Recognition of pervasive prestrain in the total-strain pattern of large folds

Abstract

Two methods are introduced for identifying states of pervasive prefold strain in the total-strain field of large domes or basins. The first method relies on the symmetry rule and is restricted to structures in which the planes of effective symmetry of the total-strain field are non-coincident with those of the fold form. The second method seeks to demonstrate the existence of a strain-induced anisotropy (foliation or lineation) prior to upright folding, and utilizes narrow décollement zones within homogeneous rock units of domes or basins. The methods are applied to large oval structures in two Precambrian gneiss terranes of Ontario.