WATER IN THE EARTH S MANTLE:

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1 WATER IN THE EARTH S MANTLE: NATHALIE BOLFAN-CASANOVA LABORATOIRE MAGMAS ET VOLCANS

2 => Heterogeneous distribution of water in the mantle > pmm wt H2O ~ pmm wt H2O ~ 1000 pmm wt H2O

3 On what form do we find water? Fluids Hydrous magmas Hydrous phases?? NAMs

4 Pearson et al. (2005)

5 Water in the transition zone H2O wt% Mg2SiO4 wadsleyite Inoue et al. (1995) H2O wt % Mg2SiO4 wadsleyite Demouchy et al. (2005) H2O wt % (Mg,Fe)2SiO4 wadsleyite Kawamoto et al. (1996) H2O wt % Mg2SiO4 Ringwoodite Ohtani et al. (2000) km 520 km 670 km 3 H 2 O wt % Ringwoodite inclusion in diamond from Pearson et al. (2014) T( C) => In agreement with water-saturated conditions

6 Water recycling through subduction

7 Peridotite + H 2 O phase diagram redrawn from Iwamory (2004) from Syracuse et al. (2010) => Slabs are not that hot after all

8 H defects are ubiquituous in most mantle samples Demouchy et al. (2004) Demouchy and Bolfan-Casanova (2015)

9 Water circulation in cratons => water content in NAMs from enoliths in kimberlite Shirey et al. (2013)

10 Water circulation in cratons => new messages from NAMs inclusions in diamonds Novella et al. (2015) => Maimum 5 ppm wt H 2 O in olivine Shirey et al. (2013)

11 Effect of CO 2 on water incorporation Sokol et al. (2013)

12 Constraints on the water content in the mantle From the water content in MORBs: -> [H2O] MORB ~3000 ppm wt -> water partitioning D solid/liquid ~0.01 -> melting degree F = 10% => [H2O]source = 300 ppm pds

13 Constraints on the water content in the mantle From the water content in MORBs From the water content in NAMs in mantle enoliths Mineral Water contents (ppm wt H 2 O) Olivine < 1 to > 100 Orthopyroene Clinopyroene up to 1200 Garnet < 1 to 200 * kimberlites and alkali basalts 250 ppm by weight in the source, the lithospheric mantle! Volatile loss during ascent Bell and Rossmann (1992)

14 Diffusion profile of H across olivine Demouchy et al. (2004) => Water content in the source under-estimated

15 Why is such water important? What are the effects of water on mantle physical properties?

16 Effect of water on mantle melting Aubaud et al. (2004) The melt fraction is higher Melting starts at higher depth

17 Effect of water on chemical diffusion Hier-Majumder et al. (2005)

18 D Me X V and X V C OH Hier-Majumder et al. (2005)

19 AC r H OHep( RT H ) Gardès et al. (2014)

20 Seismic discontiuities Frost and Doleij (2007)

21 Elastic softening Effect of hydration on density Jacobsen (2006)

22 Jacobsen (2006)

23 WHAT IS THE STORAGE OF WATER IN THE EARTH S MANTLE NATURAL SYNTHETIC Coutrsy of S. Demouchy Irifune and Isshiki (1998)

24 Water storage capacity of the Earth s? Eperimental approach + Absorption coefficient (cm -1 ) FTIR forsterite synthesized hydrothermally at 9 GPa and 1250 C // a ais // b ais // c ais Wavenumber (cm -1 ) From Bali et al. (2008)

25 Incorporation of water in NAMs In olivine: Mg 2+ = 2 H +

26 Incorporation of water in NAMs In olivine: Mg 2+ = 2 H + Notation de Kröger Vink : Mg Me + OO + H2 O = 2 OH O. + VMe + MgO i.e. MgSiO 3 + Mg Me + 2OO + H2 O = 2 OH O. + VMe + Mg 2 SiO 4

27 Incorporation of water in NAMs In olivine: Mg 2+ = 2 H + Notation de Kröger Vink : Mg Me + OO + H2 O = 2 OH O. + VMe + MgO i.e. MgSiO 3 + Mg Me + 2OO + H2 O = 2 OH O. + VMe + Mg 2 SiO 4 (2H) Me

28 Incorporation of water in NAMs In olivine: Mg 2+ = 2 H + Notation de Kröger Vink : i.e. MgSiO 3 + Mg Me + 2OO + H2 O = (2H) Me + Mg 2 SiO 4 [(2H a a Mg2SiO4 Me)] K fh2o MgSiO3 n [OH] 2 ep( RT G O ) fh2

29 Incorporation of water in NAMs In olivine: Mg 2+ = 2 H + Notation de Kröger Vink : soit MgSiO 3 + Mg Me + 2OO + H2 O = (2H) Me + Mg 2 SiO 4 [(2H a a Mg2SiO4 Me)] K fh2o MgSiO3 [OH] A(P) fh2 n ep( O n [OH] 2 ep( RT G O ) fh2 H RT P V ) and n=1

