Investigating the Paleozoic-Mesozoic low-temperature thermal history of the southwestern Canadian Arctic: insights from (U-Th)/He thermochronology

Abstract

The Arctic Amerasia Basin, located between the Canadian margin and Alaska, formed by purported Jurassic–Cretaceous rifting related to the rotation of the Arctic Alaska – Chukotka microcontinent from northern Laurentia. Rifting may have been accompanied by rift shoulder uplift and cooling that is recorded in low-temperature thermochronometers. Furthermore, the southwestern Canadian Arctic has a widespread Devonian–Cretaceous unconformity with a poorly understood burial-unroofing history. We evaluate new zircon (U–Th)/He thermochronology (ZHe) and organic maturity (vitrinite reflectance (VRo)) data from Neoproterozoic strata of the Amundsen Basin, Cambrian strata of the Arctic Platform, and Devonian strata of the Franklinian Basin to help resolve the sedimentary thickness deposited and eroded during the time represented by the regional unconformity. ZHe and VRo models identify the thermal maximum occurring between the late Paleozoic – Mesozoic interval. Proximal to the rifted Canadian margin, models estimate 3.7–4.5 km of deposition between the Devonian–Cretaceous, in marked contrast to <1 km towards the craton. Jurassic–Cretaceous exhumation is estimated at 2.3–3.5 km and is more uniform across the region. Although the magnitude of burial and erosion can be resolved by modelling, the timing of these events cannot be elucidated with confidence. The thermochronology models can be satisfied by either (1) late Paleozoic – early Mesozoic burial with a thermal maximum prior to Jurassic rifting, followed by cooling; or (2) Late Devonian maximum burial, with gradual unroofing until Cretaceous sedimentation. Although continued deposition into the Mesozoic towards the craton interior seems unlikely, it remains possible that there was continued deposition proximal to the rifted Canadian margin.