Proterozoic mafic dykes as monitors of HP granulite facies metamorphism in the Grenville Front Tectonic Zone (western Quebec)

The circa 1005 Ma age of metamorphism implies that the Molson Lake terrane is part of the Parautochthonous Belt rather than the allochthonous HP Belt.

“The circa 1005 Ma age of metamorphism implies that the Molson Lake terrane is part of the Parautochthonous Belt, as originally proposed by Rivers et al. [1989], rather than the allochthonous HP Belt as suggested by Rivers et al. [2002], an interpretation supported by the circa 1005 Ma age of HP metamorphism in the Parautochthonous Belt of western Que ´bec [Martignole and Martelat, 2005].”

In the Réservoir Dozois terrane, the Grenvillian metamorphic overprint only becomes more pervasive about 50 km southeast of the Grenville Front in the vicinity of an extensional shear zone (the Dorval detachment), where circa 1 Ga monazite ages and both Archean and Grenvillian monazite ages in single samples have been recorded.

“In this terrane, the Grenvillian metamorphic overprint only becomes more pervasive about 50 km southeast of the Grenville Front in the vicinity of an extensional shear zone (the Dorval detachment), where Childe et al. [1993] recorded circa 1 Ga monazite ages from gneisses that yielded Archean Sm-Nd model ages, and Martignole and Martelat [2005] recorded both Archean and Grenvillian monazite ages”

The HP belt is composed of two back-to-back components, one at the structural top of the Parautochthonous Belt in which HP metamorphism took place at circa 1005 Ma and one at the structural base of the Allochthonous Belt in which HP metamorphism took place at circa 1050 Ma, with the two belts separated by the Allochthon Boundary Thrust.

“Thus, considering the results of the study by Martignole and Martelat [2005] together with this study, it appears that the HP belt is composed of two back-to-back components, one at the structural top of the Parautochthonous Belt in which HP metamorphism took place at circa 1005 Ma and one at the structural base of the Allochthonous Belt in which HP metamorphism took place at circa 1050 Ma, with”

Grenvillian metamorphism is recorded in the southern part of the Grenville Front Tectonic Zone by Proterozoic mafic dykes with high-P granulite, garnet-clinopyroxene coronas around igneous phases.

“Grenvillian metamorphism is however recorded in the southern part of this zone by Proterozoic mafic dykes with high-P granulite, garnet-clinopyroxene coronas around igneous phases (Martignole and Martelat 2005).”