Variability in composition and physical properties of the sedimentary basement of Mt Etna, Italy

Abstract

The sub-volcanic basement at Mt Etna (Italy) comprises thick sedimentary sequences. An understanding of the physical, mechanical, and microstructural properties of these sequences, and an appreciation of their variability, is important for an accurate assessment of the structural stability of Mt Etna. Here, we present a combined field and laboratory study in which we explore the extent of variability of the materials comprising the sedimentary basement of Mt Etna. To this end, we sampled twelve different lithological units that span the sediments of the Apenninic-Maghrebian Chain (from both the Sicilide and Ionides sequences) and the Hyblean Plateau. X-ray diffraction analysis of the blocks collected show that calcite and quartz are the predominant mineral phases. Textural analysis highlights the wide variability in rock microstructures,with features such as the presence/absence of fractures or veins, pore size and shape, and grain size and shape varying tremendously between the samples. One consequence of this microstructural, textural, and mineralogical variability is that the rock units are characterised by very different values of porosity, P-wave velocity, uniaxial compressive strength, and static Young’s modulus. For example, strength and Young’s modulus vary by a factor of twenty and an order of magnitude, respectively. Our study affirms the vast heterogeneity of the sub-volcanic sedimentary basement of Mt Etna and, on this basis, weurge cautionwhen selecting potentially oversimplified input parameters formodels of flank stability.