OCEANIC SPREADING CENTER HOTSPOT INTERACTIONS - CONSTRAINTS FROM ALONG-ISOCHRON BATHYMETRIC AND GRAVITY-ANOMALIES

We analyzed bathymetric and gravity anomalies along present and paleoaxes of oceanic spreading centers influenced by the Iceland, Azores, Galapagos, Tristan, and Easter hotspots. Residual bathymetry (up to 4.7 km) and mantle Bouguer gravity (up to -340 Irm) anomalies are maximum at on-axis hotspots and decrease with increasing ridge-hotspot separation distance (D), until becoming insignificant at D similar to 500 km. Along-isochron widths of bathymetric anomalies (up to 2700 km) depend inversely on paleo-spreading rate, reflecting the extent to which plume material will flow along axis before being swept away by the spreading lithosphere. Flux balance arguments suggest that the five hotspots feed material to ridges with comparable fluxes of similar to 2.2 x 10(6) km(3)/m.y. Assuming that the amplitudes of these geophysical anomalies reflect temperature-dependent crustal thickness and mantle density variations, we suggest that ridge temperature anomalies are maximum (150-225 degrees C) when plumes are ridge centered and decrease with increasing ridge-hotspot distance due to cooling of the ridgeward-migrating plume material.