Structural controls on the location, geometry, and longevity of an intraplate volcanic system – The Tuatara Volcanic Field, Great South Basin, New Zealand

Intraplate volcanism is widely distributed across continents. Yet controls on the 3D geometry and longevity of individual volcanic systems remain poorly understood. Geophysical data provide insights into magma plumbing systems, but due to relatively low resolution, it is difficult to evaluate how magma transits highly heterogeneous continental interiors. We use borehole-constrained 2D seismic reflection data to characterise the 3D geometry of a volcanic field offshore New Zealand’s South Island, termed the Tuatara Volcanic Field, and investigate its relationship with pre-existing structure. The ~270km² field is dominated by a dome-shaped lava edifice, surrounded and overlain by ~69 volcanoes and >70 sills emplaced over 40 Myr from the Late Cretaceous to Early Eocene (~85 Ma–45 Ma). The Tuatara Volcanic Field is located above a basement terrane boundary represented by the Livingstone Fault; the recently active Auckland Volcanic Field is similarly located along-strike on the North Island. We suggest the Livingstone Fault controlled the location of the Tuatara Volcanic Field by producing relief at the base lithosphere, thereby focussing lithosphere detachment over ~40 Myr, and provided a pathway that facilitated magma ascent. We highlight 23 how observations from ancient intraplate volcanic systems may inform our understanding of active intraplate volcanic systems, including the Auckland Volcanic Field.