Thermo-tectonic evolution of a metamorphic internal zone documented by axial projections and petrological P-T paths, Wopmay orogen, northwest Canada

Abstract

Axial projections of the transversely folded 1.9 Ga Wopmay orogen document stratigraphic and structural relations in a metamorphic internal zone having more than 30 km of structural relief. The greater part of the metamorphic belt is separated from underlying autochthonous Archean basement and thin Early Proterozoic cover by a sole thrust coextensive with that beneath the external thrust-fold belt Site-specific metamorphic pressure-temperature ( P-T ) paths are derived from core-to-rim microprobe analyses of large zoned poikiloblastic garnets that contain abundant inclusions of biotite, plagioclase, quartz, and, in some cases, aluminosilicate. For garnet-absent units, qualitative P-T paths are deduced from overprinting mineral assemblages. The structural and metamorphic data combined with the results of geochronological and contiguous-external-belt studies show that regional metamorphism in the internal zone is the result of three overlapping, thermally additive, thermotectonic regimes: (1) onset of metamorphism during crustal thinning, (2) plutonic heat advection during crustal shortening, and (3) thermal relaxation, concurrent with uplift, as a consequence of crustal thickening.