The internal metamorphic-plutonic zone of the middle Paleoproterozoic Wopmay orogen, northwestern Canadian Shield, exposes an oblique section through a prograde Buchan-type metamorphic sequence. New petrographic, petrologic, and geochronologic analyses of pelite and quartz arenite samples from the eastern margin of the internal zone quantify the evolving conditions and timing of metamorphism and enable the discriminant evaluation of competing tectonic models. Study of fabric development and mineral growth relationships indicates that prograde metamorphism occurred late within a craton-verging, crustal-shortening (“Calderian”) deformation event. Phase equilibria modeling was used to calculate pressure-temperature (P-T) path segments and determine peak conditions from andalusite-muscovite grade at ∼3.3 kbar and 575 °C to sillimanite−K-feldspar ± granitic leucosome grade at ∼4.8−6.2 kbar and 670−745 °C. In situ monazite geochronology indicates that thermal peak metamorphic conditions were reached between 1878.6 ± 6.5 Ma and 1872 ± 9 Ma. Ages of detrital zircon within quartz arenite across the width of the metamorphic sequence document a diagnostic easterly Slave craton−Thelon tectonic zone derivation that links the metasedimentary rocks, including those previously considered to be “exotic” in a proposed tectonic klippe model for the internal zone, to the adjacent craton. Integration of these results with observations on the relatively low state of strain and the bracketing of a common (single) metamorphic field gradient for all garnet-bearing mineral zones confirm that the latter have preserved their prograde isogradic continuity from time of formation, and that the leading edge of a tectonic klippe consisting of rocks exotic to the Coronation margin does not traverse the study area.

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