2. A case study: the nepheline basanite UT- 70489 from Bow Hill in Tasmania, Australia Previous work includes: An experimental study of liquidus phase equilibria to determine conditions of garnet lherzolite saturation (~2.7 GPa and 1200 °C with 4.5 % of dissolved H 2 O and 2 % of CO 2 ) A LAM-ICP-MS and electron micro-probe study of minor and trace element partitioning between peridotite minerals and the hydrous basanite melt A single-crystal X-ray and site refinement study of experimentally produced peridotite phases

3. Objectives To produce a comprehensive and self- consistent set of peridotite/melt partition coefficients that include volatile as well as non-volatile elements To apply these data to the problem of intraplate magma genesis

4. Materials and methods Piston-cylinder experiments at 1.0- 3.5 GPa and 1025-1190 °C using conventional methods H 2 O, C (as CO 2 ), Cl, F, P and S by secondary ion mass spectrometry (SIMS) at the Carnegie Institution of Washington. Major, minor and trace elements by electron microprobe and LAM- ICP-MS at Macquarie University, Australia. Basanite UT-70489 (an intraplate basalt & potential near-solidus melt of garnet lherzolite) SiO 2 44.30plag 13.77 TiO 2 2.36or 12.41 Al 2 O 3 11.44ne 15.28 Cr 2 O 3 0.08di 25.47 Fe 2 O 3 2.01ol 21.43 FeO*10.05ilm 4.50 MnO 0.20mag 3.83 NiO 0.05ap 3.31 MgO 12.11 CaO 9.46 SrO 0.18 Na 2 O 4.24 K 2 O 2.09 P 2 O 5 1.43 Total 100.00 100 x Mg/(Mg + Fe +2 ) = 68.2

5. Run R79 1075 °C 1.0 GPa Run R80 1170 °C 3.0 GPa glass quenched melt (porous crystallite matrix) olivine + cpx graphite inner capsule Pt outer capsule pyroxenes

6. 1:1

7. H 2 O ppmF ppm Clinopyroxene 608-1390187-326 Orthopyroxene649-121182-149 Olivine94-16619-34 Garnet216-35226-35 Pargasite169004983 Phlogopite35100-391008177-10423 Cl, S and C have negligible concentrations in nominally anhydrous silicate minerals Cl and S have small to moderate solubilities in amphibole and mica ~ 0.5 wt. CO 2 is soluble in the melt phase at 1-2 GPa

8. clinopyroxene/melt partitioning of H 2 O

9. orthopyroxene/melt partitioning of H 2 O

10. olivine/melt partitioning of H 2 O

11. Garnet/melt partitioning

12. Controls on crystal/melt partitioning 1.crystal-chemical effects Tetraherally co-ordinated Al in pyroxenes 2.melt-activity relations Burnham’s (1975) solution model for H 2 O in silicate melts Silver et al.’s (1990) solution model for H 2 O in silicate melts

13. Effect of iv Al +3 in charge-balancing the addition of H + to the pyroxene lattice [pyx] H + + [iv] Al +3 + [melt] Si +4 [melt] H + + [melt] Al +3 + [iv] Si +4

15. Burnham’s speciation model for hydrous melts mixing between OH - and 8-oxygen melt units with K D = 0.0014

16. Silver et al.’s (1990) speciation model for hydrous melts mixing between OH -, molecular H 2 O and O 2- with D OH cpx/melt = 0.05 molecular H 2 O OH -

17. Melt activity relations as well as mineral composition play a role in the determination of mineral/melt (Nernst) partition coefficients for H 2 O

18. Comparisons with non-volatile elements There is a constancy of some volatile to non-volatile element ratios in intraplate (ocean island) and mid-ocean- ridge magmas H 2 O/Ce = 200 ± 50 (Michael 1995) o Higher ratios in Atlantic than Pacific, in some cases the correlation is better for La and/or varies with 87 Sr/ 86 Sr F/Nd Cl/Ba, Cl/K CO 2 /Nb, CO 2 /Ba Similar mineral/melt partition coefficients during intra-mantle fractionation involving the migration of small-degree melts from local MORB sources?

19. H2OH2O F Cl Cl and F partitioning data from Dalou et al. (2012) Garnet lherzolite/melt Partition coefficients

20. Crystal-chemical controls on D H2O /D Ce Must also consider the contributing influence of H 2 O concentrations in melts (significant for subduction zones)

21. Conclusions During peridotite melting D H2O /D Ce increases with increasing pressure and temperature (and therefore depth in the mantle), but decreases with increasing melt H 2 O Therefore - although coupled volatile and non-volatile element enrichments in OIB are consistent with peridotite/melt partitioning, this may require particular circumstances

22. Thank You

24. av. OIB normalized to av. MORB D Z peridotite/melt

25. The influence of iv Al on F in pyroxenes

26. The influence of Ti and melt H 2 O concentrations on OH in amphibole O3 sites [melt] Ti +4 + 2 [melt] O 2- + [M1,3] Mg +2 + 2 [O3] OH -  [melt] Mg +2 + 2 [melt] OH - + [M1,3] Ti + 2 O3 O 2-