The Grenville Province: revisiting the orogenic framework and integrating recent findings

The Grenville Province holds record of Mesoproterozoic orogenic processes at the Laurentian margin during the assembly of Rodinia. This contribution reviews key characteristics of the Province, integrates recently published data, and questions some earlier interpretations. Despite crustal reworking during the Grenvillian orogeny (1.09–0.98 Ga), contrasts between crustal-age domains across the Allochthon Boundary largely reflect differences between internal and external Laurentia, and allochthonous units were far-travelled in the west but not in the east. In addition, there is growing evidence towards a continuum between the Ottawan and Rigolet orogenic phases. Based on ages of metamorphism, the high-pressure segments of the hinterland reflect localized thickening at the front of the Ottawan orogen and evidence for an orogenic plateau is limited to the western Grenville. Peak metamorphic conditions in the mid-pressure orogenic core, mostly within the confines of biotite dehydration melting (max ∼900 °C) for aluminous rocks, culminated in early Ottawan and were followed by protracted extension. In addition, high-temperature granitoid magmatism was active throughout the duration of the orogeny and localized in formerly pericratonic terranes accreted at 1.4 and 1.2–1.1 Ga, indicating an influence of inherited lithospheric structures on Grenvillian mantle dynamics. The overall orogenic pattern reveals considerable lateral variations in the hinterland potentially linked to the earlier configuration of external Laurentia and is consistent with weak lithosphere supporting a broad, hot, but not necessarily high-standing orogen for most of the Ottawan, in contrast to the Rigolet phase that marks the propagation of the orogen against Archean lithosphere of internal Laurentia.