Abstract provided by author in published thesis:
At the southwestern margin of the Damara Orogen in Namibia, the dolomite-sequence of an upper-proterozoic carbonate platform underwent a two-staged deformation (Pan-African) under the metamorphic conditions of the higher greenschist facies. The relationship between the grain shape fabric, the crystallographic preferred orientation (texture) and the macroscopic structural elements (foliation, lineation, folds etc.) gives a definite indication for the structure-forming processes and the kinematics. One of the essential scopes of this study is the quantitative texture analysis of the mono- and polyphase dolomitic rocks, which was further supplemented by single grain orientation analysis and the simulation of textures
The dolomite textures can be characterised by two texture fibre-types: the c-axis fibre-type, defined by fibre-axis-parallel c-axis orientations and the a-axis-fibre-type, defined by fibre-axis-parallel a-axis-orientations. The c-axis fibre-type is associated with a preferred grain shape fabric of a strong grain elongation and a small angle (ca. 10°) between the oblique grain shape foliation and the main foliation. In contrast, the a-axis fibre-type is associated with none, or only a weak preferred grain shape orientation and a high angle (ca. 30°) between the oblique grain shape foliation and the main foliation. From the position of the samples within the fold-structures, the textures can be correlated with a strain path. If the fabric development is dominated by a strain field of coaxial flattening, as found within thinned fold limbs, the c-axis fibre-type is produced. The c-axis maximum is located within or nearby the main foliation pole. If a strain field is superimposed by rigid-body rotation, as found within fold hinges and overturned limbs, the a-axis fibre-type is developed. The c-axis orientations form a girdle whose axis is inclined against the lineation or the fold axis within a plane perpendicular to the main foliation. In accordance with the oblique grain shape fabric, the inclination can be based on a fold axis-parallel shear component. Texture simulations show that for axialsymmetric compression, pure shear and simple shear only the c-axis fibre-type is developed. This supports the idea that the a-axis fibre-type is solely produced by a strain field, which is superimposed by rigid-body-rotation
On the basis of their monoclinic symmetry, the preferred orientation of the rhombohedral planes can be used as a "way-up"-criteria for the texture. This allows conclusions to be made on the development of fold structures in greater detail. Conclusions regarding the kinematics of the microscopic scale can be drawn from single grain orientation analyses, because they prove a heterogeneous texture for coarse- and fine-grained fabric domains, but also for different fine-grained domains. For a quantitative localisation of these homogeneous texture domains, texture components are established to define orientation families. Additional interpretations on the fabric development can be ascertained from the texture analysis of dolomite/calcite-rocks, which reveal similar and different textures for dolomite and calcite. In combination with the grain shape fabric observations, the similar textures can be associated with a "texture inheritance" during exsolution process. In contrast, the different textures can be associated different strain increments. The total results show a stronger structural overprint due to the older deformation phase, which is in direct opposition to the initial field observations