Viscosity of Basic Magmas at Varying Pressure

Abstract

THE viscosity of magmas is an important parameter in problems concerning the generation and emplacement of magmatic rocks^1,2, but no experimental data exist on hydrous basaltic melts. Here I describe laboratory determinations of the viscosity of some basic melts at one atmosphere and at high water pressures and their relationship to melt chemistry³. Basic rocks ranging in composition from basic andesite to olivine melanephelinite had viscosities between 4,000–100 (±5%) poise at temperatures near the liquidus (1,200° C) at one atmosphere. At higher temperatures (1,400° C) viscosities ranged from 260–15 (±5%) poise (Fig. 1). These results are in fair agreement with previous work using a concentric-cylinder method^4–9. I also found, in agreement with previous work^9,10, that the redox state of basic melts had only a marginal effect on viscosities.