TY - JOUR

T1 - Rheological evolution of eruptible Basaltic-Andesite Magmas under dynamic conditions

T2 - The importance of plagioclase growth rates

AU - Vetere, Francesco

AU - Petrelli, Maurizio

AU - Perugini, Diego

AU - Haselbach, Sarah

AU - Morgavi, Daniele

AU - Pisello, Alessandro

AU - Iezzi, Gianluca

AU - Holtz, Francois

N1 - Funding Information: This research was funded by the Alexander von Humboldt Foundation senior research grant to F. Vetere and by European Research Council Consolidator Grant ERC-2013-COG No. 612776 (CHRONOS project) to D. Perugini. D. Morgavi acknowledge the MIUR, project no. PRIN 2017-2017LMNLAW “Connect4Carbon”. G. Iezzi and F.Vetere acknowledge PRIN ( 2017J277S9_003 ) project “Time scales of solidification in magmas: Application to Volcanic Eruptions, Silicate Melts, Glasses, Glass- Ceramics” awarded to G. Iezzi. Authors wish to thank G. Carunchio for insightful discussion. Detailed and useful comments by Dr. Fabio Arzilli and an anonymous reviewer improved the final version of this study. Precious suggestions, revisions and handling by the E. Prof. K. Russell are warmly acknowledged. Funding Information: This research was funded by the Alexander von Humboldt Foundation senior research grant to F. Vetere and by European Research Council Consolidator Grant ERC-2013-COG No. 612776 (CHRONOS project) to D. Perugini. D. Morgavi acknowledge the MIUR, project no. PRIN 2017-2017LMNLAW ?Connect4Carbon?. G. Iezzi and F.Vetere acknowledge PRIN (2017J277S9_003) project ?Time scales of solidification in magmas: Application to Volcanic Eruptions, Silicate Melts, Glasses, Glass- Ceramics? awarded to G. Iezzi. Authors wish to thank G. Carunchio for insightful discussion. Detailed and useful comments by Dr. Fabio Arzilli and an anonymous reviewer improved the final version of this study. Precious suggestions, revisions and handling by the E. Prof. K. Russell are warmly acknowledged.

PY - 2021/12

Y1 - 2021/12

N2 - The effects of crystal nucleation and growth on the viscosity of andesitic magmas are investigated at 1 atm. Pressure. The data are used to describe the rheological evolution of andesitic magmas and to derive empirical equations to model the crystallization dynamics. Viscosity experiments were performed at temperatures of 1473, 1483, and 1493 K with shear rates of 0.5 s−1 by using wide-gap concentric cylinder viscometry. We focused on eruptible magmas (i.e., crystal contents well-below ~50%) by following the time evolution of crystal nucleation and growth of a natural andesitic magma, while continuously monitoring the changes in viscosity. At near-equilibrium conditions, the basaltic-andesite contains 6, 13, and 25 area % crystals at 1493, 1483, and 1473 K, respectively, resulting in a viscosity increase of ca. 1 log unit. We show that the timescale of viscosity increase is mainly dictated by the delay time preceding crystallization and markedly decreases with increasing undercooling (from 22 to 42 K) and shear rates (from 0.1 to 1 s−1). The plagioclase growth rates estimated from our data are in the order of ~3–5 × 10−6 cm/s, which is much faster than the rates estimated for crystallization in static conditions. We conclude that the effect of the shear rate must be taken into account in modelling magmatic and volcanic processes, especially when transient changes in viscosity need to be estimated. Our results are important for understanding the dynamics of lava flows where deformation plays a significant role in promoting crystallization.

AB - The effects of crystal nucleation and growth on the viscosity of andesitic magmas are investigated at 1 atm. Pressure. The data are used to describe the rheological evolution of andesitic magmas and to derive empirical equations to model the crystallization dynamics. Viscosity experiments were performed at temperatures of 1473, 1483, and 1493 K with shear rates of 0.5 s−1 by using wide-gap concentric cylinder viscometry. We focused on eruptible magmas (i.e., crystal contents well-below ~50%) by following the time evolution of crystal nucleation and growth of a natural andesitic magma, while continuously monitoring the changes in viscosity. At near-equilibrium conditions, the basaltic-andesite contains 6, 13, and 25 area % crystals at 1493, 1483, and 1473 K, respectively, resulting in a viscosity increase of ca. 1 log unit. We show that the timescale of viscosity increase is mainly dictated by the delay time preceding crystallization and markedly decreases with increasing undercooling (from 22 to 42 K) and shear rates (from 0.1 to 1 s−1). The plagioclase growth rates estimated from our data are in the order of ~3–5 × 10−6 cm/s, which is much faster than the rates estimated for crystallization in static conditions. We conclude that the effect of the shear rate must be taken into account in modelling magmatic and volcanic processes, especially when transient changes in viscosity need to be estimated. Our results are important for understanding the dynamics of lava flows where deformation plays a significant role in promoting crystallization.

KW - Magma

KW - Melt viscosity

KW - Plagioclase growth rate

KW - Shear rate

KW - Undercooling

UR - http://www.scopus.com/inward/record.url?scp=85117371304&partnerID=8YFLogxK

U2 - 10.1016/j.jvolgeores.2021.107411

DO - 10.1016/j.jvolgeores.2021.107411

M3 - Article

AN - SCOPUS:85117371304

VL - 420

JO - Journal of Volcanology and Geothermal Research

JF - Journal of Volcanology and Geothermal Research

SN - 0377-0273

M1 - 107411

ER -