Geology 111 exam 3 deep oceans

drakes

What are the three major zones in the ocean

continental margin

deep-ocean basins

mid-ocean ridges

how do the three major zones look at different @ active, passive margins?

look up

What are passive and active margins?

two types of boundaries between oceanic and continental crust

active margins

where subduction and volcanism occur

found in the pacific ocean

the continental slope descends abruptly into a deep ocean trench in most active margins

passive margins

type of continental margin

found along most coasts in the Atlantic Ocean

3 features of passive margins

continental shelf

continental slope

continental rise

continental shelf

• gently sloping submerged surface extending from the shoreline

• flooded extension of the continents

• 80 kilometers (50 miles) wide on average

• appears to be flat plain

• composed of continental crust

continental slope

seaward edge of continental shelf

ocean floor has a sharp change in slope

boundary between lighter continental material and denser oceanic material

can be very steep

continental rise

gently sloping oceanic material at the base of the continental slope

thick accumulation of sediments

sediments move downslope by turbidity currents

deep ocean basins

between the continental margins and the mid oceanic ridges lies the deep ocean basins

these basins cover almost 30% of the earths surface

we know more about the moon and mars than we do about deep ocean basins

deep ocean basin features

extremely deep, linear canyons

remarkably flat areas known as abyssal plains

tall underwater volcanic peaks called seamounts and guyots

large flood basalt provinces called oceanic plateaus

How do accretionary wedges form? Type of metamorphism?

from active continental margins

sediments washed down from the continents and sediments scraped off the subducting plate can accumulate by the trench

creates an unusual metamorphic rock, blueschist

look up temp and pressure

why is the abbysal plain the largest in the atlantic ocean

cover 40% of the deep ocean basins

look up

much of the sediment id deposited from turbidity currents

why are there the deepest trenches in the pacific

look up

mid ocean ridges

divergent plate boundaries

the mid-oceanic ridge system is the longest topographic feature on earth, exceeding 70,000 kilometers (43,000 miles) in length

found in all major ocean basins

occur in the middle of the Atlantic/Indian oceans but not in other oceans

what is the ridge in a mid ocean ridge

broad mountain ranges

mountains typically rise 2 to 3 kilometers or more above the abyssal plain= (to a major mountain range on land)

why are there more islands in the pacific

what is a turbidite. Use knowledge of sedimentology to predict where grains deposit.

look up

Explain ophiolites

land exposure of oceanic crust

caused by plate tectonics and uplift

california, Newfoundland, cyprus, oman(below)

can you use bowens reaction series to predict the material in an ophiolites

explain the wilson cycle (ocean basin)

200 million years ago: the Atlantic forms

• magma upwelling from the mantle

• caused the overlying crust to dome upward

• cause long, linear faults and fractures from which lava erupted onto the surfaces

• plate tectonics began to pull the plates apart

• salbs sank along faults

• formed rift valley

• occured along entire boundary between africa and south america

modern day oceans in satges of wilson cycle

the atlantic

the red sea (formed when the arabian plate rifted from africa)

seafloor spreading widens the red sea

east africa

why does oceanic crust only go back 180my?

plate tectonics creates new oceans and mid ocean ridges. eventually destroys old oceans by subducting them back into the mantle

relationship between hotspots and continental rifting

slow spreading ridge

at slow spreading rates

(1-5 cm per year), such as occurs in mid-atlantic ocean ridge, a prominent rift valley is present along much of the ridge

more rugged topography

fast spreading ridge

>9 cm per year, such as occurs in the east pacific rise, rift valleys are absent

topography is less elevated, but far more elevated

the eruption of magma is continuous process and upwelling occurs along the entire length of the ridge

why do we have ridges at spreading centers (2 reasons) or why are the ridges not all elevated the same

the upwelling of the magma creates a major bulge along the length of the ridge

density of a rock (which is denser, hot or cold rock)

why dont we know much about our oceans (LAST ONE for this lecture)

bc we have only mapped 5% of the ocean

100 ships with wide scanning, high resolution, multi beam sonar (would need 100 years to map all of the ocean)

have only mapped areas of interest