Chapter 7 Tarbuck Earth Science

define continental drift

theory that plates move

define oceanic ridge system

ridge that winds through all major oceans over 70,000 km long

max age of oceanic crust

180 million years

7 major plates

NA, SA, Pacific, African, Eurasian, Australian-Indian, Antarctican

define divergent plate boundary

plates move away from each other, seafloor created

define convergent plate boundary

plates move into each other, seafloor destroyed

define transform plate boundary

plates slide past each other, seafloor not created nor destroyed

define continental rifting

upwelling of molten rocks on land causes a rift valley that eventually turns into an ocean basin

define rift valley

valley formed when continental plates diverge and rocks sink

define subduction

one plate sinking under another into the mantle

define subduction zone

area where subduction occurs

define oceanic-Continental Convergence

The dense oceanic crust subducts to the mantle, asthenosphere above subduction zone begins to melt, volcanic structures form due to this melting

define volcanic island arc

arc of volcanic islands formed in oceanic oceanic convergence

define Ocean-Ocean Convergence

Two oceanic slabs converge, one goes under the other, Volcanoes grow on ocean floor, trenches can also be created

define continental volcanic arc

belt of volcanoes formed when continental oceanic convergence occurs

define Continent-Continent Convergence

Continental rock is not dense enough to subduct, Mountain belt is formed through the collision of these plates

define transform plate boundary

Plates slide past each other

Lithosphere not created nor destroyed

Connect offset oceanic ridges if in oceans

define fracture zones

cracks where transform faults slide past and grind rock

breakup of pangaea

NA and Africa break off opening up Atlantic ocean

South America breaks off opening up southern Atlantic ocean

India travels northward to Asia to form Himayalan mountain belt

Tectonics in the Future

Baja peninsula will collide with Aleutian islands

Africa will collide with Eurasia to form mountain belt

Australia will head towards Asia

Possible supercontinent will be formed again

how did Deep Sea Drilling reveal seafloor spreading

Concluded that sediments and fossils are older the further they are from a ridge, proves seafloor spreading happens

define mantle plume

upwelling of hot rock that causes partial melting further up

define Hot spot

area of high heat and volcanism in Pacific ocean due to mantle plume

define Paleomagnetism

study of earth’s previous magnetic fields

define Normal Polarity

North and South poles like we know them today

define reverse polarity

north and south poles are opposite

Polar wandering

idea that poles could move around the earth

Bands of magnetism on the seafloor revealed that:

Oceanographers discovered bands of high and low magnetism rocks in the seafloor. High magnetism bands formed during normal polarity, low magnetism bands during reverse polarity

How is Plate Motion Measured

Geoloical evidence in the ocean floor

Radiometric dating

Satellites

define Convection

warming and cooling of rocks as they rise and fall

define slab pull

gravity naturally pulling denser rock underground (oceanic crust)

define ridge push

oceanic ridges being elevated because they are less dense

define Whole Mantle convection

Subduction sends rock to mantle, hot rock in mantle rises, this cycle of heat creates convection currents

define Layer Cake Model

Independent layers that don’t mix

Upper layer does subduction

Lower layer sends heat up but does not interact with subducted rock