Heat flow through the West Coast, South Island, New Zealand

Bottom-hole temperature data collected from 24 petroleum exploration wells have been used to calculate conductive heat flow through the West Coast, South Island. Steady-state modelling suggests a mean heat flow of 76 +/- 15 mW/m(2) (20%, 1 SD), a figure higher than those obtained previously by Funnell et al. and Funnell & Allis for the southern Taranaki and southwest South Island regions (65-70 mW/m(2) and 60 +/- 4 mW/m(2), respectively). Pliocene-Quaternary erosion over much of the West Coast has probably caused an increase in measured surface heat flow of 25-30 mW/m(2). Localised areas of heat flow in excess of 90 mW/m(2) exist in the Lake Brunner region and at the sites of Card Creek-1 and Matiri-1 wells. Convective effects caused by fluid migration along structural features in these three areas may be responsible for the highly elevated local heat flows. However, calculations of the thermal effects of late Neogene erosion in the southern Taranaki and West Coast regions suggest that the present-day discrepancy in surface heat flows may be largely due to differing magnitudes and rates of erosion.