TECTONIC EVOLUTION OF THE NEWFOUNDLAND APPALACHIAN STRUCTURAL FRONT

The Humber Arm Allochthon is a significant component of the Laurentian margin in the western Newfoundland Appalachians. It is a stack of structurally imbricated deep-water continental margin units, emplaced westward over adjacent platform rocks during the mid-Ordovician Taconian orogeny. Later Paleozoic deformation generated deep-seated, W-vergent thrusts which, in contrast, extend into Grenvillian basement. On the Port au Port Peninsula, these faults had a protracted history, starting during Proterozoic rifting, continuing during Taconian flexure, and undergoing later reactivation and inversion during Devonian Acadian deformation. Structures related to this basement-involved faulting are associated with proven oil resources. As such, this structurally complex area has been of interest to exploration companies for over 20 years; however, economic quantities of oil have yet to be discovered.

Recent interest in the Parsons Pond area of the Northern Peninsula has warranted improved geologic mapping at large scale. In this region, the Acadian thrust front has traditionally been viewed as a narrow zone dominated by the Long Range thrust, along which the Long Range Inlier is interpreted to have been thrust over rocks of the platform and Humber Arm Allochthon. The absence of younger, flat-lying stratigraphic units in the region precludes direct age control on these faults, but an Acadian age is inferred.

A combination of detailed surface mapping and 2D seismic reflection data demonstrates, 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 is a significant structural feature, juxtaposing rocks of contrasting tectonic environments. Current mapping shows the Parsons Pond thrust running offshore at Green Point and its southern extent has not been previously defined. New aeromagnetic data and reconsideration of map relationships may however give clues to a possible southern extension of this major thrust.

These new observations suggest a genetic linkage between deep-seated thrust faults in the southern and northern parts of the Newfoundland Appalachians and in turn may provide an improved foundation for oil and gas exploration in western Newfoundland.