Lesson 7: Structure and Evolution of Ocean Basins

What was the name of the supercontinent that existed less than 100 million years ago?

Pangaea.

What caused the breakup of Pangaea?

Tectonic forces and processes.

What formed as a result of Pangaea breaking apart?

Ocean basins.

What type of rock forms the ocean basins?

Volcanic rock released from fissures at mid-ocean ridges.

What is a mid-ocean ridge?

An underwater mountain range formed by plate tectonics.

What process forces the oceanic lithosphere to move under the mantle?

Subduction.

What causes subduction to occur?

High gravitational energy.

How do ocean basins change over time?

They continuously evolve through tectonic processes.

How many major ocean subdivisions exist today?

Four major ocean subdivisions.

What are the major subdivisions of the world ocean?

North and South Pacific, North and South Atlantic, Indian, and Arctic Oceans.

What is the largest, deepest, and oldest ocean basin on Earth?

The Pacific Ocean basin.

Which ocean basin experiences the most trenches and tsunamis?

The Pacific Ocean basin.

Which ocean basin is the second largest?

The Atlantic Ocean basin.

Which ocean basin is the third largest?

The Indian Ocean basin.

Which is the smallest ocean basin on Earth?

The Arctic Ocean basin.

What covers most of the Arctic Ocean basin?

Ice.

Continental shelf

Partly shallow extension of the continent underwater.

Continental slope

Transition zone of continental shelf and deep ocean floor. It starts from oceanic crust to continental crust.

Continental rise

It is where the ocean begins. All basaltic and oceanic rocks are found here. It is the place where the sediments from land are washed. The continental margin starts from continental shelf up to continental rise.

Abyssal plain

The flattest part of the ocean. 50 % of the earth’s surface is being covered by this plain.

Island

It’s not just a piece of land floating up in the middle of the sea, it is part of the ocean basin that extends up from the ocean floor.

Seamount

It is an undersea mountain. The erosion caused by waves destroyed the top of a seamount which caused it to be flattened.

Trench

It is the deepest part of the ocean.

Mid-oceanic ridge

The seafloor mountain system which is situated in the middle of the ocean basin. It is where upwelling of magma happens which causes the sea floor to spread.

Evolution of the Ocean Basin

The Wilson Cycle explains the process of the opening (beginning) and

the closing (end) of an ocean which is driven by Plate Tectonics. This process

is named after the Canadian Geophysicist J. Tuzo Wilson (1908-1993).

It is divided into 6 stages namely:

1. Embryonic Ocean Basin

2.Juvenile Ocean Basin

3. Mature Ocean Basin

4. Declining Ocean Basin

5. Terminal Ocean Basin

6. Suturing (Continental collision)

Embryonic

Motion: Uplift.  Complex system of linear rift valleys on continent. East African

Rift Valleys

Juvenile

● Motion: Divergence (Spreading) ● Narrow seas with matching coasts. Red Sea

Mature

Motion: Divergence (Spreading).  Ocean basin with continental margins. Atlantic and Arctic Oceans

Declining

● Motion: Convergent (Subduction) ● Islands arcs and trenches around basin edge. Pacific

Ocean

Terminal

● Motion: Convergent (Collision and Uplift) ● Narrow, irregular seas with young mountains. Mediterranean Seas

Suturing

● Motion: Convergence and Uplift

● Young to mature mountain belts Himalayas

Mountains