Chapter 2 Plate Tectonics.

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Presentation transcript:

Chapter 2 Plate Tectonics

Chapter Overview Much evidence supports plate tectonics theory. The plate tectonics model describes features and processes on Earth. Plate tectonic science has applications to Earth Science studies. Configuration of land and oceans has changed in the past and will continue to change into the future.

Evidence for Plate Tectonics New evidence from World War II Sea floor studies with sonar New technology enabled study of Earth’s magnetic field Photo from Wikipedia

Evidence for Plate Tectonics Earth’s magnetic field and paleomagnetism Earth has magnetic polarity North and South polarities Magnetic polarity recorded in igneous rocks Magnetite in basalt

Evidence for Plate Tectonics Paleomagnetism – study of Earth’s ancient magnetic field Interprets where rocks first formed Magnetic dip

Earth’s Magnetic Pole Apparent polar wandering Location of North Pole changed over time Magnetic dip data

Evidence for Plate Tectonics Positions of magnetic polar wandering paths more closely coincide when the landmasses are assembled.

Magnetic Polarity Reversals Evidence for Plate Tectonics Magnetic Polarity Reversals Earth’s magnetic polarity reverses periodically Recorded in ancient igneous rocks 176 reversals in past 76 million years Unpredictable pattern

Paleomagnetism and the Ocean Floor Evidence for Plate Tectonics Paleomagnetism and the Ocean Floor 1955 – deep water rock mapping Magnetic anomalies – regular pattern of north-south magnetism “stripes” Stripes were symmetrical about long underwater mountain range Photo from Wikipedia

Sea Floor Spreading Harry Hess World War II submarine captain and geologist Depth recordings show sea floor features History of Ocean Basins Seafloor spreading Mantle convection cells as driving mechanism New crust created at ridges Old crust destroyed at trenches

Plate Tectonic Processes

Sea Floor Spreading Mid-ocean ridge – spreading center New crust being produced

Sea Floor Spreading Subduction zones – oceanic trench site of crust destruction Subduction can generate deep ocean trenches.

Sea Floor Spreading Evidence Frederick Vine and Drummond Matthews (1963) Analysis of igneous rock stripes around mid-ocean ridge Sea floor stripes record Earth’s magnetic polarity

Age of Ocean Floor Late 1960s deep-sea drilling Radiometric dating of ocean rocks Symmetric pattern of age distribution about mid-ocean ridges Oldest ocean floor only 180 million years old

Age of Ocean Floor

Heat Flow Heat flow – heat from Earth’s interior released to surface Very high at mid-ocean ridges Low at subduction zones

Earthquakes as Evidence Most large earthquakes occur at subduction zones. Earthquake activity mirrors tectonic plate boundaries.

Global Plate Boundaries

Plate Tectonics Theory Lithosphere – tectonic plates that float on ductile asthenosphere Large-scale geologic features occur at plate boundaries. Two major tectonic forces Slab pull Slab suction