abundances in the universe/crust fe be mg al si pb
TRANSCRIPT
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...)
INCOMPATIBLES
U
Th
Al
He
COMPATIBILITY/INCOMPATIBILITY DURING PARTIAL MELTING
From Doin
Sea surface (Geoid)
Backgroundvelocity
Poiseuille
Stokes
Guess?
Measured
Backgroundvelocity
Poiseuille
Stokes
Hawaii 7.0 t/sBowie 0.3 t/s
All hostpots 55 t/sSlabs 650 t/s
From Hofmann
DEPLETED MORB SOURCEENRICHED HIMU, EM, CC SOURCESPRIMITIVE/DEPLETED LOIHI SOURCE?CC and MORB SOURCE complementaryNb, Pb, Ti anomalies due to subduction (CC, MORB and OIB)
D/N=D0/N+P
0/N(1-exp(t/T))
D=daughterP=parent
N=reference stable isotope of DT=time constant
P D N106
87 Sr 86 Sr 49
40 K 1U 0.7
Tln(2) Ga
147 Sm 143 Nd 144 Nd87 Rb
40 Ar 36 Ar4 He 3 He
ISOTOPIC RATIOS
Rares Gas
From Hart & Zindler
Primitive
Himu
EM2
EM1
MORB Midocean ridge basaltextracted from MORB source or DMM
OIB Oceanic ridge basaltextracted from?????
Primitive Mantle (PREMA) Loihi-Icelandic Type (Primitive HE Mantle)EM1 (Enriched Mantle=oceanic sediments?)EM2 (Enriched Mantle=continental sediments?)HIMU (high U/Pb=oceanic crust?)FOZO-C
M
Mass Balance for trace elements
Primitive Mantle = Crust+Morb source+Hidden res
40Argon
Produced in the Earth 940 pmol/g
Atmosphere 44%
Crust 3.5%
Upper mantle .9 % (25 pmol/g)
Lower mantle 52 % (720 pmol/g)
But K/U??
50-200 pmol/g
Another K-rich reservoir?
From Davies
OIBs are more heterogeneous than MORBsBut the same trends are seen in MORBs and OIBsThere is a hidden reservoirSlightly depleted=lower mantlePrimitive=50% of the mantleEnriched (D'' with MORBs composition)
Hiding a layer:
Density and density jumpsPhase changesCoupling between chemistry and phase jumpsViscous stratification
Less density chemical density difference is required at larger depth
MINERALOGY VS SEISMOLOGY
From Matas
CLAPEYRON SLOPE
P
T
Phase Dense
Light Phase
AveragePhase transition depth
From Machetel
Crust density: Mineralogy
Mantle, Lithosphere and oceanic crust
DOUBLE PHASE CHANGES
P
T
Dense Phase A
Light Phase A
Average Phase transition depthsfor A and B
Light Phase B
Dense Phase B
Seismic tomography
From Grant/Van der Hilst
Seismic tomography
Paleomap
Geoid
Comp. Geoid
The Mantle viscosity increases with depth by a factor 10-100
Can it help preserving primitive compositions?
Poloidal/Toroidal
Bercovici
Poincar₫ Section
From Ferrachat
Farnetani or Schmalzl and Hansen
Hotspot (no)Entrainment
Persistance of blobs
Spence, Manga
Persistance of blobs
Merveilleux
Stretching StretchingStretching Stretching
Reorientation Reorientation
500
myr
s
2 byrs
Mantle, Lithosphere and oceanic crust
MANTLE
Atmosphere
C. Crust
D ''
Residual lith.
MANTLE
Atmosphere
C. Crust
D ''
Residual lith.Flux fromhotspots
Uniformgrowth
Uniform growth
Degassing
No crustalrecycling
Fractionation +
Fractionation -
No real geochemical indication of the existence of primitive material
Strong indications that the 670 km depth boundary is permeable
Strong indications of a viscosity increase with depth by 10-100
This viscosity increase does not stratify the mixing
3D convection more efficient mixer with, than without plates
Highly viscous, small, primitive blobs may survive(?)
Need of a reservoir to store incompatible elements
Seems difficult to hide a dense reservoir in the mantle
Crust segregation in D'' may be the deep enriched reservoir(EM, HIMU)
The remaining lithosphere may be the depleted (''primitive-like'')reservoir