Heat Flow in the Upper Part of the Oceanic Crust: Synthesis of In-Situ Temperature Measurements in Hole 504B [chapter]

R. Gable, R. Morin, K. Becker, P. Pezard
1995 Proceedings of the Ocean Drilling Program, 137/140 Scientific Results  
A series of temperature logs was obtained from Hole 504B during Deep Sea Drilling Project (DSDP)/Ocean Drilling Program (ODP) Legs 69, 70, 83, 92, and 111; Legs 137 and 140 provided additional opportunities to measure the temperatures in the hole five years after the thermal disturbance produced during Leg 111. The successive temperature profiles recorded over the seven-year time span between Leg 69 and Leg 111 depict a slow return to thermal equilibrium in the hole resulting principally from a
more » ... gradually diminishing downward flow of cold ocean bottom water with time. Trend analysis and numerical simulations following the results of Leg 111 had forecast the gradual decay and perhaps complete cessation of downward flow by the time of Leg 137 in 1991. However, temperatures measured during Leg 137 revealed a remarkable renewal of downward flow into the hole at implied volumetric flow rates similar to those detected during Leg 83 some 10 years earlier. Moreover, the temperature log obtained during Leg 140 indicated much slower downward flows and, thus, a return to conditions approaching hydrostatic. These two latest temperature logs provide direct evidence of a highly transient and episodic hydrologic system that is contrary to previous conceptual models. Conductive heat flow in the deeper part of the hole is estimated from Leg 137 measurements to be 126.9 ± 21 mW/m 2 , a value that is consistent with the Leg 111 heat-flow estimate of 120 mW/m 2 across the same interval. A systematic reduction in conductive heat flow with depth was observed in the hole during Leg 137, as it was during Leg 111. A detailed comparison of these two data sets spanning almost five years indicates that long-term, residual cooling of the formation may have resulted from earlier drilling into the lower part of the hole.
doi:10.2973/odp.proc.sr.137140.036.1995 fatcat:sgc32r2wk5hafeo2tbf65q46qq