| In the eastern Grenville Province of central Labrador, the Grenvillian Grand Lake thrust system (GLTS) comprises part of a thick-skinned thrust system separating the allochthonous and parautochthonous Grenvillian terranes.; Detailed analysis of appropriate, low variance mineral assemblages within the GLTS and adjacent footwall and hangingwall rocks was carried out to determine the P-T conditions of thrusting during the Grenvillian orogenesis using the TWEEQU software. Resultant P-T estimates associated with Grenvillian thrusting in the GLTS yield a consistent grouping of ∼875 ± 50°C and 14 kbar using garnet-clinopyroxene and garnet-amphibole thermobarometry on the porphyroblastic assemblage, and 700 ± 50°C and 6–9 kbar using garnet-amphibole thermobarometry on the matrix assemblage, consistent with textural and mineralogical evidence of decompression. On the basis of core-rim P-T vectors in single grains it is concluded that non-synchronous closure of the geobarometric and geothermometric reactions occurred in some samples, and thus the highest P-T estimates are ‘apparent peak’ estimates that underestimate the true peak conditions. (Abstract shortened by UMI.)... |
