Abstract

An anomalous domain of complex structure occurs in the eastern Skeena Fold Belt at Mosque Mountain, at the northwestern end of a regional belt of Cretaceous Sustut Group exposure. Folds and contractional faults with northwest- and northeast- to east-trends, that are parallel and at a high angle to the regional structural trend respectively, deform Jurassic Hazelton and Bowser Lake groups and unconformably overlying Sustut Group strata in this area.

Anomalous structural trends at Mosque Mountain appear to reflect a history of superposed deformation. The older deformation occurred prior to and during deposition of the Middle Albian or younger basal Sustut Group. It caused the formation of a northwest-trending "basement" uplift of Hazelton and Bowser rocks whose abrupt northwest termination directly underlies the Mosque Mountain area. The main post late Campanian to early Maastrichtian contractional deformation formed northwest- and northeast- to east-trending structures in the Mosque Mountain area. Structural geometries and cross-cutting relationships suggest these nearly orthogonal contractional structures formed alternately. These relationships are most reasonably attributed to deformation on alternately active detachments or (blind) thrusts. Northwest-trending structures conform to regional strain patterns. Northeast- to east-trending structures were most likely caused by detachment deflection at the transverse, north end of the "basement" uplift; by movement up an oblique ramp formed by the geometric inversion of the north end of the "basement" uplift along a blind thrust, and/or reactivation of the north margin of the "basement" uplift. Geometric inversion of the early formed "basement" uplift on a footwall flat probably produced the south-facing monocline that localized the northwestern limit of preserved Sustut strata to the Mosque Mountain area. Late dextral oblique-slip and extensional faults cross-cut Skeena Fold Belt structures and indicate that transtensional deformation, common in the Central Interior of British Columbia, extended northward into the Mosque Mountain area.