Nd Isotope Mapping of Crustal Terranes in the Parent-Clova Area, Quebec: Implications for the Evolution of the Laurentian Margin in the Central Grenville Province

Mark Zelek,Alan Dickin

doi:10.3390/geosciences3030448

Abstract

Over 100 new Nd isotope analyses for the central Grenville Province in the Parent-Clova region of Quebec help fill a major gap in understanding the crustal accretion history of the province. Nd model ages show that the Parent-Clova region consists of three crustal blocks: the Archean parautochthon in the north; a central block with mixed ages interpreted as an ensialic arc; and a southerly block forming an extension of the Mesoproterozoic Quebecia arc terrane. The Allochthon Boundary Thrust is believed to define the edge of the Archean parautochthon, which is bordered for a distance of 300 km by the ensialic arc block, within which model ages decrease consistently away from the craton. A similar negative correlation between Nd model age and distance from the craton is seen in published data for the Algonquin terrane in Ontario, but with a lower range of model ages. These comparisons show that in the Parent-Clova region, a Mesoproterozoic ensialic arc was established directly on the Archean margin, but further west, the Mesoproterozoic arc was built on a younger margin consisting of accreted Palaeoproterozoic arc crust. The use of large Nd data sets allows these distinct regional growth patterns to become clear and, hence, allows an understanding of Mesoproterozoic crustal evolution in the province as a whole.

Highlights

Formed during the amalgamation of Rodinia, the Grenville Province represents a long-lived ancient orogenic belt, which comprises the southwestern margin of the Canadian Shield
Localities are based on Universal Transverse Mercator (UTM) grid references using the 1983 North
Dark blue = Archean (>2.4 Ga); red, yellow and pale blue = Palaeoproterozoic; green and pink = largely Mesoproterozoic (1.37–1.64 Ga). Based on these colour schemes, it can be seen that samples with Archean TDM ages are restricted to the area NW of the Allochthon Boundary Thrust (ABT), while the line across the middle of the map separates most samples with model ages above and below 1.64 Ga

Summary

Introduction

Formed during the amalgamation of Rodinia, the Grenville Province represents a long-lived ancient orogenic belt, which comprises the southwestern margin of the Canadian Shield. New continental crust was intruded and sutured onto the Laurentian foreland for nearly a billion years until a terminal collision at 1.1 Ga halted subduction and crustal growth. The continent-continent collision that formed the Grenville Province is analogous to that of the Himalayas [1] and resulted in considerable crustal shortening and thickening. The resulting high-grade metamorphism erased much of the evidence necessary to reconstruct the original growth history of the province and led large areas of the Grenville Province to be labeled as “seas of gneisses” [2]. Nd isotope analysis has been successfully used to estimate crustal formation ages for high-grade gneisses in the Grenville Province [3] and, to identify several large first-order accreted terranes that were amalgamated together on the Laurentian margin over the Paleo- and Mesoproterozoic (Figure 1).

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Discussion

Conclusion