DETRITAL ZIRCON HF CHARACTERIZATION OF EOCENE SEDIMENTS DEPOSITED IN THE SOUTHERN CANADIAN CORDILLERAN HINTERLAND

The hinterland of the Canadian Cordillera in southern British Columbia and northernmost Washington state contains a series of sedimentary basins that formed during the Early Eocene. We measured εHf values of detrital zircons from sedimentary samples collected in Merritt and Kelowna, British Columbia (BC), and Republic, Washington (WA), as part of an effort to better understand the tectonic and depositional history of this region. Zircons with ca. 50 Ma ages are common across the region and yield εHf values that vary between -16 and +14. Two samples from strata in Republic, WA, have detrital zircon εHf values between -7 and -16, indicating the zircons were derived from a relatively evolved magmatic source. A sample from Kelowna, BC, yields εHf values between -10 and +14, and is composed of two distinct εHf populations: a population with εHf values of +9 to +14, and a population with εHf values of -1 to -10. The sample from Merritt, BC, has ca. 50 Ma zircons with εHf values of -3 to +14, and 150-200 Ma zircons with εHf values of +4 to +14, both of which indicate a relatively juvenile source. The wide range in detrital zircon εHf values reflects the different tectonic terranes underlying the individual basins. Positive εHf values are present in Merritt, BC, which is located on an accreted terrane, whereas negative detrital zircon εHf values are present in Republic, WA, which overlies North American crust. Eocene strata in Kelowna, BC, are located along the Sr 0.706 isopleth, interpreted as the approximate boundary between North American crust to the east and accreted terranes to the west. Strata in Kelowna, BC, contain a population of detrital zircons with negative εHf values and a population with positive εHf values, suggesting sediment sources from both sides of the boundary. Collectively, our detrital zircon εHf data indicate the hinterland of the southern Canadian Cordillera contained multiple sediment sources and several discrete basins during the Eocene.