This project involves theoretical models aimed at under- standing mid-ocean ridge spreading centers and seafloor struc- ture. The principal investigators have developed 2-D time- dependent convection models that show that thermal and composi- tional density stratification of the mantle beneath spreading centers can lead to fluctuations in crustal thickness. They will now consider the effect of lower mantle viscosities and will specifically test whether high frequency variations in crustal thickness result that might explain the origin of abyssil hill lineations. They will construct 3-D models of magma flow beneath ridges, including flow in a ridge axis conduit to investigate the origin of the inside-corner bathymetric high at ridge-transform interestions and the asymmetry of the median valley near intersections. They will also explore a model for ridge segmentation and episodic spreading based on stresses and deformation in the lithosphere rather than convection in the mantle.
