Northeastward extrusion and extensional exhumation of crystalline rocks of the Monashee complex, southeastern Canadian Cordillera

North American basement and cover rocks of the Monashee complex (MC) are exposed through a tectonic window within the hinterland of the southeastern Canadian Cordillera. The complex records a history of Late Cretaceous to early Tertiary crustal thickening (F-1/F-2) related to emplacement of the Selkirk allochthon (SA). Part of the MC and overlying SA then formed a mid-crustal wedge that was extruded towards the foreland from the overthickened hinterland (F-3, F-4). Finally, the complex was exhumed by Eocene ductile and brittle extensional deformation (D-5). Rocks along the studied west flank of the MC are thoroughly transposed by F-1/F-2 (into S-2). The extent of the transposition, and a well-developed northeast-trending L-2 lineation, indicate intense strain during F-1/F-2 throughout the studied portion of the MC (4-5 km thickness exposed) and overlying SA. Ductile flow continued, resulting in northeast-verging F-3 folds in the MC, west-southwest-verging F-3 folds in the SA and broad F-4 warps in the MC and SA. A shear zone records significant reactivated slip on S-2 during D-5. Rapid exhumation of the MC is attributed to ductile how during extrusion and extensional deformation; this ductile flow is correlated with foreland thrusting, which ended in the Early Eocene. (C) 2000 Elsevier Science Ltd. All rights reserved.