HR: 1330h
AN: V12B-0586    [PDF]
TI: Rodriguez, Darwin, Wolf,...,A Third Type of Hotspot Island
AU: * Mittelstaedt, E L
EM: staggle@soest.hawaii.edu
AF: Department of Geology and Geophysics, University of Hawaii, 1680 East-West Road, Honolulu, HI 96816 United States
AU: Ito, G
EM: gito@hawaii.edu
AF: Department of Geology and Geophysics, University of Hawaii, 1680 East-West Road, Honolulu, HI 96816 United States
AB: Hotspot-ridge interactions are associated with broad seafloor swells as well as localized volcanic features such as island chains and volcanic lineaments. In several cases, notably the Galapagos, Reunion, and Kerguelen hotspots, volcanic lineaments extend from presumed off-axis hotspot centers toward nearby mid-ocean ridges. It has been proposed that such lineaments are caused by channeling of hot asthenosphere from off-axis mantle plumes toward mid-ocean ridges. Besides the classical concept of a hotspot island chain, this is a second mechanism to form volcanic lineaments [Morgan, 1978]. Alternatively, other workers suggest that these lineaments are controlled by the pattern of stress in the lithosphere. We examine this latter hypothesis by considering the effects of buoyant uplift and asthenospheric shear on the base of the lithosphere induced by a mantle plume. We simplify this 3-D problem by treating the lithosphere as a thin plate and calculating the plan view pattern of depth-integrated stresses, or stress resultants. The effects of plume shear and uplift are treated as horizontal loads on the plate. We calculate the contributions to stress resultants by approximating these loads as point forces distributed over the plate and superposing the associated Kelvin solutions. The ridge is simulated as a line experiencing uniform tension in the direction of seafloor spreading using a boundary element method. Final stress resultants are thus the combined effects of plume uplift and shear subject to the ridge boundary conditions. Results show that plume-ridge interaction can introduce anomalous tension in the lithosphere with trajectories of least tensile stress resultants radiating away from the plume center toward the ridge. We propose that magma below the lithosphere will exploit this stress resultant pattern, tending to form dikes and volcanic lineaments along these stress resultant trajectories. This is yet a third possible mechanism to form volcanic chains or lineaments over hotspots.
DE: 3035 Midocean ridge processes
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8164 Stresses--crust and lithosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting