GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.3 207 ductile to the brittle regime. Such mechanisms subsequently change the strength of the volcanic edifice (Bakker et al. , 2015). Furthermore diking can additionally control locally the brittle-ductile transition, in agreement with the observed attenuated seismicity. Dilatancy is an appropriate indicator for the brittle-ductile transition and if failure occurs within the edifice, it is likely to be brittle-dilatant with strength and stiffness reduction that blocks stress transfers within the volcanic edifice, ultimately damping surface uplifts (Parisio et al. , 2019). From the mechanical point of view the thermal damage consists of accumulation of damage induced by the propagation of pre-existing cracks and the enucleation of additional ones induced by the differential thermal expansion within and between grains. These processes have a profound effect on physical and mechanical properties. Overall a progressive decrease in physical characteristics related to the temperature increase can be observed, mirrored by an increase in porosity. In terms of mechanical properties the higher is the temperature, the lower is the strength; however, in carbonate rocks, for temperature up to 200°C, hardening effects can also be observed. The effect of key temperatures on physical and mechanical properties of carbonate rocks has been widely investigated on Comiso Limestone and Mt. Climiti limestones from South Eastern Sicily, which are representative of the Mt. Etna volcano Etna’s basement and can be applied to other strato-volcanoes with sedimentary substrata. In order to further consider the complexity and variability of carbonatic rocks, three compositionally different carbonate rocks were here analyzed from various tectonic settings and thermal histories: limestones, marbles and dolomites. They were collected in different areas of the Americas: marble and limestone samples came from the Los Humeros caldera complex, Puebla, 180 km east of Mexico City, Mexico. Marbles and dolomites came from the quarries of Carvalho, Sao Joaquim and Paraiso, Italva, 350 km north east of Rio de Janeiro in Brasil. The Los Humeros caldera comprises Pleistocene to Holocene basaltic andesite-rhyolite volcanic rocks and was originated after two main caldera-forming eruptions and multiple voluminous plinian eruptions. The volcanic rocks of this geothermal field were emplaced on intensively folded Mesozoic sedimentary rocks belonging to the Sierra Madre Oriental, that was exposed to local metamorphism due to intrusion of Granitic and syenitic plutons of Cenozoic age and basaltic dykes. The brasilian marbles and dolomites come from the Campos Basin where the main formation (Macabu formation) is composed by silicified carbonates formed by the reaction of hot igneous intrusions with carbonate rocks, due to the intracontinental rift associated with extensive intracratonic tholeitic volcanism along the continental margin with intense normal faulting that has exposed carbonate rocks to multiple episodes of heat. For each core sample porosity, ultrasonic pulse velocity (UPV), electrical resistivity (ER) and UCS were evaluated at different target temperatures (from 200°C to 600°C). In situ coda wave interferometry and permeability has been measured for selected samples. Correlations between destructive and non-destructive tests were found and deeply analyzed in the light of rock type. In agreement with previous studies, Vp velocity, density, UPV, wet electrical resistivity, uniaxial compressive strength andYoung’s moduli decrease as temperature increases. By contrast, peak strain, porosity and permeability increase. Microcracking damage, cataclastic flow and decarbonation are the leading parameters of this degradation and can successfully tracked by the evolution of the physical properties at a given targeted temperature. References Aiuppa, A., Federico, C., Giudice, G., Gurrieri, S., Liuzzo, M., Shinohara, H., Favara, R., Valenza, M., 2006: Rates of carbon dioxide plume degassing from Mount Etna volcano . Journal of Geophysical Research 111 , B09207. http:// dx.doi.org/10.1029/ 2006JB004307. Bakker R., Violay M., Benson P., Vinciguerra S.: Ductile flow in sub-volcanic carbonate basement as the main control for edifice stability: New experimental insights , Earth and Planetary Science Letters, 430 , 533-541.