NEW 40AR/39AR AGES FOR THE MONTAGNA GRANDE-MONTE GIBELE TRACHYTE SHIELD VOLCANO, PANTELLERIA (STRAIT OF SICILY RIFT ZONE), ITALY

Montagna Grande and Monte Gibele represent the western and eastern portions, respectively, of a shield volcano (hereafter “MGV”) situated entirely within the Cinque Denti caldera on Pantelleria, a volcanic island located in the Strait of Sicily rift zone between Italy and Tunisia. Montagna Grande forms the highest peak on the island, rising to 836 m. The central vent of the volcano is located on Monte Gibele (700 m). The Cinque Denti caldera formed during the 45.7 ± 1.0 ka eruption of the <1 km³ DRE pantelleritic Green Tuff. Subsequent isostatic compensation was achieved by the eruption of ~ 3 km³ of trachyte lavas within the caldera that comprise the MGV and are thought to represent continued tapping of the Green Tuff magma reservoir. The time interval between the eruption of the Green Tuff and the MGV trachytes has not been well constrained, with previous (1984-1986) K-Ar ages from K-feldspar yielding ages between 44 ± 8 and 28 ± 16 ka. In this study we report the results of new single-crystal anorthoclase incremental heating ⁴⁰Ar/³⁹Ar ages collected from three trachyte lava flows collected at different sites and at different stratigraphic heights that provided ages of 32.0 ± 1.0, 31.8 ± 4.0, and 22.5 ± 0.8 ka. Although it has been speculated that the eruption of the trachytes occurred soon after the caldera-forming ignimbrites, our oldest samples suggest the repose time between the eruption of the caldera-forming ignimbrite and the caldera-filling trachytes may be between as few as 5000 and as many as 10,000 years. Explosive and effusive pantelleritic volcanism resumed within the caldera, including on MGV, approximately 6000 years later at ~16 ka.