Late Pliocene volcanic island growth and flood basalt‐like lava emplacement in the Hyblean Mountains (SE Sicily)

Abstract

Since ∼200 Ma, the Hyblean Mountains (southeastern Sicily) have been the site of recurrent, mainly submarine, mafic volcanism. In the upper Pliocene, large volumes of tholeiitic products were erupted in a shallow marine environment, leading to the growth of volcanic islands. The deposits of this tholeiitic episode can be grouped into two main facies associations: (1) pillow lavas and hyaloclastite tuffs erupted and deposited entirely under water, and (2) submarine pillow breccias, fed from subaerial lava flows entering the ocean and subaerial lavas, which are distinguished into a coastal lava platform facies and an inland facies. Lava flows into the ocean led to the growth of lava deltas consisting of a basal flow foot breccia and an overlying sequence of pāhoehoe flow units, the latter rarely exceeding 0.5 m in thickness. In outcrop, this facies association shows evidence for significant instability of the lava deltas during growth, indicating very similar processes to those observed during the current eruption of Kīlauea volcano, Hawaii. Away from the coast of the growing island, the inland facies is characterized by thicker (up to several meters) pāhoehoe flow units showing evidence for sheet flow inflation and limited outcrops of scoria and/or bomb deposits. Evidence for lava transport through tubes exists in the form of tumuli and multiple vesicle layers; drained tubes are absent. All tholeiitic products were emitted in a single, instantaneous, voluminous event (≥120 km3), consistent with very high effusion rates similar to those of flood basalts or the 1783 Skaftár Fires (Iceland) eruption.