john r. hopper [email protected] leibniz institute for marine science, kiel, germany thomas k....
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John R. Hopper [email protected]
Leibniz Institute for Marine Science, Kiel, Germany
Thomas K. Nielsen [email protected]
Maersk Olie og Gas A/S, Copenhagen, Denmark
John R. Hopper [email protected]
Leibniz Institute for Marine Science, Kiel, Germany
Thomas K. Nielsen [email protected]
Maersk Olie og Gas A/S, Copenhagen, Denmark
Volcanic Productivity duringContinental Breakup
fromNumerical Modeling of Mantle Convection:
Application to Atlantic Rifted Margins
Volcanic Productivity duringContinental Breakup
fromNumerical Modeling of Mantle Convection:
Application to Atlantic Rifted Margins
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North Atlantic Rifted MarginsNorth Atlantic Rifted Margins
3333
2727
1818
1616 1818
~30~30
20-4020-40
<5<5
0!0!
1.5 - 41.5 - 4
0-50-5
??
??
From: Hopper et al. 2003 JGRFrom: Hopper et al. 2003 JGR
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•Single transient pulse of anomalous volcanism (double steady-state)
•Decay to background productivity in ~10m.y.
•Variation in crustal thickness since 47 Ma ± 10% - 15%
•Single transient pulse of anomalous volcanism (double steady-state)
•Decay to background productivity in ~10m.y.
•Variation in crustal thickness since 47 Ma ± 10% - 15%
Summary of Key Observations
Summary of Key Observations
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Fundamental guiding principle
Fundamental guiding principle
A successful model of breakup volcanism should naturally evolve to steady-state,
plate-driven oceanic accretion.
A successful model of breakup volcanism should naturally evolve to steady-state,
plate-driven oceanic accretion.
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Model FormulationModel Formulation
• Citcom: Multi-grid Finite Element Code
• Consider convection as a corner flow response to a constant velocity surface boundary condition (will also consider edge-driven convection)
• Viscosity varies with temperature, pressure, and degree of dehydration due to melting
• Buoyancy sources include thermal, compositional, and retained melt
• Melting is implemented following the method of Scott, 1992.
• Citcom: Multi-grid Finite Element Code
• Consider convection as a corner flow response to a constant velocity surface boundary condition (will also consider edge-driven convection)
• Viscosity varies with temperature, pressure, and degree of dehydration due to melting
• Buoyancy sources include thermal, compositional, and retained melt
• Melting is implemented following the method of Scott, 1992.
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High Viscosity CaseHigh Viscosity Case Low Viscosity CaseLow Viscosity Case
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Varying the mantle reference viscosityVarying the mantle reference viscosity
IncreasingViscosityIncreasingViscosity
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Effect of dehydration viscosity increaseEffect of dehydration viscosity increase
Various assumptions aboutviscosity andbuoyancy sources
Various assumptions aboutviscosity andbuoyancy sources
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Add 50 km thick hot layer beneath the continentAdd 50 km thick hot layer beneath the continent
100 °C100 °C
200 °C200 °C
100 °C, dehyd.100 °C, dehyd.
200 °C, dehyd.200 °C, dehyd.
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Edge ConvectionEdge Convection Edge Convection +Rifting
Edge Convection +Rifting
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Melt Production for Edge Convection + RiftingMelt Production for Edge Convection + Rifting
Previous slidePrevious slide
1% thermal perturb.1% thermal perturb.
low viscosity caselow viscosity case
intermediate visc.intermediate visc.
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ConclusionsConclusions
• Models that exhibit small scale convection and edge convection with significant excess melt productivity never evolve to steady-state oceanic accretion.
• A dehydration induced viscosity increase stabilizes the system, but lacks the time dependent behavior needed to allow small-scale convection followed by state-state spreading.
• Models that exhibit small scale convection and edge convection with significant excess melt productivity never evolve to steady-state oceanic accretion.
• A dehydration induced viscosity increase stabilizes the system, but lacks the time dependent behavior needed to allow small-scale convection followed by state-state spreading.
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ConclusionsConclusions
• Volcanic margin formation like off Greenland seems to require an exhaustible reservoir of anomalous material beneath the lithosphere at the time of breakup.
• Characterizing the nature of this layer (chemical or thermal?) and understanding how it is emplaced beneath the continent require further work.
• Volcanic margin formation like off Greenland seems to require an exhaustible reservoir of anomalous material beneath the lithosphere at the time of breakup.
• Characterizing the nature of this layer (chemical or thermal?) and understanding how it is emplaced beneath the continent require further work.
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For Future Work:For Future Work:
• Require better understanding of the thermal structure of continents prone to rupture
• Require better understanding of melt extraction/retention during early stages of melt production (pre-rupture)
• Require better understanding of the thermal structure of continents prone to rupture
• Require better understanding of melt extraction/retention during early stages of melt production (pre-rupture)