Paleomagnetic dating of the most recent silicic eruptive activity at Pantelleria (Strait of Sicily)

Abstract

We report on the paleomagnetism of ten sites in the products of the most recent silicic eruptive cycle of Pantelleria, Strait of Sicily. Previously radiometrically dated at 5-10 ka, our comparison with proxies for geomagnetic field directions allows us to narrow considerably the time window during which these eruptions occurred. The strongly peralkaline composition causes the magmas to have low viscosities, locally resulting in strong agglutination of proximal fall deposits. This allows successful extraction of paleomagnetic directions from the explosive phases of eruptions. One of our sites was located in the Serra della Fastuca fall deposit, produced by the first explosive event of the eruptive cycle. The other nine sites were located in the most recent explosive (pumice fall and agglutinate from Cuddia del Gallo and Cuddia Randazzo) and effusive (Khaggiar lava) products. The (very similar) paleomagnetic directions gathered from eight internally consistent sites were compared to reference geomagnetic field directions of the last 5-10 ka. Directions from Cuddia del Gallo agglutinate and Khaggiar flows translate into 5.9-to 6.2-ka ages, whereas the Fastuca pumices yield a slightly older age of 6.2-6.8 ka. Hence, the most recent silicic eruptive cycle lasted at most a millennium and as little as a few centuries around 6.0 ka. Paleomagnetically inferred ages are in good agreement with published (and calibrated by us) 14 C dates from paleosols/charcoals sampled below the studied volcanic units, whereas K/Ar data are more scattered and yield ∼30% older ages. Our data show that the time elapsed since the most recent silicic eruptions at Pantelleria is comparable to the quiescence period separating the two latest volcanic cycles.

Correlation of welded ignimbrites on Pantelleria (Strait of Sicily) using paleomagnetism

“…Table 2). This value is smaller than that derived (using identical methods, instruments, and paleomagnetic laboratory), after investigating lavas and scoriae from Stromboli (3.0-3.4°), Etna (4.5°), and Pantelleria (3.7°; Speranza et al 2004Speranza et al , 2006Speranza et al , 2008Speranza et al , 2010. Thus it seems that welded ignimbrites yield paleomagnetic directions that provide even better constraints than lavas, opening significant perspectives for future PSV investigation of such pyroclastic successions.…”

“…All cores were oriented by both a magnetic and a sun compass. The local field declination values (i.e., the difference between the magnetic and sun compass readings) are generally ≤|5°|, similar to evidence gathered by Speranza et al (2010) from the most recent silicic products of the island.…”

“…According to Civetta et al (1988Civetta et al ( , 1998) the post-50 ka silicic activity can be grouped in six eruptive cycles (the first being represented by the Green Tuff eruption), each separated by several kyr of quiescence. The most recent silicic activity was characterized by emplacement of pumice cones, associated lava domes, and the voluminous~6.0 ka pantelleritic Khaggiar lava (Speranza et al 2010). A submarine basaltic eruption~4 km NW of Pantelleria in 1891 AD was the most recent activity (Washington 1909).…”

“…During the last two decades, paleomagnetic directions recorded by Holocene lavas at several active Italian volcanoes have been compared to independently available reference PSV curves of Europe, yielding an excellent chronologic framework of eruptions (Rolph and Shaw 1986;Tanguy et al 2003;Speranza et al 2006Speranza et al , 2008Vezzoli et al 2009). At Pantelleria, the paleomagnetism of the most recent lavas and scoriae has constrained the most recent silicic activity of the island to 5.9-6.8 ka (Speranza et al 2010).…”

High-resolution 40Ar/39Ar chronostratigraphy of the post-caldera (<20ka) volcanic activity at Pantelleria, Sicily Strait

“…4 Ar/ 39 Ar data substantially improve the temporal framework of the post-caldera activity relative to previous K-Ar and paleomagnetic studies (Speranza et al, 2010). This is illustrated by the sharply defined peaks in eruptive frequency (bottom diagram, Fig.…”