Rheology of melts and magmatic suspensions. 1. Design and calibration of concentric cylinder viscometer with application to rhyolitic magma

Accurate rheological data for silicate melts and crystal-melt, melt-vapor, and crystal-melt vapor suspensions of both natural compositions and simple binary and ternary systems are useful in constraining theories of momentum transport in magmatic systems and theories of melt structure. Data addressing these problems are presented in a series of papers of which this is the first. A high-torque wide-gap concentric cylinder viscometer has been constructed and used for characterization of the rheometric properties of rhyolitic magma under conditions of varying temperature (1100°-1350°C) and shear rate (0.05-13 s^-1) at 10⁵ Pa total pressure. Two natural rhyolitic starting materials were used in these experiments. Four independent temperature-shear rate cycles were performed on composition RIA (~76% SiO₂) and two independent cycles on composition R2A (~74% SiO₂). Each run had a small (3-8 vol %) fraction of vapor present during viscometric testing. -from Authors