Thermal state of the Taranaki Basin, New Zealand

Abstract

The Taranaki Basin is an active‐margin basin that has been significantly affected by Miocene subduction tectonics along the Pacific‐Australian plate boundary. We have analyzed its present‐day thermal state using 354 bottom‐hole temperatures (BHTs) from 115 wells distributed throughout the basin. The measured temperatures were corrected using an exact solution to Bullard's equation rather than the Horner approximation, thereby allowing for recovery dependence on well diameter and correction for some BHTs at early time after circulation had ceased. Thermal conductivity measurements were completed on 256 samples from eight wells, and matrix conductivities were determined for six end‐member lithologies by inversion. Formation conductivities are based on the conductivity and relative proportion of each end‐member component. Corrected BHTs, in situ thermal conductivity, and estimates of sediment heat production were combined to compute the present‐day, steady state heat flow. The average heat flow is 60 mW m −2 , but important geographic variations are present: heat flow on the Western Platform is remarkably consistent at 53–60 mW m −2 , attesting to its relative stability since the Late Cretaceous; heat flow in the southern part of the basin is 65–70 mW m −2 due to as much as 3 km of late Miocene erosion; on the southern onshore and to the south of the peninsula, heat flow is 50 ± 3 mW m −2 , possibly due to the heat sink effects of crustal thickening; heat flow is highest at 74 mW m −2 on the northern peninsula adjacent to the Taranaki volcanic zone, suggesting a causal relationship between Quaternary volcanism and high heat flow.