Temperature measurements in Hole 395A, Leg 78B ( DSDP, Atlantic).

Abstract

During Leg 78B, we measured borehole temperatures in Hole 395A down to depths of 600m below the seafloor, more than 5yr after the hole had been drilled during Leg 45. Our attempts to measure an equilibrium temperature profile immediately after the initial re-entry were only partly successful, but we were able to obtain an apparent equilibrium profile by extrapolation of a subsequent pair of continuous temperature logs. This profile features an isothermal zone extending from the seafloor over 150m into basement, indicating a vigorous, pressure-driven downhole flow of bottom water into the upper levels of the basement. Results indicate predominantly conductive heat transfer deeper than about 500m below the seafloor. Low temperatures above 500m suggest shallow, lateral hydrothermal circulation in the permeable upper 300-400m of the basement, as modeled by Langseth et al 85P/2274.-from Authors