How Does Temperature Influence the Physical and Chemical Properties of the Deep Carbonate Basement and Shallow Lava Flows at Mt. Etna Volcano?

Mt. Etna is the largest and most active strato-volcano in Europe. A detailed understanding of the influence of high temperatures, as a result of magma emplacement, on the deformation of rocks that form both its edifice and deep basement is a primary target for reliable volcanic hazard assessment. This is because high-temperature assisted deformation will influence important geophysical parameters routinely monitored within the edifice. In order to accomplish this goal, experimental data are now needed for representative lithologies. The geology at Mt. Etna consists of a thin basaltic cover resting upon thick Mesozoic to Middle Pleistocene sedimentary sequences. The deepest units (10-20 km depth) are a thick Mesozoic-Neogene carbonate succession of limestone and dolomite, with repeated basic volcanic intercalations - called the Hyblean Plateau. Here therefore we present experimental data on the influence of temperature on deformation in both an important carbonate of the deep Hyblean Plateau (CL), that outcrops 70 km south of Mt. Etna at Comiso (Italy), and the most representative extrusive lava flow basalt forming the shallow volcanic cover (EB). Experiments were all performed on the high-temperature uniaxial press at LMU, München. During experimentation, the output of AE energy was monitored using two piezoelectric transducer crystals, located on the top and bottom pistons. Results from mechanical deformation experiments are coupled with chemical analyses and P-wave velocity measurements undertaken at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Rome. Firstly, we show the output of acoustic emission (AE) during heating (1°C/min) without load for both rock types; in the case of CL this is coupled with data of the mass loss during heating (TGA). Secondly, we demonstrate the influence of temperature (up to 1000°C) on deformation in CL and EB in constant strain rate (10-5 s-1) experiments. Our results show that there is an increase in strength in CL prior to decarbonation (that starts at approximately 500°C). During and after decarbonation, strength is decreased significantly and the deformation behaviour is very ductile and almost aseismic. In contrast, EB remains very brittle despite the large increase in temperature; only at 950°C is there a noticeable softening of the sample during deformation. Furthermore, P-wave velocity in EB does not change with increasing temperature. All results are discussed in terms of deformation and chemical reactions within the sedimentary basement and volcanic cover at Mt. Etna, the stresses needed for dyke emplacement and monitored seismic activity and CO2 release from the volcanic edifice.