HR: 1340h
AN: V53C-1583    [Abstracts]
TI: Non-Newtonian Rheology of Calc-Alkaline Obsidian at High Stresses and Strain Rates
AU: * Dingwell, D B
EM: dingwell@lmu.de
AF: LMU, Department of Earth and Environmental Sciences, Munich, 80333 Germany
AU: Hess, K
EM: hess@lmu.de
AF: LMU, Department of Earth and Environmental Sciences, Munich, 80333 Germany
AU: Lavallee, Y
EM: yanlavallee@hotmail.com
AF: LMU, Department of Earth and Environmental Sciences, Munich, 80333 Germany
AU: Cordonnier, B
EM: cordonnier@min.uni-muenchen.de
AF: LMU, Department of Earth and Environmental Sciences, Munich, 80333 Germany
AU: Mueller, S
EM: mueller@min.uni-muenchen.de
AF: LMU, Department of Earth and Environmental Sciences, Munich, 80333 Germany
AB: The importance of the Non-Newtonian regime at high stress and strain rates has been reported for a variety of silicate melts subject to different tests but never for natural samples bearing their original contents of magmatic water and microlite content. Here, we used a unique high-load (<500 MPa), high-temperature (<1300°C) deformation apparatus for studying in situ the Non-Newtonian flow behaviour of magmas. A series of experiments were performed on calc-alkaline obsidian lavas from Lipari (Italy), Iceland, and Cougar Creek Dome, Yellowstone (USA), and compared to depolymerized melt (NIST 710). The samples were heated to relevant magmatic effusive temperatures that yielded similar relaxation timescales and were deformed under constant stress in the range of 100 to 200 MPa.
The onset of the Non-Newtonian flow regime, registered by a decreasing viscosity with time (at fixed strain rate), occurred at 120 MPa for the depolymerized melt. The Non-Newtonian flow behavior was observed up to pressures as high as approx. 180 MPa, where the samples fragmented readily (hot cracking). In contrast, all three calc-alkaline rhyolitic melt remained in a Newtonian regime up to approx. 160 MPa. The window of Non-Newtonian behavior was, however, very narrow and most samples fragmented instantaneously in the attempt of pursuing the deformation. If this is not an experimental artefact, we conclude that modeling of the flow behaviour of a ascending crystal- and bubble-free calc-alkaline rhyolitic dome magma can be performed using a simple Newtonian fluid approximation. Thus the Non-Arrhenian model of Hess and Dingwell (1996) for the compositional and temperature dependence of viscosity could be applied.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8425 Effusive volcanism
DE: 8428 Explosive volcanism
DE: 8429 Lava rheology and morphology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005