1 / 25

Divergent Plate Boundaries

Divergent Plate Boundaries. Finz 2012. Plate Tectonics. Plates move about 2 inches/year - about the same rate as your fingernails grow!. There are 3 types of plate boundaries: 1. divergent 2. convergent 3. transform. Tectonic Plate Boundaries. Divergent boundaries Plates move apart

onawa
Download Presentation

Divergent Plate Boundaries

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Divergent Plate Boundaries Finz 2012

  2. Plate Tectonics Plates move about 2 inches/year - about the same rate as your fingernails grow! There are 3 types of plate boundaries: 1. divergent 2. convergent 3. transform

  3. Tectonic Plate Boundaries • Divergent boundaries • Plates move apart • Magma rises, cools and forms new lithosphere • Typically expressed as mid-oceanic ridges • Transform boundaries • Plates slide past one another • Fault zones, earthquakes mark boundary • San Andreas fault in California • Convergent boundaries • Plates move toward each other • Mountain belts and volcanoes common • Oceanic plates may sink into mantle along a subduction zone, typically marked by a deep ocean trench

  4. Divergent Plate Boundaries: Divergent plate boundaries are where seafloor spreading occurs, producing new oceanic crust. Material from mantle intruded into fractures as plates are move apart. The crust of the ocean is basaltic rock on top and gabbro on the bottom. Ocean basins form when continents split apart!

  5. Early evidence of seafloor spreading Old mountain belts show us where continents used to be connected Old mountains belts (Appalacians and Caledonides) now separated but if continents are fit together, mountain chains form a continuous belt

  6. More recent evidence of seafloor spreading 1. Symmetry of magnetic stripes (defined by polarity of magnetic minerals in basaltic rock of seafloor) The pattern of normal and reverse polarities on either side of a divergent boundary can only be explained if new crust was being formed and repeatedly split apart as magnetic field reversed

  7. But how does seafloor spreading (divergence) start? Hot plume in mantle upwarps lithosphere of continent Cracks develop forming rift valleys Rift zones allow further spreading to produce an ocean because the water moves into the low area created from the divergence • http://www.iris.edu/hq/files/programs/education_and_outreach/aotm/11/AOTM_09_01_Divergent_480.mov

  8. Red Sea-Gulf of Aden: An ocean basin in the making East African Rift will probably stop spreading and become a “failed arm” Future ocean basin

  9. Divergent boundaries • Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. • The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years. • The mechanism that drives seafloor spreading was thermal convection cells in the mantle • hot magma rises from mantle to form new crust • cold crust subducts into the mantle at oceanic trenches, where it is heated and recycled Mid-Atlantic Ridge

  10. Oceanic Crust Is Young

  11. Divergent Boundaries • Ridges also have • high heat flow • and basaltic flows or pillow lavas • Pillow lavas have • a distinctive bulbous shape resulting from underwater eruptions

  12. Divergent Boundaries • Divergent boundaries • Beneath a continent, • magma wells up, and • the crust is initially • elevated, • stretched • and thinned

  13. Rift Valley • The stretching produces fractures and rift valleys. • Example: East African Rift Valley

  14. Narrow Sea • As spreading proceeds, some rift valleys • will continue to lengthen and deepen until a narrow linear sea is formed, • Examples: • Red Sea • Gulf of California

  15. Modern Divergence • View looking down the Great Rift Valley of Africa. • Little Magadi soda lake

  16. Oceanic Divergent Boundary Example: Mid-Atlantic Ridge

  17. Continental Divergent Boundary Example: Red Sea / E. African Rift

  18. Continental Divergent Boundary Example: Baja California

  19. Spreading ridges As plates move apart new material is erupted to fill the gap Divergent Boundaries

  20. Iceland has a divergent plate boundary running through its middle Iceland: An example of continental rifting

  21. Divergent Boundary • http://www.youtube.com/watch?v=FK1s1-OJ5BE

  22. How rifting of a continent could lead to formation of oceanic lithosphere. e.g., East Africa Rift e.g., Red Sea e.g., Atlantic Ocean

  23. Presumably, Pangea was ripped apart by such continental rifting & drifting.

  24. Divergent Cross Section View

More Related