The theory of Plate Tectonics

Plate Boundaries

Theory of Plate Tectonics

●A theory stating that the lithosphere is divided into plates which float on and travel independently over the mantle interacting with one another at boundaries●The entire crust is split into plates (some plates are just continental crust, some just oceanic crust, and some are a combination of both)

Proof of Plate Tectonics

●“puzzle-like-fit”

●paleontological data

●paleoclimate data

●paleomagnetic data

●continental drift

●convection theory

●sea floor spreading

The Scientists behind Plate Tectonics

●Alfred Wegener - first person to propose the idea of continental drift

●Arthur Holmes - used the idea of heat in the core driving convection currents to explain continental drift and then plate tectonics

●Harry Hess and Robert Dietz - boat captains studying the ocean floor discovered mountains leading to the idea of sea floor spreading explaining plate tectonics

Plate Boundaries

●Why do we care about plate boundaries?

Plate Boundaries

●Plate boundaries are where two plates meet and move relative to one another

●Volcanoes and earthquakes most often occur where tectonic plates come together.

●At plate boundaries, many other geologic features, such as mountains and rift valleys, can also occur.

Plate Boundaries

●There are three basic types of plate boundaries:

1. Divergent2. Convergent3. Transform

Divergent Boundary

●A divergent boundary occurs where two plates divide (move away from one another) and create a gap between them.

Divergent Boundary

●There are two types of divergent boundaries○ Oceanic-Oceanic crust○ Continental-

Continental crust

Oceanic - Oceanic Divergent Boundary

●Where the two plates divided, hot rock rises from the asthenosphere (upper part of mantle) through the crack in the crust and cools to form new lithospheric rock.

●Diverging plates then pull newly formed lithosphere away from gap.

●New lithosphere (oceanic crust) is formed.

Oceanic – Oceanic Divergent Boundary

●Oceanic – Oceanic Crust●Mid-oceanic ridges are mountain ranges at

divergent boundaries in oceanic crust.

Oceanic – Oceanic Divergent Boundary

●Features: Earthquakes, mid-ocean ridge, volcanoes, sea floor spreading

●Real Life Example: Mid-Atlantic Ridge

●Mid-Atlantic Ridge runs through Atlantic Ocean from Arctic Ocean to an area off the southern tip of South America.

Continental – Continental Divergent Boundary

●Where the two plates are dividing on land.

●The crust is too thick to be pulled apart for magma to fill it in. Instead the land just has fractures across it from the stress of being pulled apart.

●Sometimes rivers and streams form at the deepest part

Continental – Continental Divergent Boundary

●Crust is not created nor destroyed

●Features: Rift Zone, Earthquakes

●Real Life Example: East African Rift Zone

●This runs through Northeast Africa pulling apart the land and leaving a zone of fractures

Convergent Boundary

●A convergent boundary occurs where two plates collide (move toward one another).

Convergent Boundaries

●There are two types of convergent boundaries:

1. Subduction2. Collision

Convergent Boundary - Subduction

●Subduction is the process by which one lithospheric plate moves beneath another plate.

Oceanic – Oceanic Convergent Boundary

●Subduction - crust is being destroyed

●Two oceanic plates collide and the more dense oceanic plate moves beneath the less dense oceanic plate. The denser plate sinks into the mantle where it melts. That melted plate rises up to create island arcs (volcanoes) in the ocean.

Oceanic – Oceanic Convergent Boundary

●Features: Volcanoes, Island Arcs, earthquakes, trenches

●Real World Example: Mariana Trench

●The Mariana Trench is East of the Philippines and occurred from one ocean plate moving under the other leaving a large depression in the ocean.

Oceanic – Continental Convergent Boundary

●Subduction - crust is being destroyed

●Oceanic and continental plate collide. The thin, denser oceanic plate collides with the less dense, thick continental plate. The oceanic plate is forced under the continental plate into the mantle where it melts. That melted plate rises up to create a volcanic arc on the continental crust. The continental crust is also pushed up causing mountains.

Oceanic – Continental Convergent Boundary

●Features: Earthquakes, Volcanic Arcs, Mountains, Trenches

●Real World Example: Andes Mountains

●This is on the West Coast of South America. The oceanic plate is subducting under the continental plate causing a trench in the ocean and the Andes Mountains to form.

Continental - Continental Convergent Boundary

●Collision - crust is not created or destroyed

●Two continental plates collide and the pressure pushes them upward creating mountains

Continental - Continental Convergent Boundary

●Features: Earthquakes, Mountains

●Real Life Example: Himalayan Mountains

●Above India. Formed when India crashed into Eurasia and pushed together forming mountains.

Transform Boundary

●A transform boundary occurs where two plates slide past one another. The plates’ jagged edges get stuck, and once they unstick the jolt sends out waves causing earthquakes.

Transform Fault Boundary

●Crust is not created nor destroyed

●Features: Faults, earthquakes

●Real World Example: San Andreas Fault

●On the coast of California two plates slide past one another creating the San Andreas Fault.

New Madrid Fault System