EXPLORATION OF MIDOCEAN RIDGES WITH A FREQUENCY-DOMAIN ELECTROMAGNETIC SYSTEM

Electromagnetic-survey methods using controlled sources have been applied to ocean floor and mid-ocean-ridge surveys and have shed new light on the distribution of fluids within these structures. The present state of knowledge of the electrical nature of oceanic crust is reviewed and some alternative mid-ocean-ridge electromagnetic surveys are simulated using a numerical-modelling algorithm to see what further information they could provide. This simulation considers the response of both large-scale crustal targets such as magma bodies and zones of hydrothermal circulation, and also the effect of near-surface heterogeneity that may spatially alias the data. The magnitude of this heterogeneity is estimated and it is shown that it could be large enough to prevent useful structural constraints being obtained. If the effect spatial aliasing was negligible, or could be removed, a trans-ridge experiment could delinate zones of partial melting and hydrothermal circulation within the oceanic crust.