Block rotations along the strike‐slip Finlay‐Ingenika fault, north‐central British Columbia: Implications for paleomagnetic and tectonic studies

Abstract

Structure developed in association with oblique motions on the dextral, strike‐slip Finlay‐Ingenika fault (FIF) in the McConnell Creek area, north‐central British Columbia, is dominated by subvertical to vertical strike‐slip faults. Some of the faults cut the area into discrete, fault‐bounded blocks several kilometres wide. Stress tensors for 24 sites were inverted from the regional cleavage which predates the block‐bounding faults. The site‐mean stress tensors indicate that the fault‐bounded blocks were rotated clockwise about a subvertical axis during progressive oblique motions on the FIF. Rotation varies systematically, being maximal (58.7±3.3°) close to the FIF and minimal (0.0±1.6°) about 20 km away. Paleomagnetic samples were collected from 13 sites in the widespread Early Jurassic to Cretaceous plutonic rocks. Interpretable magnetic components of presumed Late Cretaceous age were obtained from six sites. The observed paleopole is significantly different from the Late Cretaceous reference pole for cratonal North America (CNA). After corrections for the local block rotations, the precision is much improved (K increased from 48 to 383), and the paleopole moves closer to the reference pole but is not coincident with it. Rotation about the Eulerian pole for the best‐fitting small circle to the Tintina trench and northern Rocky Mountain trench fault zone, however, brings the observed pole into coincidence with that for CNA and requires ∼670 km of dextral displacement on the fault zone. It is evident therefore that local structures associated with large dextral strike‐slip faults could account for at least part of the paleomagnetic disparity between some western parts of the Canadian Cordillera and CNA.