30 Incorporation of water in NAMs In garnet : Si 4+ = 4 H + Notation de Kröger Vink : Si Si + OO + 2 H2 O = 4 OH O. + VSi + SiO 2

31 Incorporation of water in NAMs In garnet : Si 4+ = 4 H + Notation de Kröger Vink : Si Si + OO + 2 H2 O = 4 OH O. + VSi + SiO 2 (4H) Si

32 Incorporation of water in NAMs In garnet : Si 4+ = 4 H + Notation de Kröger Vink : Si Si + OO + 2 H2 O = 4 OH O. + VSi + SiO 2 [(4H Si )] a K SiO2 f 2 H2O n [OH] 4fH2O ep( RT G )

33 Incorporation of water in NAMs Dans le grenat : Si 4+ = 4 H + Notation de Kröger Vink : Si Si + OO + 2 H2 O = 4 OH O. + VSi + SiO 2 [(4H Si )] a K SiO2 f 2 H2O [OH] A(P) fh2 n ep( O n [OH] 4fH2O ep( RT G ) H RT P V ) and n=2

34 Incorporation of water in NAMs In enstatite: incorporation of aluminum Anhydrous case: Mg 2+ + Si 4+ = 2Al 3+ (Mg Al)(Al Si) O 6 (Tschermak) Hydrous case 1: 2 Mg 2+ = Al 3+ + H + (H Al)(Si Si) O 6 Hydrous case 2: Si 4+ = Al 3+ + H + (Mg Mg) (Al H) Si O 6 Keppler and Bolfan-Casanova (2006)

35 Recycling of H at low temperature in the wedge mantle Thermodynamics of H incorporation [OH] 2 ep( RT G O ) fh2 Pression kj/mole) S J/mole/K) V cc/mole) GPa 37.1 ± ± Kohlstedt et al. (1996) Mosenfelder et al. (2006) Zhao et al. (2006) Bali et al. (2008) Férot and Bolfan-Casanova (2012)

36 Recycling of H at low temperature in the wedge mantle 10 4 Thermodynamics of H incorporation [OH] 2 ep( RT G O ) fh2 Pression kj/mole) S J/mole/K) V cc/mole) GPa 37.1 ± ± log [H2O] ppm wt GPa 2.5 GPa 5 GPa 7.5 GPa Kohlstedt et al. (1996) Mosenfelder et al. (2006) Zhao et al. (2006) Bali et al. (2008) Férot and Bolfan-Casanova (2012) T( C)

37 Recycling of H at low temperature in the wedge mantle 10 4 Thermodynamics of H incorporation [OH] 2 ep( RT G O ) fh2 Pression kj/mole) S J/mole/K) V cc/mole) GPa 37.1 ± ± log [H2O] ppm wt GPa 2.5 GPa 5 GPa 7.5 GPa 3 GPa Kohlstedt et al. (1996) Mosenfelder et al. (2006) Zhao et al. (2006) Bali et al. (2008) Férot and Bolfan-Casanova (2012) T( C)

38 410-km Water storage in olivine in simple MFASH system 1600 Férot and Bolfan-Casanova (2012) Ardia et al. (2012) 1450 C Tenner et al. (2012) 1400 C Water content (ppm wt H 2 O) P (GPa)

39 Partitioning of water into orthopyroene Férot and Bolfan-Casanova (2012)

40 Partitioning of water into orthopyroene 3 y = ² 2.5 Dp/ol P(GPa) Férot and Bolfan-Casanova (2012)

41 Water storage in the convecting upper mantle For garnet : D water gt/ol of 0.9 Novella et al. (2014) at 6 GPa and 1400 C water storage (ppm wt H O) Ol contribution OPX contribution CPX contribution GT contribution Mantle storage curve +/- 100 ppm depth (km)

42 Water storage in the convecting upper mantle ~ 800 ppm wt H 2 O at the base of the upper mantle => In agreement with estimates for the source of Reunion Island OIB water storage (ppm wt H O) Ol contribution OPX contribution CPX contribution GT contribution Mantle storage curve +/- 100 ppm depth (km) From Férot and Bolfan-Casanova (2012)

43 Rewind Water content in the deep upper mantle is anchored at a minimum of 800 ppm wt H 2 O. Olivine can transport ~1000 ppm wt H 2 O in the subducting slab. Different type of fluids travel through cratons through their history.

44 Eperimentally determined water storage in olivine Low Velocity Zone P (GPa) Water storage average Water content (ppm wt H 2 O) /- 100 ppm wt H 2 O in simple MFASH system km From Férot and Bolfan-Casanova (2012) depth (km) => Water storage in olivine reaches ~ 1000 ppm wt H 2 0 at the 410 km discontinuity

45 Implications for the water content determination in the upper mantle Low velocity layer above the 410 km discontinuity Tauzin et al. (2010) LVL interpreted as being due to the occurence of melt The presence of water is necessary to invoke melting

46 L eau dans le manteau inférieur Bolfan-Casanova et al. (2000)

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