The Campi Flegrei Volcanic District (CFVD) includes the Campi Flegrei caldera, the islands of Procida and Ischia, and it is among the most dangerous volcanic systems of the world. The volcanic activity that has characterized the recent eruptive history of the CFVD includes both effusive and hydromagmatic eruptions that resulted in a variety of igneous products from alkaline basalts to trachytes. Among CFVD products, basaltic lava fragments dispersed in the hydromagmatic tuff of the Solchiaro eruption (Procida island) result to be representative of near-primary melts on the basis of their geochemical and isotopical signatures. The knowledge of the viscosity of primitive magmas at high pressure and temperature is needed to model their mobility and ascent rate. These variables allow us to predict the potential volcanic activity at surface. In this study, we investigated the viscosity and melt structure of APR16 alkaline basalt, a lava fragment of the Solchiaro eruption. The anhydrous glassy starting material was prepared at Bayerisches Geoinstitut by using a gas-mixing furnace, by melting the APR16 rock powder at 1400 °C for 15 minutes at atmospheric pressure and oxygen fugacity buffered at Nickel-Nickel Oxide level using a CO/CO2 gas mixture. Experiments were performed at pressure between 0.7 and 2.3 GPa and temperatures of 1200 °C-1700 °C using the Paris- Edinburgh press combined with synchrotron X-ray technique at beamline 16-BM-B (HPCAT) of the Advanced Photon Source (Argonne National Laboratory, Illinois, USA). Viscosity measurements were conducted with the falling sphere technique. The falling velocity of the platinum probing sphere was measured at each run by ultrafast X-ray radiography using a high-speed camera at 500 frames per second as recording rate. The viscosity was, then, calculated from the Stokes’ equation including the correction factors for the effect of the wall and the end effect (Kono et al., 2014). Structural measurements of the liquid at 1700 °C and 2.3 GPa were also performed using multi-angle (2θ angle between 3° to 35°) energy dispersive X-ray diffraction technique. Preliminary results show the viscosity increasing from 0.1 to 1 Pa·s as pressure decreases from which an increase in the polymerization during decompression can be inferred. Our results are used to constrain the mobility and ascent velocity of primitive alkaline basalts considered to be parental magmas at Campi Flegrei with important implications for the potential volcanic hazard of the area. Kono, Y., Park, C., Kenney-Benson, C., Shen, G. & Wang, Y. (2014): Toward comprehensive studies of liquids at high pressures and high temperatures: Combined structure, elastic wave velocity, and viscosity measurements in the Paris- Edinburgh cell. Phys. Earth Planet. Inter., 228, 269-280.
Viscosity of alkaline basalts at high pressure: constraints on the pre-eruptive system of Campi Flegrei (Italy) / Bonechi, B.; Stagno, V.; Kono, Y.; Ziberna, L.; Perinelli, C.; Gaeta, M.. - STAMPA. - (2018), pp. 410-410. (Intervento presentato al convegno Congresso congiunto SGI-SIMP "Geosciences for the enviroment, natural hazards and cultural heritage" tenutosi a Catania).
Viscosity of alkaline basalts at high pressure: constraints on the pre-eruptive system of Campi Flegrei (Italy)
Bonechi B.
;Stagno V.;Perinelli C.;Gaeta M.
2018
Abstract
The Campi Flegrei Volcanic District (CFVD) includes the Campi Flegrei caldera, the islands of Procida and Ischia, and it is among the most dangerous volcanic systems of the world. The volcanic activity that has characterized the recent eruptive history of the CFVD includes both effusive and hydromagmatic eruptions that resulted in a variety of igneous products from alkaline basalts to trachytes. Among CFVD products, basaltic lava fragments dispersed in the hydromagmatic tuff of the Solchiaro eruption (Procida island) result to be representative of near-primary melts on the basis of their geochemical and isotopical signatures. The knowledge of the viscosity of primitive magmas at high pressure and temperature is needed to model their mobility and ascent rate. These variables allow us to predict the potential volcanic activity at surface. In this study, we investigated the viscosity and melt structure of APR16 alkaline basalt, a lava fragment of the Solchiaro eruption. The anhydrous glassy starting material was prepared at Bayerisches Geoinstitut by using a gas-mixing furnace, by melting the APR16 rock powder at 1400 °C for 15 minutes at atmospheric pressure and oxygen fugacity buffered at Nickel-Nickel Oxide level using a CO/CO2 gas mixture. Experiments were performed at pressure between 0.7 and 2.3 GPa and temperatures of 1200 °C-1700 °C using the Paris- Edinburgh press combined with synchrotron X-ray technique at beamline 16-BM-B (HPCAT) of the Advanced Photon Source (Argonne National Laboratory, Illinois, USA). Viscosity measurements were conducted with the falling sphere technique. The falling velocity of the platinum probing sphere was measured at each run by ultrafast X-ray radiography using a high-speed camera at 500 frames per second as recording rate. The viscosity was, then, calculated from the Stokes’ equation including the correction factors for the effect of the wall and the end effect (Kono et al., 2014). Structural measurements of the liquid at 1700 °C and 2.3 GPa were also performed using multi-angle (2θ angle between 3° to 35°) energy dispersive X-ray diffraction technique. Preliminary results show the viscosity increasing from 0.1 to 1 Pa·s as pressure decreases from which an increase in the polymerization during decompression can be inferred. Our results are used to constrain the mobility and ascent velocity of primitive alkaline basalts considered to be parental magmas at Campi Flegrei with important implications for the potential volcanic hazard of the area. Kono, Y., Park, C., Kenney-Benson, C., Shen, G. & Wang, Y. (2014): Toward comprehensive studies of liquids at high pressures and high temperatures: Combined structure, elastic wave velocity, and viscosity measurements in the Paris- Edinburgh cell. Phys. Earth Planet. Inter., 228, 269-280.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.