Water-rock interaction in genesis of perlite at Monte Arci volcanic complex (West Sardinia, Italy)

At Monte Arci (West Sardinia) Plio-Pleistocene rhyolitic lavas with hyaline texture outcrop. A detailed investigation has been conducted to define the geochemical characteristics of the nonhydrated (obsidian) and hydrated (perlite) volcanic glasses recognized to date. XRF analysis was used to determine major and trace elements in whole rock, and glass inhomogeneity was detected using EPMA methodology. deltaD and delta O-18 isotopes and FTIR analyses were also performed. Perlite may have originated from later hydration by meteoric water giving rise mainly to Na2O removal. A negative correlation between Na2O and H2O, lower deltaD and delta O-18 values and higher OH-/H2O ratios in obsidian seem to support this hypothesis.