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Zusammenfassung:
Alteration of basaltic glass and in situ mineral growth are fundamental processes that influence
the chemical and material properties of Earth’s oceanic crust. These processes have evolved at
the basaltic island of Surtsey (SW Iceland) since eruptions terminated in 1967. Here, subaerial and
submarine lapilli tuff samples from a 192 m-deep borehole drilled in 2017 (SE-02b) are characterized
through petrographic studies, X-ray powder diffraction analyses, and SEM–EDS imaging and chemical
analyses. The integrated results reveal (i) multi-stage palagonitization processes in basaltic glass
and precipitation of secondary minerals from matrix pore fluids, (ii) multi-stage crystallization of
secondary phillipsite, analcime and Al-tobermorite in the vesicles of basaltic pyroclasts and (iii)
variations in palagonitization processes as a function of thermal and hydrological domains. Although
temperature appears to be an important factor in controlling rates of secondary mineralization, the
chemistry of original basaltic components and interstitial fluids also influences reaction pathways in
the young pyroclastic deposits. The integration of systematic mineralogical analyses of the 50-yearold
tuff from one of the most carefully monitored volcanic sites on Earth, together with temperature
monitoring in boreholes since 1980, provide a reference framework for evaluating mineralogical
evolution in other Surtseyan-type volcanoes worldwide.
