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1 Department of Geology, School of Geosciences, Queen's University of Belfast BT7 1NN, UK
2 Department of Geology and Petroleum Geology, King's College, University of Aberdeen AB9 2UE, UK
Recent mapping in the Glen Shee Area, Central Scotland, has revealed an array of several large-scale F1 folds within the 'Flat Belt' of the Tay Nappe. Strata within the 'Flat Belt', 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 'Flat Belt'. The upper limit of D2 deformation forms the boundary between the strongly deformed and inverted 'lower limb' and the right-way-up 'upper limb' 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.
Keywords: Dalradian, shear zones, nappes, strain, orogeny.
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