Intermission: Intermission: Plate Tectonics

National Oceanic and atmospheric Administration/National Geophysical Data Center

Alfred Wegener

Evidence: (1) Continents Fit Together

Evidence: (2) Rocks & Structures Match Up

Evidence: (3) Glacial Features

Evidence: (4) Fossils

Pangea

Animation Link

“If we are to believe Wegener’s Hypothesis, we must forget everything which has been learned in the last 70 years and start over again.” –Critic of Continental Drift in 1928

Harry Hess

Evidence: Seafloor

Seafloor Spreading

Seafloor Age

Plate Tectonics

Earth’s “surface” (lithosphere) is broken into plates Plates move on asthenosphere “Geology happens” where the plates interact with one another Basic Plate Tectonics

What do we mean by the Outer Part of the Earth?

Three Layers: Based on Composition LayerComposition CrustRock: Felsic & Mafic MantleRock: Ultramafic CoreMetal: Iron & Nickel

Crustal Properties CrustDensityCompositionThicknessAge continental ~2.8 g/cm 3 Felsic Thick: km Old: up to 4 Byrs oceanic ~3.2 g/cm 3 Mafic Thin: 2-10 km Young: <200 Mys

Five Layers: Based on Physical Properties Layer“State” LithosphereSolid / Rigid AsthenospherePartly Liquid / “Plastic” Lower MantleSolid Outer CoreLiquid Inner CoreSolid

Part #1 of Plate Tectonics Definition Earth’s “surface” is broken into rigid plates Surface = Lithosphere (includes Continental Lithosphere and Oceanic Lithosphere)

Part #2 of Plate Tectonics Definition Plates move… …on the “plastic” Asthenosphere …at about 1-10 cm/yr

Part #3 of Plate Tectonics Definition “Geology happens” where the plates interact with one another

Earthquake Distribution

Volcanoes and Plate Tectonics

Part #3 of Plate Tectonics Definition “Geology happens” where the plates interact with one another How do they interact? 1.Pull Apart from one another (Diverge) (New rock is formed) 2.Push into one another (Converge) (Rock is destroyed) 3.Slide past one another (Rock is conserved)

Divergent Boundary Results in the formation of Oceanic Crust

Examples:

Transform Boundary

Transform Example

San Andreas Fault

Convergent Boundary: Subduction Results in the formation & growth of Continental Crust and destruction of Oceanic Crust Melting Produces More Felsic Magma

Example: Pacific Northwest

Example: Andes Mountains

Convergent Boundary: Collision Results in the growth of Continental Crust

1.Earth’s lithosphere is broken into rigid plates 2.Plates move about 1-10 cm/yr on the plastic Asthenosphere 3.“Geology happens” where the plates interact with one another along Divergent, Transform, Subduction and Collisional Boundaries Basic Plate Tectonics - Revised

What Drives Plate Tectonics? Internal Heat

Convection Models

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