Abstract

It is a frequently reported feature of basement terranes that dikes intruded late in the deformation sequence become sheared parallel to the dike margins. It is proposed that such sets of sheets with internal fabrics produced by this shearing along their walls are structures which are dynamically analogous to reactivated faults. This would imply that orientation data from dike attitude and internal foliation can be analyzed in a similar fashion to fault/striation data and used to determine a regional stress tensor. To illustrate the possible form the analysis would take, a newly devised method, the "right trihedra method" of striation analysis, is applied to data from deformed intrusive sheets in Donegal and western Greenland. The results consist of estimates of the orientation of principal axes of paleostress (σ1, σ2, and σ3) and the ratio of the principal stress differences, R [=(σ23)/(σ12)].

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