Geological and geomorphological aspects of mud volcanoes located on south-western slope of Mt. Etna volcano: Hypotesis abouth their genesis

Abstract

Three groups of mud volcanoes, located on the lower south-western slope of Mt Etna volcano (Eastern Sicily), have been studied for this paper They are located between Paternd and Belpasso villages; on the basis of their location, they have been named "Salinelle dei Cappuccini", "Salinelle del Fiume" and "Salinelle del Vallone Salato". Their genesis is connected with a structural trap, formed by a brachyanticline of Pleistocenic clays forming the Etna basement Our research consists of: a) a detailed geological survey, wich permits the reconstruction of stratigraphic sequence of the interested area: the geological study results very important for the knowledge of mud fluids rising; b) study of morphological and phenomenological evolution of mud volcanoes, during 4 years (1996-2000); c) geochemical study of waters. Stratigraphic sequence consist in: - Numidian Flysch, brownisch clays alternating with yellowisch quarzarenites (Oligocene - Lower Miocene); - Varicoloured Clays, with caotic texture overthrusted on Numidian Flysch (Upper Cretaceous - Eocene); - Polizzi Formation, grey-green marly silty clays with intercalations of sandstones, white marls and marly limestones (Eocene); - Terravecchia Formation, marls with sandy intercalations (Tortonian); - Tripoli, Basal Limestones and Gipsum (Messinian); - Trubi, white marls and marly limestones with globigerine (Lower Pliocene); - Bluish Marly Clays, marly clays with no clear stratification (Lower - Middle Pleistocene); - Sands, Sandstones and Conglomerates, yellow quartzose sands, sandstones and polygenetic conglomerates containing quarzarenitic clasts (Middle Pleistocene); - Basal Subalkaline Lavas, subaerial lava sheets cut by river terraces (Middle Pleistocene); - Lavas, Tephra and Tuffaceous Sediments From The Ancient Alkalic Centres, highly degraded lavas cut by river terraces, often with olivina and pyroxene megacrists (Middle Pleistocene); - Fluvial, Lacustrine and Marine Terraced Deposits (Tyrrenian - Holocene); - Lava Flows of the Ancient and Recent Mongibello (Holocene). Detailed geological survey together with drilling data, permits us to say that in two places (Salinelle dei Cappuccini and Salinelle del Fiume) fluids uprise through pre-existing volcanic necks; in a third case (Salinelle del Vallone Salato) they uprise through a presumed fault plane. This is in contrast with a model till available in literature. Detailed morphological researches suggest a zonation of mud apparatuses based on morphological and phenomenological features and on manifestations intensity. The morphological types have a good correlation with the Brown (1990) classification. Morphological evolution depends mainly on density of emitted muds, and secondarely on caracteristics of preexisting ground surface. On the basis of chemical analisys, it results that water coming out from the mud volcanoes is fossil marine water, hosted in the Miocene sedimentary rocks of the Mt. Etna basement. C02 is the copiousest escaping gas, and it is prevalently of magmatic origin.