Testing local and extraregional sediment sources for the Late Cretaceous northern Nanaimo basin, British Columbia, using 40Ar/39Ar detrital K-feldspar thermochronology

Abstract Detrital K-feldspar 40Ar/39Ar thermochronology was conducted on clastic sedimentary rock samples collected from northern exposures of the Upper Cretaceous Nanaimo Group Vancouver Island and adjacent Gulf Islands British Columbia to constrain denudation history local Coast Mountains batholith source region determine origin extraregional sediment supplied basin. Strata deposited between 86 83 Ma (Comox Extension formations) exhibit a 130–85 age distribution detrital ages that lack maxima. These are interpreted have been sourced southwestern batholith. Younger strata 72 (Cedar District De Courcy yield broader range (150–85 Ma) with an maximum near depositional age. results indicate focused deeper-seated rocks east Harrison Lake fault. The youngest units after (Geoffrey, Spray, Gabriola primarily younger than 75 pronounced maxima This extraregionally relative We sought by measuring thermal histories 74 basement throughout Pacific Northwest, compiling database over 2400 biotite K/Ar cooling predominantly batholiths along western North American margin. analysis upon two previously proposed regions: Idaho Mojave-Salina margin southern California. distributions favor peraluminous Late its Proterozoic Belt-Purcell Supergroup wall as more likely disfavor Baja–British hypothesis for 2000–4000-km-scale translation during Cretaceous.