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Physical Geology 1330 116-S&R 1 Ocean Floor and Seafloor Spreading Dr. Mike Murphy [email protected] 333-S&R-1 www.uh.edu/~mamurph2/homepage.html Today’s Outline Continental Drift Seafloor Spreading Movie: “The birth of a theory” Continental Drift – the hypothesis that the continents once fit together to form a supercontinent and have since drifted apart to their present positions. Evidence Supporting the Continental Drift Hypothesis 1. 2. 3. 4. What caused the continents to drift? Why was the Continental Drift hypothesis rejected? Seafloor Spreading - The process whereby plates move apart and magma wells up into newly created fractures and generates new slivers of oceanic lithosphere Evidence supporting Seafloor Spreading 1. 2. 3. What didn’t the Seafloor Spreading hypothesis explain? Paleomagnetism - The study of natural remnant magnetization preserved in rocks in order to determine the intensity and direction of the Earth’s magnetic field in the geologic past Earth’s Magnetic Field This angle is called the inclination When Fe-rich minerals cool below their Curie Point they become magnetized in in a direction parallel to the existing magnetic lines of force Curie point - the temperature at which a mineral become magnetized (~580 C). Two kinds of data paleomagnetism provides are: 1. 2. Polar Wandering – Geomagnetic Reversals – Normal polarity – Reverse polarity – Magnetic Stripes – parallel stripes of normally and reversely magnetized rock present on the seafloor and symmetric about mid-ocean ridges. Paleomagnetic Time Scale – established by measuring the magnetic polarity of lava flows of known age. Spreading Rate at a Mid-Ocean Ridge Plate Tectonics1. A model explaining how the Earth works. 2. A set of ideas explaining the observed motion of Earth’s lithosphere through the mechanisms of subduction and seafloor spreading, which in turn, generate Earth’s major features, including continents and ocean basins (T&L). The strong, rigid lithosphere, which lies above the weak asthenosphere, is broken into several plates. Plates are continuously changing their shape and size because of deformation at their boundaries. Seven Major Plates are recognized: 1. North American 2. South American 3. Pacific 4. African 5. Eurasian 6. Australian 7. Antarctic Plate Boundaries (Divergent, Convergent, Transform) Divergent Boundary – Convergent Boundary – Transform Boundary – Divergent Boundary Evolution – Early Stage referred to as ________________. Later Stage referred to as ________________________.