Gravity and magnetic modelling of crustal structure in central Victoria: What lies under the Melbourne Zone?

Abstract

Three gravity and magnetic profiles through the central and eastern part of the Melbourne Zone, Lachlan Fold Belt, have been modelled, with tight control from surface geology to investigate the deep crust. The largely non-magnetic upper crust (folded Ordovician to Lower Devonian strata of the Melbourne Zone intruded by Devonian granite plutons) has been modelled using recently acquired density measurements, providing a good match with the gravity profiles. The top of the basement is modelled at ~10-15 km depth in the centre of the zone, and ~8-10 km depth in the south of the zone, reflecting a thinning of the folded cover sequence toward the south, consistent with outcrops of basement Cambri..