1. Modelling the Composition of Melts Formed During the Continental Break-up of the North Atlantic J. Armitage, T. Henstock, T. Minshull and J. Hopper

2. Motivation Recreate the volume of melt generated during the opening of the North Atlantic. Understand what the effect would be on the composition of primary melts.

3. Outline Introduction Model set-up and evolution Steady state composition Constant spreading rates Fast spreading upon opening Summary

4. Composition Parameterisation Melting occurs when upwelling mantle crosses the solidus. We use the parameterisation of Watson & McKenzie (1991). Relates major element composition to instantaneous melt depletion. Integrate over the whole melt region

5. Model Set-up Top is driven to the right at a chosen half spreading rate. No flow of material or heat across the boundaries. Optional hot layer with temperature increases of 100 and 200 ºC. 120 km 50 km

6. Mantle potential temperature of 1325 ºC. Half spreading rate of 10 mm/yr

15. Steady State Composition For models run at mantle potential temperatures of 1300 to 1325ºC and half spreading rates of 10 to 20 mm/yr.

16. Southeast Greenland

17. Two Scenarios Constant spreading –variation in hot layer temperature Fast spreading upon opening –Variation in hot layer temperature

18. Mantle potential temperature of 1325 ºC. Half spreading rate of 10 mm/yr Primary melt estimates from Thy et al 1998 and Larsen et al 1999

19. Igneous thickness from Holbrook et al 2001

20. Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001

21. Second Scenario The S.E. Greenland margin opened with a pulse of elevated spreading rates. Hopper et al (2003) estimate 33 mm/yr, Larsen and Saunders (1998) give 44 mm/yr abating to 12 mm/yr. We include this with a pulse of fast spreading of 40 mm/yr for 4 Myrs that abates to 10 mm/yr.

22. Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001

23. Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001

24. Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001

25. Summary We can re-create the volume of melt generated. The effect is a temporal variation in primary melt composition. Is this prediction backed up by geochemical evidence?

26. More Evolved Rocks Peak Production Steady State

27. Composition Parameterisation Also tested Niu and Batiza (1991) parameterisation. Relates melt composition to the incremental melt production. Then integrate at over the whole melt region.