Pseudoclastic hydrothermal alteration textures occur within
quenched coherent dykes forming part of a subaqueous dome complex (~4 Ma) onPonza Island, Italy. These textures are similar to
those observed in considerably older (~500 Ma) subaqueous volcanic rocks at a
number of localities throughout the Mount Read Volcanics in Tasmania and
elsewhere in ancient volcanic sequences of this type in Australia. This is
significant because the processes of formation, hydrothermal alteration and
secondary mineralisation of ancient volcanic sequences may be better understood
if we can make comparisons with modern analogues. Observations at Ponza imply
that these pseudoclastic alteration features form synvolcanically or immediately
after dyke emplacement and lava extrusion. This is compatible with scenarios
presented for their formation in ancient sequences in the Mount Read Volcanics,
Tasmania.