Kinematics of long-lasting Paleoproterozoic transpression within the Thompson Nickel Belt, Manitoba, Canada

摘要

This paper presents a reappraisal of kinematics and tectonic history of the Thompson Nickel Belt, a major Paleoproterozoic deformation zone along the western boundary of the Archean Superior Province in Manitoba. The study, based on the analysis of foliation trajectory maps and associated shear zone arrays, emphasizes that the overall strain pattern results from transpression. Strains are large, marked by strong subvertical stretch and NW-SE subhorizontal shortening, combined with along-strike stretch. From these, we infer distributed crustal shortening, involving steeply plunging flow rather than large horizontal displacements, although kinematic indicators show that top-to-the-west motions were dominant. Along-strike shear indicators are poorly expressed but suggest a component of bulk dextral strike-slip. Synkinematic thermal indicators and new geochronological data indicate that transpression could have been a long-lasting, circa 100 Ma, event in the area.