Temporal evolution of the Fogo Volcano magma storage system (Cape Verde Archipelago): a fluid inclusions perspective

Abstract

The architecture of the magma storage system underneath Fogo Volcano (Cape Verde Archipelago) is characterised using novel fluid inclusion results from fifteen basanites, spanning the last 120 thousand years of volcanic activity, and encompassing a major flank collapse event at ~73 ka. Fluid inclusions, hosted in olivine and clinopyroxene, are made of pure CO2, and based on their textural characteristics, are distinguished in early (Type I) and late (Type II) stage. Inclusions homogenize to a liquid phase in the 2.8 to 30.8 ◦C temperature range. Densities values, recalculated assuming an original 10% H2O content at the time of trapping, range from 543 to 952 kg⋅m3, and correspond to entrapment or re-equilibration pressure ranges of 500–595 MPa, 700–740 MPa, and 245–610 MPa respectively for pre-collapse, early post-collapse, and Holocene/historical eruptions. These entrapment pressures are interpreted as reflecting the existence of two main magma accumulation zones at ~25 km and ~ 13–21 km depth, and a zone of fluid inclusion re-equilibration at 9–12 km depth. There is evidence of a complex temporal evolution of the magma system. Historical eruptions, and especially the three most recent ones (occurred in 1951, 1995 and 2014–25), bring fluid inclusion evidence for transient, pre-eruptive shallow (9–17 km depth) magma ponding. Early post-collapse (60 ka) volcanics, in contrast, document fast magma transport from ~25 km, and suggest a reconfiguration of the magma system after the Monte Amarelo collapse event.