HR: 1340h
AN: MR23B-1326    [Abstracts]
TI: An EBSD study of texture development and hybrid deformation mechanisms in fine grained calcite aggregates deformed in direct shear
AU: * Maeder, X
EM: maeder@geo.uu.nl
AF: Departement of Earth Sciences, Utrecht University, P.O. box 80021, Utrecht, 3508 TA, Netherlands
AU: Trullenque, G
EM: trullenq@uni-mainz.de
AF: Institut fuer Geowissenschaften, Johannes Gutenberg Universitaet, Becherweg 21, Mainz, 55099, Germany
AU: Drury, M R
EM: martynd@geo.uu.nl
AF: Departement of Earth Sciences, Utrecht University, P.O. box 80021, Utrecht, 3508 TA, Netherlands
AU: De Bresser, J
EM: j.h.p.debresser@geo.uu.nl
AF: Departement of Earth Sciences, Utrecht University, P.O. box 80021, Utrecht, 3508 TA, Netherlands
AB: Understanding of texture development and its relation to grain size sensitive (GSS) deformation mechanism is of great importance since the rheological behavior of rocks varies substantially depending on which deformation mechanisms are controlling. Recent studies on naturally and experimentally deformed calcite and olivine aggregates have demonstrated that even fine grained materials that are expected to deform by grain size sensitive (GSS) mechanisms, develop a weak but distinct LPO (texture) at high strain. To investigate this behavior we conducted new deformation experiments on Solnhofen limestone in direct shear. This study is part of a wider investigation on large strain deformation in different deformation modes from G. Trullenque, in collaboration with D.L. Kohlstedt (Minneapolis, USA), R. Heilbronner and H. Stuenitz (Basel, Switzerland) and the Utrecht group. The samples have been deformed to high strain both in the conditions of the transition between the GSS and GSI creep regime and in the GSS creep regime. We used Electron Backscatter Diffraction (EBSD) to determine the texture strength of the samples, the distribution of misorientation axes and the grain size distributions. The results show an oblique shape preferred orientation at 35° to 40° to the shear plane and a moderate LPO. The c-axis preferred orientation shows a girdle with one main maximum at a high angle to the shear plane, displaced towards the shortening direction of the imposed shear. The a-axes present a weak girdle perpendicular to the c-axis. Grain growth occurred during high deformation. The misorientation angle distribution has a main peak at low angle. This is due to the progressive subgrain formation and rotation which occurred mainly in the larger grains. Subgrain rotation with misorientations up to 10° occured but most boundaries are low angle (< 5°). This shows the formation of new high angle boundaries and grain size reduction. The formation of subgrains and subgrain rotation, along with the fact that the larger grain fraction shows a slightly stronger LPO than the fine grain fraction, suggest a component of dislocation creep in the coarser grains. We suggest therefore that the GSS regime in the fine grain aggregates may be a transient stage evolving into hybrid deformation (GSI and GSS mechanisms) at high strain. The next steps in this study will be to quantify the contribution of the GSI and GSS mechanisms through the EBSD study and develop a new flow law for the hybrid deformation of the Solnhofen limestone.
DE: 3902 Creep and deformation
DE: 8030 Microstructures
DE: 8032 Rheology: general (8160)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting