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Title: | Nd isotope delineation of crustal terranes in the Bancroft area of Ontario and the Saguenay and Baie Comeau regions of central Quebec: Ensialic rifting and arc formation |
Authors: | Hynes, Eden E. |
Advisor: | Dickin, Alan P. |
Department: | Geography and Earth Sciences |
Keywords: | Earth Sciences;Geography;Earth Sciences |
Publication Date: | Apr-2010 |
Abstract: | <p>The Grenville Province is a highly metamorphosed region of the Canadian shield which contains numerous lithotectonic domains of various ages and characteristics all affected by the c.a. 1.0 Ga Grenville Orogeny. The present study investigates, through reconnaissance neodymium isotope mapping, three under-mapped areas of the Province: the Weslemkoon study area of Ontario and the Saguenay and Baie Comeau study areas of central Quebec. These locations represent areas where previous studies have identified the presence of older crustal blocks which predate the Grenville Orogeny. But further detailed mapping is required to test and formulate interpretations regarding their evolutionary history.<br /> The Weslemkoon Study area is found within the Central Metasedimentary Belt (CMB) of Ontario. The CMB has been interpreted as a composite arc belt (on the basis of structural studies of shear zones) or alternatively, as a failed ensialic rift zone (on the basis of isotope evidence and geometrical relationships). The Grimsthorpe Domain found within the CMB is of major importance in investigating both of these interpretations. In the situation where the CMB is viewed as a composite arc belt, the Grimsthorpe Domain has been interpreted as an allochthon on the basis of its bounding shear zones. However, in current research which views the CMB as a juvenile rift zone, the Grimsthorpe Domain has been interpreted as a horst structure composed of remnant old crust that formed in situ. The latter situation considers evidence from isotope signatures as well as the en echelon geometry of marble domains which are predominant on either side of, but completely absent from the Grimsthorpe Domain. This raises the possibility that the Grimsthorpe Domain did indeed form in situ. The Weslemkoon Batholith largely lies within the Grimsthorpe Domain but extends past the eastern shear zone of the Grimsthorpe Domain. Thus it provides an ideal location to test whether the Grimsthorpe Domain is an allochthon or a horst. <br /> The present study finds that there are consistent Nd isotope signatures spanning the boundary of the Grimsthorpe Domain indicating that the shear zones are reflective of metamorphism, but not transportation of this block of crust. As well, the extent and geometry of old crust is defined and found to have isotope signatures relating this structure to the flanks of the rift zone and thus strengthening the argument that the Grimsthorpe Domain represents a horst structure. Further, the juvenile and old blocks have a ringed geometry in which inter-fingered lobes are identified.<br /> The Saguenay and Baie Comeau study areas of central Quebec are located within the Central Gneiss Terrain and Baie Comeau Segment found within the Allochthonous Polycyclic Belt. While anorthosite-mange ritecharnockite- granite suites have received much attention in the literature, the basement rocks have only recently been studied in any detail with identification of Quebecia. Quebecia, a broad juvenile 1.5 Ga arc terrane has been defined on the basis of relatively homogenous Nd isotope signatures indicating a common basement. Previous studies identified a few isolated areas of crust with signatures predating the Quebecia terrane and these are investigated in detail in this study.<br /> Through more detailed isotope analysis and mapping of the Saguenay and Baie Comeau regions, the extent and geometry of these old blocks of crust have been defined. These old crustal blocks are completely encompassed by the Quebecia arc terrane which the present study interprets as indicating that Quebecia represents a composite arc where fragments of old crust were incorporated into an area dominated by juvenile subduction-related magmatism. These fragments are possibly connected to form a 'panel' of old crust running through the younger Quebecia arc terrane. Hence their identification provides a critical piece of evidence in understanding the geological evolution of the central Grenville Province.</p> |
URI: | http://hdl.handle.net/11375/9020 |
Identifier: | opendissertations/4180 5198 2030123 |
Appears in Collections: | Open Access Dissertations and Theses |
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fulltext.pdf | 35.19 MB | Adobe PDF | View/Open |
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