TEMPORAL VARIATIONS OF FLEXURAL DEFORMATION IN HAWAII

We present a simple time-progressive model for the Hawaiian Island cha in bathymetry and the associated flexural response of the elastic ocea nic lithosphere. The model is used to study the vertical tectonic hist ory of Cross seamount, a Cretaceous guyot brought close to the Hawaiia n hot spot by plate motion. Geological evidence indicates that Cross w as truncated at sea level, but its flat top is presently 400 m below s ea level. Our reconstruction suggests the seamount was elevated on the Hawaiian Swell and truncated about 3.2 m.y. ago. The post-truncation subsidence is attributed to the flexural moat that developed around th e growing Hawaiian Islands. Flexural isostatic adjustment explains the current depth of Cross seamount provided the elastic plate thickness is in the 30-35 km range.