THE GRENVILLE PROVINCE REVISITED: AN OVER 700 MA RECORD OF PROTEROZOIC CRUSTAL GROWTH ALONG THE LAURENTIAN MARGIN

The Proterozoic Grenville Province of southeastern Laurentia comprises one of the longest records of plate interactions and associated crustal growth, with multiple episodes of granitoid and anorthosite-mangerite-charnockite-granite (AMCG) magmatism. The diversity and space-time distribution of Proterozoic granitoid magmatism, along and across the orogen, signal major changes in geodynamic settings, ranging from arc complex to post-collisional continental extension.

The Grenville foreland and Parautochthonous Belt are underlain by Archean to Paleoproterozoic rocks that were extensively intruded by granitoid plutons in the 1.8-1.6 Ga interval, as were the Labrador and Yavapai-Mazatzal orogens of Labrador and southwest USA. The distribution of U-Pb igneous zircon crystallisation and Sm/Nd model ages suggest development of an Andean-arc setting. Due to intense overprinting, field evidence for this arc is, however, scarse.

Conversely, there is compelling evidence, from Labrador to Mexico, for the successive development of arcs along and outboard the Laurentian margin in the 1.5-1.35 Ga interval. While, the 1.45 Ga volcanosedimentary succession of the Montauban Group and the 1.35-1.28 Ga juvenile plutonic rocks of the Parry Sound Allochthon are attributed an island-arc or backarc origin, the regionally extensive 1.4-1.38 Ga calc-alkaline rocks of La Bostonnais Complex testify to an Andean-arc complex. Similar, time correlative rocks may also occur in the mid-continent and southwest USA. Construction of the La Bostonnais arc was accompanied by regional metamorphism.

The Grenvillian orogenic cycle (1.3-0.95 Ga) was reflected in older crustal domains by multiple intrusions of gabbroic rocks, granitoid plutons and AMCG complexes. The tectonic role and consequences of anorthosite intrusion remain current subjects of debate. The Allochthon Monocyclic Belt, which collided with Laurentia at, or prior to 1.19-1.18 Ga, is generally interpreted as an oceanic terrain. Although widely viewed as a collage of terranes, the evolution of this part of the Grenville Province could alternatively be considered as a reworked Andean-arc system. Granitoid plutonism resumed during extensional unroofing ca. 1.0 Ga.