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doi:10.2204/iodp.proc.346.105.2015

Downhole measurements

In situ temperature and heat flow

APCT-3 downhole temperature measurements were performed in Hole U1424A at two depths, including the mudline. In situ temperature was 4.45°C at 35.3 m CSF-A. Because this value was in good agreement with the in situ temperature data set acquired at the same site during Leg 127 (Site 794 [Shipboard Scientific Party, 1990]), no additional APCT-3 measurements were performed at Site U1424 (Fig. F41). The bottom water temperature at this site was estimated to be 0.45°C, based on the average mudline temperature. The lowest temperature measured at the mudline was 0.22°C and was in good agreement with temperatures measured at Sites U1422 and U1423.

At Site 794, the measured geothermal gradient was 125°C/km (Shipboard Scientific Party, 1990) and the estimated heat flow ranged between 103 (Shipboard Scientific Party, 1990) and 105 mW/m² (Langseth and Tamaki, 1992). Heat flow has been reestimated following the method proposed by Pribnow et al. (2000) (Fig. F41). In order to assess the possible impact of thermal conductivity measurements on heat flow estimates, this estimation has been done using two distinct sets of thermal conductivity data (Leg 127 Site 794 and Expedition 346 Site U1424; see “Physical properties”) and a geothermal gradient of 125°C/km. The calculated heat flows were 106 and 107 mW/m², respectively, and were in good agreement with previous calculations at this site.

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