| I present a new interpretation of the tectonic evolution of Orpheus basin, a narrow Mesozoic rift basin on the passive margin of offshore eastern Canada. This work incorporates insights gained from a scaled experimental modeling study that simulates multiphase deformation on a basin with a synrift ductile unit, to show that the structural deformation observed within this basin cannot completely be attributed to salt-related buoyancy-driven processes. Seismic data show that the Orpheus and overlying Scotian basins experienced at least four stages of development: Triassic-Early Jurassic rifting, shortening during the rift/drift transition in the mid-Early Jurassic, regional uplift and erosion during the earliest Cretaceous, and a fourth event that had, at least locally on the North Step, a compressional component during the Oligocene.The presence of the synrift Argo salt profoundly affected the style of deformation during both the formation of the basin, and the subsequent tectonic events. The synrift salt decoupled the cover deformation from basement deformation. Forced folds and salt ridges developed in the cover above the salt, whereas, faulting accommodated basement extension below the salt. During subsequent tectonic events, deformation was mainly accommodated above the basement faults by: (1) reactivating preexisting extensional structures such as passive salt diapirs and salt ridges, and (2) further amplifying preexisting forced folds that formed during the rifting phase. The presence of multiple unconformities, disharmonic sets of synclines and salt-cored anticlines (which developed from preexisting extensional forced folds), vertical salt welds, and detached thrusts indicate that this basin underwent multiple episodes of shortening, uplift, and erosion after rifting ended in the Early Jurassic. |
