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1; movies

1; movies. Topography of a fast spreading ridge (EPR). Topography of a slow spreading ridge (south atlantic). 2; topography. Melt beneath a fast-spreading ridge (East Pacific Rise). Ophiolites. 3; classic ophiolites. Oman ophiolite. Pillow lavas. Sheeted Dikes. Layered Gabbros.

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1; movies

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  1. 1; movies

  2. Topography of a fast spreading ridge (EPR)

  3. Topography of a slow spreading ridge (south atlantic)

  4. 2; topography

  5. Melt beneath a fast-spreading ridge (East Pacific Rise)

  6. Ophiolites

  7. 3; classic ophiolites

  8. Oman ophiolite

  9. Pillow lavas

  10. Sheeted Dikes

  11. Layered Gabbros

  12. Stokes law Vs is the particles' settling velocity (vertically downwards if ρp > ρf, upwards if ρp < ρf) g is the acceleration due to gravity, ρp is the density of the particles, and ρf is the density of the fluid

  13. 4; settling

  14. Massive gabbro

  15. Banded harzburgite Impregnated dunnite

  16. Hot spot volcanism: a global phenomenon

  17. 5; Hawaii-emperor chain

  18. The origin of hot spot volcanoes from melting of plumes

  19. Dynamic models of mantle convection Plumes coming up Plates going down Rapid, small-cell convection on Io

  20. Why does the mantle melt to produce hot spot magmas? • Isentropic decompression melting • Fluxing by volatiles • Heating of the lithosphere by a hot plume • Unconventional heat sources

  21. Simple variations on the decompression melting theme • Variations in potential temperature -- hotter mantle produces deeper melting, more magma • Variations in the thickness of the lithosphere -- controls the depth at which melting terminates • Fractional vs. batch melting • All of these can vary from hot spot to hot spot and within a single volcano, producing distinctive chemical signatures

  22. Temperature variations near head of plume 3D Model by Ribe and Christensen

  23. Why does the mantle melt to produce hot spot magmas? • Isentropic decompression melting • Fluxing by volatiles • Heating of the lithosphere by a hot plume • Unconventional heat sources

  24. Why does the mantle melt to produce hot spot magmas? • Isentropic decompression melting • Fluxing by volatiles • Heating of the lithosphere by a hot plume • Unconventional heat sources

  25. Hawaii (topography/bathymetry)

  26. Geological map of the big island of Hawaii

  27. HSDP drilling in 1993 and 1999 into the flank of Mauna Kea volcano • >95% recovery, to a total depth of 3.1 km below sea level • Penetration through ~1 km of subaerial lavas, ~2 km of submarine deposits, both hyaloclastites and pillows

  28. estimate of average subsidence rate

  29. hyaloclastite formation -- “prograding delta” volcano growth

  30. Trace elements and isotopic ratios are generally correlated with variations in SiO2 content (Kurz et al, 2003)

  31. What if the length scales of compositional heterogeneities are small?

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