T35 Proterozoic Tectonic Evolution of the Grenville Orogen in Eastern North America II

Monday, 5 November 2001
1:30 PM - 5:30 PM

THE TRUE NATURE OF THE WAKEHAM AND MANITOU TERRAINS, EASTERN GRENVILLE, QUEBEC, CANADA

Paper number: T35-6
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Recent mapping, structural analyses, and isotopic studies have shed new light on the nature and evolution of the eastern part of the Grenville Province in Quebec, Canada. First, the whole eastern part of the Grenville seems to have formed on a Labradorian basement (> 1.6 Ga). Uplift of this basement with subsequent erosion produced the Wakeham and Manitou sediments deposited between 1.6 and 1.5 Ga. Intrusive and volcanic activity occurred in the Wakeham terrain, the result of probable continental arc magmatism between 1 545 Ma and 1 495 Ma at the onset of the Pinwarian thermal event. The country rocks were also affected by metamorphism and remobilization near the end of the orogeny (around 1.5 Ga). Both the Wakeham and Manitou terrains were then affected by continental intra-plate magmatism of Elzevirian age (1.37 Ga – 1.24 Ga) in a continental back-arc environment. Extensional episodes probably facilitated the emplacement of numerous mafic dykes throughout the Manitou-Wakeham block and anorogenic granitoids in the Manitou area ca. 1170. This was followed finally by the Grenville orogeny per se during which large anorthosite bodies were emplaced along a major SW-NE structural zone. The different units were then telescoped during a compression episode to form the orogen. Late orogenic granites intruded the whole assemblage at the end of the Grenville orogeny (~970 Ma).

It has become clear that most of the Manitou and Wakeham terrains were formed quite close spatially to one another at an early time in the evolution of the area (no later than 1.3 Ga and probably before). It also appears that the Manitou terrain represents a lower structural level of the crust when compared to the Wakeham assemblage; the Wakeham terrane shows very little isotopic resetting resulting from the Grenville orogeny and the rocks are less metamorphosed. In contrast to earlier interpretations, it is now clear that the Wakeham terrain is polycyclic in nature.