Two reliable determinations of downhole temperatures were made at depths of 32.9 and 65.5 mbsf at Site 1174 using the Adara temperature tool and the Davis-Villinger temperature probe (DVTP). Table T23 summarizes the deployments, and the station data are shown in Figures F44 and F45. A DVTP measurement at 165.5 mbsf was considered unreliable because of a faulty thermistor. A measurement attempt at 209.1 mbsf was not successful because the temperature record indicated invasion of seawater. No deeper penetrations were attempted.
In situ temperatures were estimated by extrapolation of the station data to correct for the frictional heating on penetration using an average thermal conductivity of 1.0 W/(m·°C). The estimated in situ temperatures from the mudline temperature and the two measurements suggest a linear gradient of 0.183°C/m in the upper 65.5 m (Fig. F46). For thermal conductivities of 1.0 W/(m·°C), conductive near-surface heat flow at Hole 1174A would be 183 mW/m2. This value is considerably higher than estimated for ODP Site 808, located 3 km arcward (130 mW/m2; Taira et al., 1991). However, seafloor heat flow data show considerable variability near the deformation front (Yamano et al., 1992).
Assuming purely vertical conductive and steady state heat flow, in situ temperatures of ~140°C are projected at the bottom of the hole (see "Physical Properties"). However, because this site is located near the deformation front, it may have experienced input of warm fluids or faulting that would render this assumption invalid. Because both influx of warm fluids and thrust faulting would cause near-surface heat-flow measurements to overestimate heat flow from basement, 140°C should be considered a maximum value.
Pressures were also recorded during a DVTP-P deployment at 65.5 msbf (Fig. F47). As noted in "In Situ Temperature and Pressure Measurements" in the "Explanatory Notes" chapter, postcruise modeling and processing is required to estimate in situ pressures, but preliminary interpretation of the raw data indicates a near-hydrostatic pressure, which is not unexpected at this relatively shallow depth.