Benoit M Saumur, Stephen T Johnston, Diane R Skipton, Marc R St-Onge

The Isortoq Shear Zone (ISZ), a 100km-scale structure in northern Baffin Island, was originally identified through the interpretation of regional geophysical surveys. In the field the ISZ is cryptic, and its significance ambiguous with respect to the regional structural framework of northern Baffin Island. Mapping along the ISZ and within the spatially associated Archean Isortoq and Eqe Bay greenstone belts shows that the two belts form one continuous folded supracrustal package deformed by nappe tectonics likely during the early Paleoproterozoic Trans-Hudson Orogeny. The northern NE-striking, moderately SE-dipping Isortoq belt is structurally thinned, metamorphosed, sheared (by the ISZ) and overturned, with strata younging down-section to the NW. In contrast, the southern NE-striking, steeply dipping Eqe Bay belt is structurally thickened, comparatively less metamorphosed, exhibits weaker deformation, and stratigraphically youngs to the SE. New mapping and available geophysical data show that the two belts are folded around a hinge zone located offshore to the SW, and together form an asymmetric synformal anticline. Structural and stratigraphic relationships are consistent with the fold forming part of the lower limb of a map-scale southeast-verging nappe, with the ISZ formed at the base of this nappe as a consequence of horizontal transport. The Isortoq Nappe occurs along strike with SW-verging Rinkian nappes exposed >200 km to the NE, on Baffin Island and in Greenland. This implies that south-verging tectonics during the THO, opposed to and predating the dominant N-verging nappes of the Foxe Fold Belt, are more important in spatial extent than previously considered.