Fig. 7
From: Volcanic crystals as time capsules of eruption history
Schematic interpretation of the crustal plumbing system feeding Mt. Etna. The transcrustal magma plumbing system is composed of multi-level mush regions, concentrated along stratigraphic boundaries (crustal stratigraphy and rock densities for pressure scale are after refs. 78 and 79; see also Fig. 4). Our data support a main storage region at ~10 km depth, at the transition between the crystalline basement and the sedimentary sequence. Magma ascent is interpreted between the high-Vp body (HVB; depth range and dimensions after ref. 52), detected below the summit and eastern Valle del Bove caldera and considered a major solidified plutonic complex, and the shallow low-Vp zone (LVZ)49,50,51,52. Magma storage depths inferred from geophysical data are represented with vertical blue bars49,50,51,52,53. A wide region of low-Vp in the uppermost mantle (<34 km; below the sketch) is interpreted as the source region52. Mantle-derived magmas are buffered to trachybasaltic compositions at upper mantle to lower crustal levels, through continuous supply and mixing of primitive melts and crystallisation of Mg-rich olivine and clinopyroxene26,31,32. From the storage region at ~10 km and upwards, the system is governed by degassing and mixing in highly dynamic shallow mush pockets32, dominated by crystallisation of plagioclase27, olivine29 and clinopyroxene. Since the 1970s, repeated batches of new mafic magma are intruding into and mixing with resident mushes. This magma has erupted quickly through deep dykes feeding eccentric eruptions and progressively migrated into the shallow, largely crystalline, and degassing central conduits (see yellow dashed pathways). Major and trace element zoning and thermobarometry of clinopyroxene can be explained by (1) recycling of low-mid crustal, relatively evolved mushes; (2) crystallisation of Cr-rich zones (yellow) from intruding magma in the main storage region; and (3) crystallisation of Cr-poor zones (blue) upon final magma ascent and degassing. Progressive intrusion of primitive undegassed magma correlates with increasing eruptive activity in the last 40 years (Fig. 3). We calculate that the time elapsed between replenishment of the main storage system and eruption can be shorter than 2 weeks (Figs. 5 and 6)
