Overview of the Tertiary Deformation History of Northern Yukon and Beaufort Foldbelts, Based on Apatite FT Modelling

Larry S. Lane and Dale R. Issler
Geological Survey of Canada, Calgary, AB, Canada.

The North Yukon Fold Complex is the onshore continuation of the arcuate Beaufort Foldbelt of the western Beaufort Basin. The age progression of the Beaufort Foldbelt is constrained biostratigraphically from wells penetrating the seismic sequences and by seismically imaged unconformities. Onshore, deformed Paleocene outcrops together with examples of onshore-offshore structural continuity require that the adjacent onshore deformation has the same timing and tectonic drivers. The onshore fold complex extends 500 km southward, as far as the Ogilvie Mountains. Knowledge of the region’s Tertiary structural evolution permits modelling of the basins and their petroleum systems; and helps clarify scenarios for Cretaceous plate geometries on the resource-rich Arctic continental margin. This overview discusses the ages of deformation, uplift and cooling of the North Yukon Fold Complex based on apatite fission track (AFT) ages from across the region; and reviews the regional tectonic setting.

AFT cooling ages document a Paleocene to early Eocene event coincident with the regionally dominant deformation offshore. Long fission tracks are typical, indicating rapid cooling through the partial annealing zone (PAZ). In the British, Richardson and Keele mountains, AFT cooling ages typically vary between 60 Ma and 40 Ma. Farther south, Proterozoic strata yielded a 68 Ma cooling age from an inlier in the southern Nahoni Range; and a 35 Ma cooling age from the northernmost Mackenzie Mountains. In the latter case, shortened track lengths indicate slow or incremental cooling through the PAZ; and further modelling is required to clarify the cooling history. Finally, two Cretaceous samples from northernmost Eagle Plain produced cooling ages older than the depositional ages of the units. These incompletely annealed samples will also undergo further modelling to assess the local cooling history.

These data largely quantify our understanding of Paleocene to early Eocene deformation ages across northern Yukon. Additional data from northeastern Brooks Range and Kandik Basin provide similar results. In adjacent Alaska, and offshore Beaufort Sea, Miocene deformation pulses are locally significant; and indications of Neotectonic displacements are locally documented. The AFT dataset presented here does not reveal evidence of these younger deformation episodes, partly because most samples were rapidly cooled through the PAZ. Also, the Neotectonic setting suggests primarily dextral strike-slip kinematics on major north-trending structures. Although secondary uplifts are expected locally, their magnitudes may be too modest to resolve using AFT. Additional modeling of the partially annealed samples and further targeted analyses are in progress to elucidate the ages of these cooling events.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.