Formation de la Terre

1. Formation de la Terre

2. Abundances in the Universe/Crust Mg Al Si Fe Pb Be

3. Melting Temperature

4. Goldschmidt Classification

5. Chondrite Atmophile (N, He...) Lithophile (Si, Mg, Ca, Al, K...) Siderophile (Fe, Ni...)

6. L’interieur de la Terre: proprietes radiales

7. Geophysical Observations Seismics: - 1st order spherical - lower BC - material Prop.

9. Nature of the core 1) • Mass of the Earth M : 6. 1024 kgRadius of the Earth R : 6371 km, of the core Rn=3470 kmAverage density rhobar : 5.5 g/cm3 Inertia I : 0.33 MR2The average inertia is larger that the density of crustal silicates (around 2.8 g/cm3) and mantle silicates (around 3.2 g/cm3). The deep Earth is thus denser The inertia is lower than that of an homogeneous Earth (2/5MR2). The deep Earth is thus denser • Exercise : compute the mass, average density and inertia of a two layer sphere. Estimate the Earth’s mantle and core densities • solution : rho1 = 12.7 kg m3, rho2=4.2 kg m3. The core mass is 37% of Earth’s mass.

10. Nature of the core 2) • The composition of sample mantle rocks is typically (Mg0.9 Fe0.1)2 Si O4 Olivine Solid solution of Forsterite Mg2 Si O4 & Fayalite Fe2 Si O4 In chondrites and solar wind a molar ratio Fe/Mg=.84 is observed • What is the mass of the iron core? (The molar masses of Mg, Fe, Si, O are 24.3, 56, 28 et 16). The total number of Fe moles is NFe=Mnoyau/mfe+0.2 Mmanteau/mOl The total number of Mg moles is NMg=1.8 Mmanteau/mol as NFe/NMg is .84 the core mass is 33 % of the Earth’s mass

11. Average Composition of the Continental Crust Average Composition Of the Oceanic Crust

12. Molar %

13. The total Earth’s composition is similar to that of the refractory part of the Universe • The total Earth’s composition is similar to chondrites (non-differenciated meteorites) • The siderophile elements went into the Core • The lithophile elements went into the crust+mantle • The most incompatible elements are in the crust (oceanic but mostly continental)

14. R=6371 km 7 km oceans crust basalt 30 km continents crust granite Mantle pyrolite R=3500 km Core Iron (+Nickel +O,S,Si…) Stratification of the Earth: Composition

15. Stratification of the Earth: Mineralogy Upper mantle 410 km depth olivine+pyroxene+garnet 520 km depth olivine beta (wadsleyite)+garnet+pyroxene 610 km depth olivine gamma (ringwoodite)+garnet+pyroxene Lower mantle oxides magnesiowustite Mg-Fe perovskite Ca-perovskite

18. Molecular clouds • contraction (0.1-1 ma) • Disk formation • Condensation • Coagulation of dust • Up to km-size Orion Nebula

19. 4566 Ma Ca-Al- Inclusions Chondrite 4563 Ma Chondrules Iron meteorites t0+5-15 Earth Core t0+30 t0+50 Moon formed End of accretion t0+100

20. Datation: ex U/Pb sur zircons ZrSiO4 (accepte U rejete Pb)

21.   = stable 183W  = radioactif 182Hf  = radiogénique 182W Half-life 9 ma

22. W « siderophile » Hf « lithophile » Core segregation after Hf decay Same 182/183W ratio in the mantle and in undifferenciated objets

23. W « siderophile » Hf « lithophile » Cor formation before Hf decay Larger 182/183 W ratio in the mantle than in undifferenciated objets

25. Une planete active

26. Des mouvements horizontaux… La tectonique des plaques sur le million d’annee

27. La tectonique des plaques sur l’annee

28. Distance Pac-Fr

30. Observations of plate motion Modèle de la tectonique des plaques

31. Des mvts verticaux… Finland Hudson Scotland

32. Bretagne

33. Estimates of the viscosity:

34. Observation of heat flux :

36. Using Earth heat flow, in how much time can I boil the water for my coffee cup?? t~108 s = 3.5 ans

37. Can we expore the mantle • KTB, Kola

38. Hotspots: seem too: - exist over long time - being stationary - independent of the plate motion - are geochemically distinced

41. Stratification of the Earth: Rheology Lithosphere ~100 km ~1026 Pa s solid Asthenosphere ~1019-22 Pa s solid « real asthenosphere » 1019-21 Pa s solid deep mantle 1021-22 Pa s solid D ’’ <<1021 Pa s ? solid Outer core 10-3 Pa s liquid Inner core ? Not so solid

42. Liquide Solide

43. Liquide Solide

44. Stratification of the Earth: Temperature Clapeyron slopes of phase transformations Olivine-wadsleyite Ringwoodite-perovskites+oxides 1870 K Liquid iron/solid iron 5000 K Modelisation…

45. Seismic tomography

46. On a smaller scale:

47. From Grant/Vander Hilst

48. La convection