A Re-evaluation of the Geothermal Potential in Western Queensland, with Stochastic Thermal Modelling

Abstract

A large subsurface elevated temperature anomaly is well documented in Central Australia. High Heat Producing Granites (HHPGs) intersected by drilling at Innamincka are often assumed to be the dominant cause of the elevated temperatures, although their presence in other parts of the temperature anomaly has not been confirmed. Geological controls on the temperature anomaly remain poorly understood. Additionally, methods previously used to predict temperature at 5 km depth in this area are simplistic and possibly do not give an accurate representation of the true distribution and magnitude of the temperature anomaly. We propose a new temperature map at 5 km depth for the Queensland part of the temperature anomaly and re-evaluate the geological controls on the geothermal potential using a stochastic thermal model. Estimated temperature and heat flow at 5 km depth are most sensitive to the thermal conductivity of the strata. Nevertheless, the lack of correlation between the predicted geothermal gradient and the inverse of mean thermal conductivity of the sedimentary cover thickness suggests that thermal blanketing is not the sole cause of high geothermal gradients. In addition, the small mean temperature errors between modelled and observed temperature profiles indicate that the assumption of steady-state, purely conductive heat transfer may be valid and that effects of advective, convective or transient heat transfer are likely to be minor on the regional scale. Estimations of the relative contributions of mantle versus crustal heat input from below 5 km depth suggest that the observed high geothermal gradients are unlikely to be generated by elevated mantle heat flow alone. Consequently, we conclude that the crust between 5 and 40 km depth is relatively high heat producing in the region of anomalously high crustal temperatures. Our study supports evidence for a felsic continental lower crust enriched in heat producing elements. A SW-NE trend of lower heat flow and inferred average heat production through the study area correlates with structural trends and may relate to zones of thinned continental crust and therefore lower total crustal heat production.