THE ENDS OF THE TRANS-HUDSON OROGEN

The Trans-Hudson Orogen (THO), a Paleoproterozoic collisional zone that welds the Superior, and the Hearne-Rae-Wyoming (HRW) cratons to form the core of Laurentia, represents a significant suture within the Nuna supercontinent. In detail, the THO consists of multiple collisional events that culminated in the closure of the Manikewan Ocean at ca. 1.83 Ga followed by significant tectonothermal reworking of the internal part of the orogen and the HRW hinterland. However, the lack of outcrop or detailed mapping has made interpretation of the southern and northeastern ends of the THO in North America challenging.

The southern end of the exposed THO in central Canada consists of a collage of ca. 1.9 to 1.85 Ga ocean floor and arc-related rocks that were thrust over an Archean microcontinent (Sask craton) trapped between the Superior and HRW. Interpretation of geophysical anomalies lend support to the southern extrapolation of the domains of the THO under Phanerozoic cover into N. and S. Dakota, until they are cut by the NE-trending Yavapai province. Igneous and metamorphic ages younger than 1.8 Ga at the S. end of the THO have been used to suggest that the ocean between the Superior and Wyoming cratons closed later than to the north, although they could represent activity related to accretionary episodes along the Yavapai margin.

The northeastern extrapolation of the THO onto SE Baffin Island is controversial, partly because some areas have only been mapped at reconnaissance scale. Tectonic blocks that meet in this region include the Archean Rae and North Atlantic (NA) cratons, and the Metaincognita (MI) microcontinent, all of which have been deformed and metamorphosed during the THO. The Baffin Suture (between the Rae and the NA/MI), for example, has been placed in two different locations based on correlation of supracrustal rocks on these blocks or geophysical signatures. Also, recent work on the Cumberland Peninsula has now shown that Archean tonalitic gneisses dominate, with the Paleoproterozoic Hoare Bay Group (HBG) being of limited extent. The correlation between the HBG and the other supracrustal sequences, such as the Piling or Lake Harbour groups, is problematic as stratigraphy and volcanic rock compositions differ, and thus they all may have formed on distinct older blocks prior to final Paleoproterozoic collisions.