Magmatic processes driving the 1970 eruption on Deception Island, (Antarctica)

Deception Island, the most active volcanic system in the South Shetland Islands (Antarctica), has recorded over 20 explosive monogenetic eruptions in the past two centuries. The island’s most recent eruption in 1970 was one of its most violent, with a Volcanic Explosivity Index (VEI) of 3. This event generated a column height of up to 10 km and produced an estimated bulk eruptive volume exceeding 0.1 km³, with tephra fallout recorded over 150 km away on King George Island. To investigate the magmatic processes leading up to this significant eruption, we conducted detailed geochemical and textural analyses of near-vent pyroclastic deposits and distal tephra fall-out layers preserved in Livingston Island’s glaciers. Near-vent deposits include dilute pyroclastic density currents (PDCs) and lithic-rich breccias. Olivine crystals in these deposits exhibit two distinct populations: low-forsterite (Fo_65–70 mol.%) and high-forsterite (Fo_80–85 mol.%), with similar CaO contents (0.1–0.5 wt.%) but varying NiO concentrations (0–0.4 wt.% in low Fo; 0.02–0.10 wt.% in high Fo). Pyroxene microanalyses also reveal two distinct populations: i) augite-diopside (En_45–50, Fs_5–25, Wo_38–50) and ii) enstatite (En₉₀, Fs₁₀, Wo₀). Augite-diopside crystals can be further subdivided based on their Mg# (Mg# = Mg/(Mg+Fe) x 100) and TiO₂ contents. The first group shows Mg# values between 80–85 mol.% and TiO₂ ranging from 0.5 to 3.0 wt.%, while the second group displays Mg# values of 55–70 mol.% and narrower TiO₂ concentrations (0.5–1.25 wt.%). Notably, the enstatite population was not found in distal tephra layers. Plagioclase crystals range in composition from Bytownite to Andesine (An_85–40 mol.%). Comparative analyses with distal tephra layers confirm the presence of both olivine populations and overlapping augite-diopside compositions but lack enstatite. Plagioclase compositions show consistency between near-vent and distal deposits. These findings align the 1970 eruption deposits with compositional trends observed in other post-caldera collapse eruptions, shedding light on the island's eruptive history and magmatic evolution.

 

This work has been partially financed by the grant PID2023-151693NA-I00 funded by MCIN/AEI/10.13039/501100011033.This work is part of the CSIC Interdisciplinary Thematic Platform (PTI) Polar zone Observatory (PTIPOLARCSIC) activities. This research was partially funded by the MINECO VOLCLIMA (CGL2015-72629-EXP) and HYDROCAL (PID2020-114876GB-I00) MICIU/AEI/10.13039/501100011033 research project. Sampling was founded by CICYT (ANT91-1270, ANT93-0852 and ANT96-0734) and MICINN grant CTM2011-13578-E.