Thermal properties of the AND-2A borehole in the southern Victoria Land Basin, McMurdo Sound, Antarctica

Abstract

The ANDRILL (Antarctic Geological Drilling Program) Southern McMurdo Sound Project (SMS) drilled a 1138-m-deep borehole (AND-2A) within Neogene strata in the southern Victoria Land Basin of the West Antarctic Rift in the Ross Sea, Antarctica, during the 2007–2008 austral spring. An extensive downhole logging program was carried out in the SMS borehole that included temperature and spectral gamma ray logs. These logging data were combined with lab measurements of the thermal conductivity of core samples to deduce several thermal parameters of the borehole country rock. The results indicate a bottom-hole temperature of 57.8 °C and an average temperature gradient of 51.9 K/km. Thermal conductivities on core samples range from 1.22 to 2.95 W/mK and average 1.57 W/mK. Thermal conductivities coupled with the average temperature gradient yield an average heat flow of 81.5 mW/m2, a minor amount (1.1 mW/m2) of which is generated by radiogenic heat production. Temperature, gradient, and heat flow are considered as possible minimum values. The average heat flow determined for the SMS borehole therefore provides important confirmation that heat flows are locally above average values for continental crust in the southern Victoria Land Basin of the West Antarctic Rift system. This new heat flow constraint is consistent with extension and volcanism within the Terror Rift, which was active in Neogene time.