The roles of fabric and micas in the deformation of foliated rocks : an experimental study /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | I have investigated the transitional, brittle-plastic deformation of mica-rich polycrystals by shortening samples of 15 schists and gneisses with mica contents of 15% to 75% (by volume) at 45° (orientation x45z) and 90° (orientation z) to foliation (S) at nominally-dry, shallow crustal conditions, and correlating initial and deformed microstructures with the mechanical behavior observed. At room temperature (7'), 200 MPa confining pressure (P[c]), and a constant strain rate of 10^-5 s^-1, strains in all samples were localized within discrete shear zones oriented at 28° to 50° to the compression axis, and were accommodated by slip and intense micro-kinking in micas and microcracking in all phases. In both the x45z and z orientations, distinct deformation regimes of brittle fracture, transitional strain-softening response, and ductile shear were recognized. Extensive microcracking of strong silicate bridges is required for strain localization to occur in brittle and transitional samples, while ductile shear zones localize through the nucleation and coalescence of dense sets of intragranular micro-kink bands (MKBs) within inclined zones of nearly-interconnected micas. Strength and ductility correlate most directly with the contiguity of micas along prospective failure planes, which in z-oriented samples is similar to bulk mica content. Shear zones localize parallel or at shallow angles to S in x45z-oriented samples, and ductile shear is favored with increasing interconnectedness of discrete, foliation-parallel mica segregations. At low mica contents (< 20%) the degree of mechanical anisotropy increases with increasing preferred orientation of micas parallel to S, while at higher mica contents, strong mechanical anisotropies were only observed in rocks in which mica contiguity varies markedly along planes inclined at different angles to foliation. The most mica-rich schist (75% biotite) exhibited isotropic response, and I investigated its rheology at strain rates from 10^-4-10^-7 s^-1, temperatures from 25° to 400°C, and P[c] 's to 500 MPa... |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Geology." |
| Physical Description: | xi, 172 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |