Plate Tectonics: Movement and Plates

• Plate Tectonics is a theory explaining the movement of Earth's plates.
• The theory includes:
• Continental drift
• Sea-floor spreading
• Continental drift and plate movement
• Ireland's position now and in the past
• Global plate distribution
• Plate boundaries

Main Plates of the Earth

• The Earth's main plates include:
• North American
• South American
• Eurasian
• African
• Australian
• Antarctic
• Pacific
• Nazca
• Arabian
• Indian
• Philippine

Theory of Plate Tectonics

• "Plate Tectonics" explains the movement of Earth's plates.
• Alfred Wegener proposed the idea in 1912.
• Earth's crust has plates that move or float on the mantle.
• Convection currents in the mantle cause plate movement.
• Plates can pull apart, collide, or slide past each other.

Magma Convection Currents

• Magma convection currents cause plate movement.
• Magma heats, rises, and moves towards the upper mantle.
• Then the magma flows sideways, cools, and sinks.
• Plates move with the sinking magma.

Sea Floor Spreading

• New rock forms at split plate locations like Iceland.
• The ocean floor widens as magma rises from the mantle, filling openings.
• Magma cools to form new ocean floor.
• New sea floor is youngest at the mid-ocean ridge.
• Older rocks are found further from the plate divide towards continents.

Theory of Continental Drift

• Continents move across the planet due to convection currents.
• Continental drift is still occurring.
• Continents were once joined as Pangaea, a supercontinent.
• Pangaea began to break apart approximately 200 million years ago.
• Convection currents fuel the drifting of continents, dividing Pangaea into Laurasia and Gondwanaland.

Process of Subduction

• Subduction happens when continents collide.
• The oceanic plate being heavier than the continental plate
• Results in the ocean floor being pulled down into the mantle where subduction occurs

Plate Boundaries

• There are three types of plate boundaries:
• Divergent (construction boundaries)
• Convergent (destruction boundaries)
• Conservative

Divergent (Constructive) Boundaries

• New crust forms at divergent boundaries.
• Mid-ocean ridges like the Mid-Atlantic Ridge are created.
• Plates separate and move away from each other.

Convergent (Destructive) Boundaries

• Three types of destructive boundaries exist:
  • Oceanic-continent: where an ocean and continental plate collide
  • Oceanic-oceanic: where two ocean plates collide
  • Continent-continent: where two continental plates collide
• Heavier oceanic plates subduct.
• Magma rises to create volcanoes on the continental plate.
• Continental plates buckle and fold mountains form.
• Heavier and older plates dip and subduct beneath lighter, younger plates, developing deep sea trenches.
• Lithosphere subducts when plates neither sink on collision.
• Continental crusts buckle and fold mountains form.

Conservative (Passive) Boundaries

• Crust is neither created nor destroyed.
• Plates slide past each other.
• Fault lines mark where the plates slide.
• Conservative boundaries are known as transform faults.

The Position of Ireland

• Ireland was split into two sections 850 million years ago.
• One section: part of the North American Plate, positioned near the equator with Scotland.
• The other section: part of another continent with England and Wales.
• Plates collided around 400 million years ago, forming Ireland.
• The position of Ireland had moved south of the equator around 380 million years ago.
• North Ireland was above sea level, while the south was submerged.
• Sea levels rose about 350 million years ago and covered Ireland.
• This is when Ireland's most common rock, limestone, formed.
• Continental drift moved Ireland north between 200 and 140 million years ago.
• Ireland is constantly changing as erosion, deposition, and weathering shape its landscape.