--> Low Temperature Paleogene Thermal History of the British Mountains, Yukon, Canada, Quantified by Apatite and Zircon U-Th/He Dating

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Low Temperature Paleogene Thermal History of the British Mountains, Yukon, Canada, Quantified by Apatite and Zircon U-Th/He Dating

Abstract

The age and rate of exhumation of the British Mountains is tied to the timing of deformation in the Beaufort Sea, an active site for hydrocarbon exploration. The British Mountains, the eastern extent of the Brooks Range in Alaska, include Paleogene structures that are the onshore portion of the Beaufort fold belt. In the Beaufort Sea, deformation is dominated by thin-skinned folding and thrusting of Paleocene to Oligocene sediments that are sourced from the British Mountains. Onshore, Paleogene deformation overprints multiple older structural events. The low temperature thermal history of the onshore Paleogene structures is determined through U-Th/He dating of apatite (AHe) and zircon (ZHe). Previous work on the thermal history of northern Yukon and the North Slope of Alaska provides a regional framework for the region's low temperature-time history. These regional studies of the northern Yukon and Alaska yielded Paleocene to Eocene (60Ma – 40Ma) apatite fission track (AFT) cooling ages that progressively young to the north, consistent with geological evidence for northward propagating deformation. This study aims to improve the understanding of the Paleogene tectonic activity of the British Mountains and the deformation history of the Beaufort fold belt. A sampled transect through the British mountains, in the Firth River Valley, along with several regional sample locations and Devonian plutons in the Barn Mountains, provides good resolution of regional cooling rates. Both AHe and ZHe results show rapid cooling (up to 30C/m.y. in some locations) from the late Paleocene to early Eocene, 65-50 Ma. AHe and the ZHe ages almost completely overlap, indicating a major structural event. The rapid cooling is consistent with previous AFT and thermal maturation reflectance data, suggesting to the removal of 6-7 km of strata above costal Yukon. These results are used to relate the onshore time-temperature history with the development of offshore structures in the Arctic Canadian Cordillera.