HR: 0830h
AN: T41C-0240    [PDF]
TI: Iceland, the Scotian Basin, and the Farallon Slab: Dynamic Topography of the North Atlantic
AU: * Conrad, C P
EM: cpconrad@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C.C. Little, 425 E. University Ave., Ann Arbor, MI 48109 United States
AU: Lithgow-Bertelloni, C
EM: crlb@umich.edu
AF: Department of Geological Sciences, University of Michigan, 2534 C.C. Little, 425 E. University Ave., Ann Arbor, MI 48109 United States
AU: Louden, K E
EM: Keith.Louden@Dal.Ca
AF: Department of Oceanography, Dalhousie University, 1355 Oxford St., Halifax, NS B3H 4J1 Canada
AB: Upwelling or downwelling flow in the Earth's mantle is thought to elevate or depress the earth's surface on a continental scale. Direct observation of this ``dynamic topography'' has been elusive, however, because it is obscured by isostatically-supported topography caused by near-surface density variations. We calculate the non-isostatic topography of the North Atlantic by correcting seafloor depths for the isostatic effects of lithospheric cooling and sediment loading. We also predict dynamic topography of the North Atlantic seafloor using a model of mantle flow driven by tomographically-inferred mantle densities. Predicted and observed topography fields show several similar features, suggesting that these features have a dynamic, rather than isostatic, origin. We show that anomalously high topography near Iceland and the Azores can be predicted dynamically, but that only the Icelandic high has an upper mantle origin, which suggests a different dynamic origin for these hotspots. The Scotian Basin, an anomalously deep area off the coast of Nova Scotia, may be associated with the downwelling component of edge-driven convection at the continental boundary. Finally, we find that seafloor west of the Mid-Atlantic Ridge is an average of 0.5 km deeper than it is to the east. About 50-80% of this topographic difference can be explained by dynamic topography associated with downwelling of the Farallon slab, which is currently situated in the lower mantle beneath the east coast of North America. The fact that a whole mantle flow model underpredicts the North Atlantic dynamic topography while successfully predicting the geoid (60% variance reduction) may suggest additional complexity for mantle flow. One possibility is that upwelling flow experiences stronger layering, and thus produces less dynamic topography, than slab-induced downwelling flow.
DE: 1214 Geopotential theory and determination
DE: 3045 Seafloor morphology and bottom photography
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8164 Stresses--crust and lithosphere
DE: 9325 Atlantic Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting