Elastic thickness of the lithosphere in the Marquesas and Society Islands

Abstract

Analysis of sea surface gravity data along six profiles collected during the Crossgrain 2 and EW9103 expeditions to the Marquesas Islands demonstrates that the elastic plate thickness Te is remarkably uniform, with a value of 18±2 km over the entire chain. Given the 50 Ma age of the Marquesan lithosphere at the time of loading, this Te value agrees with the empirical relationship between elastic plate thickness and plate age for hotspot volcanoes in the North Pacific, Atlantic, and Indian oceans. Using more limited gravity data from the Society chain, we find that the best fitting elastic plate thickness there is resolvably higher, 23±2 km. In both cases, our values for Te are larger than those derived from analysis of satellite altimetry profiles. We attribute the low Te values derived from satellite altimetry to inaccuracies in available gridded bathymetric databases for this part of the world and the assumption of a high value for the density of the seafloor. Although our shipboard data sample only two French Polynesian island chains, the results suggest that the amount of elastic plate thinning over the South Pacific Superswell may be less than previously proposed, thus eliminating conflict between estimates of the thermal structure of the Superswell lithosphere as derived from elastic plate thickness and that derived from heat flow, depth anomalies, and Love wave dispersion.