Nd model-age mapping of Grenville lithotectonic domains: mid- Proterozoic crustal evolution in Ontario

Nd model ages are used to determine the time of crust formation of gneisses within lithotectonic domains in the Central Gneiss Belt of the Grenville Province. The similarity of model-age values to published crystallization ages on suites of plutonic rocks suggests that the ages represent real geological events rather than mixing of older and younger components. The model-age evidence and the chemistry together suggest the existence of two arc - back-arc associations, one of Killarnian (1.75 Ga) and the other of Middle Proterozoic (1.55 to 1.35 Ga) age, established on the Lower Proterozoic - Archean foreland. -from Authors