Tertiary extension in the central British Columbia Intermontane Belt: magnetic and paleomagnetic evidence from the Endako region

New magnetic and paleomagnetic data for central British Columbia support an d quantify the hypothesis that the area underwent significant Tertiary-age transtensional deformation. Paleomagnetically determined tilts in Eocene ro cks indicate that four fault-bounded pits, which constitute the Endako moly bdenum mine, were displaced on a series of normal (probably listric) faults that have separations of less than a kilometre. The interpretation also su ggests there can be little vertical offset on the Denak West Fault, which s eparates the Denak East and Denak West pits. Regional paleomagnetic data in dicate a predominance of easterly directed tilts to the east of the Casey F ault, but to the west a large variation in the orientation and magnitude of tilts is observed. Results at one site proximal to the Casey Fault indicat e a component of dip-slip displacement on this dominantly dextral strike-sl ip fault. Mapped northeast- and northwest-trending faults commonly correspo nd to linear zones of steep magnetic gradient and near-surface magnetic sou rces. Several additional northwest- and northeast-trending lineaments are i maged in the magnetic data where no faults are mapped (particularly over ma ssive and lithologically homogeneous phases of the Endako batholith). Euler deconvolution solutions confirm most such lineaments are also associated w ith shallow magnetic sources. In profile, they have either a fault or dyke character and are interpreted to be unmapped faults, some locally intruded by mafic dykes, which cut the region into a series of fault-bounded blocks.