Alan Bischoff, Andrew Nicol, Jim Cole, DDarren Gravley

Large volumes of magma emplaced and deposited within sedimentary basins can have an impact on their architectural style and geological evolution. Over the last decade, continuous improvement in techniques such as seismic volcano-stratigraphy and 3D seismic visualization of igneous rocks buried in sedimentary basins has helped increase knowledge about these “volcanic basins”. Here, we unravel the complete architecture of the Maahunui Volcanic System (MVS), a middle Miocene monogenetic volcanic field now buried in the offshore Canterbury Basin, South Island of New Zealand. We show the location, geometry, size, and stratigraphic relationships between 25 main intrusive, eruptive, and sedimentary architectural elements in a comprehensive volcano-stratigraphic framework that explains the evolution of the MVS from emplacement to complete burial. The plumbing system of the MVS comprises of seven main architectural elements, including saucer-shaped sills, dikes and sills swarms, minor stocks and laccoliths, and pre-eruptive strata deformed by intrusions. These endogenous elements occur in five distinctive plumbing-types, controlled by the emplacement depth, and by the geometric relationships between the intrusions and the enclosing strata. The exogenous volcanic architecture is defined by a combination of eruptive and associated sedimentary architectural elements, with minor and localized shallow intrusions. Characteristic volcano-types of the MVS are interpreted as the deep-water equivalents of crater and cone-type volcanoes. Crater-type volcanoes have eight main architectural elements (i.e. root zone, lower and upper diatreme, tephra ring, tephra plain, intra-crater cones, overspill wedge and tephra fallow carpet). Cone-type volcanoes have five main architectural elements (i.e. basal cone, central crater, tephra flank, cone apron and tephra fallout carpet). After volcanism has ceased, the process of degradation and burial of the volcanic edifices produces five main sedimentary architectural elements (i.e. inter-cone plains, epiclastic plumes, canyons and gullies, burial domes and seamount-edge fans). Understanding the relationships between these diverse architectural elements allow us to reconstruct the complete architecture of the MVS, and to recognize the main volcano-stratigraphic trends in the study area. The characterisation of architectural elements of the MVS can be applied to explore opportunities to find valuable geoenergy resources such as oil, gas and geothermal energy with buried and active monogenetic volcanic systems.