Depth and geoid anomalies over oceanic hotspot swells: A global survey

Abstract

The broad depth and geoid anomalies associated with 23 hotspot swells in oceanic areas have been analyzed. Maximum height and geographical extent of the topographic swell, and of the geoid anomaly as well, have been measured for each hotspot. The results indicate a clear increase of the topographic swell height with age of the underlying lithosphere, from values in the range 300–500 m at young ages to values in the range 1500–2000 m at ages larger than 100 Ma. The geoid anomaly amplitude also increases with plate age from nearly zero close to mid‐ocean ridges, to 6–8 m over old plates. On the other hand, the geographical extent of the swell does not show any clear relationship with plate age. The mean lateral extent of swells range from 1000 to 1500 km. Swells located close to spreading ridges show a significant non zero depth anomaly but are associated with negligeable geoid signal. These results complete those of a previous study where the apparent compensation depth of oceanic hots pot swells was showed to increase linearly with the square root of plate age and coincide roughly with the base of the thermal lithosphere. This trend may either be interpreted in terms of lithospheric thinning or dynamical support. Besides both seem necessary to explain the observed bathymetry, in proportion evolving with aging of the lithosphere.