Plate Tectonics

Plate Tectonics The Continental Drift Hypothesis Plate Tectonics – Overview Divergent Boundaries Convergent Boundaries Transform Boundaries Testing the Theory of Plate Tectonics Measuring Plate Motion What Makes Plates Move?

The Continental Drift Hypothesis GEOL131: Plate Tectonics The Continental Drift Hypothesis

Alfred Wegener (1880-1930) German paleoclimatologist GEOL131: Plate Tectonics: Continental Drift Alfred Wegener (1880-1930) German paleoclimatologist Studied evidence for ancient climates Traveled extensively, collected thousands of samples Published continental drift ideas in 1915 Died during expedition to Greenland in 1930

Pangaea “All lands” 200 million years ago GEOL131: Plate Tectonics: Continental Drift Pangaea “All lands” 200 million years ago

Wegener’s Evidence The “continental jigsaw puzzle” GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence The “continental jigsaw puzzle” Trans-oceanic fossil matching Trans-oceanic rock matching Ancient climates

Wegener’s Evidence: Continental Jigsaw GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence: Continental Jigsaw

Wegener’s Evidence: Matching Fossils GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence: Matching Fossils

Wegener’s Evidence: Matching Fossils GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence: Matching Fossils

Wegener’s Evidence: Matching Rocks GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence: Matching Rocks Pangaea Present

Wegener’s Evidence: Ancient Climates GEOL131: Plate Tectonics: Continental Drift Wegener’s Evidence: Ancient Climates Pangaea Present

Reaction to Wegener’s Ideas GEOL131: Plate Tectonics: Continental Drift Reaction to Wegener’s Ideas Other scientists were highly critical Major problem: no good explanation for how continents could move Wegener proposed Moon’s gravity moved continents Continents pushed through ocean crust like icebreaker ships

Reaction to Wegener’s Ideas GEOL131: Plate Tectonics: Continental Drift Reaction to Wegener’s Ideas Moon’s gravity too weak Ocean crust too dense and strong Most scientists concluded continental drift was incorrect

Plate Tectonics: Overview GEOL131: Plate Tectonics Plate Tectonics: Overview

Earth’s Layers: Two schemes GEOL131: Plate Tectonics: Plate Tectonics Overview Earth’s Layers: Two schemes Based on composition Crust, mantle, core Based on seismic wave behavior Lithosphere, asthenosphere, mesosphere, outer core, inner core Lithosphere, asthenosphere most important for plate tectonics

Earth’s Layers: Two schemes GEOL131: Plate Tectonics: Plate Tectonics Overview Earth’s Layers: Two schemes Asthenosphere

Lithospheric Plates Rigid, brittle Continents are “embedded” in them GEOL131: Plate Tectonics: Plate Tectonics Overview Lithospheric Plates Rigid, brittle Continents are “embedded” in them

Why is plate tectonic theory successful? GEOL131: Plate Tectonics: Plate Tectonics Overview Why is plate tectonic theory successful? Provides plausible explanation for how continents move Doesn’t require them to “plow” through ocean crust

Two types of lithosphere GEOL131: Plate Tectonics: Plate Tectonics Overview Two types of lithosphere Oceanic Thin, dense, able to subduct into mantle “asphalt” Continental Thick, low density, buoyant, does not subduct “styrofoam”

GEOL131: Plate Tectonics: Plate Tectonics Overview Plate Motion

Plate Boundaries: Divergent GEOL131: Plate Tectonics Plate Boundaries: Divergent

Plates separate at divergent boundaries GEOL131: Plate Tectonics: Divergent Boundaries Plates separate at divergent boundaries New crust created by undersea volcanism

Creation of Divergent Boundaries GEOL131: Plate Tectonics: Divergent Boundaries Creation of Divergent Boundaries 1. Continental lithosphere pushed up by upwelling magma 2. Lithosphere stretched & thinned, forming a continental rift

Creation of Divergent Boundaries GEOL131: Plate Tectonics: Divergent Boundaries Creation of Divergent Boundaries 3. Ocean water floods rift, creating narrow seaway 4. Seaway continues to widen as plates separate

