more dense mantle. 3. These plates move over time

Rift Valley

A deap valley formed by two plates moving away from each other.

Magnetic Reversals support P.T.

As Magma (with iron atoms) emerges and the magma cools, the atoms line up toward magnetic north (which flips every 500,000 years). Shows growth of the ocean floor and movement of the continents over time.

Convection Cell

Causes plate movement. 1. magma in the mantle is heated by the core 2. heated magma rises toward the crust 3. as magma rises, it cools 4. cool magma sinks back toward the core

Lithosphere

Crust at the very top of the mantle; cool and brittle

Outer Core

Dense layer of iron and nickel that is VERY HOT and heats the mantle; spins with the Earth and generates Earth's magnetic field.

Geologic Phenomena from Transform boundaries

Earthquakes; some warping of the crust.

Geologic Phenomena from Divergent boundaries

Iceland (formed on top of Mid-Atlantic Ridge); Vocanos; Earthquakes; Mountains (fault block); mid-ocean ridges; rift valleys; spreading zones.

Early Evidence for Continental Drift

Jigsaw fit, continents seem to have once fit together; Fossil evidence; climate records/rock samples; glacial records; geologic formations 'across' continents.

Mid-ocean ridges support P.T.

Magma forcing plates apart/creating new crust gives evidence of plates/plate boundaries and gives a mechanism for how plates can move (be forced apart)

35 minor plates

Most important: Juan de Fuca, Nazca, Cocos, Arabian, Caribbean, Indian, Philippine

Crust: Continental

Outermost layer of the earth: part that is thicker and more dense

Crust: Ocianic

Outermost layer of the earth: part that is thinner and less dense. Primarily made of silicon and oxygen.

7 major plates

Pacific, South American, North American, Eurasian, African, Australian, Arctic

Divergent boundaries

Plates diverge or move away from each other; new crust is created as magma forces plates apart; Example: Mid-Atlantic Ridge.

Transform Boundary

Plates move past each other laterally (side to side); neither plate is destroyed; Example: San Andreas Fault (formed by North American and Pacific plates).

Convergent Boundary

Plates move toward each other and collide; crust is destroyed.

Continent-Continent

Two continents colliding; pushes the crust together to form mountains; Example: Indian and Eurasian plates colliding to form the Himalayas and Mount Everest.

Oceanic-Oceanic

Two ocean plates collide; the older one sinks under the newer one; creates a volcanic island arc; Example: Mariana Islands fromed by the Philippine and Pacific Plates; Japan, New Zealand; ... (NOT Hawaii)

Continent-Oceanic

Type of Convergent boundary where an ocean plate collides with a continent; the ocean plate sinks and melts (magma for volcano); a trench is formed where the plate subducts under the other. Example: Juan de Fuca subducts under North American Plate creating the Cascade Mountains in CA, OR, WA.

Mid-Oceanic Ridge

Undersea mountain chain that is also a plate boundary; most are under water; magma comes up from the mantle and forces plates apart creating new crust; example: Mid-Atlantic Ridge

Asthenosphere

Upper portion of the mantle/below lithosphere; where solid rock begins melting/begins to flow; where PLATES BEGIN TO MOVE.

SONAR

Used during WW2 to map the ocean floor; found Mid-Atlantic Ridge where the ocean floor pushed away from the ridge which showed the seafloor was spreading=explained continental drift.

Geologic Phenomena from Convergent boundaries

Volcanos (explosive); Earthquakes (big); Mountains (folded); Trenches/subduction zones; Volcanic Island Chains

Subduction

Where one plate sinks underneath another and is forced into the mantle (then melted)

Mantle

Zone of melted rock below the crust; dense, semi-liquid rock; 2/3 of the Earth's mass

Trenches support P.T.

boundaries formed when two plates collide leads to crust being destroyed. Shows evindence of plates. Creates lots of earthquakes showing evidence of plate movement. Explains how volcanos are formed

How plates move

convection currents in the mantle move plates around

Island Chains supports P.T.

extra hot reagion of mantle causes volcanic islands which move with the plate and away from the hot spot. We can measure movement of a plate.

hot spot

long-lasting, extra hot region in the mantle which causes volcanism. Example=Hawaii

Fault Block Mountains

one side is dropping lower as the crust spreads.

island chain

sline of lvolcanic island and seamounts caused by a hot spot

Inner Core

solid iron

continental drift

the gradual movement of the continents across the earth's surface through geological time.