ABSTRACT

Phanerozoic strata of the Peace River Arch (PRA) region, northern Alberta Basin, record a complex succession of uplift and subsidence events. In an effort to obtain quantitative constraints on the thermal evolution of this economically important area, outcrop and subsurface core samples were collected for apatite fission track analysis. Sediment (mainly Devonian and Cretaceous sandstones) and Precambrian basement samples were taken along a transect through the axis of the PRA extending from the Rocky Mountains-Foothills region west of Chetwynd, British Columbia to an area east of Fort McMurray (Twp. 87, Rge. 22W4M). Fission track parameters were used to constrain burial history models based on geological reconstructions and present temperature data. The majority of samples processed to date have Mesozoic and younger ages with mean confined track lengths of 10-11 µm, indicating a significant residence time in the 80 to 100°C temperature zone. Therefore, published kinetic models for track length annealing were used to interpret the data.

Preliminary results suggest that, during the Cenozoic, thermal gradients may have remained relatively stable directly over the PRA (as outlined by the Leduc Reef). Combined vitrinite reflectance and fission track data from a thermally immature Cretaceous sample constrain its maximum paleotemperature to be less than 70°C. Assuming a time-invariant geothermal gradient, this provides an erosion estimate of approximately 1.2 km centred on the PRA at 118°W. East and north of the PRA, there is strong evidence for an anomalous Tertiary heating event that occurred close to or was coeval with peak Laramide burial. Inferred paleothermal gradients are at least two to three times higher than present values and are opposite to the present-day pattern, which shows thermal gradients decreasing from approximately 35°C/km to 20°C/km from west to east. This paleotemperature distribution is best explained by regional ground-water flow discharging hot fluid along the flank of the basin.

End_of_Record - Last_Page 168-------