Deep crustal geothermal measurements, Hole 504B, Deep Sea Drilling Project Legs 69 and 70.

Seven temperature logs at Deep Sea Drilling Project Hole 504B reveal the geothermal state of the ocean crust to a depth of 836 m. A linear temperature profile in the 275 m of sediments fixes the heat flow at 196 W/m², by dominantly conductive means. Two logs after Leg 69 drilling to 489 meters strongly indicate drawdown of bottom water into basement. Equilibrium temperatures fix the flow rate at 90+ or -5 m/hr, and indicate that the mass flux is directed into a thin zone from 330 to 360 m sub-bottom. Extrapolation to equilibrium temperature of two logs after completion of all drilling shows that the gradient is linear from 489 to 837 m, with a dominantly conductive heat flow of 188 mW/m², in excellent agreement with the value obtained in the sediments. In combination with the in situ pressure data of Zoback and Anderson (this volume) , the temperature data indicate that the aquifer from 330 to 360 meters has anomalously high permeability of 0.2 darcy (2 X 10^-13m²), and extends radially at least 1 km from the hole. -Authors