Deformation studies in the Irish Caledonides

SUMMARY: An interpretation of the major structure of parts of the Irish Caledonides is made, based on the results of mapping of the main early penetrative fabrics. Interpretation of major changes in fabric are attributed to strain variation, and models are developed to explain these changes. The regional nappe structures in the Dalradian rocks have been modified by (1) D, slide zones, and (2) a D, sinistral shear zone adjacent to the Main Donegal Granite in NW Donegal. In N Mayo the major structure is interpreted in terms of a steep dextral E-W shear zone modifying the early formed nappe pile. The strain history adjacent o the Iapetus suture in central Ireland is described and a wide zone of non-axial planar cleavage discussed. In SE Ireland the regional strain pattern is modified in the tectonic aureole of the Leinster Granite. The main features of Caledonian structure in Ireland have been summarized by Phillips et al. (1976), and discussed in relation to the British Caledonides by Johnson et al. 1979. The purpose of this paper is to present the results ot a project involving the compi-lation and analysis of shape fabric and other data o