Orientation analysis and relationships between joints, faults and lamprophyres of the Monashee Complex, Southeastern Canadian Cordillera, British Columbia.

Abstract

The Monashee complex, southeast British Columbia is an area of high-grade metamorphic rock, within are two crystalline basement exposures: Thor-Odin and Frenchman's Cap. The complex has undergone a series of deformation periods, involving folding, refolding shearing and faulting. The last period of deformation occurred in the Eocene, and involved ductile and brittle extension, pegmatite and lamprophyre intrusion. It is believed that the brittle faulting occurred during the end of the Eocene as the region cooled, and that lamprophyre intrusion occurred during both ductile and brittle extension. The faults within northern Thor-Odin fall within four distinct orientation groups: of large, regional faults such as the Victor Creek fault; the major glacial valley lineaments; then more local smaller faults; and lastly splay faults with minimal displacement associated with the smaller faults. All except one of the lamprophyres are oriented similarly to the local smaller faults thus, it is probable that most lamprophyres post-date faulting, and intruded along these pre-existing planes of weakness. • The majority of lamprophyres found within northern Thor-Odin have only undergone low grade retrograde metamorphism however, one lamprophyre was found to be completely recrystallised and fractured within a pegmatite in a shear zone. It is probable that this lamprophyre intruded while ductile shearing was occurring, thus indicating that the lamprophyres in this region intruded over a period of time, during and after extensional shearing and faulting.