GEOL 1340 Lecture Notes - Lecture 20: Mantle Convection, Electromagnet, Seismic Wave
14 Oct 2016
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Upper marks change from olivine to spinel crystal structure. Lower marks change from spinel to perovskite crystal structure. Seismic waves bend outward when traveling through deeper mantle due to increase v with: transition zone depth, mesosphere, outer core, inner core, magnetic field. V of p and s waves increase with depth. Rocks solid but hot and capable of flow. Seismic studies suggest made of liquid iron. Bending o p-waves in outer core create p-wave shadow zone. S waves can"t travel thru this part. Liquid iron in outer core stirred into convective motion by internal heat. Mag poles inclined at angle of earth"s axis of rotation. T increase with depth at rate known as geothermal gradient. Average between 20-30 degrees c per km in crust. Heat flow: mvmt of heat from interior towards surface: internal heat engine. High flow along mid-ocean ridges and other volcanically active regions. 2 layer mantle convection: separate convection cells, boundary btwn (670km transition zone)
