Origin and Structure of the Ocean Basins

I. Continental Drift Theory proposed by Alfred Wegener Theory proposed by Alfred Wegener “super-continent” named Pangaea “super-continent” named Pangaea Continents drifted across oceans Continents drifted across oceans No evidence for No evidence for

A. Pangaea 240 mya 240 mya Evidence: Evidence: 1. puzzle like fit of continents 2. Fossils 3. Glacial deposits 4. Mountain belts

B. Separation of Pangaea 2 land masses 2 land masses 1. Laurasia 2. Gondwana Rift forms to create the Atlantic Ocean Rift forms to create the Atlantic Ocean

II. Plate tectonics Various plates comprise ocean floor and land masses Various plates comprise ocean floor and land masses Seven major plates Seven major plates 1. Pacific 2. African 3. Antarctic 4. Indian-Australian 5. Eurasian 6. N. American 7. S. American Plates in motion Plates in motion

Plate Boundaries There are 3 types of Plate Boundaries: 1. Convergent 2. Divergent 3. Transform

1. Convergent Colliding Colliding a. Oceanic-oceanic: subduction occurs, earthquakes occur due to friction, deep trenches form, subducting plate melts and magma rises to surface (volcano) b. 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 Moving in opposite directions Causes sea floor spreading Causes sea floor spreading Growth of the plates Growth of the plates Forms ridges Forms ridges Forms hydrothermal vents Forms hydrothermal vents Can form entire ocean basins Can form entire ocean basins

3. Transform Plates sliding past each other Plates sliding past each other Occur at regions between ridge sediments with motion in opposite directions Occur at regions between ridge sediments with motion in opposite directions Forms faults Forms faults Cause friction and earthquakes Cause friction and earthquakes

B. Hot spots 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. 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. Other places which earthquakes and volcanoes occur (not always at plate boundaries) Other places which earthquakes and volcanoes occur (not always at plate boundaries) Huge chamber of melted rock deep within mantle Huge chamber of melted rock deep within mantle

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 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 Coastline is thought to have moved over time A. Blue ridge region may once have been a coast; piedmont an island B. Ice age – coast line 100 miles out from Charleston, sea level falls, higher salinity C. Non-ice-age – coast line at boundary of Sandhills and Piedmont, sea level rises, lower salinity D. Evidence – marine fossils and land fossils