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

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

Formation de la Terre

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

Melting Temperature

Goldschmidt Classification

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

Linterieur de la Terre: proprietes radiales

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

" Mass of the Earth M : 6. 10 24 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)

" 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)

Average Composition Of the Oceanic Crust Weight % SiO 2 50.0 Al 2 O 3 16.0 CaO11.3 FeO10.0 MgO7.7 Na 2 O2.8 TiO 2 1.5 K2OK2O0.15 P2O5P2O5 0.12 Average Composition of the Continental Crust Weight% SiO 2 66.0 Al 2 O 3 15.5 FeO4.6 CaO3.7 K2OK2O3.5 Na 2 O3.2 MgO2.4 TiO 2 0.6 P2O5P2O5 0.2

Molar %

" 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)

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…)

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

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

4566 Ma Ca-Al- 4563 Ma Chondrules t 0 +5-15 Iron meteorites t 0 +30 Earth Core t 0 +50Moon formed t 0 +100 End of accretion Chondrite Inclusions

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

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

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

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

Une planete active

La tectonique des plaques sur le million dannee Des mouvements horizontaux…

La tectonique des plaques sur lannee

Distance Pac-Fr

Observations of plate motion Modèle de la tectonique des plaques

Finland Hudson Scotland Des mvts verticaux…

Bretagne

Estimates of the viscosity:

Observation of heat flux :

Using Earth heat flow, in how much time can I boil the water for my coffee cup?? t~10 8 s = 3.5 ans

Can we expore the mantle " KTB, Kola

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

Stratification of the Earth: Rheology Lithosphere ~100 km ~10 26 Pa s solid Asthenosphere ~10 19-22 Pa s solid « real asthenosphere » 10 19-21 Pa s solid deep mantle 10 21-22 Pa s solid D <<10 21 Pa s ? solid Outer core 10 -3 Pa s liquid Inner core ? Not so solid

Liquide Solide

Liquide Solide

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

Seismic tomography

On a smaller scale:

From Grant/Van der Hilst

La convection

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