Calcite c-axis textures along the Gavarnie thrust zone, central Pyrenees

Orientations of calcite c-axes have been measured in limestones from the eastern part of the Gavarnie thrust zone, central Pyrenees. They show preferred orientations (textures) with one or more maxima. By comparing the textures with existing experimental and theoretical data, it was possible: a) to confirm the regional sense of movement along the thrust, b) to interpret a significant contribution of pure shear to the total strain in the thrust zone, and c) to recognize natural patterns which have not been reported before. It is suggested that the studied limestone samples were deformed at a temperature of about 200°C in a transitional regime with textures ranging from low to high temperature types. Specific rock properties may have governed the local predominance of a high or conversely of a low temperature type. The data, however, appear to exclude grain size as a controlling factor. -Author