Xenolith geotherms and crustal models in Eastern Australia

Lower crust and upper mantle rocks occurring as xenoliths in basaltic host rocks from eastern Australia have been used to provide pressure and temperature estimates which allow the construction of an empirical geotherm consistent with variations in the deep-seated stratigraphy. High gradients in the resulting geotherm at shallow depths (24-30 km) are inconsistent with thermal conduction models for heat flow. Consequently new models are proposed incorporating heat input from basaltic intrusions around the crust-mantle boundary. The best fit to the empirical geotherm is obtained if the basaltic magma is assumed to form a layer 4 km thick at 28 km depth with rates of intrusion approaching 900 m/Ma. This model is consistent with tectonic uplift rates for the eastern Highlands and with seismic reflection profiles showing a layered lower crust.