Tectono-metamorphic history of the eastern Taureau shear zone, Mauricie area, Québec: Implications for the exhumation of the mid-crust in the Grenville Province

Renaud Soucy La Roche (1) , Félix Gervais , Alain Tremblay (2) , James L. Crowley (3) , Gilles Ruffet (4)

1 SET - Laboratoire Systèmes et Transports
2 Département des Sciences de la Terre et de l'Atmosphère
3 Department of Geosciences [Boise]
4 Terre, Temps, Traçage

This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P–T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from 775 to 675 °C and from 800 to 650 MPa were registered in its upper structural levels prior to and/or during shearing along the eastern Taureau shear zone that was active at 1064 ± 15 Ma. The Shawinigan domain records P–T conditions ranging from 850 to 625 MPa and from 775 to 700 °C, P–T values that are similar to or slightly lower than those for retrogressed samples from the upper structural levels of the Mékinac-Taureau domain, but clearly lower than the peak metamorphism values of the latter domain. Finally, the area cooled below 550–600 °C at ∼1000–1030 Ma and below 450 °C at ∼900–970 Ma on the basis of 40Ar/39Ar geochronology on amphibole and biotite. Structural and metamorphic characteristics of the Mauricie area are similar to those expected from a metamorphic core complex formed during post-convergence orogenic collapse in a gravity-driven fixed-boundary mode. The Mékinac-Taureau and Shawinigan domains were thus probably exhumed by a similar process, which supports the orogenic collapse model recently proposed to explain the exhumation of mid-crustal metamorphic core complexes in the Grenville Province.

Keywords: Geochronology; Thermobarometry; Grenville Province; Eastern Taureau shear zone; Middle crust exhumation

Domains: Earth Sciences

Renaud Soucy La Roche, Félix Gervais, Alain Tremblay, James L. Crowley, Gilles Ruffet. Tectono-metamorphic history of the eastern Taureau shear zone, Mauricie area, Québec: Implications for the exhumation of the mid-crust in the Grenville Province. Precambrian Research, 2015, 257, pp.22-46. ⟨10.1016/j.precamres.2014.11.012⟩. ⟨insu-01096499⟩