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Plumes, hotspots and the CMB

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  1. Plumes, hotspots and the CMB Lecture 6: Geodynamics Carolina Lithgow-Bertelloni

  2. Earth’s temperature profile

  3. Scales of Convection [from Geoff Davies]

  4. Plumes and Hotspots Hotspots Island chains and age progression Importance for plate motions, TPW Fixity Chemistry Origin Plumes Difference with large-scale upwellings Heads and tails Effects of viscosity on morphology Plume initiation and flood basalts How much entrainment Comparison to geochemistry Effects of composition Shape, heterogeneity, hotspot fixity Relationship between large-scale upwellings and plumes? Capture by plate-scale flow Consequences for heat flow Where do they come from? Relationship to CMB structure

  5. Hotspots Concentrated volcanic activity. Linear volcanic chains in the interiors of the plates. Age progression along chain Chemistry of erupted lavas is significantly different than MOR or IA Some hotspots have broad topographic swell ~ 1000 m [Steinberger et al., 2004]

  6. 25-43 Ma Hotspots and Plates 43-48 Ma

  7. Hotspots, fixity and plate motions

  8. Hotspot fixity and mantle wind [Steinberger et al., 2004]

  9. Chemistry [Barfod et al., 1999]

  10. Plumes and hotspots • Rayleigh-Taylor instability • Large head, thin tail • Rheology • Vigor of convection • Compositional vs thermal buoyancy • Ascent times • Rheology • Deflection, capture by mantle wind • Compositional vs thermal buoyancy [Griffiths and Campbell, 1990]

  11. Rise time estimate r = 500 km    V =80 km/My r v  Ratio of buoyancy force to viscous forces B = -4r3g/3 =cv/r; R=r cv Forces on the sphere balanced velocity constant B+R=0 V= -gr2/3c If viscosity of sphere and surrounding different c = /  c ~ 1-1.5

  12. Generating a mantle plume [from Geoff Davies]

  13. Large-scale upwellings and plumes [Boschi and Dziewonski,1999] [Ni et al.,2002]

  14. Plume morphology: effects of viscosity [Whitehead and Luther, 1975]

  15. Plumes heads and tails CIDER-KITP [Lithgow-Bertelloni et al., 2001]

  16. Head & Tail Radii [Lithgow-Bertelloni et al., 2001]

  17. Thermochemical Plumes [Farnetani, 2004]

  18. Entrainment and mixing

  19. Plumes and geochemical heterogeneity [Samuel and Farnetani, 2003]

  20. Evolution of heterogeneity [LeBars and Davaille, 2004]

  21. Plumes and large-scale upwellings [Davaille, 2000]

  22. Thermochemical plumes and fixity [Jellinek and Manga, 2002]

  23. Plume capture by large-scale flow [Jellinek et al., 2002]  and Pe control BLT and Q  ~ (Pe)1/3  Q ~ (Pe)1/2 V and hot/int No effect V<< 1  ~ 1 Suppression V> 10  > 100 Sweeping V intermediate f(

  24. Where do plumes originate? [Davaille, 2000]

  25. The plume source region: CMB [Sidorin et al., 1999]

  26. Plume Frequency 3 Different Experiments

  27. Episodic Crustal Production? Condie, 1998