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doi:10.2204/iodp.proc.323.109.2011 Downhole measurementsThe only downhole measurements made at Site U1345 were three deployments of the APCT-3 tool in Hole U1345A. The measured temperatures range from 4.92°C at 42.4 m DSF to 8.15°C at 108.9 m DSF (Table T20), indicating a local geothermal gradient of 48.5°C/km (Fig. F36). A simple estimate of heat flow can be obtained from the product of the geothermal gradient by the average thermal conductivity (1.064 W/[m·K]; see "Physical properties"), which gives a value of 51.6 mW/m2, which agrees with existing measurement in the area (the global heat flow database of the International Heat Flow Commission can be found at www.heatflow.und.edu/index.html). Considering the variations in thermal conductivity with depth, a more accurate measure of heat flow in a conductive regime can be given by a "Bullard plot," in which the thermal resistance of an interval is calculated by integrating the inverse of thermal conductivity over depth. If the thermal regime is purely conductive, heat flow will be the slope of temperature versus the thermal resistance profile (Bullard, 1939). Thermal resistance calculated over the intervals overlying each APCT-3 measurement is shown in Table T20, and the resulting linear fit of temperature to thermal resistance gives a slightly lower heat flow value of 50.9 mW/m2. |
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