High-resolution 40Ar/ 39Ar chronostratigraphy of the post-caldera (

Abstract

The island of Pantelleria (Sicily Strait), the type locality for pantellerite, has been the locus of major caldera-forming eruptions that culminated, ca. 50 ka ago, in the formation of the Cinque Denti caldera produced by the Green Tuff eruption. The post-caldera silicic activity since that time has been mostly confined inside the caldera and consists of smaller-energy eruptions represented by more than twenty coalescing pantelleritic centers structurally controlled by resurgence and trapdoor faulting of the caldera floor. A high-resolution 40Ar/ 39Ar study was conducted on key units spanning the recent (post-20 ka) intracaldera activity to better characterize the present-day status (and forecast the short-term behavior of) the system based on the temporal evolution of the latest eruptions. The new 40Ar/ 39Ar data capture a long-term (> 15 ka) decline in eruption frequency with a shift in eruptive pace from 3.5 ka −1 to 0.8 ka −1 associated with a prominent paleosol horizon marking the only recognizable volcanic stasis around 12–14 ka. This shift in extraction frequency occurs without major changes in eruptive style, and is paralleled by a subtle trend of decreasing melt differentiation index. We speculate that this decline probably occurred (i) without short-term variations in melt production/differentiation rate in a steady-state compositionally-zoned silicic reservoir progressively tapped deeper through the sequence, and (ii) that it was possibly modulated by outboard eustatic forcing due to the 140 m sea level rise over the past 21 ka. The intracaldera system is experiencing a protracted stasis since 7 ka. Coupled with recent geodetic evidence of deflation and subsidence of the caldera floor, the system appears today to be on a wane with no temporal evidence for a short-term silicic eruption.