Exploring Mid-to-Lower Crustal Magma Plumbing of Santorini and Kolumbo Volcanoes Using PmP Tomography

Abstract

Deep-crustal magma plumbing at arc volcanoes controls the volume, frequency, and composition of magma being transported to and stored in the upper crust. However, the mid-to-lower crust remains a challenging region to image. We explore the mid-to-lower crustal velocity structure beneath the Christiana-Santorini-Kolumbo Volcanic Field (CSKVF) to better understand how an established stratovolcano and flanking volcano (Santorini and Kolumbo) are fed through the mid-to-lower crust. We use active-source seismic data to obtain a P-wave velocity model of the crust below the CSKVF. We invert direct and reflected P phases to cover the entire depth extent of the crust and solve for the Moho interface depth. Our model requires a curved Moho interface representative of crustal thickening via underplating. Results show a high Vp anomaly in the lower crust under Santorini and a mid-crustal low Vp anomaly offset from both Santorini and Kolumbo. We find that accumulation of magma is located under the local extensional basin in the upper mid-crust (<10 km) but is offset at deeper depths. We find evidence for melt storage at 11–13 km depth feeding volcanism at the Kolumbo volcanic chain. This melt is also a plausible source for the 2025 seismic swarm and dike intrusion. Resolution is limited in the mid-crust below the Santorini caldera, leaving Santorini's mid-crustal magma plumbing unconstrained. We think it likely that Santorini and Kolumbo have entirely separate crustal plumbing systems and mantle sources, but allow the possibility of a connection in the mid or lower crust.