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Unformatted text preview: Geol 1100 Principles of Geology (Section 1) Lecture 4 Highlights 30 January 2008 Sea Floor Spreading o Proposed by H. Hess in 1960 o New sea floor created at _________________ o Old sea floor is sonsumed at ________________ o Earth is neither contracting nor expanding, but stays about the same size o Hess proposed the Convection in the earth drives ocean spreading Convection: fluid flow driven by _____________________ Supporting evidence o Magnetic Reversal History & Magnetic anomaly stripes (recall from last time) o Earthquake locations o Ocean Drilling: Sediment layer thicker and older away from ridges; oceanic crust basalt older away from ridges, too o Heat flow The rate that heat radiates (conducts) through the surface of the earth from the interior Relatively high at mid ocean ridges -- suggests partially molten rock Plates and Plate Boundaries o Rigid plates of lithosphere as the outer shell of the Earth Lithosphere Rigid over long timescales (i.e., tens of thousands of years) Crust and uppermost mantle (Crust-Mantle boundary is composition change with significant density difference) Asthenosphere Flowing (albeit slowly) over long timescales Similar composition to mantle part of lithosphere Lithosphere-Asthenosphere Boundary is defined by temperature (~1200 - 1300 C), not composition with very small density difference: Hotter asthenosphere mantle is slightly lower density than colder lithosphere mantle o Plates move about so that as new sea floor is created, old sea floor is consumed o Boundaries between plates are where the activity happens All boundaries are well defined by the concentrations of earthquakes Some plate boundaries also have volcanoes and non-volcanic mountains o Three types of plate boundaries Divergent plates moving away from one another (e.g., mid-ocean ridge)plates moving away from one another (e....
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- Spring '08