Indentor tectonism in the eastern Grenville Province

The easternmost Grenville Province behaved in a structurally distinct manner from the remainder of the eastern Grenville Province (EGP) during Grenvillian orogenesis (1085–985 Ma). Geochronological, structural and geophysical data are used to demonstrate that, in contrast to frontal-thrust ramp tectonics in western and central Labrador, Grenvillian orogenesis in eastern Labrador mostly involved a dextral strike-slip, lateral-ramp regime. It is also argued that allochthonous terranes in the western part of the EGP were displaced 150 km northwest, relative to their eastern counterparts during the late Grenvillian. Whereas central and western Labrador and adjacent Quebec can be successfully modeled in terms of frontal, collisional tectonism, utilizing channel-flow models that have been applied to the Himalayan–Tibetan tectonic system, eastern Labrador cannot. The point where frontal-thrust ramp tectonics gives way to a lateral-ramp regime is interpreted as an indentor corner. In contrast to the Himalayan situation where India is being subducted under Asia, the indenting crust in the EGP was thrust over pre-Grenvillian Laurentia. The lateral-ramp concept has important implications with respect to Rodinia reconstructions between eastern Laurentia, western Baltica and northern Amazonia.