Implications for geothermal profiling from magnetotelluric data

Abstract

Laboratory studies of the temperature dependence of the electrical conductivity of rock materials can be used to relate electrical conductivity to temperature in the Earth. Electrical conductivity models advanced for central and southeastern Australia are compared with profiles predicted from such laboratory measurements, and are then used to generate representative magnetotelluric response curves. The response curves differ sufficiently to give confidence in their use to detect gross conductivity changes at depth. Observed data from Broken Hill and Ivanhoe, NSW, are interpreted to indicate a temperature contrast in the upper mantle of some 200°C between these two sites (hotter to the east beneath Ivanhoe). The temperature at these large depths is a vital factor in constraining models of crustal underplating and intrusion.