HR: 08:00h
AN: V31F-01    [Abstracts]
TI: Explaining the Morphological Range of Hotspot Tracks Formed by Plume-Ridge Interactions: Towards a 3D Crustal Flow Model for the Oceanic Crust
AU: * Haugh, E
EM: haughe@tcd.ie
AF: Dept. of Geology, Trinity College, University of Dublin, College Green, Dublin, Dublin, 2, Ireland
AU: Jones, S M
EM: stephen.jones@tcd.ie
AF: Dept. of Geology, Trinity College, University of Dublin, College Green, Dublin, Dublin, 2, Ireland
AB: Hotspot tracks formed by plume-ridge interactions show a large morphological diversity. The Greenland-Iceland- Faroes Ridge (GIFR) forms a sharp-edged plateau, with width of up to 700 km. The observed plateau which forms the GIFR is not a direct reflection of the underlying mantle convective structure, as it is at least three times wider than the Iceland plume, as imaged by seismic studies. Other tracks caused by ridge-hotspot interaction (e.g. segments of the Walvis and Chagos ridges) tend to be triangular with widths of about 300 km. It has been recently suggested that ductile flow of the lower crust is an important process in the explanation of off- axis crustal thickness changes in Iceland. Here we suggest that the dominant effect which produces the vastly different structure seen at the GIFR is the relatively slow spreading rate compared to those at the other ridges for which observations of plume-ridge interactions have been made. As a result of this slower spreading rate there are larger crustal thickness gradients, and this means that off-axis crustal mass distribution is an important factor. Two-dimensional modelling has previously been used to show that the crustal flow process can cause a morphology similar to what is observed, and that the flow must be primarily parallel to the axis. The present study considers the three-dimensional crustal flow problem, comparing and contrasting results using two different approaches to modelling very viscous flow: lubrication theory (`thin layer') and flow at low Reynolds number ('slow flow'). Initial work suggests that lubrication theory can only provide an accurate solution for the lower part of the channel in which the flow occurs, and that the 'slow flow' approach is more suitable elsewhere in the model. Further work will involve extending the model to incorporate more geologically reasonable boundary conditions and an analysis of the importance of hydrothermal cooling.
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting