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The Marine Environment Ocea 101 The Oceans--Fall 2007 Raphael Kudela Global Plate Tectonics Introduction Terms and Concepts Lithosphere vs. Asthenosphere History of Plate Tectonics Pre-20th Century Deep Sea Drilling Project Evidence for Continental Drift Oceanic Evidence for Plate Tectonics Sea Floor Spreading Plate Boundaries Divergent, Convergent, Transform boundaries Growth of the Ocean Basins Evidence for Continental Drift Jigsaw Puzzle It looks like the continents should fit! Fossil Record/Climate Shifts Coral reefs in the Himalayas Age/composition of rocks Similar age/composition across continents Apparent Polar Wandering Magnetic anomalies suggest continents moved around…no other explanation 1 Recall: Layered Earth •Recall on formation: •gravity pulled heavy elements (Fe, Ni) inward to core •lighter elements, Al, Si, Mg, O bonded to form less dense compounds that migrated toward the surface • Where did the continents come from? Think: “Distillation” Light stuff rises up, heavy molecules left behind 2 Think Distillation? Light stuff rises up, heavy molecules left behind Again- Final Structure of Earth Surface: cool, “light” (less dense), brittle Deeper: Hot, Heavy (denser), plastic or fluid 3 Convection: the soup analogy.. Convection Cells? 4 P-waves and S-Waves High Pressure Waves Through the Earth Based on the distribution of earthquake activity globally, and the degree of refraction combined with the timing of events, we can determine that there are several layers in the earth of differing densities and compositions 5 Isostasy and Isostatic Balance Fig. 3.6 6 Oceanographic Evidence 1998: NeMO Started 1912: Wegener 1947: Ewing’s Abyssal Plains 1956: Ewing & Heezen propose Ridge/Rift system 1900 1950 1925: Meteor Expedition 1947: Scripps Scientists--sediment problem 1950’s: Paleomagnetism 2000 1963: Vine & Matthews, Deep-Sea Drilling Project 1960: Hess proposes Seafloor spreading Deep Sea Drilling Project Started in 1963, Glomar Challenger 1) More sediment accumulation in older crust 2) Fossils should be related to the age 3) Radio-isotopes should give same dates 4) Magnetic “striping” should change around expansion zones 7 Fig. 3.4 © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Heat Flow Data from J.G. Sclater and J. Crowe, On the Variability of Oceanic Heat Flow Average in Journal of Geographical Research, 81:17 (June 1976), p. 3004. American Geophysical Union, Washington, DC. 8 Oceanographic Evidence 1998: NeMO Started 1912: Wegener 1900 1947: Ewing’s Abyssal Plains 1956: Ewing & Heezen propose Ridge/Rift system 1950 1925: Meteor Expedition 1947: Scripps Scientists--sediment problem 1950’s: Paleomagnetism 2000 1963: Vine & Matthews, Deep-Sea Drilling Project 1960: Hess proposes Seafloor spreading Fig. 3.19 9 Fig. 3.19.a Fig. 3.19.b 10 Fig. 3.19.c Fig. 3.19.d 11 Fig. 3.19.e Fig. 3.19.f 12 Fig. 3.19.g 13 14 © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Age of Ocean Floor 15 Earthquake Activity The Ring of Fire 16 Fig. 3.8 Fig. 3.8.a 17 Fig. 3.8.b Fig. 3.8.c 18 San Andreas is a Transform Fault Fig. 3.9 19 Fig. 3.10 Fig. 3.11 20 Convection Cells? Fig. 3.20 21 Fig. 3.21 “Ridge-Push, Slab-Pull” Model…. Takes into account the fact that the plates are HEAVY, and get HEAVIER as the cool! So, does plate tectonics (continental drift) explain EVERYTHING? Wegener’s evidence Similar fossils and rocks “jigsaw” puzzle Magnetic stripes in rock--formed at different times! Age of the ocean crust--only 200 mya old, versus 5 bya Rock is cooler as we move away from spreading zones Volcanos are associated with plate boundaries Earthquakes are also at plate boundaries island arcs, trenches, and mountain ranges…. But what about the Hawaiian Islands? 22 Major Concepts The Earth is made of layers The outer layer is made of “plates” These plates move around--the ocean basins are constantly being remade Plate boundaries can be divergent, convergent, or transform--where there’s friction, there are earthquakes, where the plates are melting, we get volcanoes Some places have heat rising from much deeper than the lithosphere-asthenosphere boundary-this creates (for example) the Hawaiian Islands At some point, we will run out of heat, and the plates will stop moving 23
