Geo-electrical responses associated with hydrothermal fluid circulation in oceanic crust: feasibility of magnetometric and electrical resistivity methods in mapping off-axis convection cells

Abstract

Recent developments in theory and instrumentation have led to increasing interest in the use of geo-electrical techniques to map seafloor structure and to explore mineral deposits. Electrical experiments conducted at sea are difficult and costly to perform, reinforcing the need for theoretical design studies before any sea­going programs get underway. I present in this paper the first theoretical investigation of geo-electrical responses associated with hydrothermal fluid circulation in a mid-ocean ridge flank environment. A 2D conceptual electrical model is constructed based on hydrothermal modelling results, and its responses to two major ?galvanic? techniques (magnetometric resistivity (MMR) and electrical resistivity methods) are calculated using a finite difference computer package. Forward modelling results reveal that the marine MMR method is capable of detecting off-axis hydrothermal convection cells with equivalent or even greater resolution than traditional seafloor heat flow surveys. However, the electrical resistivity method is not applicable because this system suffers a very severe ?shorting effect? of the overlying seawater layer, which almost totally masks the contribution from the underlying oceanic crust.