Geophysical tests of petrological models of the spreading lithosphere

Abstract

The cooling of the lithospheric plate as it moves away from its source in oceanic ridges should result in lateral zonation, because the varying pressure-temperature field induces thermal contraction, phase changes, and other changes in physical properties. We assume that the source region and the base of the lithosphere are at the solidus. Petrological models are constructed for peridotite, gabbro, and other starting materials. For each model, the topographic change, gravity anomaly, heat flow, surface-wave dispersion, P delay, and seismic refraction curves are computed as a function of distance from the ridge. The results show how appropriately designed experiments can distinguish between models. The few experimental data now available, if accepted, lead to the definite elimination of some models. No models fit all the available data. This may be because the data are incomplete and erroneous. The models may have been poorly posed. A preferred model, which fits a more restrictive data subset chosen by the authors, is tentatively offered. It consists of a lithosphere with gabbro and peridotite in the upper part and a mixture of garnet peridotite with pockets of eclogite in the lower part.