Thermal measurements and seawater downflow into 35-Ma-old ocean crust, central North Atlantic.

Abstract

Measurements of temperature gradients in sediments, thermal conductivity and drill-hole temperatures (by wireline logging) were made in 3 holes drilled into basement in 35Ma-old crust in the central N Atlantic during DSDP Leg 82. The temperature gradient and thermal conductivity values make a reliable estimate of the ambient heat flow value possible. Downhole temperatures measured by wireline logging after drilling indicate cooling of the hole in excess of that expected from the drilling process. This excess cooling effect is interpreted as a result of a substantial downflow of ocean water; a lower limit to the necessary volume of flow is derived from the data. If the downflow is a secondary effect of hydrothermal circulation within oceanic crust, these data support the increasing body of evidence that hydrothermal circulation continues within ocean crust to considerable ages covered by a blanket of sediment allowing only conductive heat flow. -AuthorsDept of Geol, Leicester Univ, Univ Rd, Leicester, LE1 7RH, UK.