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Modelling the Composition of Melts Formed During the Continental Break-up of the North Atlantic J. Armitage, T. Henstock, T. Minshull and J. Hopper
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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.
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Outline Introduction Model set-up and evolution Steady state composition Constant spreading rates Fast spreading upon opening Summary
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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
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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
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Mantle potential temperature of 1325 ºC. Half spreading rate of 10 mm/yr
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Steady State Composition For models run at mantle potential temperatures of 1300 to 1325ºC and half spreading rates of 10 to 20 mm/yr.
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Southeast Greenland
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Two Scenarios Constant spreading –variation in hot layer temperature Fast spreading upon opening –Variation in hot layer temperature
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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
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Igneous thickness from Holbrook et al 2001
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Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001
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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.
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Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001
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Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001
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Primary melt estimates from Thy et al 1998 and Larsen et al 1999 Igneous thickness from Holbrook et al 2001
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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?
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More Evolved Rocks Peak Production Steady State
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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.
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