Paleo-phreatomagmatic eruption on Daru Island, Papua New Guinea: evidence for carbonate-basalt magma mingling and peperite formation

This study presents evidence for a maar-type paleo-phreatomagmatic eruption on Daru Island, Papua New Guinea (PNG), an understudied region of the southwest Pacific. Integrated field observations, petrographic and back-scattered electron (BSE) ash mapping, mineral chemistry, and whole-rock geochemistry reveal that ash generation was controlled by repeated interaction between ascending basaltic magma and seawater-saturated carbonate sediments at shallow crustal levels. Ash textures, morphologies, vesicularity, and juvenile-lithic proportions record spatial changes in quenching efficiency, degassing behavior, and sediment entrainment during magma emplacement. Three end-member interaction zones were classified based on ash-mapping: (1) a marginal quench zone (Dark to Black Ash-type), (2) an intermediate interaction zone (Brown Ash-type), and (3) an interior insulated magma zone (Mixed Ash-type). These variations record repeated fragmentation and recycling of ash populations, producing maar-type volcaniclastic tuffs and providing new insights into basaltic volcanism processes in carbonate-dominated sedimentary basins such as the Fly Platform in PNG.