Transcript Origin and Structure of the Ocean Basins - GMCbiology

Origin and Structure of the
Ocean Basins
I. Continental Drift
• Theory proposed by Alfred Wegener
• 1912
• “super-continent” named Pangaea
• Continents drifted across oceans
• No evidence for
A. Pangaea
•
•
1.
2.
3.
4.
240 mya
Evidence:
puzzle like fit of continents
Fossils
Glacial deposits
Mountain belts
B. Separation of Pangaea
• 2 land masses
1. Laurasia
2. Gondwana
• Rift forms to create the Atlantic Ocean
II. Plate tectonics
• Various plates comprise ocean floor and
land masses
• Seven major plates
1.
2.
3.
4.
5.
6.
7.
Pacific
African
Antarctic
Indian-Australian
Eurasian
N. American
S. American
• Plates in motion
Plate Boundaries
There are 3 types of Plate Boundaries:
1. Convergent
2. Divergent
3. Transform
1. Convergent
• Colliding
a. Oceanic-oceanic: subduction
b.
occurs, earthquakes occur due to
friction, deep trenches form,
subducting plate melts and
magma rises to surface (volcano)
Oceanic-continental: ocean
plate subducts under continental,
forms trench, earthquakes and
volcanoes
c. Continental-continental:
friction causes rocks to bend,
fold, mountain chains form
2. Divergent
•
•
•
•
•
•
Moving in opposite directions
Causes sea floor spreading
Growth of the plates
Forms ridges
Forms hydrothermal vents
Can form entire ocean basins
3. Transform
• Plates sliding past each other
• Occur at regions between
•
•
ridge sediments with motion
in opposite directions
Forms faults
Cause friction and
earthquakes
B. Hot spots
Other places which
earthquakes and volcanoes
occur (not always at plate
boundaries)
• Huge chamber of melted
rock deep within mantle
•
• Hot, solid rock rises to the hot spot from greater
depths. Due to the lower pressure at the shallower
depth, the rock begins to melt, forming magma. The
magma rises through the Pacific Plate to supply the
active volcanoes. The older islands were once located
above the stationary hot spot but were carried away
as the Pacific Plate drifted to the northwest.
C. Other changes
1. Seamounts - Volcanic islands which have
sunk below the surface
2. Trenches – dip in the ocean floor from
plates colliding
3. Ridges – rises in the ocean floor from
plates colliding
D. Driving forces for these changes
• Thermal convection hypothesis
High temperature from the core heats
the mantle; decreased density causes
movement closer to the crust (lower
density above is heated and starts moving
due to heat below); circular motion occurs
called thermal convection cells
III. SC Ocean Basin Changes
• Coastline is thought to have moved over
time
A. Blue ridge region may once have been a coast;
B.
C.
D.
piedmont an island
Ice age – coast line 100 miles out from
Charleston, sea level falls, higher salinity
Non-ice-age – coast line at boundary of
Sandhills and Piedmont, sea level rises, lower
salinity
Evidence – marine fossils and land fossils