Plate Tectonics: Grand Unifying Theory of everything... for the Geosciences, at least! Plate Tectonics: Grand Unifying Theory of everything... for the Geosciences, at least!

A video

Plate tectonics theory says that the Earth’s core is broken up into pieces that move by plowing through the other rocks on Earth’s surface? A. True B. False A. True B. False

Introduction Plate Tectonics Theory > > explains location of and actions associated with Volcanoes (distribution and composition) - - Earthquakes (distribution, strength, depth) - - Mountain Ranges (of all types) - - Natural resources (distribution and formation of Coal, Mineral Resources, & Oil) - - Ocean basins ( age, shape, and size) - - biologic distribution and behavior + + (fossils and modern animals) - - seemingly incompatible climate records A theory that unified the geosciences by explaining nearly all geological phenomena

Plate Tectonics and Continental drift are NOT the same thing! Continental drift was the hypothesis postulated by Alfred Wegener that was rejected due to the wrong explanation for how the continents were moving Plate tectonics built upon Wegener’s rejected hypothesis and added a lot of new information Sea floor spreading Paleomagnetism Age of sea floor along oceanic ridges

Plate Boundaries, Earthquakes and Volcanoes Red boxes show the location of the next three slides

A small shield volcano in Iceland thin lava is created at a divergent plate boundary The low viscosity lava creates the shield volcano

Confirmation of Sea-Floor Spreading Deep sea drilling supports the hypothesis that ocean crust is forming at the ridges and moving away from the ridges.

Mt Rainier in Washington State- a classic example of a stratovolcano The lava associated with this type of volcano is created as oceanic crust melts and pushes through continental crust along convergent subduction plate boundaries Mt Rainier in Washington State- a classic example of a stratovolcano The lava associated with this type of volcano is created as oceanic crust melts and pushes through continental crust along convergent subduction plate boundaries

Convergent Subduction (Oceanic-Continental) Plate Boundary ･ Denser oceanic crust subducted beneath continental crust. ･ Andesitic volcanic arcs form on the leading edge of the continental plate. ･ Andes Mountains, Cascades ･ Denser oceanic crust subducted beneath continental crust. ･ Andesitic volcanic arcs form on the leading edge of the continental plate. ･ Andes Mountains, Cascades

A couple of cinder cones and a lava flow in New Mexico This type of volcanic cone is often found associated with other volcanoes, and commonly where plates have been completely subducted and the melted material is in its last gasps. A couple of cinder cones and a lava flow in New Mexico This type of volcanic cone is often found associated with other volcanoes, and commonly where plates have been completely subducted and the melted material is in its last gasps.

Alfred Wegener & Continental Drift Hypothesis : Alfred Wegener > > proposed a hypothesis called "continental drift". Continents were once together > > Supercontinent; Pangaea (Pan = all, Gaea = land). Based on a lot of geological evidence > > mountain ranges, fossils, continental fit, & similar rocks Wegener's theory lacked a scientifically valid explanation for how the continents could move. - - Hypothesis was rejected for the above reason An alternative to the “Contracting Earth” model favored by many geoscientists at the time

Continental Fit 1965: Edward Bullard proposed modification of Wegener’s idea of fitting continents by using the 2,000 m isobath, which corresponds to the continental slope and the edge of continental crust.

Similarity of Rock Sequences Identical Carboniferous rocks on Gondwana is tough to explain if the continents were not joined at that time

Various mountain ranges are currently widespread. Rejoining separated continents shows the linear nature of the mountain chains.

Tropical locations have geological evidence of Carboniferous glaciation. The former parts of Gondwanaland are widely separated today, but were not in the distant geological past.

The Gondwana Ice Cap If the continents are reassembled, the glacial evidence makes sense. At the same time most of Laurasia was in the tropics.

