HR: 09:10h
AN: V41G-05    [Abstracts]
TI: Ridge jumps associated with plume-ridge interaction: Mantle plume-lithosphere interaction and hotspot magmatism
AU: * Mittelstaedt, E
EM: mittelst@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East West Rd., Honolulu, HI 96816, United States
AU: Ito, G
EM: gito@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East West Rd., Honolulu, HI 96816, United States
AB: Interaction of mantle plumes and young lithosphere near mid-ocean ridges can lead to changes in spreading geometry by shifts of the ridge-axis toward the plume as seen at various hotspots, notably Iceland and the Galapagos. Previous work has shown that, with a sufficient magma flux, heating of the lithosphere by magmatism can significantly weaken the plate and, in some cases, could cause ridge jumps. Upwelling hot asthenosphere can also weaken the plate through thermal and mechanical thinning of the lithosphere. Using the finite element code CITCOM, we solve the equations of continuity, momentum and energy to examine deformation in near-ridge lithosphere associated with relatively hot upwelling asthenosphere and seafloor spreading. The mantle and lithosphere obey a non-Newtonian viscous rheology with plastic failure in the cold part of the lithosphere simulated by imposing an effective yield stress. Temperatures of the lithospheric thermal boundary region are initially given a square-root of age thermal profile while a hot patch is placed at the bottom to initiate a mantle-plume like upwelling. The effect of upwelling asthenosphere on ridge jumps is evaluated by varying three parameters: the plume excess temperature, the spreading rate and the distance of the plume from the ridge axis. Preliminary results show plume related thinning and weakening of the lithosphere over a wide area (100's of km's) with the rate of thinning increasing with the excess temperature of the plume. Initially, thinning occurs as the plume approaches the lithosphere and asthenospheric material is forced out of the way. As the plume material comes into contact with the lithosphere, thinning occurs through heating and mechanical removal of the thermal boundary layer. Thinning of the lithosphere is one of the primary factors in achieving a ridge jump. Another is large tensile stresses which can facilitate the initiation of rifting at this weakened location. Model stresses induced by the buoyant asthenosphere are significant fractions of the lithospheric yield strength near the plume and reach a maximum at the center of plume upwelling. Models predict that ridge jumps are not likely to occur by lithosphere interaction with the hot upwelling plume alone but require the added effects of magmatic weakening at the hotspot.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8164 Stresses: crust and lithosphere
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting