ABSTRACT: A New Structural Interpretation of the Appalachian Structural Front, Port au Port Peninsula, Western Newfoundland: Implications for Regional Tectonics and Hydrocarbon Exploration

STOCKMAL, GLEN S., Geological Survey of Canada, Institute of Sedimentary and Petroleum Geology, Calgary, Alberta, Canada, and JOHN W. F. WALDRON, Saint Mary's University, Halifax, Nova Scotia, Canada

Detailed mapping of Port au Port Peninsula, western Newfoundland, coupled with nearby offshore multichannel seismic data in the public domain, require reassessment of the traditional interpretation of the Appalachian structural front in this area. Our new interpretation implies that much of the Cambrian-Ordovician carbonate platform of western Newfoundland, traditionally considered autochthonous to parautochthonous, was transported tens of kilometers and structurally duplicated during the Acadian (Silurian-Devonian) orogeny.

The seismic data are interpreted to image a structural triangle zone, a feature common to thrustfold belts. A strong reflector, in the immediate hanging wall of the triangle zone upper detachment, intersects the sea floor along strike from island exposures of the Late Ordovician Lourdes Formation. On the basis of limited exposures on Port au Port, the Lourdes has traditionally been interpreted to unconformably overlie the Humber Arm Allochthon, constraining its position at the end of the Taconian (Middle Ordovician) orogeny. However, the structural position of the Lourdes in our interpretation, coupled with our new mapping of Port au Port, implies that both the Allochthon and the underlying platform lie within the triangle zone and are therefore transported.

Mapping indicates the triangle zone upper detachment had jumped eastward, in an out-of-sequence fashion, duplicating the platform on Port au Port. Late west-vergent thrusting reflects inversion of an early major normal fault. Balanced cross sections, constructed considering known structural involvement of Grenvillian crystalline basement only 15 km east of Port au Port, imply that the triangle zone also contains transported basement.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)