A TIME-DOMAIN ELECTROMAGNETIC SURVEY OF THE TAG HYDROTHERMAL MOUND

A conductivity survey of the TAG mound was made using innovative trans ient electric dipole-dipole instrumentation. The receiver was deployed on the sulfide mound 30 m south of the central black smoker while the submersible ALVIN carried the transmitter on a survey path around the receiver at a radius of approximately 70 m. Conductivity measurements of the seafloor between the transmitter and receiver were made at 5 m inute intervals. The survey lasted 4 hours. Measurements made at 12 si tes are initially interpreted in terms of an apparent conductivity of a uniform seafloor. A more complex model in which the seafloor has two layers is then used. Apparent conductivities range from 1.4 to 15.9 S /m, generally higher than that of seawater. The results suggest possib le focusing of hydrothermal convection in the northern quadrant of the mound, adjacent zones of anhydrite accumulation and fluid convection in the north-eastern quadrant, heterogeneity and layering in the Kreml in zone, and unexpected spatial variability in the western quadrant. T he data from several sites show evidence of distortion attributed to 3 -D anomalies.