ABSTRACT

The Peace River Arch (PRA) is a major northeast-southwest trending crustal structure in northwest Alberta consisting of uplifted Precambrian igneous and metamorphic rock. The feature has strongly influenced Phanerozoic structure and sediment distribution. The Arch was a positive feature during the early Paleozoic; its trend was imposed upon the pre-existing regional, northwest-southeast trending basement structural fabric created by the accretion of several terranes during the Proterozoic. Contacts between these lithologically distinct terrances are probably deep-seated crustal fault zones or geosutures, representing sites of reactivation throughout the Phanerozoic.

The PRA has an asymmetric north-south profile, with a steeply dipping northern flank and a more gently dipping southern margin. The northern edge is marked by a distinct east-northeast - west-southwest fault zone, here referred to as the northern boundary fault (NBF). The NBF defines the northern limit of recognizable PRA structural influence, which includes: 1) Granite Wash and Gilwood clastic distribution; 2) location of the northern margin of the Leduc fringing reef trend; and 3) location of the structural and depositional axes of the Peace River Embayment of early Mississippian age. Since the late Mississippian (Stoddart Group), the NBF appears to have remained inactive. Elsewhere in the region, pre-existing basement, and superimposed PRA structural and depositional trends have influenced: 1) the overall structural offset of the PRA into eastern and western blocks; 2) the east-west dispersal pattern of the Granite Wash clastics; 3) the Dunvegan fault zone (including the location of the Sturgeon Field); 4) the Wabamun dolomite trend; 5) the eastern margin of the Permo-Triassic basin; 6) the Cretaceous Fox Creek Escarpment.

Available data suggest that following latest activity of the NBF, the axis of the Peace River Embayment moved southwards and became more NESW in orientation. This shift aligned it parallel to the location of the Devonian PRA crest and the future axis of the Cretaceous deep basin. The nature of the NBF is poorly understood at this time, although this zone probably provides the key understanding the origin of the PRA.

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