Age versus depth relationship of normal oceanic basement in the Argentine Basin

Abstract

To explain the deviation of large areas of seafloor from "normal" age-depth relations, Heestand and Crough [ 1 98 1 ] proposed that hotspots perturb the normal cooling process of ocean lithosphere, and thereby cause flattening of the age-depth relation. Because most other old seafloor has been thermally perturbed during its evolution, Heestand and Crough [1981) suggest the Argentine Basin in the South Atlantic as an appropriate region to test their hypothesis that seafloor that is both old and distant from hotspots cools according to the half-space model. Because of the errors contained in globally gridded topography datasets (ETOP05) [Smith, 1993], this study tests Heestand and Crough's [ 198 1 ] hypothesis using precision depth recorder (PDR) and single-channel seismic data from the Argentine Basin. A simple linear fit of the depth (m) to basement as a function of NFt (Ma)" yields d(t) = (2313 ︢16) + (431 ︢9),Ft with a RMS error of 157 m. However, a quadratic fit to the data gives a lower RMS error of 128 m for the age-depth relation d(t) = (27499︢5)+(2513︢4)@t +(153︢)t. Since neither the half-space nor the plate model exhibits this type of behavior, a model combining half-space cooling of the lithosphere and dynamic flow in the asthenosphere is employed [Phipps Morgan and Smith, 1992] to explain the second-degree polynomial relation. This new relation may have significant implications for a weak asthenosphere layer which is fed from below by mantle plumes [Phipps Morgan and Smith, 1995].