Generation of the Tay Nappe, Scotland, by large-scale SE-directed shearing

Abstract

Recent mapping in the Glen Shee Area, Central Scotland, has revealed an array of several large-scale F1 folds within the 9Flat Belt9 of the Tay Nappe. Strata within the 9Flat Belt9, forming part of the lower limb of the Tay Nappe, are thus not entirely inverted, and the traditional view that the Nappe in this area comprises a single SE-facing, recumbent anticline is rejected. It is demonstrated that the sense of shear of D2 was top-to-the-SE, resulting in NW-verging F2 folds by strong D2 strain partitioning. Strain estimates indicate adisplacement of 10–50 km during D2 shearing. In the proposed model, originally upright F1 folds were modified by a major D2 shearing event that produced a shallow NW dipping S2 foliation in the 9Flat Belt9. The upper limit of D2 deformation forms the boundary between the strongly deformed and inverted 9lower limb9 and the right-way-up 9upper limb9 which is undeformed by D2, and is now mostly removed by erosion. The D2 shear event was responsible for the gross stratigraphic inversion in the Flat Belt. The Tay Nappe is considered here as formed by a crustal-scale shear zone; in this model there is no necessity to invoke a root zone.