High-pressure (HP), granulite-facies thrusting in a thick-skinned thrust system in the eastern Grenville Province, central Labrador

• Main Author: Krauss, Jason B.
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2002
• Subjects: Lake Melville; Mealy Mountains; Rigolet
• Online Access: https://research.library.mun.ca/6613/; https://research.library.mun.ca/6613/1/JasonBKrauss.pdf; https://research.library.mun.ca/6613/3/JasonBKrauss.pdf

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. North-northwest directed thrusting on the GLTS during the Grenvillian orogeny carried the Labradorian (1710-1600 Ma) rocks of the Cape Caribou River Allochthon (CCRA) and the overlying Mealy Mountains terrane (MMT), onto a footwall composed of similar aged granitoid gneisses of the Groswater Bay and Lake Melville Terranes (GBT and LMT). The CCRA is principally composed of an AMCG suite, with the GLTS comprising a basal shear zone about 1km thick characterized by mylonite and straight gneisses developed under granulite- and upper amphibolite-facies conditions. Lithologies in the GLTS include highly strained dioritic to granitic orthogneiss (straight gneiss) comprising alternating mafic and felsic layers consisting of a mineralogy composed of garnet, clinopyroxene, amphibole, plagioclase, quartz and minor orthopyroxene which locally defines the stretching lineation. The footwall rocks of the GBT and LMT were metamorphosed under upper amphibolite facies conditions during Labradorian orogenesis. -- Field studies and published U-Pb data indicate that the extent of mylonitization and recrystallization induced by thrusting along the GLTS diminish rapidly upward into the allochthon and downward into the footwall rocks. U-Pb metamorphic ages within the CCRA and footwall rocks are Labradorian (1710-1600 Ma), whereas U-Pb metamorphic ages from the recrystallized rocks of the GLTS define two Grenvillian populations at 1040 and ~1010 Ma, which are correlated with the Ottawan and Rigolet orogenies respectively. -- 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 ...