Detrital zircon U-Pb ages and Hf-isotopes from Eocene intermontane basin deposits of the southern Canadian Cordillera

Lower Eocene strata exposed in the hinterland of the southern Canadian Cordillera were deposited in extensional-transtensional basins and provide insights into the evolution of the orogen. We measured stratigraphic sections and collected 22 sandstone samples for detrital zircon uranium-lead (U-Pb) geochronology (n = 2995) and hafniumisotope (epsilon Hf) values (n= 67) in order to reconstruct the Eocene physiography and sedimentary history of the region. Early Eocene sedimentation in the interior of the southern Canadian Cordillera occurred in alluvial fan, fluvial, lacustrine and paludal settings in multiple compartmentalized basins. In most locations, detrital zircons have ages of ca. 50 Ma, which are interpreted to be derived from the syndepositional Challis-Kamloops volcanics. Several locations have dominant detrital zircon populations with ages between ca. 145 and 200 Ma, suggesting distinct sediment sources and paleodrainageswithin the southern Canadian Cordillera. Maximumdepositional ages record coeval sedimentation across the southern Canadian Cordillera hinterland, supporting the hypothesis that upper crustal deformation and basin subsidence occurred at the same time across the orogen interior. epsilon Hf(t) values of ca. 50 Ma and 145-200 Ma detrital zircons vary between -16 and +12, with more evolved epsilon Hf(t) values in the eastern portion of the study area and more juvenile eHf(t) values in the west. Differences in epsilon Hf(t) are interpreted to reflect crustal changes across the region, likely related to underlying Laurentian basement rock. Detrital zircons fromintermontane basins may provide an additional tool for examining crustal heterogeneity in cordilleran orogens. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The Lower Eocene strata in the southern Canadian Cordillera hinterland were deposited in multiple compartmentalized basins in alluvial fan, fluvial, lacustrine, and paludal environments. Detrital zircons with ages around 50 Ma are interpreted to be derived from volcanic activity, while another population with ages between 145 and 200 Ma indicates different sediment sources and paleodrainages within the southern Canadian Cordillera.