Extensional development of the Fundy rift basin, southeastern Canada

Abstract

AbstractThe Fundy rift basin of Nova Scotia and New Brunswick, Canada, is part of the Eastern North American rift system that formed during the breakup of Pangaea. Integrated seismic‐reflection, field, digital‐elevation and aeromagnetic data indicate that the Fundy rift basin underwent two phases of deformation: syn‐rift extension followed by post‐rift basin inversion. Inversion significantly modified the geometries of the basin and its rift‐related structures. In this paper, we remove the effects of inversion to examine the basin's extensional development. The basin consists of three structural subbasins: the Fundy and Chignecto subbasins are bounded by low‐angle, NE‐striking faults; the Minas subbasin is bounded by E‐ to ENE‐striking faults that are steeply dipping at the surface and gently dipping at depth. Together, these linked faults form the border–fault system of the Fundy rift basin. Most major faults within the border–fault system originated as Palaeozoic contractional structures. All syn‐rift units imaged on seismic profiles thicken towards the border–fault system, reflecting extensional movement from Middle Triassic (and possibly Permian) through Early Jurassic time. Intra‐rift unconformities, observed on seismic profiles and in the field, indicate that uplift and erosion occurred, at least locally, during rifting. Based on seismic data alone, the displacement direction of the hanging wall of the border–fault system of the Fundy rift basin ranged from SW to SE during rifting. Field data (i.e. NE‐striking igneous dykes, sediment‐filled fissures and normal faults) indicate NW–SE extension during Early Jurassic time, supporting a SE‐displacement direction. With a SE‐displacement direction, the NE‐striking border–fault zones of the Fundy and Chignecto subbasins had predominantly normal dip slip during rifting, whereas the E‐striking border–fault zone of the Minas subbasin had oblique slip with left‐lateral and normal components. Sequential restorations of seismic‐reflection profiles (coupled with projections from onshore geology) show that the Fundy rift basin underwent 10–20 km of extension, most of which was accommodated by the border–fault system, and was considerably wider and deeper prior to basin inversion. Post‐rift deformation tilted the eastern side of the basin to the northwest/north, producing significant uplift and erosion. Copyright © 2009 John Wiley & Sons, Ltd.