HR: 0800h
AN: V21A-0597    [Abstracts]
TI: Stress-Driven Melt Segregation and Organization in Partially Molten Rocks I: Experimental Observations of Coupled Evolution of Melt Distribution and Rheological Properties
AU: * Hustoft, J W
EM: hust0059@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AU: Holtzman, B K
EM: holtz007@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AU: Kohlstedt, D L
EM: dlkohl@umn.edu
AF: University of Minnesota, Dept of Geology and Geophysics 310 Pillsbury Dr SE, Minneapolis, MN 55455 United States
AB: In this series of three papers, we present an experimental study on synthetic partially molten olivine-dominated rocks deformed at high temperatures and pressures, equivalent to several kilometers into the Earth's mantle. During progressive deformation of samples of olivine + MORB, olivine + FeS melt + MORB, and olivine + chromite + MORB, an initially homogeneous melt distribution evolves into well-defined networks of melt-rich bands or channels. These experiments demonstrate the effectiveness of deviatoric stress as a driving force for melt segregation and organization. To explore the dynamics of this process (and ultimately to understand its importance for melt extraction in the Earth and planets), we demonstrate several fundamental observations: (1) With increasing strain (or time), melt progressively segregates and organizes into anastomosing networks of channels not unlike braided streams in two dimensions. (2) The rate of melt-segregation and formation of the melt-rich networks appears to depend on compaction length, a length scale combining several two-phase transport properties and applied stress, to which the compaction length is coupled through stress-dependent viscosity. (3) The characteristic morphology of the melt-rich networks also appears to depend very strongly on applied stress. We demonstrate these phenomena using several statistical descriptions of the melt distribution combined with rheological data. The bulk rheological properties are strongly influenced by the segregation of melt and demonstrate complex relationships between strain partitioning and deformation mechanisms. In the companion papers, we present further aspects of the same data set to provide a global picture of the coupling of melt segregation and strain partitioning into the melt-rich, and thus relatively weak, networks.
DE: 8162 Rheology--mantle
DE: 5112 Microstructure
DE: 5114 Permeability and porosity
DE: 3902 Creep and deformation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting