title: Magma storage in a strike-slip caldera.
abstract: Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
authors.forename: J
authors.initials: J
authors.lastname: Saxby
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.|Cabot Institute, University of Bristol, Bristol BS8 1UJ, UK.
authors.forename: J
authors.identifier: 0000-0001-9280-4011
authors.initials: J
authors.lastname: Gottsmann
authors.affiliation: School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.|Cabot Institute, University of Bristol, Bristol BS8 1UJ, UK.
authors.forename: K
authors.initials: K
authors.lastname: Cashman
authors.affiliation: Area de Vulcanologia, Observatorio Ambiental, MARN, San Salvador, El Salvador.
authors.forename: E
authors.initials: E
authors.lastname: Gutiérrez