Origin and evolution of the Deception Island caldera (South Shetland Islands, Antarctica)

Abstract

Deception Island has been interpreted variously as a classical ring fault caldera, as a tectonically controlled collapse caldera or as a tectonic depression. Review of previous studies combined with new fieldwork has allowed us to obtain a more precise model of the formation and internal structure of the Deception Island caldera. It formed as a result of the explosive eruption of basaltic-to-andesitic magmas, mostly as pyroclastic density currents representing in total a bulk volume of the order of 90 km(3). Caldera collapse occurred rapidly along a polygonal structural network consisting of several pre-existing major normal faults. These faults, which originated as a result of regional tectonics, controlled pre- and post-caldera volcanism on the island. The formation of the caldera generated a very active geothermal system inside its depression, which is responsible for most of the present-day seismic activity and may also have a significant influence on the observed surface deformation. Our results do not support the hypothesis that there is a large but shallow, active magma chamber beneath the current caldera; instead we suggest that recent eruptions have been fed by small batches of deeper-sourced magmas. The intrusive remains of these eruptions and probably of other minor intrusions that have not reached the surface provide the main heat source that sustains the current geothermal system.