1. Ce que nous apprennent les roches* du manteau sur la migration des magmas dans le manteau Peter Kelemen * Roches experimentales, volcaniques et du manteau

2. Minerals in the mantle and lower crust OlivineMg 2 SiO 4 - Fe 2 SiO 4 OrthopyroxeneMg 2 Si 2 O 6 - Fe 2 Si 2 O 6, etc ClinopyroxeneCaMgSi 2 O 6 - CaFeSi 2 O 6, etc Spinel(Mg,Fe)(Cr,Al) 2 O 4, etc Garnet(Mg,Fe,Ca) 3 Al 2 Si 3 O 10, etc PlagioclaseCaAl 2 Si 2 O 8 - NaAlSi 3 O 8 Melting reactions P > 20 kilobars (2 Gpa) Ol + Opx + Cpx + Gnt = melt 8 kb < P < 20 kb Opx + Cpx + Sp = Ol + melt P < 8 kb Opx + Cpx + Plag = Ol + melt if fertile Opx + Cpx + Sp = Ol + melt if depleted

3. really low F ~3 to 20% melting really high F

4. mantle solidus liquid adiabat olivine saturation pyroxene saturation  Depth Temperature  { peridotite dissolves (even olivine), MgO up { pyroxenes dissolve olivine precipitates, SiO 2 up

5. Rare Earth Elements in order of increasing Z periodic table in approximate order of crystal/liquid partitioning

7. Bottom up: Diffuse porous flow Melting & diapirs Magma fracture Focused porous flow Sills & lenses at “top” Top down: MORB composition MORB focusing MORB ascent rate Arc composition Arc focusing Hotspot flux, comp, focusing  = WF  s /(  w  f ) STEADY STATE! (  = 1) w = kΔ  g/(  f ) “DARCY’S LAW”

9. w = kΔ  g/(  f ) k = d 2  3 /c Von Bargen & Waff Wark, Watson, et al. k = d 2  3 /270 Faul et al.

10. Von Bargen & Waff

11. Grain size variation: some grains smaller, more melt on triple grain boundaries (= grain edges) At low melt fraction, little or no melt on large grain edges If rock is banded in grain size,  low permeability  to banding

12. hz ol+sp ol HARZBURGITE (+)OL + SP (  ) OL only (  )

13. hz ol+sp ol Faul et al. Von Bargen & Waff Wark, Watson, et al. quartzite marble

14. compositional variation across a large dunite in the Josephine peridotite

15. upper bound estimate of “permeability threshold” based on upper bound estimate of “trapped melt”, based on CaO in whole rock - olivine

16. w = kΔ  g/(  f ) k = d 2  3 /c Wark, Watson, et al. k = d 2  3 /270 Von Bargen & Waff Wark, Watson, et al. Faul et al. X X

17. Wetting angles may vary depending on crystallographic orientation and mineral At low melt fractions, “unfavorable” grain edges have no melt at all Positive or negative feedback on permeability? k = d 2  3 /c c is a “geometric factor”

19. ol + melt ol + opx + melt ol ± opx NO initial melt 6h ol + opx + melt ol ± opx NO initial melt 6h

20.  3 = 270  WF  s /(d 2  g  f ) from  = WF  s /(  w  f ) STEADY STATE! (  = 1) w = kΔ  g/(  f ) “DARCY’S LAW” k = d 2  3 /270 Wark et al.

21. Bottom up: Diffuse porous flow OK, prefer Wark et al. (for now) field evidence? Melting & diapirs Magma fracture Focused porous flow Sills & lenses at “top” Top down: MORB composition MORB focusing MORB ascent rate Arc composition Arc focusing Hotspot flux, comp, focusing

22. Models of regional pervasive porous flow conflict with structural and seismic evidence that fractures control fluid transportation in the upper mantle. Effects of porous-medium flow have been inferred in studies of mantle peridotite … but are well documented only on scales of centimeters or decimeters. In all these [cases], porous flow is fundamentally controlled by proximity to magma-filled fractures. Nielsen & Wilshire, 1993

29. melt out residual porosity nothing coming in melt out melt coming in residual porosity nothing out MORB coming in nothing out local melt coming in

32. light REE “enriched” light REE depleted low Al high Al

33. coarse, granular (high T) Porphyroclastic (low T) light REE depleted (“MORB source”) Light REE Enriched (addition of low degree melts)