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1 Plate Tectonics Def.: A theory that explains the behavior of the Earth’s lithosphere in terms of several moving plates. 2 Lithosphere broken into plates Seven (or more) major plates In motion and continually changing in shape and size Largest is the Pacific plate Several include an entire continent plus a large area of seafloor 3 4 Fig. 19.17, p. 532-533 5 3 Types of plate boundaries: Diagram of plates showing movement direction and velocity Divergent Convergent Transform 6 Divergent plate boundaries Seafloor spreading occurs along the oceanic ridge system Fig. 19.18 p. 534 7 Divergent plate boundaries Continental rifts Split landmasses East African rift & Rhine Valley Not all develop into full-fledged spreading centers Fig. 19.20, p. 538 8 Bouger gravity anomaly map of the Midcontinent of North America http://csd.unl.edu/csd/resource/vol-13/oldrocks.htm Shows the extent of the 1.1 billion year old Midcontinent Rift, across Minnesota, Wisconsin, Iowa, Nebraska and Kansas. Manifested in outcrop by basalt flows and associated gabbro intrusions, plus flanking sediment basins 9 Convergent plate boundaries Fig. 19.22, p. 540 Oceanic plates return to the mantle in these destructive plate margins Surface expression an ocean trench Called “subduction zones” Average angle of descent is about 45° 10 Types of convergent boundaries Oceanic - Continental Oceanic - Oceanic Continental - Continental 1 11 Types of boundaries Transform Faults 12 WHY Plate Tectonics? Fig. 19.A, p. 535 13 Driving Mechanisms for Plate Tectonics Plate movements are result of Earth dissipating interior heat Ridge Push Slab Pull Ch. 17, pp. 489-491 Ch. 19, pp. 550-553 14 Mantle Convection Double-layer Whole Mantle Deep Layer Fig. 19.32, p. 552 15 Mantle Convection Investigations using: Seismic Tomography (CAT scans using seismic energy) Numerical Modeling Fig. 17.D, p. 491 http://www.cacr.caltech.edu/Publications/annreps/annrep94/earth-01.html 2