Geophysical interpretation of the Torngat orogen along the North River – Nutak transect, Labrador

Abstract

A 19.3 mGal (1 Gal = 1 cm/s2) positive Bouguer gravity anomaly and a broad aeromagnetic low coincide with the Tasiuyak domain of the early paleo-Proterozoic Torngat orogen. The domain evolved during the collision of the western margin of the Archean Nain Province with an inferred, eastward-facing, platform-to-rise, sedimentary wedge sited on a proto-continent of Churchill (Rae) Province.A density contrast of +0.065 g∙cm−3 was measured between rocks of the Tasiuyak domain and those of the flanking Lac Lomier complex of the orogen and Nain Province. Using this contrast, a two and one-half dimensional model shows that rocks of Tasiuyak domain constitute a triangular prismatic body with maximum thickness of 13 km adjacent to Nain Province, which thins westward to a feather edge. The model is compatible, qualitatively, with the aeromagnetic anomaly and consonant with geological interpretation of an eastward-facing and thickening continental slope deposit. Deep exhumation of the Torngat orogen may account for the absence of paired gravity anomalies characteristic of many sutures elsewhere in the Canadian Shield.