Fold mechanisms in the Canton Schist: constraints on the contribution of flexural flow

Fold mechanisms operating in the Canton Schist have been resolved using the geometric relationship between folds and spiral inclusion trail geometries . Of the four end-member fold mechanisms, tangential-longitudinal strain fo lding and slip folding are unable to produce the observed inclusion trail a nd fold geometries, but a combination of flexural flow and pure shear foldi ng is consistent with the geometric constraints. The maximum flexural flow component during each fold event was determined from the geometric data. Du ring F-3 and F-4, flexural flow produced less than or equal to 27% and less than or equal to 37% of measured limb rotation, respectively, which corres ponds to a maximum of 24 degrees limb rotation by flexural flow in each fol d event. To satisfy the geometric constraints, the remainder of limb rotati on must be a product of pure shear folding. The maximum possible component of flexural flow folding during F3 and F4 increases with increased variatio n in vorticity between layers in the rock mass. In the flexural flow-pure s hear model, a maximum of 28% of inclusion trail curvature is produced by ro tation of porphyroblasts relative to (irrotational) fold limbs, with a mini mum 72% curvature due to rotation of fold limbs relative to (irrotational) porphyroblasts. All model solutions produce less than approximate to 8 degr ees syn-folding porphyroblast rotation relative to geographic coordinates. (C) 2001 Elsevier Science Ltd. All rights reserved.