Abstract Understanding the magmatic processes that drive unrest at silicic calderas remains a major goal in Volcanology. Rabaul in Papua New Guinea is an exceptional location because after two decades of unrest and a peak in seismicity and deformation in 1983–85, eruptive activity began in 1994 and is still ongoing. A particularly large sub-Plinian eruption occurred from Tavurvur in October 2006. Whole-rock compositions are andesitic and reflect mixing/mingling between basaltic and dacitic magmas from the same system. The magmas that fed the 2006 eruption were stored at about 930°C, with 1–3 wt% H 2 O, 25–520 ppm CO 2 , and 50–2500 ppm SO 2 in the melt. Melt inclusions hosted in pyroxene, and plagioclase phenocrysts record fractional crystallization at ≤200 MPa under relatively dry and poorly oxidizing conditions. Magma mixing/mingling is expressed as heterogeneous glass compositions, strongly zoned phenocrysts, and mafic crystal aggregates. A textural maturation from fine, acicular to large, blocky crystal clots implies different relative ages of formation. Modelling the chemical zoning of plagioclase shows that mafic–silicic interactions started a couple of decades prior to the 2006 eruption and continued until days to weeks prior to eruption. Basaltic replenishments have been driving unrest and eruption at the Rabaul caldera since the 1970s. Supplementary material: Tables and figures reporting the composition of the Tavurvur 2006, Kombiu and 1.4 ka BP caldera samples and showing thermodynamic modelling with MELTS are available at http://www.geolsoc.org.uk/SUP18816

Abstract Crustal xenoliths are key subvolcanic material for studying processes that operate in a magma dyke during intrusion into its surrounding country rock. The Biot number is the appropriate parameter to advance knowledge of the rock–magma thermal interaction. We present an interactive approach that combines the petrological study of natural subvolcanic samples, through crustal xenoliths, which represents an essential pilot to explore and constrain the input parameters and boundary conditions in numerical simulations of fluid dynamics under a volcano. Our results – as a function of different dyke depths, aspect ratios and temperature gradients at the host and dyke – allow an accurate interpretation of the thermal history of magma flow in the dyke, revealing significant differences in heat transfer and thermal resistance between the crust and ascending magma. Conclusively, melt flow within rigid-walled channels depends directly on the depth (pressure gradient) and width of the dyke according to a balance between the rate of magma input and heat loss that determines how fast the magma may ascend. In addition, and with implications for crustal assimilation, there is evidence of a strong relationship between the preconditioning temperature and the integrity of the host rock over the time that xenoliths are immersed in the magma dyke.