ABSTRACT

The crystalline basement of the Peace River Arch (PRA) is characterized by north trending, curvilinear aeromagnetic highs and lows. These correspond to distinct tectonic domains that have been recently "mapped" and subdivided using potential field data and U-Pb geochronology of samples from cored basement. From east to west, these domains are the Buffalo Head Terrane (2.32-1.99Ga), Chinchaga Low (2.17-2.08Ga) and the Ksituan High (1.99-1.90Ga). The juxtaposition of these domains is believed to be the result of tectonic collisions that occurred between 2.0 and 1.9Ga, as these tectonic elements were accreted to the western edge of the Canadian Shield.

Recent seismic refraction studies have confirmed the earlier interpretation of low pass filtered gravity anomaly data that indicated no dramatic crustal anomaly associated with the PRA. The refraction data also demonstrate a slight thinning of the crust along the axis of the arch (approx. 44-38 km), the presence of gently outward-dipping (away from the Arch) lower crustal structure, and the presence of several kilometres of intermediate velocity lower crust beneath the Arch.

The magnitude and wavelength of the PRA and its orientation at a high angle to basement fabric suggest that its origin lies at the crustal or lithospheric scale. The presence of intermediate velocity lower crust has been interpreted as reflecting the presence of mafic sills that may be the mark of a thermal driving force for the anomalous behavior of the PRA. At a smaller scale, it appears that basement anisotropies between and within domains have acted to localize sedimentation and diagenetic processes in the sedimentary cover (i.e. the Wabamun dolomite trend, Tangent-Normandville reservoirs and the marked reentrant in the South Kaybob reef complex).

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