Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Plate Motions
Document related concepts
Transcript
David Allison GY305 Physics of Tectonic Plate Motions Global Positioning Systems Earth’s Magnetic Field Radiometric Decay & Age Determinations Uplift Rates Earth’s Gravity Field Earth’s Heat Flow Kinematic Physics of Deformation Tectonic Plates 2 Criteria Composition (i.e. mineralogy and geochemistry) Seismic (mechanical behavior) Depth Thick Layer 7-50km 650km Crust Upper mantle 700km Basalt (3.0) Diorite (2.7) Peridotite (3.3) 2200km Lower mantle Garnet Lherzolite (3.5-5.5) 2200km Outer core Ni-Fe-S Alloy (10-12) 1300km Inner core 2900km 5100km 6400km Ni-Fe Alloy (13) Depth Thick Layer 70-150km 550km Brittle Lithosphere Asthenosphere 700km Ductile 2200km Mesosphere Brittle 2200km Outer core Liquid (very ductile) 1300km Inner core 2900km 5100km 6400km Brittle Primary plates These seven plates comprise the bulk of the Earth’s Lithosphere: Pacific Ocean. African Plate Antarctic Plate Eurasian Plate Indo-Australian Plate North American Plate Pacific Plate South American Plate • Vectors are proportional to plate spreading velocity • Note that the Pacific is spreading much faster than the Atlantic GPS-determined Absolute Plate Motion Rates • Convection Cells in the Mantle • Note that “Slab Pull” is due to older denser ocean lithosphere Seismic Activity is confined mainly to plate boundaries Paleomagnetic “stripes” generated by sea floor spreading Phanerozoic Plate Motions Plate Motion on the Earth Spheroid The 3 possible plate boundary configurations Divergent Convergent Transform Plate Motion on the Earth Spheroid The 6 possible dextral transform configurations 2 Plates on a Flat Earth A 3-Plate Configuration • Plate velocity vectors are additive 1st order tensors A 3-Plate Circuit Diagram • Start with any plate • Calculate relative velocity in a specific direction (C or CC) • Continue to calculate velocity in C or CC direction BVC Plate Motion on the Sphere of the Earth • 2 plates always move relative to each other relative to a pole of rotation • Transform boundaries are the “small circles” of the plate motion • The angular velocity (w) is constant but the linear velocity of relative plate motion increases from 0 at pole to a max. at 90 degrees to the pole of rotation • Transform boundaries are small circle paths relative to rotation pole • On a Mercator projection the transforms are parallel to latitude lines • Stereographic Projections may be used to track plate motions relative to rotation pole Implications of Plate Boundary Interactions Absolute Plate Motions • Hot Spots: assumed to have constant position in asthenosphere • GPS: Satellite geometry calculates absolute latitudelongitude position to within millimeters Emperor Seamounts & Hawaiian Islands
