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.

Jigsaw Evidence

Fossil Evidence

Rock Evidence

Problems With Wegner’s Theory Wegner’s theory lacked a mechanism to explain how the plates actually moved. Theories proposed by Wegner were not supported by his colleagues. It was not until the 1940’s that evidence surfaced that proposed a Mechanism that explained how the plates moved.

MECHANISM FOR PLATE TECTONICS

Mechanism Seafloor Evidence

Mechanism “Sea Floor Evidence” 1940’s Seafloor mapped revealing: 1.Sediment thinner near the Ocean sea floor ridges. 2.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”

Depth & Age of marine sediments

Mechanism “Sea Floor Evidence” Paleomagnetism the study of the alignment of magnetic minerals in rock, spcifically as it relates to the reversal of Earth’s magnetic poles; also the magnetic properties that rock acquires during formation As magma solidifies to form rock, iron-rich minerals in the magma align with Earth’s magnetic field. When the rock hardens, the magnetic orientation of the minerals becomes permanent.

Magnetic field lines While magma cools, it is imprinted with the magnetic field lines. Periodically the magnetic poles reverse directions. N becomes S & S becomes N. New magma will be imprinted with the new magnetic field lines.

Earth’s Magnetic field

Mechanism Paleomagnetism

Mirror image of stripes either side of spreading zone

Mechanism Driving Force

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

Convection cells in asthenosphere

Ridge Push

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

Plate Boundaries

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

Plate Boundaries

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)

Supercontinent Cycle

The Supercontinent Cycle Supercontinent Cycle the process by which supercontinents form and break apart over millions of years Pangaea the supercontinent that formed 300 million years ago and that began to break up beginning 250 million years ago Panthalassa the single, large ocean that covered Earth’s surface during the time the supercontinent Pangaea existed

The Supercontinent Cycle, Using evidence from many scientific fields, scientists can construct a general picture of continental change throughout time. Several times in the past, the continents were arranged into large landmasses called supercontinents. Supercontinents broke apart to form smaller continents that moved around the globe. Eventually, the smaller continents joined again to form another supercontinent. The process by which supercontinents form and break apart over time is called the supercontinent cycle.

The Supercontinent Cycle

Breakup of Pangaea About 250 million years ago (during the Paleozoic Era), Pangaea began to break into two continents— Laurasia and Gondwanaland. Laurasia became the continents of North America and Eurasia. Gondwanaland became the continents of Africa, South America, India, Australia, and Antarctica.

The Supercontinent Cycle

The Modern Continents Slowly, the continents moved into their present positions. As the continents drifted, they collided with terranes and other continents. New mountain ranges, such as the Rocky Mountains, the Andes, and the Alps, formed. Tectonic plate motion also caused new oceans to open up and caused others to close.

The Supercontinent Cycle,

The Supercontinent Cycle Geography of the Future As tectonic plates continue to move, Earth’s geography will change dramatically. Scientists predict that in 250 million years, the continents will come together again to form a new supercontinent.

The End