1	Building Continents AND Oceanic Basins, Mountain Ranges & Continental Basins
2	The Earth Through Time Transgression, Regression Continents Collide, Continents Diverge Mountains Build, Mountains Erode Oceans Open, Oceans Close Basins Subside, Basins Uplift HOW? Answer: Plate Tectonics
3	Before Plate Tectonic Theory Early Attempts to Explain Continents & Oceans Pacific created in catastrophic event from which: Moon was torn Crust was broken into continents Doubling of Earth’s size Cracked Crust Geosyncline Origin of Mountains Continental Drift
4	Origins of Plate Tectonic Theory 1962, Harry Hess Proposed the ‘spreading ridge’ New sea floor produced on ridge Ocean floor like conveyer belt moving in opposite directions Thermal cells cause spreading 1963, F.J. Vine, D.H. Matthews proposed relationship between magnetic signatures of sea floor and sea floor spreading Paleomagnetism- history of reversals from mafic lavas Can recreate paleo latitude, also
5	Vine/Matthew’s Discovery Symmetrical magnetic pattern on sea crust Calculated spreading rates from 2-18 cm/yr Spreading began: Mid-Atlantic Ridge 150-200 ma Indian Ocean Ridge 80-100 ma Antarctica-Australia separation- 65 ma Suggested no Paleozoic ocean crust remains N. Atlantic, W. Pacific- Mesozoic Rest = Cenozoic! No direct record of plate movement before Mesozoic (Jurassic) Calculations confirmed by modern methodologies
6	Modern Plate Tectonic Theory The lithosphere is composed of plates, both oceanic & continental, that move with respect to one another. Plate movement is driven by spreading, both sea-floor spreading & continental rifting, due to convection & possibly mantle plumes.
7	Plate Margins Active vs. Passive Divergent boundaries Separate continents Create ocean basins Transform boundaries Move continents Deform crust Convergent boundaries Continents grow Build Mountains
8	Making a Sedimentary Basin Sedimentary Basin: Down-warping of crust Area of thick sediment accumulation Areas of rich oil & natural gas resources Formed tectonically by: Subduction Crustal-thinning Loading Principle of Isostacy
9	Making a Mountain Range Orogenesis- “Birth of Mountains” Orogeny- Mountain-Building episode. Results in uplift Primarily caused by tectonic plate collisions compress crust Produce large scale folding and thrust faulting Mountain-building magnitude depends upon type of collision Rate of collision Area of collision Time (length of collision)
10	Cross-Section of a Fold & Thrust Belt
11	End lecture segment
12	‘Geosynclinal’ Theory Hall, Dana, late 1800’s Predecessor to Plate Tectonic Theory Attempt to explain formation of basins & mountains Order of Events in Theory: Crust became downwarped Marine sediments accumulated in a geosyncline Elongate, geographically-fixed trough Vertical Uplift due to Cooling & Contraction of Earth caused orogeny Orogeny- mountain building episode
13	Geosynclinal Theory of Orogenies
14	Obsolete Geosyncline Problems with theory: No contemporary examples seemed to exist Tectonic features were classified without understanding origin Popular theory until the 1960’s & Plate Tectonic Theory
15	Alfred Wegener’s Continental Drift Theory 1912 Wegener observed: Similar fossil distributions on continents Fossils indicated different climates Shape of continents like puzzle pieces Same mountain ranges on 2 different continents Appalachian mountains & the Scottish Highlands Karroo system, South Africa & the Santa Catarina system in Brazil Wegener helped: Establish foundation for modern Plate Tectonic Theory Continents have MOVED over time!
16	Wegner Suggested…….. inThe Origin of Continents and Oceans (1915) Existence of Pangaea, 300 ma Separation of Pangaea to current continental positions Tidal forces drove movement North America & Europe separating at over 250 cm/year
17	Principle of Isostasy Why don’t continents erode completely away? Elevation of land depends on thickness & density of crust Continental crust-thicker, less dense, stands higher Oceanic crust- thinner, more dense, is lower Isostatic Adjustments Subsidence Addition of mass = sinking Rebound Removal of mass = rising