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Formation de la Terre. Abundances in the Universe/Crust Fe Be Mg Al Si Pb.

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Presentation on theme: "Formation de la Terre. Abundances in the Universe/Crust Fe Be Mg Al Si Pb."— Presentation transcript:

1 Formation de la Terre

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

3 Melting Temperature

4 Goldschmidt Classification

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

6 Linterieur de la Terre: proprietes radiales

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


9 " Mass of the Earth M : kg Radius of the Earth R : 6371 km, of the core R n =3470 km Average density rhobar : 5.5 g/cm 3 Inertia I : 0.33 MR 2 The average inertia is larger that the density of crustal silicates (around 2.8 g/cm 3 ) and mantle silicates (around 3.2 g/cm 3 ). The deep Earth is thus denser The inertia is lower than that of an homogeneous Earth (2/5MR 2 ). The deep Earth is thus denser " Exercise : compute the mass, average density and inertia of a two layer sphere. Estimate the Earths mantle and core densities " solution : rho 1 = 12.7 kg m 3, rho 2 =4.2 kg m 3. The core mass is 37% of Earths mass. Nature of the core 1)

10 " The composition of sample mantle rocks is typically (Mg 0.9 Fe 0.1 ) 2 Si O 4 Olivine Solid solution of Forsterite Mg 2 Si O 4 & Fayalite Fe 2 Si O 4 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 N Fe =M noyau /m fe +0.2 M manteau /m Ol The total number of Mg moles is N Mg =1.8 M manteau /m ol as N Fe /N Mg is.84 the core mass is 33 % of the Earths mass Nature of the core 2)

11 Average Composition Of the Oceanic Crust Weight % SiO Al 2 O CaO11.3 FeO10.0 MgO7.7 Na 2 O2.8 TiO K2OK2O0.15 P2O5P2O Average Composition of the Continental Crust Weight% SiO Al 2 O FeO4.6 CaO3.7 K2OK2O3.5 Na 2 O3.2 MgO2.4 TiO P2O5P2O5 0.2

12 Molar %

13 " The total Earths composition is similar to that of the refractory part of the Universe " The total Earths 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 Stratification of the Earth: Composition 7 km oceans crust basalt 30 km continents crust granite R=6371 km R=3500 km Mantle pyrolite Core Iron (+Nickel +O,S,Si…)

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 Ma Chondrules t Iron meteorites t Earth Core t 0 +50Moon formed t End of accretion Chondrite Inclusions

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

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

22 W « siderophile » Hf « lithophile » Core segregation after Hf decay Same 182/183 W 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 La tectonique des plaques sur le million dannee Des mouvements horizontaux…

27 La tectonique des plaques sur lannee

28 Distance Pac-Fr


30 Observations of plate motion Modèle de la tectonique des plaques

31 Finland Hudson Scotland Des mvts verticaux…

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~10 8 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 ~10 26 Pa s solid Asthenosphere ~ Pa s solid « real asthenosphere » Pa s solid deep mantle Pa s solid D <<10 21 Pa s ? solid Outer core 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/Van der Hilst

48 La convection

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