The genesis of garnet and cordierite in acid volcanic rocks: Evidence from the Cerberean Cauldron, Central Victoria, Australia

Abstract

In the acid volcanic rocks of the Cerberean Cauldron of Central Victoria, four almandine garnet types can be distinguished. Types 1 and 2 are the most important. Type 1 garnets, about 1 mm across, euhedral and free of inclusions, occur mainly in the Rubicon Rhyolite. Type 2 garnets, up to 1 cm across, often irregular and always with inclusions, are most abundant in the Lake Mountain Rhyodacite. Type 1 garnets are enriched in Fe and Mn and depleted in Mg and Ca with respect to Type 2 garnets. Zoning patterns in Type 1 garnets show enrichment of Fe and Mn in the cores. Conversely Type 2 garnets have Fe and Mn enriched rims, although the zoning is frequently less regular. Fe rich cordierite occ..