STRUCTURE AND DEFORMATION HISTORY OF THE APPALACHIAN THRUST FRONT IN WESTERN NEWFOUNDLAND

A significant component of the Humber Zone in western Newfoundland is the Humber Arm Allochthon - a stack of structurally imbricated deep-water continental margin successions that have been assembled and emplaced over adjacent platform rocks during the mid-Ordovician Taconian orogeny. Later Paleozoic deformation generated a zone of deep-seated, west-vergent thrusts which, unlike Taconian thrusts, extend into Grenvillian basement. On the Port au Port Peninsula, these faults are interpreted to have a protracted history, starting during Proterozoic rifting, continuing during Taconian flexure, and undergoing later reactivation and inversion during Acadian deformation. On the Port au Port Peninsula, fault scarp deposits constrain timing of Ordovician activity while later inversion is constrained by unconformable relationships.

Along the Northern Peninsula the Acadian thrust front has traditionally been viewed as a narrow, weakly emergent zone dominated by the Long Range thrust. The Long Range Inlier is interpreted to have been thrust over platform rocks and rocks of the Humber Arm Allochthon along this main fault. The absence of younger, flat-lying stratigraphic units in the region disallows direct age control on these faults, but an Acadian age is inferred.

Surface mapping and 2D seismic reflection data demonstrate, however, that the deep-seated thrust faults on the Northern Peninsula are structurally analogous to faults on the Port au Port Peninsula and may share a similar protracted history. The Parsons Pond thrust structurally juxtaposes rocks of highly contrasting tectonic environments. Deep-water carbonates and siliciclastics of the Shallow Bay Formation and Lower Head Formation, respectively, are structurally overlain by correlative platform rocks and, at Portland Creek, by siliciclastics of the mid-Ordovician Goose Tickle Group. Limestone conglomerates within the Goose Tickle Group reside in the hanging wall of the Parsons Pond thrust and may represent fault-scarp deposits, formed during Taconian flexure.

These new observations may provide a genetic linkage between deep-seated thrust faults in the southern and northern parts of the Newfoundland Appalachians, suggesting an extensive basement-involved Acadian thrust front along the length of the Humber Zone in western Newfoundland.