TESTING NEW IDEAS IN THE GRENVILLE PROVINCE

Thermomechanical modelling of orogenic systems has sparked renewed interest in Grenvillian tectonics. It has resulted in the development of new conceptual models involving convergence phases accommodated by processes related to orogenic wedge and various forms of channel flow, as well as gravitational collapse phases accommodated by the formation of metamorphic core complexes (MCC) or by foreland-directed flow. The realization that the Grenville Province does not represent a slice of the deep orogenic crust, but constitutes a collage of crustal blocks deformed and metamorphosed diachronously at different structural depths opened the possibility for studying boundaries between these blocks and thus for testing the models. Taking advantage of mapping campaigns of the Ministère de l’Énergie et des Ressources naturelles du Québec, my research team has been conducting several projects in the Grenville Province since 2011. This contribution summarizes recent developments that provide some answers to several key questions aimed at testing the proposed conceptual models and at improving our knowledge of the economic potential of the province:

1) Parautochtonous Belt: i) was convergence purely accommodated by orogenic wedge processes or if a component of channel flow was involved during the Rigolet phase of the Grenvillian Orogeny (ca. 1.0-0.98 Ga)? ii) was the Archean basement pervasively reworked or not? iii) what exhumation process(es) led to the juxtaposition of the belt with unaffected rocks of the Superior Province?

2) Allochtonous Belt: i) is the proposed channel-flow model applicable? ii) could gravitational collapse forming MCC explains the juxtaposition of rocks from the orogenic lid with higher metamorphic-grade rocks structurally underneath?

3) Economic geology: i) do metamorphosed hydrothermally altered volcanic systems associated with Iron-Oxyde-Copper-Gold (IOCG) deposits produce systematic mineral parageneses that could be used as exploration vectors in high metamorphic-grade terrains?; ii) do Grenvillian REE come from rocks belonging to the Allochtonous or to the Parautochtonous Belt, or from deeper mantellic sources?