TY - JOUR

T1 - Water diffusion in Mount Changbai peralkaline rhyolitic melt

AU - Wang, Haoyue

AU - Xu, Zhengjiu

AU - Behrens, Harald

AU - Zhang, Youxue

N1 - Funding Information: Acknowledgments We thank Bruce Watson and an anonymous reviewer for their insightful and constructive comments, and Huaiwei Ni for providing a sketch of the experimental assembly. H.W. thanks Huaiwei Ni for both helps in the lab and constructive discussion about water diffusion. This research is supported by Chinese NSF grant 40640420141 and US NSF grant EAR-0537598 and EAR-0711050.

PY - 2009/3/12

Y1 - 2009/3/12

N2 - Diffusion couple experiments with wet half (up to 4.6 wt%) and dry half were carried out at 789-1,516 K and 0.47-1.42 GPa to investigate water diffusion in a peralkaline rhyolitic melt with major oxide concentrations matching Mount Changbai rhyolite. Combining data from this work and a related study, total water diffusivity in peralkaline rhyolitic melt can be expressed as: DH2Ot = DH2Om (1- 0.5 - X/√[4exp(3110/T - 1.876) - 1](X - X2) + 0.25), with DH2Om = exp[- 12.789 - 13939/T - 1229.6P/T + (-27.867 + 60559/T)X], where D is in m2s-1, T is the temperature in K, P is the pressure in GPa, and X is the mole fraction of water and calculated as X = (C/18.015)/(C/18.015 + (100 - C)/33.14), where C is water content in wt%. We recommend this equation in modeling bubble growth and volcanic eruption dynamics in peralkaline rhyolitic eruptions, such as the ∼1,000-ad eruption of Mount Changbai in North East China. Water diffusivities in peralkaline and metaluminous rhyolitic melts are comparable within a factor of 2, in contrast with the 1.0-2.6 orders of magnitude difference in viscosities. The decoupling of diffusivity of neutral molecular species from melt viscosity, i.e., the deviation from the inversely proportional relationship predicted by the Stokes-Einstein equation, might be attributed to the small size of H2O molecules. With distinct viscosities but similar diffusivity, bubble growth controlled by diffusion in peralkaline and metaluminous rhyolitic melts follows similar parabolic curves. However, at low confining pressure or low water content, viscosity plays a larger role and bubble growth rate in peralkaline rhyolitic melt is much faster than that in metaluminous rhyolite.

AB - Diffusion couple experiments with wet half (up to 4.6 wt%) and dry half were carried out at 789-1,516 K and 0.47-1.42 GPa to investigate water diffusion in a peralkaline rhyolitic melt with major oxide concentrations matching Mount Changbai rhyolite. Combining data from this work and a related study, total water diffusivity in peralkaline rhyolitic melt can be expressed as: DH2Ot = DH2Om (1- 0.5 - X/√[4exp(3110/T - 1.876) - 1](X - X2) + 0.25), with DH2Om = exp[- 12.789 - 13939/T - 1229.6P/T + (-27.867 + 60559/T)X], where D is in m2s-1, T is the temperature in K, P is the pressure in GPa, and X is the mole fraction of water and calculated as X = (C/18.015)/(C/18.015 + (100 - C)/33.14), where C is water content in wt%. We recommend this equation in modeling bubble growth and volcanic eruption dynamics in peralkaline rhyolitic eruptions, such as the ∼1,000-ad eruption of Mount Changbai in North East China. Water diffusivities in peralkaline and metaluminous rhyolitic melts are comparable within a factor of 2, in contrast with the 1.0-2.6 orders of magnitude difference in viscosities. The decoupling of diffusivity of neutral molecular species from melt viscosity, i.e., the deviation from the inversely proportional relationship predicted by the Stokes-Einstein equation, might be attributed to the small size of H2O molecules. With distinct viscosities but similar diffusivity, bubble growth controlled by diffusion in peralkaline and metaluminous rhyolitic melts follows similar parabolic curves. However, at low confining pressure or low water content, viscosity plays a larger role and bubble growth rate in peralkaline rhyolitic melt is much faster than that in metaluminous rhyolite.

KW - Bubble growth

KW - H<inf>2</inf>O diffusion

KW - Peralkaline rhyolite

KW - Stokes - Einsteine quation

UR - http://www.scopus.com/inward/record.url?scp=84940363643&partnerID=8YFLogxK

U2 - 10.1007/s00410-009-0392-7

DO - 10.1007/s00410-009-0392-7

M3 - Article

AN - SCOPUS:84940363643

VL - 158

SP - 471

EP - 484

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 4

ER -