The study of ancient, deeply eroded orogenic belts can provide information about tectonic processes in the deep crust that is unobtainable from upper crustal sections in younger belts. In this light, the Paleoproterozoic Torngat Orogen in northeastern Canada is ideal because it is well exposed and eroded to maximum depths of 28 km, revealing information about transpressional deformation mechanisms during continent-continent collision between the Archean Nain and southeastern Rae provinces. Evidence from detailed structural mapping, metamorphic petrology, and geothermobarometry of a 115-km transect of the orogen is combined with previously published geochronology to construct pressure-temperature-time-deformation (P-T-t-d) paths for rocks from the granulite-facies core and amphibolite-facies Foreland zone of the orogen. Results show that rocks followed a clockwise P-T-t path, but different parts of the orogen reached peak conditions at different times. The orogen evolved through three temporally and kinematically distinct events over ∼80 m.y., rather than continuous deformation. Events were separated by gaps of 15-30 m.y. and include (1) crustal thickening during continental collision at ca.1860 Ma under peak metamorphic conditions of 9.5 ± 0.5 kbar and 950° ± 50°C in the core of the orogen, and prethermal peak conditions of 4.5 kbar and 550°C in the Foreland zone; (2) sinistral transpressional shear at ca. 1845-1822 Ma under post-peak conditions of 7.3 ± 0.5 kbar and 750° ± 50°C in the core of the orogen, but at thermal peak conditions of ∼5 kbar and 700°C in the Foreland zone; and (3) west-directed exhumation of the orogen at 1794-1740 Ma, under lower-grade conditions of up to ∼5 kbar and 600°C. The overall transpressional features of the orogen are shown to be a cumulative result of three distinct tectonic events which can be related to changes in plate/subduction configurations across the rest of NE Laurentia.
ASJC Scopus subject areas
- Geochemistry and Petrology