OROGEN-PARALLEL AND OROGEN-OBLIQUE STRIKE SLIP-FAULTS AND THE DEVONIAN-PENNSYLVANIAN EVOLUTION OF THE MARITIMES BASIN, ATLANTIC CANADA

Dextral strike-slip faults frame the deepest parts of the Maritimes Basin of Atlantic Canada, an enormous sedimentary basin that ranges in age from Devonian to Pennsylvanian or Early Permian. Beneath the Gulf of St. Lawrence, it contains over 12 km of sediment, and accounts for nearly one third of the thickness of the crust. Two main orientations of strike-slip faults are present. Faults that strike NW-SE, parallel to the trend of the Appalachians, were probably initiated early, in Devonian or Mississippian time, during substantial dextral strike-slip that also affected the southern Appalachians, where structural trends inherited from Iapetan rifting of the former Laurentian margin were truncated. In the Canadian Appalachians, however, a large former offset in the Laurentian margin was not truncated, but instead formed a right-handed stepover. Considerable thinning of the crust occurred in the resulting transtensional zone, initiating the Maritimes Basin.

The east-west Minas Fault zone also shows evidence on its south side for early dextral movement, but the main activity along its northern margin was not until the latest Mississippian - earliest Pennsylvanian. This east-west movement was kinematically consistent with oblique convergence on the Central Piedmont shear zone in the southern Appalachians, and probably occurred at about the same time. In the Maritimes Basin, movement on this trend was responsible for the inversion of sub-basins formed during earlier, orogen-parallel strike-slip. The proposed model would predict a majority of subsidence in the Devonian or Mississippian, whereas much of the fill of the deepest part of the basin is Pennsylvanian. However, withdrawal of thick evaporites occurred during the Pennsylvanian, suggesting that the Pennsylvanian succession partially re-filled accommodation space created in the Mississippian. Additional Pennsylvanian subsidence may have been caused by loading at transpressional boundaries of the basin.