The direction of magma flow in the formation of the Ferrar Large Igneous Province 180 million years ago, Coombs Hills, Victoria Land

Exposed at Coombs Hills are vertical bladelike bodies of basaltic rock that cut across older white sedimentary rocks and through deposits of a Jurassic volcanic complex (Mawson Formation). The majority are inferred to be related to lava eruptions at the surface but there is no evidence that any of them pre-dated the explosive activity that produced the Mawson Formation. How magma reached the surface to feed massive basaltic lava flows of the Ferrar Large Igneous Province at Coombs Hills was investigated. Numerous rock samples were analysed by anisotropic magnetic susceptibility (AMS). Field observations of dyke texture, vesicularity, crystal population and lithic fragment content, dyke contacts with the country rock and joint patterns within the dykes was recorded. Systematic field investigations, aerial photograph studies of dyke orientation patterns and cross cutting realtionships between Jurassic Ferrar Dolerite dykes and associated fractures in the area, the fracture length distribution analysis of the dykes, a petrological study to determine mineralogy and degree of glassiness (which is a good indicator of magma fluidity) and a geochemical study of collected rock samples was used to interpret the overall magma distribution of the area.