Insights into the Phanerozoic tectonic evolution of the northern Laurentian margin: detrital apatite and zircon (U–Th)/He ages from Devonian strata of the Franklinian Basin, Canadian Arctic Islands

Abstract

Middle to Upper Devonian strata of the Franklinian Basin in the Canadian Arctic contain a rich record of Phanerozoic tectonic events along the northern margin of Laurentia. We report detrital thermochronometric zircon (U–Th)/He ages (ZHe; number of aliquots, n = 72) and apatite (U–Th)/He ages (AHe; n = 38) from these Paleozoic strata in an effort to better understand the sediment source regions and the exhumation history of the basin. Detrital ZHe ages are older than corresponding stratigraphic ages and were not reset during subsequent burial, thus constraining both maximum burial depths (<7 km) within the basin and source terrane thermal–tectonic evolution. Paleocurrent data, sediment composition, εNd values and detrital zircon U–Pb ages from previous studies indicate Middle to Upper Devonian strata of the Franklinian Basin are derived from two principal sediment source regions, the East Greenland Caledonides and a northern continental landmass (referred to as Crockerland). However, ZHe ages indicate these two distinctly different source regions experienced coeval exhumation in the Silurian Period. ZHe ages from Crockerland-derived sediment provide evidence that this landmass, which collided with northern Laurentia during the Ellesmerian Orogeny, was associated with the Caledonian Orogen. AHe ages from Middle to Upper Devonian strata are younger than depositional ages, indicating the AHe ages are at least partially reset since deposition and hence record information about exhumation of the strata and not the sediment source region. Dispersion of AHe single-grain ages from Middle Devonian strata along the southeastern margin of the basin suggest complex initial single-grain characteristics and may indicate long residence time in the He partial retention zone. AHe ages from Upper Devonian samples from the western margin of the basin are also dispersed but indicate the region experienced protracted exhumation from 330 to 190 Ma during early stages of Sverdrup Basin development. AHe ages from Middle Devonian samples from the western margin of the basin suggest two potential periods of prolonged exhumation in Early Cretaceous (Valanginian to Aptian) and Late Cretaceous (Campanian) times. These ages partially coincide with regional erosional or nondepositional events followed by deposition of major clastic units in the adjacent Sverdrup Basin.