Creation of Divergent Boundaries GEOL131: Plate Tectonics: Divergent Boundaries Creation of Divergent Boundaries Stage 1: Yellowstone NP - Continental lithosphere being pushed up by magma below

Creation of Divergent Boundaries GEOL131: Plate Tectonics: Divergent Boundaries Creation of Divergent Boundaries Stage 3: Red Sea and Gulf of Aden- Narrow seaways Stage 2: East African Rift - Lithosphere being stretched and thinned

Creation of Divergent Boundaries GEOL131: Plate Tectonics: Divergent Boundaries Creation of Divergent Boundaries Stage 4: Atlantic Ocean – wide ocean basin with divergent boundary at center

Plate Boundaries: Convergent GEOL131: Plate Tectonics Plate Boundaries: Convergent

Plates come together at convergent boundaries GEOL131: Plate Tectonics: Convergent Boundaries Plates come together at convergent boundaries Three types, based on lithosphere involved Oceanic-oceanic Oceanic-continental Continental-continental

Oceanic-oceanic boundaries GEOL131: Plate Tectonics: Convergent Boundaries Oceanic-oceanic boundaries

Oceanic-continental boundaries GEOL131: Plate Tectonics: Convergent Boundaries Oceanic-continental boundaries

Continental-continental boundaries GEOL131: Plate Tectonics: Convergent Boundaries Continental-continental boundaries A.k.a. “continental collision zones” Example: India and Asia

GEOL131: Plate Tectonics: Convergent Boundaries India-Asia Collision: Example of a continent-continent convergent boundary

Plate Boundaries: Transform GEOL131: Plate Tectonics Plate Boundaries: Transform

Plates slide past each other at transform boundaries GEOL131: Plate Tectonics: Transform Boundaries Plates slide past each other at transform boundaries

San Andreas Fault: A transform boundary GEOL131: Plate Tectonics: Transform Boundaries San Andreas Fault: A transform boundary Los Angeles is moving northwest San Francisco is moving southeast

San Andreas Fault: A transform boundary GEOL131: Plate Tectonics: Transform Boundaries San Andreas Fault: A transform boundary

Testing the Plate Tectonic Theory GEOL131: Plate Tectonics Testing the Plate Tectonic Theory

Much evidence comes from ocean drilling GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Much evidence comes from ocean drilling Research ships drill into ocean sediments and rock Drill cores are collected that show cross-section of ocean floor at that location

Major Lines of Evidence GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Major Lines of Evidence Sediment thicknesses Ocean crust ages Hot spot tracks Apparent polar wandering Paleomagnetic striping

Sediment Thickness and Crustal Age GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Sediment Thickness and Crustal Age Both increase away from oceanic ridges

GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Hot Spot Tracks

Apparent Polar Wandering GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Apparent Polar Wandering Earth has a magnetic field Some minerals are magnetic These minerals act like compass needles They record where magnetic poles were located at the time the minerals formed

Apparent Polar Wandering GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Apparent Polar Wandering Rocks in North America and Eurasia seem to show that magnetic poles have moved thousands of miles Continents have moved, not the poles

Paleomagnetic Striping GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Paleomagnetic Striping Earth’s magnetic field has reversed many times Normal polarity: North magnetic pole near north geographic pole Reversed polarity: N. magnetic near S. geographic Magnetic field polarities over the last 4 million years. Periods of normal polarity shown in white.

Paleomagnetic Striping GEOL131: Plate Tectonics: Testing the Plate Tectonic Theory Paleomagnetic Striping Oceanic crustal rocks record the polarity in effect at the time they formed Symmetrical “stripe” pattern of normal and reversed polarity created in ocean crust

GEOL131: Plate Tectonics What Makes Plates Move?

Three mechanisms: slab pull, ridge push, mantle drag GEOL131: Plate Tectonics: What Makes Plates Move? Three mechanisms: slab pull, ridge push, mantle drag * * *

GEOL131: Plate Tectonics End of Chapter