Structural evolution of the eastern Amisk collage, Trans-Hudson Orogen, Manitoba

Abstract

Deformation recorded in the Amisk collage in the central part of the Paleoproterozoic Flin Flon Belt (southeastern Trans-Hudson Orogen) is divided into pre-, early, late, and post-Hudsonian orogeny, distinguished by significant changes in metamorphic conditions and the orientation of structures. Detailed structural analysis, petrography, and high-precision geochronology, combined with previous mapping and geochemical studies, indicate a structural history spanning 180 Ma in the Amisk collage, and the database provides an excellent opportunity to study the structural evolution of Precambrian greenstone belts. Accretion of the 1.92-1.88 Ga tectono-stratigraphic assemblages in the Amisk collage began prior to 1.868 Ga. The deformational history records six generations of ductile structures (F1-F6), followed by development of brittle-ductile and brittle structures (F7), which may have continued as late as 1.690 Ga, during exhumation of the collage. The steep, generally north-northeast macroscopic structural grain is dominated by two regional foliations (S2 and S5), and contrasts strongly with the less steeply inclined, east-west grain in the adjacent Kisseynew Domain. Maximum displacements between tectono-stratigraphic assemblages occurred along early rather than late shear zones. Vertical extension was important in post-D1 deformations, even in the later stages. Postorogenic, low-angle extensional features that are common to many mountain belts appear to be absent, possibly indicating that erosion was the dominant unroofing mechanism.