Geology 12 Plate Boundaries There are three types of plate boundaries 1. Divergent (or constructive) plate boundary 2. Convergent (or destructive) plate boundary 3. Transform (or slip & slide) plate boundary Good site?

Divergent Plate Boundary

 Plates move away from each other, often causing mountain or ridge building (constructive)  Result is to create new ocean basins (such as the Atlantic) or huge valleys on land (called rift valleys)  As the plates move away from each other, magma flows from the mantle (same as water between two blocks of wood)

Divergent Plate Boundary  Mid-ocean ridges are formed when plates move apart. They are giant undersea mountain ranges that extend around the world. One example is the Mid-Atlantic Ridge.  Earthquakes & eruptions of rock are frequent along the ridges. Iceland formed atop a ridge.  Exotic creatures often live along ridges.

Convergent Plate Boundaries  With convergent plate boundaries, plates move toward each other  There are three possible collisions: 1.Oceanic crust colliding with oceanic crust causes one to dive under the other (often forming deep trenches or island chains) 2.Heavier, denser and thinner oceanic crust colliding with the continental crust causes the oceanic crust to dive (often forming deep trenches) 3.Two colliding continental crusts cause crumpling & mountain building (ex. Himalayas & Mt. Everest; Appalachians of Eastern North America, including the mountains of Eskasoni)

Convergent Plate Boundaries

Transform Boundaries  With transform boundaries, one plate slides horizontally past another plate  The result is often a fault or massive “crack” in the Earth’s crust (ex. San Andreas fault in California; Aspy Fault in C.B. Highlands)  Earthquakes are very common (and often violent) along transform boundaries

Transform Boundaries

Major Plates of the World

Model of Mantle Convection

What causes plate motions? Scientists once thought that heat from the core causes the plates to move. However, it is now believed that three types of forces are at work: 1. Ridge Push: Plates near mid-ocean ridges are pushed apart by the rising magma. The plates then slide down the oceanic ridges. 2. Slab Pull: The cold, dense leading edge of the sinking plate may pull the rest of the plate with it. 3. Trench Suction: If a sinking plate falls at a steep angle into a trench, the rest of the plate is “sucked” forward.

What are mantle plumes? Mantle plumes are narrow columns of hot, rising magma. These plumes form “hot spots” of active volcanism at the Earth’s surface. Mantle plumes have formed Iceland, the Hawaiian Islands, and Ol’Faithful in Yellowstone Park (USA)

Mantle Plume

Results of Magma Plumes Formation of “hot spots” of active volcanism around the world Formation of “hot spots” of active volcanism around the world May help to drive plates apart (ex. Mid- Atlantic Ridge) May help to drive plates apart (ex. Mid- Atlantic Ridge) Formation of domes, or bulges in the crust, which may produce volcanic eruptions Formation of domes, or bulges in the crust, which may produce volcanic eruptions Continent splitting (ex. Yellowstone Park in U.S.A.) Continent splitting (ex. Yellowstone Park in U.S.A.) Formation of seamounts and guyots, often in chains Formation of seamounts and guyots, often in chains

Importance of Understanding Plate Tectonics Explains many geological features, such as volcanoes, earthquakes, sea-floor spreading, seamounts, hot spots, and general features of Earth Explains many geological features, such as volcanoes, earthquakes, sea-floor spreading, seamounts, hot spots, and general features of Earth Important to the prediction of volcanoes and earthquakes to help protect people Important to the prediction of volcanoes and earthquakes to help protect people Explains much of the geology of Canada, including the hills of Eskasoni and the Canadian Shield Explains much of the geology of Canada, including the hills of Eskasoni and the Canadian Shield

Importance of Understanding Plate Tectonics Explains the breakup of the Pangea Supercontinent Explains the breakup of the Pangea Supercontinent Important mineral resources often formed at plate margins Important mineral resources often formed at plate margins BASICALLY, THE THEORY OF PLATE TECTONICS CONNECTS TOGETHER MOST TOPICS IN GEOLOGY, INCLUDING THIS COURSE!!! BASICALLY, THE THEORY OF PLATE TECTONICS CONNECTS TOGETHER MOST TOPICS IN GEOLOGY, INCLUDING THIS COURSE!!!

Seamounts

Define the following: Hot spot Hot spot Volcanic dome Volcanic dome Seamount Seamount Guyot Guyot Pangea Pangea