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

This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mekinac-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 Mekinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mekinac-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 degrees C prior to 1082 +/- 20 Ma. Retrograde conditions varying from 775 to 675 degrees 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 degrees C, P-T values that are similar to or slightly lower than those for retrogressed samples from the upper structural levels of the Mekinac-Taureau domain, but clearly lower than the peak metamorphism values of the latter domain. Finally, the area cooled below 550-600 degrees C at similar to 1000-1030 Ma and below 450 degrees C at similar to 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 Mekinac-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. (C) 2014 Elsevier B.V. All rights reserved.