Gondwanaland Animal and Plant Fossils

Sea-Floor Spreading Sea floor mapped during the 1950s - - revealed the Mid oceanic ridge system. Magnetic reversals recorded in the rocks were discovered later and verified Hess’ hypothesis > > patterns were symmetrical with respect to the ridge axis. 1962: Captain Harry Hess (US Navy) > > proposed Sea-floor Spreading to account for continental movement and size of oceans. The mountain chain had a down-dropped valley in the middle, called a rift valley. could only be caused by pulling apart The mountain chain had a down-dropped valley in the middle, called a rift valley. could only be caused by pulling apart

Magnetic Data and the Mid Ocean Ridge Rift valley an example of an Oceanic crust divergent boundary Magnetic Data and the Mid Ocean Ridge Rift valley an example of an Oceanic crust divergent boundary proof for sea floor spreading and a mechanism to move continents as Part of the larger tectonic plates

Age of the Ocean Basins Final verification of sea floor spreading.

Which is not something that was used to support Continental drift hypothesis? A.The fit of the continents B.The alignment of mountains C.The locations of fossils on various continents D.The arrangement of unique rocks on continents E.All of the above were used to support Continental Drift hypothesis A.The fit of the continents B.The alignment of mountains C.The locations of fossils on various continents D.The arrangement of unique rocks on continents E.All of the above were used to support Continental Drift hypothesis

Plate Boundaries Convergent : where two plates meet, with one being subducted or both being forced upward > >  oceanic-oceanic subduction;  >continental-oceanic subduction;  Continental-continental collision  oceanic-oceanic subduction;  >continental-oceanic subduction;  Continental-continental collision.. Divergent : where two plates spread apart at a ridge or rift valley. Divergent : where two plates spread apart at a ridge or rift valley. Transform : where two plates or plate segments slide past each other. Transform : where two plates or plate segments slide past each other. > driven by convection cells within the mantle, the plates interact with each other > faults and earthquakes often occur along plate boundaries > driven by convection cells within the mantle, the plates interact with each other > faults and earthquakes often occur along plate boundaries  oceanic  >continental  oceanic  >continental

Earthquakes Occur along breaks in the Crust known as faults Energy stored along faults released as rock strength and friction are overcome releasing energy waves Three kinds of energy waves P-waves (fastest)-move through any substance S-waves (next fastest)-move through solids ONLY Surface waves (slowest)-move along the Earth’s surface Earthquakes Occur along breaks in the Crust known as faults Energy stored along faults released as rock strength and friction are overcome releasing energy waves Three kinds of energy waves P-waves (fastest)-move through any substance S-waves (next fastest)-move through solids ONLY Surface waves (slowest)-move along the Earth’s surface

Convection currents drive plate motion

Earthquake waves allow us to determine what the internal structure of Earth looks like concentric spheres of material, each layer with specific characteristics that influence seismic wave movement

3D maps of the Earth’s convection currents based on seismic wave analysis-complicated, but likely more realistic!

Continental-Convergent Plate Boundary Convergent Continental-Continental Plate Boundary Continental crust Continental crust

Tibet Plateau Tibet Plateau Himalayas Indian subcontinent Indian subcontinent

Convergent Subduction (Oceanic-Continental) Plate Boundary Western coast of South America

Oceanic-Oceanic Plate Boundary Convergent subduction Oceanic-Oceanic Plate Boundary ･ Volcanic island arcs form nearly parallel to the subduction zone, which is expressed as a deep ocean trench. ･ Most modern island arcs are in the Pacific Ocean. ･ Volcanic island arcs form nearly parallel to the subduction zone, which is expressed as a deep ocean trench. ･ Most modern island arcs are in the Pacific Ocean.

Sea of Japan To RoC Island Arc N N Pacific Ocean

East African Rift Valley East African Rift Valley ･ Eastern Africa appears to be rifting away from the rest of the continent. Continental Divergent boundary

San Andreas Fault- a Transform Boundary

Which type of plate boundary is not commonly associated with volcanoes? A.Continent-Oceanic convergent subduction B.Divergent C.Transform A.Continent-Oceanic convergent subduction B.Divergent C.Transform