Insights into the origin and correlation of the Brown Tuffs on the Aeolian Islands, Italy

The Brown Tuffs (BT) are widespread lithologically-homogeneous, reddish-brown to grey, ash-rich pyroclastic deposits in the post-80 ka stratigraphic sequences of most of the Aeolian Islands and on the Capo Milazzo peninsula (Sicily). Here we present a revised stratigraphy and new grain-specific volcanic glass (electron microprobe) chemistry for the different BT units on the islands of Lipari, Vulcano and Salina, which provide constraints on their large-scale correlation and insights into the eruptive and depositional mechanisms. The three stratigraphic macro-units in which the BT are principally subdivided, Lower (70-56 ka; LBT), Intermediate (56-27 ka; IBT) and Upper (24-8 ka; UBT), can be geochemically distinguished based on the SiO2, alkali and TiO2 glass contents. There is a significant increase in the degree of evolution of the magmas through the succession, from basaltic trachy-andesites to trachytes. Compositions are consistent with an origin from the area of La Fossa Caldera on Vulcano. Here, we highlight that the UBT compositions are similar to those of the early pyroclastic products (Punte Nere) erupted at the active La Fossa cone indicating the magmatic system typically erupts homogenous melts. In different BT depositional units on Lipari we have observed the presence of a minor component of rhyolitic pumice clasts compositionally correlated to the underlying (local) pyroclastic units (P. di Perciato, Falcone, M. Guardia, V. del Gabellotto). The incorporation of these older pumices is evidence of abrasion of the unconsolidated substratum during the emplacement of the PDCs that deposited the BT in proximal to mid-proximal areas. The interlayered tephra layers which provide stratigraphic boundaries between the BT units have been geochemically related to widespread central Mediterranean isochronous markers, particularly recording a multiple ash fall activity from the Ischia volcano. Importantly, some of these tephra layers have not been previously reported in the volcanic stratigraphies of the Aeolian Islands.