Development of a transverse to orogen parallel extension lineation in a complex collisional setting, Trans-Hudson Orogen, Manitoba, Canada

Abstract

In the southeastern Trans-Hudson Orogen (THO), the wide dispersion in orientation of the L3 extension lineation from orogen-parallel to transverse is considered primary as it cannot be accounted for by simple overprinting of a single precursor orientation. Interpretation of the origin of this extension lineation is complicated by the fact that its gently northeast-plunging orientation at the north end of the study area is inconsistent with the evidence for sinistral, east side up movement of the steep oblique slip D3 faults. The hypothesis presented here to explain the complicated lineation pattern is based on evidence that the preceding period D2 southwest-directed transport, overlapped temporally and spatially with D3 northwest-southeast transpressional shortening. D2 and D3 are attributed to successive, but overlapping, collisional events. D3 transpressional shortening is interpreted to have propagated westward through the THO resulting in a prolonged and complex transition between D2 and D3 deformation regimes. The dispersion of the L3 extension lineation is interpreted to reflect the competing effects of both deformation regimes which appear to have been partitioned in the crust with D2 effects best developed in higher metamorphic grade rocks and D3 effects best developed in lower metamorphic grade rocks.