Rift Development, Tectonic Forcings, and Magmatic Feedbacks at Santorini and Kolumbo Volcanoes Constrained by Scientific Drilling and Core‐Seismic Integration

Volcanism in continental rifts, rifted volcanic arcs, and back-arc basins is fundamentally coupled with crustal extension. However, the precise geometry and timing of the fault systems that facilitate magma transport and accommodate extension remain poorly constrained. The Christiana–Santorini–Kolumbo volcanic field lies within the Santorini–Amorgos Tectonic Zone, an actively extending back-arc rift where volcanism transitioned from dominantly effusive and moderately explosive andesitic activity (∼570–250 ka) to repeated caldera-forming silicic eruptions after ∼250 ka. Here we integrate scientific drilling results from IODP Expedition 398 with a dense grid of high-resolution seismic profiles and identify a previously unrecognized rift structure, the Kolumbo Graben, bounded by the NE–SW–striking Kolumbo Fault and hosting Kolumbo Volcano and the Kolumbo Volcanic Chain. Subsidence and fault throw rates across the rift system accelerated between ∼330 and ∼160 ka, with the Kolumbo Fault accommodating ∼220 m of displacement. This phase of accelerated extension preceded the emergence of Kolumbo and the onset of repeated caldera-forming silicic eruptions at Santorini. Volcanic edifices of the Kolumbo Volcanic Chain cluster within the graben interior rather than along the master fault, indicating that distributed intra-graben deformation and locally reduced horizontal stresses provided preferred pathways for magma ascent. Structural continuity further suggest that the Kolumbo Graben extends beneath Santorini. We conclude that accelerated rifting and strain localization exerted first-order control on magma ascent and the transition to highly explosive volcanism over the past ∼250 kyr, while magma intrusion and associated thermal weakening likely provided a positive feedback that further localized deformation during periods of peak activity.