Maximum depth of magnetisation of Australia, its uncertainty, and implications for Curie depth

Abstract

The Curie depth is the depth at which the crust and uppermost mantle cease to be ferromagnetic or ferromagnetic, the main cause of crustal magnetism, due to the action of geothermal effects. One method to estimate the Curie depth for Australia is to map the base of magnetisation derived from observations of magnetic intensity. We have used a nonlinear direct sampling inverse technique to fully explore the parameter space of a fractal forward model of magnetisation. This produces an ensemble of models that allow us to produce maps of both the maximum depth of magnetisation and its uncertainty for Australia. The base of magnetisation varies significantly across the continent, between 10 and 70 km depth, with an uncertainty of 7–10 km. The variations in magnetisation depth conform with the boundaries of geological provinces due to their differing magnetic properties: In general, cratons and older provinces generally show a deeper base of magnetisation results and hence may be inferred to have deeper Curie depths, reflecting that these areas are on the whole cooler. We also find general agreement in our results with known geothermal anomalies.