Magmatic heat and fluids can interact with a volcanic host rock to form secondary minerals, such as
phyllosilicates, zeolites, sulfates, sulfides and oxides. The water-rock reactions, inducing alteration of the
primary volcanic material, strongly depend on the magma chemistry and volatile flux, and the nature of the
aquatic environment (i.e., sea/ocean and meteoric) and its properties such as temperature, salinity, redox
and pH. The newly-grown alteration minerals result from the chemical reaction between the host rock and
they can indicate particular physico-chemical conditions. Hence, the mechanisms controlling the formation
of secondary mineral associations can be critical, not only for assessing the role of hydrothermally altered
host rocks in moderating eruptions styles but also for volcano flank instabilities.
In this study, we applied mass balance calculations and thermodynamic modelling to establish the
formation and equilibria environments of alteration minerals and hydrothermal fluids at three active
volcanic suites: Ruapehu (New Zealand), Mt. Zao (Japan) and Deception Island (Antarctica). Results indicate
that the secondary minerals follow different precipitation sequences as a function of the magma
composition and the primary mineral assemblage (basalt-andesitic to dacitic for Ruapehu, andesitic for Mt.
Zao, and basaltic for Deception Island). Temporal variations in composition and abundances of the
hydrothermal paragenesis in Ruapehu and Mt. Zao determinate the evolution of acid¿sulfate alteration
zones.
We conclude that the combination of the proposed petrologic-geochemical approach, the regional and local
tectonic features, and the spatial distribution of the alteration minerals within the volcanic edifices can be
used for the assessment of future hydrovolcanic eruptions (including multiple eruption phases) and/or
instability flanks episodes. In addition, the biological submarine and global change communities can also
benefit from this geochemical procedure in other worldwide submarine volcanoes as the water-rock
chemical reaction has direct implication in the oceanic productivity
