upper mantle dynamics expressed in hotspot basalt chemistry garrett ito, todd bianco, john mahoney,...
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Upper Mantle Dynamics Expressed in Hotspot Basalt Chemistry
Garrett Ito, Todd Bianco, John Mahoney, Janet Becker, & Michael GarciaDept. of Geology & Geophysics, SOEST, Univ. Hawaii
Upper Mantle Dynamics Expressed in Hotspot Basalt Chemistry
Garrett Ito, Todd Bianco, John Mahoney, Janet Becker, & Michael GarciaDept. of Geology & Geophysics, SOEST, Univ. Hawaii
Mantle is heterogeneous on scales smaller than melting zones
Melting depth/temperature is composition-dependent
Vertical variations in upper mantle flow can influence rates that different materials melt
Case 1: Geochemical variations along the Mid-Atlantic Ridge (MAR) near Iceland reflect differences in flow and lithospheric thickness [Ito & Mahoney, 2005]
Case 2: Rejuvenated & arch volcanism in Hawaii caused by decompression melting beneath flexural arches. Geochemical differences from flow reflect “plume” versus “arch-driven” flow [Bianco et al., 2005].
Mantle is heterogeneous on scales smaller than melting zones
Melting depth/temperature is composition-dependent
Vertical variations in upper mantle flow can influence rates that different materials melt
Case 1: Geochemical variations along the Mid-Atlantic Ridge (MAR) near Iceland reflect differences in flow and lithospheric thickness [Ito & Mahoney, 2005]
Case 2: Rejuvenated & arch volcanism in Hawaii caused by decompression melting beneath flexural arches. Geochemical differences from flow reflect “plume” versus “arch-driven” flow [Bianco et al., 2005].
Case 1:Geochemical between Iceland and Mid-Atlantic Ridge
Case 1:Geochemical between Iceland and Mid-Atlantic Ridge
NS
Mantle Flow and Melting Model Mantle Flow and Melting Model
Case 1:Geochemical Variations Along the Mid-Atlantic Ridge
Case 1:Geochemical Variations Along the Mid-Atlantic Ridge
Case 2: Origin of Secondary (Rejuvenated & Arch) Hotspot Volcanism [Bianco et al. 2005]
Case 2: Origin of Secondary (Rejuvenated & Arch) Hotspot Volcanism [Bianco et al. 2005]
Evidence for Arch Uplift Causing Secondary VolcanismEvidence for Arch Uplift Causing Secondary Volcanism
Arch Versus Shield Isotope CompositionsArch Versus Shield Isotope Compositions
Conceptual Model: Decompression of hot plume material beneath arch causes secondary magmatism
Conceptual Model: Decompression of hot plume material beneath arch causes secondary magmatism
Magma Fluxes Beneath Arch vs. ShieldMagma Fluxes Beneath Arch vs. Shield
Example Starting Source Mixture: 90%DM, 9.5%EM, 0.5%PXExample Starting Source Mixture: 90%DM, 9.5%EM, 0.5%PX
Example Model Sources(90% DM, 9.5% EM, 0.05% PX)Example Model Sources(90% DM, 9.5% EM, 0.05% PX)
Successful solutions for lithosphere thickness and
plume potential temperature
Successful solutions for lithosphere thickness and
plume potential temperatureRejuvenated & ArchRejuvenated & Arch ShieldShield
143Nd144Nd
143Nd144Nd
87Sr86Sr
87Sr86Sr
Successful solutions for lithosphere thickness and
plume potential temperature
Successful solutions for lithosphere thickness and
plume potential temperatureRejuvenated & ArchRejuvenated & Arch ShieldShield
143Nd144Nd
143Nd144Nd
87Sr86Sr
87Sr86Sr
Future Opportunities: Relate isotope/trace-element variations to
length scales of flows in upper mantle
Future Opportunities: Relate isotope/trace-element variations to
length scales of flows in upper mantle
Future OpportunitiesFuture Opportunities
Relate upper mantle dynamics to major element chemistry. Will require implementing thermodynamic models of melting (e.g., MELTS).
Lava composition also influenced by melt-solid interaction during magma transport. Requires calculations of magma & solid, chemical, & energy transport.
Relate upper mantle dynamics to major element chemistry. Will require implementing thermodynamic models of melting (e.g., MELTS).
Lava composition also influenced by melt-solid interaction during magma transport. Requires calculations of magma & solid, chemical, & energy transport.
ConclusionsConclusions
Upper mantle processes of solid flow, melting, & magma transport can lead to large variations in magma composition.
Geodynamic models will allow us to use magma geochemistry to infer key aspects of the upper mantle dynamics.
And to quantitatively relate lava composition to source, & thus to understand the chemical structure & evolution of the mantle.
Upper mantle processes of solid flow, melting, & magma transport can lead to large variations in magma composition.
Geodynamic models will allow us to use magma geochemistry to infer key aspects of the upper mantle dynamics.
And to quantitatively relate lava composition to source, & thus to understand the chemical structure & evolution of the mantle.
Melting Beneath Shield vs. ArchMelting Beneath Shield vs. Arch
Shield melt flux (radial flow, Vr) x (fraction extracted,Fe)Shield melt flux (radial flow, Vr) x (fraction extracted,Fe)
Arch melt flux (vertical flow, Vz) x (productivity dFe/dz)Arch melt flux (vertical flow, Vz) x (productivity dFe/dz)