HR: 11:40h
AN: U52A-05    [Abstracts]
TI: Ridge Jumps Associated with Plume-Ridge Interaction 1: Off-axis Heating due to Lithospheric Magma Penetration
AU: * Mittelstaedt, E
EM: mittelst@hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawai'i, Manoa, 1680 East West Rd, Honolulu, HI 96816 United States
AU: Ito, G
EM: gito@hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawai'i, Manoa, 1680 East West Rd, Honolulu, HI 96816 United States
AB: In many hot spot-ridge systems, changes in the ridge axis geometry occur between the hot spot centers and nearby mid-ocean ridges in the form of ridge jumps. Such ridge jumps likely occur as a result of anomalous lithospheric stresses associated with mantle plume-lithosphere interaction, as well as weakening of the hot spot lithosphere due to physical and thermal thinning caused by rising buoyant asthenosphere and magma transport through the lithosphere. In this study, we use numerical models to quantify the effects of excess magmatism through the near-ridge lithosphere. Hot spot magmatism can weaken the lithosphere both mechanically through fracturing and thermally through conduction and advection of heat into the plate. Here we focus on the effects of thermal weakening. Using a plane-strain approximation, we examine deformation in a 2-D cross section of a visco-elastic-plastic lithosphere with the finite element code FLAC. The model has isothermal top and bottom boundaries and a prescribed velocity equal to the half spreading rate is imposed on the sides to drive seafloor spreading. The initial condition, as predicted for normal mid-ocean ridges, is a square root of lithospheric age cooling curve with a corner flow velocity field symmetric about the ridge axis. A range of heat inputs are introduced at various plate ages and spreading rates to simulate off-axis magma transport. To reveal the physical conditions that allow for a ridge jump and control its timing, we vary 4 parameters: spreading rate, lithospheric age, crustal thickness and heat input. Results indicate that the heating rate required to produce a ridge jump increases as a function of lithospheric age at the location of magma intrusion. The time necessary for a ridge jump to develop in lithosphere of a particular age decreases with increasing crustal thicknesses. For magma fluxes comparable to those estimated for Galapagos and Iceland, lithospheric heating by the penetrating magma alone is sufficient to cause a ridge jump, even without the other effects.
DE: 3035 Midocean ridge processes
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 4255 Numerical modeling (0545, 0560)
SC: Union [U]
MN: Fall Meeting 2005