Tectonic evolution of the Fundy rift basin, Canada: Evidence of extension and shortening during passive margin development

Abstract

Seismic and field data show that the Fundy rift basin of southeastern Canada experienced two distinct episodes of deformation during Mesozoic time. The first episode, during Middle Triassic to Early Jurassic time, was extensional. Rifting associated with NW–SE extension reactivated NE trending Paleozoic compressional structures as normal faults, forming the northwestern boundary faults of the Fundy basin. Displacements on the low‐angle boundary faults locally exceeded 10 km. Rifting also reactivated east trending Paleozoic compressional structures as oblique‐slip faults with normal and sinistral strike‐slip components, forming the northern boundary faults of the Fundy basin. Several kilometers of sediments and lava flows filled the basin during rifting. The second deformational episode occurred during or after Early Jurassic time and probably before or during Early Cretaceous time. Inversion associated with NW–SE shortening occurred along all faulted margins of the Fundy basin. The northwestern boundary faults experienced several kilometers of reverse displacement, broad anticlines developed within their hanging walls, and the Fundy basin acquired its synclinal form. The northern boundary faults of the Fundy basin became oblique‐slip faults with reverse and dextral strike‐slip components. Gentle synclines, tight anticlines, and faults with reverse separation deformed the synrift strata near the northern margin of the Fundy basin. Neither collision nor subduction zones existed near the Fundy basin during Mesozoic time. Hence we believe that tectonic processes associated with seafloor spreading (e.g., incipient ridge push forces, continental resistance to plate motion) produced the shortening in the Fundy basin. Shortening occurred during the transition from rifting to drifting as North America separated from northern Africa and/or during the early stages of drifting as the seafloor‐spreading centers of the North Atlantic propagated northward.