The direction of magma flow in the formation of the Ferrar Large Igneous Province 180 million years ago, Mt Gran and Terra Cotta Mountain, Victoria Land

An outcrop of the 'plumbing system' of one of the largest volcanic events known was investigated at Mt Gran and Terra Cotta Mountain (Victoria Land) to determine how magma reached the surface to feed massive basaltic lava flows of the Ferrar Large Igneous Province. The study provides information on the properties of the magma that was moving through Gondwana Land 180 million years ago. To determine flow direction, numerous rock samples were take for rock-magnetic analysis using anisotropic magnetic susceptibility (AMS) which measures the alignment of magnetic minerals with orientated rock samples. AMS was cross checked by measuring the alignment of elongated phenocrysts within the same samples. A group of samples was analysed for major and trace elements as a parallel with orientated AMS samples. This allowed the identification of different magma types to draw conclusions on the timing of intrusions, whether single dikes record one or multiple magma injections and how sills and dikes are related to one another. Samples were searched for melt inclusions in crystals to assess magma volatiles at phenocryst forming depths. A single large intrusion with distinct compositional layering was measured for composition, thickness, 3d shape and extent of the layers. Traverses of closely spaces samples from their base to the top, couple with descriptions of the appearance of the rocks, layers and mineral alignment was recorded. Detailed photos of the traverses was used to add detail to sample descriptions. Samples were collected for geochemistry, AMS and mineral alignment studies.