Volcanology and evolution of the Werribee Plains intraplate, basaltic lava flow-field, Newer Volcanics Province, southeast Australia

Volcanism in the Werribee Plains at the eastern end of the Cenozoic Newer Volcanics Province began ca 4.6 Ma, the formation of eruptive fissures partly controlled by the orientation of pre-existing basement structures, The exposed eruption centres are small-volume scoria cones and lava shields, and both produced significant lava flows. Calculations of the emplacement times of the lava flows suggest the lava shields were active for about 6 months on average, Scoria cone eruptions probably lasted days to weeks. Despite relatively long repose periods between eruptions (about one eruption per 97 000 years), few interflow sediments are preserved, Minimal physical erosion of the lavas probably reflects the shallow gradient of the Werribee Plains and the onset of and climatic conditions in the late Cenozoic, Inflated pahoehoe lavas are the dominant volcanic facies in the Werribee Plains. Other lava facies identified include spongy (S-type) pahoehoe, ponded lavas, transitional lavas, and a thick, distal aa lava facies. The characteristics of the volcanic facies and their distribution in this volcanic province resemble those in the type example of basaltic plains provinces, the Snake River Plain, USA. Basaltic plains provinces are produced by a unique style of volcanism which has been largely unexplored compared with basaltic volcanism in other tectonic settings (such as flood basalt and ocean island volcanism), This study expands our understanding of the processes involved in the evolution of basaltic plains provinces. The volcanic facies association typical of basaltic plains provinces is better characterised here, thus aiding the future identification of these unique lava flow-fields elsewhere, in both modern and ancient sequences.