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
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
•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
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.
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.
High Viscosity CaseHigh Viscosity Case Low Viscosity CaseLow Viscosity Case
Varying the mantle reference viscosityVarying the mantle reference viscosity
IncreasingViscosityIncreasingViscosity
Effect of dehydration viscosity increaseEffect of dehydration viscosity increase
Various assumptions aboutviscosity andbuoyancy sources
Various assumptions aboutviscosity andbuoyancy sources
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.
Edge ConvectionEdge Convection Edge Convection +Rifting
Edge Convection +Rifting
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.
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.
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.
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)