Abstract
Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 explosive eruptive events registered over the past two centuries. Recent eruptions (1967, 1969, and 1970) and the volcanic unrest episodes that happened in 1992, 1999, and 2014–2015 demonstrate that the occurrence of future volcanic activity is a valid and pressing concern for scientists, technical and logistic personnel, and tourists, that are visiting or working on or near the island. We present a unifying evolutionary model of the magmatic system beneath Deception Island by integrating new petrologic and geochemical results with an exhaustive database of previous studies in the region. Our results reveal the existence of a complex plumbing system composed of several shallow magma chambers (≤10 km depth) fed by magmas raised directly from the mantle, or from a magma accumulation zone located at the crust-mantle boundary (15–20 km depth). Understanding the current state of the island’s magmatic system, and its potential evolution in the future, is fundamental to increase the effectiveness of interpreting monitoring data during volcanic unrest periods and hence, for future eruption forecasting.
Highlights
Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 explosive eruptive events registered over the past two centuries
We propose a new and all-encompassing evolutionary model of Deception Island (DI)’s magmatic system following an interdisciplinary approach that combines petrological and geochemical data (Supplementary Materials 1–6) with geophysical observations (Supplementary Material 7), detailed Pressure-Temperature (P-T) estimates, and fractional crystallization modelling (Supplementary Material 8)
Our results indicate that DI magmas form through fractional crystallization of basaltic melts with an initial 0.5–0.75 wt.% H2O under fO2 conditions of 0–1 log units above Quartz-Fayalite-Magnetite (QFM) buffer at pressures from 2 to 5 kbar, which are in accordance with the proposed model (Supplementary Material 8)
Summary
From pressures >6.5 kbar (i.e., depths ≥ 25 km, assuming an average crust density of 2650 kg/m3), which suggests a mantle origin (Moho depth beneath DI is between 15 and 20 km deep[56]). Pressure estimates from recent post-caldera juvenile samples from Crater Lake area (e.g., DI-1INF, DI-4SUP) (Fig. 3), point to the existence of a magma source located at similar depths, such as the presumably destroyed reservoir R2 This may indicate that, since the collapse event, new pulses of fresh magma coming from R1 or directly from the mantle, would have created new chambers at comparable depths (R2′). Magma stagnation in shallower reservoirs (P < 1 kbar) within a cooler country rock (e.g., R5 or R6) promotes faster and larger differentiation, generating the most evolved magma compositions in the DI system (e.g., Cross Hill eruption samples DI-39OBS, DI-41) (Fig. 5) This might be similar to the caldera-collapse event, in which the arrival of fresh and hotter magma from the deeper reservoirs could have acted as an eruption trigger for the case of the recent eruptions (see glass mixing evidence in compositional figures of Supplementary Materials 5 and 8). The wide compositional ranges of the 1967 and 1970 eruptive materials (all assigned to R4), which are interpreted as related to magma mingling and mixing, and to reservoir stratification[15] (Supplementary Material 5), when compared to the compositional homogeneity of the R3 samples, allows assuming the existence of at least two distinct reservoirs at similar depths
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