HR: 1340h
AN: T23A-0529    [Abstracts]
TI: Plume-Lithosphere Interaction Beneath a Moving Plate: 3-D Numerical Explorations
AU: * Yamamoto, M
EM: michiko@geology.cornell.edu
AF: Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853 United States
AU: Phipps Morgan, J
EM: jp369@cornell.edu
AF: Earth and Atmospheric Sciences, Cornell University, Snee Hall, Ithaca, NY 14853 United States
AU: Parmentier, E
EM: EM_parmentier@Brown.edu
AF: Geological Sciences, Brown University, 324 Brook Street, Providence, RI 02912 United States
AB: Two prominent features mark the passage of oceanic lithosphere over a hotspot. The first is the initiation of oceanic volcanism leading to a chain of islands or seamounts. The second is the generation of a ~1-km-high, ~1000-km-wide bathymetric swell around the volcanic island chain. While hotspot swells are well-accepted bathymetric features, their origin is still controversial. At least three different mechanisms have been proposed for swell generation: (1) Thermal reheating (or 'rejuvenation') of the lithosphere within a ~1000-km region centered on the hotspot; (2) Compositional underplating of depleted, hence more viscous mantle residue from hotspot melting; (3) Dragging of hot and less viscous plume asthenosphere by the overriding lithosphere. The primary reason for the multiplicity of theoretical models for the origin of swells is that there are few geophysical constraints on the structure of the lithosphere and sub-lithosphere beneath a swell. Here we use numerical experiments to explore the consequences of these different scenarios for plume-lithosphere interaction. We use a 3-D variable viscosity finite difference code that incorporates the effects of melting on changing the density and viscosity of melted mantle to study different modes of a plume rising beneath moving lithosphere. Several scenarios are assessed for plumes rising beneath young and old moving lithosphere: (1) A buoyant plume rising within an isoviscous mantle beneath a more viscous oceanic lithosphere; (2) A temperature-dependent low-viscosity buoyant plume impinging on (cooler) more viscous oceanic lithosphere; (3) A temperature and composition-dependent rheology where hotspot melt extraction leads to a higher than asthenosphere viscosity within the most melted and depleted portions of the restite residues created by plume upwelling and melting. In contrast to the first two scenarios, the latter scenario can lead to efficient mechanical plume erosion of the lowermost ~25km of overlying lithosphere, a region whose viscosity is comparable to that of the restite swell-root. We also examine the effects of an obliquely-striking fracture zone passing over the plume and compare the predicted melt distribution and swell-evolution with the observed asymmetries of the Hawaiian swell around the Molokai Fracture Zone.
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3225 Numerical approximations and analysis (4260)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Tectonophysics [T]
MN: Fall Meeting 2005