Regional structure and syntectonic granite intrusion in the Dalradian of the Gweebarra Bay area, Donegal

Abstract

6 phases of deformation are recognized in the Appin Group (Lower Dalradian) metasediments around Gweebarra Bay. The major early folds are F 2 in age (including the Crohy and Maghery Anticlines) facing up to the N or NE. S 2 transposes an earlier fabric (S 1 ) which is only rarely preserved. No major or minor F 1 folds are recognized and the facing of S 1 is unknown. D 3 produces structures verging S on S 2 but does not produce major folds comparable with D 2 . The Maghery Anticline, previously interpreted as changing from an open upright fold in the SE to overturned in the NW, is shown to be overturned throughout. Previous interpretation involving the re-folding of the Maas Syncline by the upright Mulnamin Anticline is not supported and both major folds are now interpreted as D 4 , in age, with the axial plane of the Mulnamin Anticline dipping moderately or gently S. D 4 , is a regional deformation phase synchronous with the intrusion of the Ardara Granite. D 5 , structures are upright or face to the N. The development of a major NE–SW trending sinistral shear zone adjacent to the SW end of the Main Donegal Granite is synchronous with D 5 , deformation, F 5 , folds rotating into sub-parallelism with the shear planes.