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Earth’s Interior and divergent plate boundaries

Earth’s Interior and divergent plate boundaries

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Earth’s Interior and divergent plate boundaries

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  1. Earth’s Interior and divergent plate boundaries • Instructor: Prof. Dr. Boris Natalin

  2. Gravity and Layered Planet • Metallic core→ rocky mantle → water → gas • Gravity force • Increase of pressure and density with depth • Mineral phase change

  3. Probing Earth’s interior • The deepest well is 12.3 km (Kola Peninsular, Russia) • Seismic waves:- earthquakes- explosions • Wave front • Ray path • Mineral physic experiments • Meteorites studies • Xenolith studies Earthquakes Mw = 6 are recorded all around the globe

  4. Seismic waves • P waves • S waves

  5. Seismic wave paths and analysis

  6. Analysis of seismic wave paths Refraction Reflection

  7. Seismic waves and their velocity in the layered Earth

  8. Cross-sectional view of Earth Rheological and compositional layering • Crust: • Continental crust • Oceanic crust

  9. Mohorovich discontinuity (Moho) The lover boundary of the crust is Moho = The Mohorovičić discontinuity

  10. The crust • Oceanic crust • 7 km thick • Density 3.0 g/cm3 • Basalt, gabbro • Continental crust • 35-40 km thick (max. 70 km) • Density 3.0 g/cm3; too light, float • Average composition: 1) granodiorite and diorite; 2) anorthosite/basalt

  11. Core/mantle boundary

  12. Core/mantle boundary

  13. - Upper mantle - Transition zone - Lower mantle The mantle Crust + upper mantle = lithosphere

  14. Mantle • Composition • Seismic anisotropy • Lower velocity zone (asthenosphere) • Transition zone between 410-660 km • Phase changes in the transition zone

  15. The lithosphere and asthenosphere

  16. The core • 13.5 g/cm3 • Iron- nickel • Segregated during the earliest stage of accretion of the Earth • Convection in the outer core generates the magnetic field

  17. Earth temperature (5500° at center) • Heat from impacts and rate of impacts • Temperature rise because of compression • Heat from radioactive disintegration • Heat flow at surface 87 mW/m2 Conduction – collision of atoms or electron flow Convection – fluid-like heat transport Radiation– t the thermal motion of charged particles in matter Types of Heat Transport - conduction - convection - radiation

  18. Heat transfer in the Earth Conduction Convection + conduction Convection Radiation

  19. Seismic tomography Seismic waves are faster in cooler rocks and slower in hot rocks

  20. Morphology of oceans

  21. Sizes of mid-oceanic ridges

  22. Divergent plate boundaries seafloor spreading

  23. Depth-age relations • Depth-age: Solid line indicates theoretical topography limiting thickness at 80Ma; Dash line – ever-thickening lithosphere • D = 2500 + 350 √T • Depth-age controlled by time • Mechanism: thermal contraction of the newly formed lithosphere

  24. Spreading rate and ridge topography • Slow spreading 1-5 cm/y • Intermediate spreading is 5-9 cm/y • Fast spreading is more than 9 cm/y

  25. Deep-water sediments Nature of oceanic crust Basaltic pillow lavas Sheeted dyke complex Gabbro Ophiolite succession Layered gabbro and dunite Peridotite (upper mantel)

  26. Divergent plate boundaries: Continental rifts East African rift valleys and the opening of the Read Sea and the Gulf of Aden

  27. Continental splitting

  28. Definitions • Rifts are elongated depressions where the entire thickness of the lithosphere is deformed under the influence of extensional forces • Grabens are those extensional structures that do not penetrate the entire thickness of the lithosphere • Taphrogens are lithospheric-scale structures commonly formed from a linked system of rifts and grabens that stretch the lithosphere

  29. Origin of continental rifts

  30. Pangea supercontinent 250 Ma Continental crust is isolator for heat dissipationMantle plume

  31. Slab pull force and rifts