Magma ascent dynamics at Mount Gambier (Berrin) Volcano, Newer Volcanics Province, Australia: Insights from olivine textures and compositions

Australia hosts at least two continental basaltic volcanic provinces with Holocene eruption ages, yet little is understood about magma ascent and mantle to surface magmatic pathways and timescales in these regions. Such information advances our understanding of potential eruption warning timeframes of future volcanic activity. In this study we conducted mineral-scale textural and chemical investigation of a suite of stratigraphically constrained volcanic rocks from the Mount Gambier (Berrin) volcano. The ~5 ka maar-cone complex is the youngest volcano within the Newer Volcanics Province and mainland Australia and produced effusive magmatic to explosive (VEI 4) phreatomagmatic eruptions. The textural diversity and chemical zoning patterns in olivine and clinopyroxene in the volcanic rocks reveal a complex history of magma ascent. Olivine is classified into several types based on texture and composition: Normally zoned olivine at the margins of mantle xenoliths and rims of mantle-derived xenocrysts; skeletal, euhedral and polyhedral diffuse normally zoned (dominant type); reversely zoned olivine; and as reaction rims on xenocrystic orthopyroxene. Olivine compositions and zoning (diffusion) profiles are used to map out the magmatic plumbing system and determine the timescales of magma ascent to the surface. The information gained from this work provides new insight into pre-eruptive magmatic history and magma ascent at Australian volcanoes. These results yield important implications for better preparedness to future volcanic hazards in Australia.