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doi:10.2204/iodp.proc.342.109.2014 Downhole loggingHeat flowHeat flow at Site U1408 was determined according to the procedure of Pribnow et al. (2000). Four temperature measurements were made in Hole U1408A using the advanced piston corer temperature tool (APCT-3), including a measurement of the mudline temperature at the seafloor. The deployment during Core 324-U1408-4H was lost when the APCT-3 failed to couple properly with the formation and the recorded data could not be used. Measured heat flow values ranged from 5.1°C at 61.3 m drilling depth below seafloor (DSF) to 7.39°C at 118.3 m DSF (Table T24), giving a geothermal gradient of 39.2°C/km (Fig. F36). The seafloor temperature was 2.72°C based on the average of the four minimum temperature values in the APCT-3 temperature profiles. Thermal conductivity measured in the laboratory was converted to in situ values using the method of Hyndmann et al. (1974) (see “Physical properties” in the “Methods” chapter [Norris et al., 2014a]). The calculated in situ values are ~2.5% lower than the measured laboratory values. Considering the variations in thermal conductivity with depth, a measure of heat flow in a conductive regime can be given by a “Bullard plot.” Thermal resistance is calculated by cumulatively adding the inverse of the in situ thermal conductivity values over depth intervals downhole. If the thermal regime is purely conductive, the heat flow will be the slope of the temperature versus the thermal resistance profile (Bullard, 1939). The thermal resistance calculated over the intervals overlying the APCT-3 measurements is shown in Table T24, and the resulting linear fit of the temperature gives a heat flow value of 43.4 mW/m2, which is a typical value for the ocean floor. |
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