""We have investigated the effect of undercooling. and deformation on the evolution of the texture and the. crystallization kinetics of remelted basaltic material from. Stromboli (pumice from the March 15, 2007 paroxysmal. eruption) and Etna (1992 lava flow). Isothermal crystallization. experiments were conducted at different degrees of. undercooling and different applied strain rate (T = 1,157–. 1,187 C and _ci = 4.26 s-1 for Stromboli; T = 1,131–. 1,182 C and _ci = 0.53 s-1 for Etna). Melt viscosity. increased due to the decrease in temperature and the increase. in crystal content. The mineralogical assemblage comprises. Sp ? Plg (dominant) ± Cpx with an overall crystal fraction. (\\\/) between 0.06 and 0.27, increasing with undercooling and. flow conditions. Both degree of undercooling and deformation. rate deeply affect the kinetics of the crystallization. process. Plagioclase nucleation incubation time strongly. decreases with increasing DT and flow, while slow diffusionlimited. growth characterizes low DT—low deformation rate. experiments. Both Stromboli (high strain rate) and Etna (low. strain rate) plagioclase growth rates (G) display relative. small variations with Stromboli showing higher values. (4.8 ± 1.9 9 10-9 m s-1) compared to Etna (2.1 ± 1.6 9. 10-9 m s-1). Plagioclase average nucleation rates J continuously. increase with undercooling from 1.4 9 106 to 6.7 9. 106 m-3 s-1 for Stromboli and from 3.6 9 104 to 4.0 9 106. m-3 s-1 for Etna. The extremely low value of 3.69104m-3. s-1 recorded at the lowest undercooling experiment for Etna. (DT = 20 C) indicates that the crystallization process is. growth-dominated and that possible effects of textural. coarsening occur. G values obtained in this paper are generally. one or two orders of magnitude higher compared to. those obtained in the literature for equivalent undercooling. conditions. Stirring of the melt, simulating magma flow or. convective conditions, facilitates nucleation and growth of. crystals via mechanical transportation of matter, resulting in. the higher J and G observed. Any modeling pertaining to. magma dynamics in the conduit (e.g., ascent rate) and lava. flow emplacement (e.g., flow rate, pa¯hoehoe–‘a‘a¯ transition). should therefore take the effects of dynamic crystallization. into account.""
Vona, A., Romano, C. (2013). The effects of undercooling and deformation rates on the crystallization kinetics of Stromboli and Etna basalts. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 166(2), 491-509 [10.1007/s00410-013-0887-0].
The effects of undercooling and deformation rates on the crystallization kinetics of Stromboli and Etna basalts
VONA, ALESSANDRO;ROMANO, Claudia
2013-01-01
Abstract
""We have investigated the effect of undercooling. and deformation on the evolution of the texture and the. crystallization kinetics of remelted basaltic material from. Stromboli (pumice from the March 15, 2007 paroxysmal. eruption) and Etna (1992 lava flow). Isothermal crystallization. experiments were conducted at different degrees of. undercooling and different applied strain rate (T = 1,157–. 1,187 C and _ci = 4.26 s-1 for Stromboli; T = 1,131–. 1,182 C and _ci = 0.53 s-1 for Etna). Melt viscosity. increased due to the decrease in temperature and the increase. in crystal content. The mineralogical assemblage comprises. Sp ? Plg (dominant) ± Cpx with an overall crystal fraction. (\\\/) between 0.06 and 0.27, increasing with undercooling and. flow conditions. Both degree of undercooling and deformation. rate deeply affect the kinetics of the crystallization. process. Plagioclase nucleation incubation time strongly. decreases with increasing DT and flow, while slow diffusionlimited. growth characterizes low DT—low deformation rate. experiments. Both Stromboli (high strain rate) and Etna (low. strain rate) plagioclase growth rates (G) display relative. small variations with Stromboli showing higher values. (4.8 ± 1.9 9 10-9 m s-1) compared to Etna (2.1 ± 1.6 9. 10-9 m s-1). Plagioclase average nucleation rates J continuously. increase with undercooling from 1.4 9 106 to 6.7 9. 106 m-3 s-1 for Stromboli and from 3.6 9 104 to 4.0 9 106. m-3 s-1 for Etna. The extremely low value of 3.69104m-3. s-1 recorded at the lowest undercooling experiment for Etna. (DT = 20 C) indicates that the crystallization process is. growth-dominated and that possible effects of textural. coarsening occur. G values obtained in this paper are generally. one or two orders of magnitude higher compared to. those obtained in the literature for equivalent undercooling. conditions. Stirring of the melt, simulating magma flow or. convective conditions, facilitates nucleation and growth of. crystals via mechanical transportation of matter, resulting in. the higher J and G observed. Any modeling pertaining to. magma dynamics in the conduit (e.g., ascent rate) and lava. flow emplacement (e.g., flow rate, pa¯hoehoe–‘a‘a¯ transition). should therefore take the effects of dynamic crystallization. into account.""I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
