TY - JOUR

T1 - The effect of water on the viscosity of a synthetic calc-alkaline basaltic andesite

AU - Robert, Geneviève

AU - Whittington, Alan G.

AU - Stechern, André

AU - Behrens, Harald

N1 - Funding Information: We thank J. Knipping at Leibniz Universität Hannover (LUH) for KFT analyses, A. Sehlke and S. Wilke at LUH for help with IR measurements, and O. Dietrich at LUH for impeccable sample preparation. Constructive reviews by Kai-Uwe Hess and an anonymous reviewer improved the manuscript. This research is supported by NSF CAREER grant EAR-0748411 (AGW). Additional support by the German DFG grant BE 1720/24-1,2 (HB) and DAAD and NSERC fellowships (GR) is acknowledged.

PY - 2013/5/27

Y1 - 2013/5/27

N2 - The viscosity of a series of 6 Fe-free, synthetic basaltic andesite liquids, containing up to 3.76wt.% dissolved water, was measured in the range of the glass transition (108-1013Pas) by parallel-plate viscometry. Concentric-cylinder and falling-sphere viscometry provided high-temperature measurements (10-103Pas) on basaltic andesite liquids containing up to 2wt.% dissolved water. The viscosity (· in Pas) of Fe-free basaltic andesite can be described as a function of temperature (T in Kelvin) and water content (w in wt.%) by the expression log(·)=-4.81+6940.7/(T-{491.9-272.5 log[w+0.49]}).This parameterization reproduces 55 viscosity data with a root-mean-square-deviation (RMSD) of 0.24 log units in viscosity. The results of this viscometry study suggest that basaltic andesite liquids should remain very fluid, even while undergoing equilibrium degassing, to pressures as low as 50MPa (i.e., less than 2km depth). Only a modest increase in viscosity of at most a factor of 100 would occur in the last 2km of ascent. Furthermore, our results show that water affects the viscosity of a wide range of depolymerized melts to a similar degree. For example, the addition of 2wt.% dissolved H2O reduces the viscosity of andesite, basaltic andesite, basalt and their alkalic counterpart liquids by a factor of ~15-50.

AB - The viscosity of a series of 6 Fe-free, synthetic basaltic andesite liquids, containing up to 3.76wt.% dissolved water, was measured in the range of the glass transition (108-1013Pas) by parallel-plate viscometry. Concentric-cylinder and falling-sphere viscometry provided high-temperature measurements (10-103Pas) on basaltic andesite liquids containing up to 2wt.% dissolved water. The viscosity (· in Pas) of Fe-free basaltic andesite can be described as a function of temperature (T in Kelvin) and water content (w in wt.%) by the expression log(·)=-4.81+6940.7/(T-{491.9-272.5 log[w+0.49]}).This parameterization reproduces 55 viscosity data with a root-mean-square-deviation (RMSD) of 0.24 log units in viscosity. The results of this viscometry study suggest that basaltic andesite liquids should remain very fluid, even while undergoing equilibrium degassing, to pressures as low as 50MPa (i.e., less than 2km depth). Only a modest increase in viscosity of at most a factor of 100 would occur in the last 2km of ascent. Furthermore, our results show that water affects the viscosity of a wide range of depolymerized melts to a similar degree. For example, the addition of 2wt.% dissolved H2O reduces the viscosity of andesite, basaltic andesite, basalt and their alkalic counterpart liquids by a factor of ~15-50.

KW - Basaltic andesite

KW - Explosive volcanism

KW - Viscosity

KW - Water

UR - http://www.scopus.com/inward/record.url?scp=84876980401&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2012.10.004

DO - 10.1016/j.chemgeo.2012.10.004

M3 - Article

AN - SCOPUS:84876980401

VL - 346

SP - 135

EP - 148

JO - Chemical geology

JF - Chemical geology

SN - 0009-2541

ER -