Title

A new HPHT rheometer for measuring the viscosity of volatile-bearing magmas

Abstract

Magma rheology provides the primary control on magma flow and eruptive dynamics. Consequently, reliable measurements of the viscosity of volatile-bearing magmatic melts at the high pressures and high temperatures (HPHT) experienced in magma chambers and conduits are needed to constrain models. To-date measurements of the viscosity of high temperature melts have been largely limited to anhydrous melts (ambient P, HT) due to the technical challenges posed in making rheological measurements inside a pressurized device. In this talk, we will present a new HPHT rheometer that is capable of achieving pressures and temperatures up to 250 MPa and 1200C and measuring viscosities in the range 100Pas-30,000Pas. This is a concentric cylinder HPHT instrument that connects an external rheometer head to an internal spindle using a magnetic coupling. We will discuss the technical features and challenges that result in an uncertainty on the viscosity measurements of ±5%. We will also present preliminary data obtained for pantellerite melts.

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