Flexural-slip folding in the Meguma Group, Nova Scotia, Canada

Abstract

Flexural-slip folding has been established for two anticlines in the Meguma Group, Nova Scotia. Flexural slip postdates the main Acadian episode of flexural-flow fold growth and represents a late, brittle-ductile reactivation of the fold belt. Flexural-slip structures are dominated by bedding-parallel movement horizons, but include a linked system of frontal and lateral ramps and conjugate movement horizons. Slip amount calculated from displacement of discordant quartz veins, combined with vein spacing, indicates an average local shear strain of approximately 0.5. However, because flexural-slip occurred when the fold limbs were steep, the shear strain accounts for a small change in limb dip (4–8°). Variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons.The presence of quartz veins along flexural-slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent, separated by periods of ductile deformation and build up of fluid pressure. Flexural-slip veins in the Ovens Anticline are auriferous and a flexural slip model may be appropriate for other similar Meguma gold deposits.Thrust sheets, up to 10m thick, occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode. Thrusting may have assisted the transformation of a box fold into a chevron.