Detailed stress analysis is of great importance to the structural geologist in the interpretation of various structural features. Of the many methods which have been devised to aide in dynamic analysis, the more promising has been in the use of calcite twin lamellae for the derivation of principal stress orientations.

Most work to date has centered on the analysis of detrital calcite grains in experimentally and naturally deformed limestones.

This paper summarizes research on the dynamic analysis of calcite twin lamellae occurring in calcite-filled fractures.

Four hand samples containing calcite-filled fractures were removed from the Lincolnshire Formation, an Ordovician limestone of the central Appalachians near Strasberg, Virginia. Before removal of the samples, the fracture type, relative age, and orientation were recorded. The standard techniques of dynamic analysis developed for such studies were applied to data from thin sections prepared from each sample.

It is presumed that the development of fractures and the subsequent filling with calcite occur in progressive stages throughout the phase of deformation. It is expected that the dynamic analysis of each calcite-filled fracture will yield information concerning the stress orientations present at the time of the associated stage of fracture development.

By sampling calcite-filled fractures of differing ages it is possible to follow the principal stress orientations throughout the progressive stages of deformation. Thus, by this method it is possible to derive the incremental stress orientations for each stage of fracture development. Present methods of dynamic analysis using detrital calcite provide only the principal stress orientations of the finite deformation.

By being able to derive the incremental stress orientations of a progressive deformation, a more detailed deformational history is obtained.

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