Plate Tectonics

OVERVIEW Defining Plate Tectonics Review of Earth’s Layers Focus: Crust & Asthenosphere Evolution of Plate Tectonic Theory Visual Evidence Initially One Landmass Landmass Moved Mechanism for Movement Heat, Gravity, Kinetic Energy Effects of Plate Tectonics Effects of Plate Movement & Plate Interactions Plate Movement & Interaction of Moving Plates Deformation (Mountain Building) Earthquakes/Volcanoes Mineral/Rock Formation Effects of Continental Change Supercontinent Cycle

Plate Tectonics Defined Theory that the Earth’s Crust is fragmented into a series of pieces or “Plates”. These plates move or drift on the Earth’s surface like large “Rafts” of rock. Plate tectonics describes: 1.Plate Material (Oceanic & Continental Crust) 2.How the Plates move or mechanism 3.Effects of the movement of Plate

Plate Tectonics

Review of Earth’s Structure and Composition

Earth’s Layers Defined Based on 2 Criteria 1.Composition (3 Layers) 1.Crust Moho: Boundary between the Crust and Mantle 2.Mantle 3.Core 2.Structure (5 Layers) 1.Lithosphere – Composition: Upper Mantle & Crust 2.Asthenosphere – Composition: Mantle 3.Mesosphere – Composition: Mantle 4.Outer Core - Core 5.Inner Core - Core

Lithosphere = crust + upper mantle

The Crust Outer layer km thick Silica Rich 2 types of crust Oceanic (very dense, made of basalt) Continental (less dense, made of granite)

Ocean & continental crust

Crust OCEAN crust Denser Thinner Eventually is subducted Relatively young CONTINENTAL crust Less dense Thicker Rarely/never subducted Oldest crust on Earth

Earth profile by Texture LITHOSPHERE Hard & brittle Crust & upper mantle “Plate” ASTHENOSPHERE Plastic “silly putty” Lower mantle Convection current that carries the plates

History of Plate Tectonics

Plate Tectonics began with Alfred Wegner, who proposed the theory: “Continental Drift” Wegner’s theory was based on visual observations that suggested the Continents were all connected in the past, i.e. Pangea.

Wegener’s Evidence 1.Jigsaw Evidence: continents connect together like a jigsaw puzzle. 2.Fossil Evidence: fossils of the same plants and animals could be found in areas of continents that had once been connected. 3.Rock Formations: ages and types of rocks in the coastal regions of widely separated areas matched closely. 4.Climatic Evidence: changes in climatic patterns suggested the continents had not always been located where they are now.

Problems With Wegner’s Theory Wegner’s theory lacked a mechanism to explain how the plates actually moved.

Mechanism “Sea Floor Evidence” 1940’s Seafloor mapped revealing: 1.SEDIMENT THICKNESS. Sediment thinner near the Ocean sea floor ridges. 2.AGE OF ROCKS. Oceanic rocks were younger than Continental. 1950’s Additional evidence presented by Harry Hess, who proposed his theory of Sea Floor Spreading, which was based on: 3.“PALEOMAGNETISM”

Mechanism “Driving Force” 3 Sources 1.Convection 2.Ridge Push 3.Slab Pull

Effects of Plate Tectonics

Plate Interactions 3 types of Plate Interactions or Boundaries 1) diverging, spreading plates 2) collision, colliding, converging plates 3) sliding beside, transform faults

Diverging Zones CONTINENT Rift zone Valley w/ basalt flows E.g. Red Sea, Rift Valley in Africa OCEAN Creates new ocean floor Mounds of basalt E.g. Mid-Atlantic Ridge, East Pacific Rise

Convergent Ocean- Continent Denser ocean crust is subducted under Deep trench, strong earthquakes Volcanic Mt range on continent E.g. Andes Mts, Cascade Mts

Convergent Continent- Continent Piles & piles of crumpled, folded crust = tall mountains Thick crust, earthquakes E.g. Himalayan Mts, Appalachian Mts, Alps

Convergent Ocean-Ocean Slower plate is subducted under Deep trench, strong earthquakes, tsunamis Volcanic island archipelago E.g. Aleutian Islands, Japanese Islands, Indonesian Islands, Caribbean Islands

Comparing Oceans Pacific Ocean is shrinking Subduction zones Oldest sediments are farthest from spreading zone Atlantic Ocean is widening Spreading zones Oldest sediments are farthest from spreading zone

Effects of Continental Change Climate Change. Ice that once covered the globe melted. Mountains formed. Result of plate movement. New Species Evolved. Movement caused separation of organisms and evolution of new species. (i.e., Australia)

The Supercontinent Cycle Supercontinent Cycle the process by which supercontinents form and break apart over millions of years Wilson Cycle (3 Parts) 1.Opening of an Ocean Basin 2.Sedimentation 3.Closing of an Ocean Basin Pangaea: Large land mass Panthalassa the single large ocean

The End