Talk at Muenster university

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Talk at Muenster university

  1. 1.
  2. 2. Artwork copyright 2006 Don Dixon/cosmographica.com<br />
  3. 3.
  4. 4. Fromearly to modern Earth<br />Nicolas Coltice<br />
  5. 5. J. Monteux<br />J. Hernlund (Berkeley)<br />Y. Ricard<br />F. Dubuffet<br />N. Flament<br />B. Marty (Nancy)<br />P. Rey (Sydney)<br />R. Yokochi (Chicago)<br />S. Labrosse <br />
  6. 6. What’sleftfrom the magma ocean phase?<br />
  7. 7. Meltingcaused by impacts<br />
  8. 8. Heatreleased by coresegregation<br />Monteux et al., 2009<br />
  9. 9. ULVZ at the base of the Earth’smantle<br />Rost et al., 2005<br />
  10. 10. Deepmantlemelting<br />Vp and Vs reduction up to 10 and 30% respectively (Rost et al., 2005)<br />Density of the melt up to 50% higher than solids <br />Thickness of 40km maximum<br />
  11. 11. A dense melt?<br />Chemicaleffect: Fe enrichment<br />Structural effect: densitycross-over of the meltaround 80GPa<br /> (Mosenfelder et al., 2007)<br />
  12. 12. Magenticfieldgenerated by a dynamo core cooling(5TW)<br />1000K of coolingthrough 4.5Ga<br />Deepmelts are as old as the planet<br />When has this melt formed?<br />
  13. 13. Basal magma ocean model<br />Labrosse, Hernlund & Coltice, 2007<br />4.52 Ga<br />4.50 Ga<br />3.50 Ga<br />today<br /><ul><li> Crystallizing dense melt richer and richer in Fe
  14. 14. Forming denser and denser piles
  15. 15. No melt entrainment</li></li></ul><li>Consequences on the generation of the magnetic field<br />
  16. 16. FromHadean to ArcheanEarth<br />Artwork copyright 2006 Don Dixon/cosmographica.com<br />
  17. 17. 129I<br />244Pu + 238U<br />Xenon isotope as geodynamictracers<br /> (Kunz, Staudacher, Allègre 1998)<br />Half-lives :<br />129I  16 Ma<br />244Pu  82 Ma<br /> 238U  4450 Ma<br />
  18. 18. Present-day mantle mantle <br />Closed-system<br />mantle<br />6800<br />2-22<br />Constraints on the timing of degassing<br />30<br />0.25-1.5<br />1<br />1<br />136Xe<br />136Xe<br />129Xe<br />136Xe<br />136Xe<br />129Xe<br />244Pu<br />129I<br />244Pu<br />129I<br />238U<br />238U<br />
  19. 19. How does Xe degass?<br />Accretion(shock)<br />Magma ocean (melting)<br />Earthcooling (convection)<br />Complete and instantanneous<br />Partial and continuous (~ 4.4By)<br />
  20. 20. Couplingdegassing and thermal history<br />To compute D(t)weneed T(t) et S(t)<br />
  21. 21. No hypothesis on the physics of cooling<br />
  22. 22. No more on the melting area generated<br />
  23. 23. Magmatic histories consistent with Xe isotopicconstraints<br />Coltice et al., 2009<br />
  24. 24. Thermal histories consistent with Xe isotopicconstraints<br />Coltice et al., 2009<br />
  25. 25. FromArchean to modern Earth<br />
  26. 26. Archean water world<br />Archean (~3.5 Ga) pillow lava (P. Rey)‏<br />From Kump and Barley (2007)‏<br /> Flood volcanism on submerged continental platforms is:<br /><ul><li>common in the Precambrian
  27. 27. rare to absent throughout the Phanerozoic</li></ul> These lavas have interacted with differentiated material<br /> (N. Arndt, 1999)‏<br />
  28. 28. No granite above sea-level before 2.7Ga<br />Shales are a proxy for the composition of Earth's emerged surface:<br /><ul><li>Mafic sources:
  29. 29. no Eu anomaly
  30. 30. Low LREE/HREE
  31. 31. High [Sc]
  32. 32. Felsic sources:
  33. 33. Eu anomaly
  34. 34. High LREE/HREE
  35. 35. Enriched in Th, U</li></ul>From Taylor and McLennan (1985)‏<br />Pas de granite en surface? Pas d’érosion ?<br />
  36. 36. Thermal causes?<br />
  37. 37. Flat and hot Archean continents<br />
  38. 38. Slopes develop after the Archean<br />Rey et Coltice, 2008<br />
  39. 39. Consequences on hypsometry<br /><ul><li>Higher sea-level</li></li></ul><li>Modelling freeboard<br />Bathymetry:<br />Half-space cooling model<br />Comparison between two <br />recent thermal evolution <br />models:<br /><ul><li>Korenaga (2006)‏
  40. 40. Labrosse and </li></ul>Jaupart (2007)‏<br />Isostasy:<br />Volume conservation:<br />Flament et al., 2008<br />
  41. 41. Prediction for early Archean<br />Mantle 200 °C hotter ; continental area 20 % ; Archaean hypsometry<br />
  42. 42. Prediction for late Archean<br />Mantle 150 °C hotter ; continental area 80 % ; Archaean hypsometry<br />
  43. 43. Prediction for Proterozoic<br />Mantle 100 °C hotter ; continental area 100 % ; present-day hypsometry<br />
  44. 44. Today<br />
  45. 45. Fromearly to modern Earth<br />Remnants of magma ocean stage at the base of the mantle<br />Intese and widespsreadvolcanism in the Hadean (no plate tectonics)<br />Flooded and flat ArcheanEarth<br />Slowlycooling modern Earthwithstrongcrust and uppermantle<br />

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