Patterns of pervasive shear strain near the boundaries of the La Ronge Domain, inner Trans-Hudson Orogen, western Canadian Shield

The Saskatchewan segment of juvenile Paleoproterozoic crust, inner Trans-Hu dson Orogen (Reindeer Zone), is widely regarded as a NW-dipping stack of li the-structural domains. The metavolcanic-metasedimentary La Ronge Domain (L RD), whose least deformed portion has the geological map pattern of an Arch ean greenstone belt, is underlain by metasedimentary rocks of the Kisseynew Domain and overlain by migmatitic rocks of the Rottenstone Domain. In easi ly accessible parts of LRD boundary walls, the horizontal patterns of tange ntial (boundary-parallel) strain accumulated under peak metamorphic conditi ons are investigated. Utilizing the strain patterns and recently published reflection seismic profiles, we estimated the direction and derived the sen se of tangential shear-strain components on various horizontal scales. In a ll parts of boundary walls investigated, the dip shear has the sense of duc tile thrusts, but the strike-shear sense varies with position, on scales ra nging from 100 m to 10 km. The regional persistence of thrust shear in both LRD walls accords with tectonic scenarios of protracted horizontal converg ence of juvenile crust, after initial collision between the Archean Superio r and Hearne continents. The patterns of strike shear, on the other hand, a re difficult to reconcile with indentation hypotheses or counter-clockwise oroclinal rotation. (C) 2001 Elsevier Science B.V. All rights reserved.