STRUCTURAL AND TECTONIC EVOLUTION OF THE HUMBER ZONE, WESTERN NEWFOUNDLAND .1. IMPLICATIONS OF BALANCED CROSS-SECTIONS THROUGH THE APPALACHIAN STRUCTURAL FRONT, PORT-AU-PORT PENINSULA

The Appalachian structural front in western Newfoundland, which is pri ncipally a submarine feature that comes ashore on Port au Port Peninsu la. is interpreted to be a structural triangle zone, or tectonic wedge . Rocks within the triangle zone, which are therefore transported, inc lude the Taconian (Middle Ordovician) Humber Arm Allochthon, Taconian foreland clastic sediments, and the Cambro-Ordovician platform success ion. The transported clastic sediments and platformal rocks, as well a s structurally involved Grenville crystalline basement exposed east of the peninsula, compose the Acadian (Siluro-Devonian) Port au Port All ochthon, which carried the Humber Arm Allochthon as a high structural slice; Acadian transport of tens of kilometers westward is suggested. This interpretation contrasts markedly with the traditional and widely accepted interpretation of the Taconian and Acadian orogenies in west ern Newfoundland. Here we reinforce our earlier arguments for an alloc hthonous interpretation by presenting a series of six closely spaced, balanced cross sections across die Port au Port Peninsula. These secti ons illustrate our interpretation of complex and noncylindrical struct ures within the triangle zone, as well as the envisioned structural li nkage between exposures on Port au Port Peninsula and the geometry of the triangle zone interpreted from offshore seismic data 23 lan along strike to the northeast, The southeast vergent Tea Cove thrust, which formed an early upper detachment to the triangle zone, is offset and o verturned by the north-northwest vergent Round Head thrust. The Round Head thrust is interpreted to flatten into a second southeast vergent thrust, the Red Brook detachment, which formed a late upper detachment to the triangle zone. Some map-scale structures are interpreted as fa ult-bend folds above oblique ramps on the Red Brook detachment. Alloch thonous crystalline basement within the triangle zone, beneath its att ached platformal cover, is interpreted as a result of thrust reactivat ion of a preexisting basement-cutting normal fault, which may have for med during rifting of the early Paleozoic Iapetus Ocean. This interpre tation is suggested by the stratigraphy and geometry of spatially rest ricted coarse conglomeratic units on Port au Port Peninsula, and is su pported by the restored cross sections.