Imaging the Bracciano caldera system by aeromagnetic data inversion (Sabatini Volcanic District, Central Italy)

Abstract

Bracciano Lake, located in central Italy, 30km northwest of Rome, is a volcano-tectonic depression developed in Pleistocene time representing the Sabatini Volcanic District (SVD) western eruptive center. Little is known about Bracciano caldera deep structure and potential field methods are appropriate to probe through a volcanic pile.In this paper, we present a 3D magnetic inversion model of the Bracciano caldera system based upon new aeromagnetic data and paleomagnetic measurements carried out by Istituto Nazionale di Geofisica e Vulcanologia (INGV).Magnetic modelling provides a reconstruction of Bracciano caldera morphology whose extension is about 20km north-south and 15km east-west; the maximum collapse depth is up to 1km and the depocentre area appears localised to the north of the present Bracciano Lake shoreline. Considering the geological records of the main Bracciano caldera forming events, we have interpreted the resulting magnetic model as an overlap of two collapse structures generating a nested system whose location was strictly influenced by tectonic processes. Our 3D magnetic model confirms and consolidates the validity of the magnetic method to highlight deep structures in volcanic environments.