Williams, Rebecca

Pantelleria volcano has a particularly intriguing evolutionary history intimately related to the peralkaline composition of its explosively erupted magmas. Due to the stratigraphic complexity, studies over the last two decades have explored either only the pre-Green Tuff ignimbrite volcanism or the post-Green Tuff activity. We here focus on the whole evolutionary history, detailing the achieve- ments since the first pioneering studies, in order to illustrate how the adoption and integration of pro- gressively more accurate methods (40Ar/39Ar, paleomagnetism, petrography, and detailed field study) have provided many important independent answers to unresolved questions. We also discuss rheo- morphism, a distinct feature at Pantelleria, at various scales and possible evidence for multiple, now hidden, caldera collapses. Although the evolutionary history of Pantelleria has shown that each ign- imbrite event was followed by a period of less intense explosivity (as could be the present-day case), new geochronological and geochemical data may indicate a long-term waning of volcanic activity.

A new, pre-Green Tuff (46 ka) volcanic stratigraphy is presented for the peralkaline Pantelleria Volcano, Italy. New 40Ar/39Ar and paleomagnetic data are combined with detailed field studies to develop a comprehensive stratigraphic reconstruction of the island. We find that the pre-46 ka succession is characterised by eight silica- rich peralkaline (trachyte to pantellerite) ignimbrites, many of which blanketed the entire island. The ignimbrites are typically welded to rheomorphic, and are commonly associated with lithic breccias and/or pumice deposits. They record sustained radial pyroclastic density currents fed by low pyroclastic fountains. The onset of ignimbrite emplacement is typically preceded (more rarely followed) by pumice fallout with limited dispersal, and some eruptions lack any associated pumice fall deposit, suggesting the absence of tall eruption columns. Particular at- tention is given to the correlation of well-developed lithic breccias in the ignimbrites, interpreted as probable tracers of caldera collapses. They record as many as five caldera collapse events, in contrast to the two events re- ported to date. Inter-ignimbrite periods are characterised by explosive and effusive eruptions with limited dis- persal, such as small pumice cones, as well as pedogenesis. These periods have similar characteristics as the current post-Green Tuff activity on the island, and, while not imminent, it is reasonable to postulate the occur- rence of another ignimbrite-forming eruption sometime in the future.