Evolution of the northwestern Iblean Mountains, Sicily: uplift, Plicocene/Pleistocene sea-level changes, paleoenvironment, and volcanism

The Late Miocene to Pleistocene evolution of the northwestern Iblean plateau (Sicily) is marked by a complex interplay of subaerial and submarine volcanism, subsidence and uplift, eustatic sea-level changes, and shallow-water carbonate and clay sedimentation. Volcanic activity occurred in distinct phases, differing drastically in volume, chemical composition, eruptive and depositional sites, and eruptive mechanisms. Six of the newly defined formations in the northwestern Iblean plateau are either entirely volcanic or contain significant amounts of volcanics. The eastern part of a shallow marine basin was filled completely by Late Pliocene tholeiitic lava flows (Militello Formation) that had advanced subaerially from the south–southeast. Lava deltas advanced southwestward on top of earlier pillow breccia debris flow deposits intertongued with soft Trubi marls and chalks. True submarine eruptions (Monte Caliella Formation) simultaneously produced densely packed pillow piles up to 250?m thick. Inferred water depths based on volcanologic and paleoecologic criteria of interbedded and overlying calcarenites agree well. Subsequent alkalic, more explosive Pleistocene volcanic eruptions (Poggio Vina Formation) changed from initially submarine to late subaerial indicating growth of edifices above sea level, sea-level rise, or land Subsidence by ca. 50?m. They and the latest Militello volcanics are interlayed with minor shallow-water calcarenites. The Poggio Vina volcanics were submerged during a second sea-level rise amounting to up to 100?m. The sea was generally shallow, i.e., <100?m deep, throughout most of the Late Pliocene and early Pleistocene. The Poggio Vina volcanism took place prior to the Emilian transgression. The sea-level rise might represent a continuation of the subsidence trend that caused the Lower Pliocene Trubi marine basin. Subaerial conditions were reached twice in the approximate time interval 1.9–1.6?Ma during phases of voluminous volcanism that outpaced subsidence. Uplift of approximately 600?m (Palagonia) to 950?m (Monte Lauro) occurred subsequent to emplacement of the Pleistocene alkalic volcanics. Bioclastic carbonates deposited concurrently with uplift drape a major fault scarp east of Palagonia with uplift rates in excess of 0.5?mm/a, provided most uplift occurred during ca. 1?Ma. Basinning continued beneath the half graben of the present Piana di Catania where volcanics several hundreds of meters thick – at least some of them alkalic in composition – occur at a depth of approximately 500–1500?m below the present surface. Quaternary uplift of the northwestern Iblean plateau may have been due to a major phase of underplating or rise of partially melted mantle. Composition of the volcanic rocks, total volume, and mass eruptive rates are well-correlated. The volumetrically very minor highly mafic Messinian nephelinites may have formed in response to Messinian lithosphere unloading following draining of the Mediterranean resulting in very low-degree partial melting. The nephelinitic to basanitic Poggio Inzerillo and Poggio Pizzuto pillow lavas may herald a major mantle decompression event, possibly the rise of a mantle diapir. The remarkably homogeneous bronzite-bearing, relatively SiO₂-rich Militello tholeiites, representing a very short-lived but voluminous eruptive phase, resemble E-MORB and reflect a major high-degree partial melting event. The Pleistocene Poggio Vina alkali basalts to nephelinites resemble the late-stage alkalic phase in intraplate magmatic systems. The Iblean cycle of a brief but intense phase of widespread tholeiites followed by alkali basaltic volcanism resembles that of Etna Volcano where widespread basal tholeiites erupted at approximately 0.5?Ma and were followed by (evolved) alkali basaltic lavas. The immediate cause-and-effect relationship between volcanism and tectonism remains speculative.