HR: 0830h
AN: S11C-0296    [PDF]
TI: 3D Strain Geometry and Crystallographic Fabric in Experimental HT Deformation of Solnhofen Limestone
AU: * Llana-Funez, S
EM: sergio.llana-funez@man.ac.uk
AF: Rock Deformation Lab Dept. of Earth Sciences University of Manchester, Oxford Road, Manchester, M13 9PL United Kingdom
AU: Rutter, E H
EM: e.rutter@man.ac.uk
AF: Rock Deformation Lab Dept. of Earth Sciences University of Manchester, Oxford Road, Manchester, M13 9PL United Kingdom
AB: Under conditions where calcite deforms plastically, high temperature deformation tests on Solnhofen limestone have been run using different strain configurations: axi-symmetric shortening and extension, and direct shear. The aim of the work is to relate strain geometry and the development of crystallographic fabrics in different strain paths. We produced constrictional, flattening, and nearly plane strain deformations. In addition to this, we were also able to obtain strain geometries where the vorticity axis in a non-coaxial deformation was either perpendicular to the extension direction (as in simple and sub-simple shear) or parallel to it. In order to keep constant as many parameters as possible, all experiments used the same starting material and the same experimental conditions of temperature 600 \deg C, confining pressure 200 MPa and comparable strain rates 10$^{-4}$s$^{-1}$. At these conditions, and taking into account the special features of Solnhofen limestone (i.e. fine grain size and the presence of impurities preventing grain growth), the predominant deformation mechanism was intracrystalline plasticity. We used pole figures of different calcite lattice elements, measured by electron back-scattered diffraction techniques (EBSD), to characterize the asymmetry of the crystallographic patterns and particularly {\it c}-axis pole figures to identify the presence of different fabric components. Further analysis of inverse pole figures in particular experimental directions allowed us to characterize the extension and compression directions of the strain ellipsoid as they geometrically determine the operation of slip systems. Two main aspects can be highlighted from our experimental results. First, it proved particularly useful to combine inverse pole figures with pole figures to characterize not only the shape of the strain ellipsoid in predominantly plastic deformation but also the sense of shear. Second, there is an extraordinary sensitivity of crystal-plastic deformation of calcite to changes in strain geometry, involving changes in shape of the strain ellipsoid but also variations in non-coaxiality. We would expect the same principle to apply to other mineral phases, as long as crystal plasticity is the predominant deformation mechanism.
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 5120 Plasticity, diffusion, and creep
DE: 5194 Instruments and techniques
DE: 8030 Microstructures
SC: Seismology [S]
MN: 2003 Fall Meeting