<p> Detailed Neodymium isotopic mapping was performed on grey gneisses from the Algonquin Park area of Ontario, in the Central Gneiss Belt of the southwestern Grenville Province. The Neodymium model ages determined were based upon the Depleted Mantle Model of DePaolo ( 1981c ) . The use of this model is supported by Lead-Lead dating of zircons obtained from an orthogneissic sample. </p> <p> The wide range of model ages found ( 1.5 - 1.86 Ga ) is attributed to the presence of a northwestward dipping, Andean style, ensialic continental margin arc that was active in the Mid-Proterozoic between 1.50 Ga and 1.65 Ga. The diapiric rise of plutons produced by the subduction zone intruded continental margin at least as old as 1.86 Ga as indicated by the oldest pluton in the field area. Variable amounts of mixing occurred between these orogenic rocks and the existing crustal rocks as illustrated by the variable Neodymium model ages determined for grey gneisses collected between 10 Km and 60 Km north of the Central Metasedimentary Belt Boundary Zone. Major element analysis and subsequent tectonic and petrographic discrimination diagrams such as the AFM plot and the granitoid discrimination diagram of LeFort and Debon ( 1983 ) also indicate that the rocks in the Algonquin Park area are calc-alkaline, and are similar to the Peruvian Coastal Batholith. </p> <p> For grey gneisses analyzed within 10 Km of the Central Metasedimentary Belt Boundary Zone, the range of ages is far more restricted, suggesting that an island arc approximately 1.45 Ga was transported by the subducting slab and later sutured onto the existing continental margin. </p> / Thesis / Bachelor of Science (BSc)

<P> Detailed Nd isotopic mapping in the southwestern Grenville Province between North Bay, Ontario, and Temiscaming, Quebec has revealed the precise trend of the proposed Penokean-aged suture discovered during reconnaissance isotopic mapping by Dickin and McNutt (1989). </p> <p> Lithotectonic domains proposed by Easton (1989} for the greater North Bay area are cross-cut by the suture. As presently located, the Tilden-Tomiko domain boundary effects no apparent offset of the suture which would be expected during low angle differential Grenville thrusting. Although a lack of apparent offset suggests these domains are not significant Grenville structures a definitive answer must await more precise mapping of their boundaries. There appears to be some potential for unravelling aspects of Grenville tectonism through such cross-cutting relationships. </p> <p> In the North Bay-Temiscaming area the full model age transition from ca 1.90 Ga to ca 2.70 Ga is negotiated in stepwise fashion through metasediments of intermediate Nd model age spanning an area from a few kilometers to a few tens of kilometers in width. This suggests the suture boundary is better described as a suture zone. Presently two groups of intermediate aged metasediments are recognized (1} a 2.00-2.39 Ga group and ( 2) a 2. 40-2.60 Ga group. These age groups correspond to rocks of two different lithologies separated along strike of the suture in the Temiscaming and North Bay areas respectively. Although the ages of metasediments comprising the suture zone more or less spans the entire interval between 1.90 and 2.70 Ga, there is no well defined transect wherein the whole range of intermediate aged crust is recorded within a single rock type. Therefore a 'splitting' rather than 'lumping' approach is deemed justified for the intermediate aged crust until provenance studies using zircons can be undertaken to show in a definitive manner whether or not the two groups are related in a genetic sense. </p> <p> The absence of plutonism with crystallization ages between 2.00 and 2.60 Ga in the North Bay-Temiscaming area suggests that metasediments of the suture zone acquired their model age from sedimentological mixing between crust of Archean (ca 2.70 Ga) and Proterozoic (ca 1.90 Ga) provenance. The arrangement of mixed provenance metasediments coincident with the suture suggests a genetic relationship. It is proposed that the mixed provenance metasediments are part of a foreland basin assemblage which formed in response to downloading of the cratonal edge by the combined effect of an overriding island arc and the attempted subduction of the Superior craton. </p> <p> Major element analyses show that mixed provenance and arc derived sediments of the proposed foreland basin display a wide range in their maturity. This is consistent with the foreland basin environment where sediments can be reworked to varying degrees in response to tectonically controlled local sea level fluctuations. Contrasting the dynamic environment of the foreland basin the belt of Archean crust north of the suture with model ages of ca 2.72 Ga shows a very restricted range of reworking implying a uniform depositionary environment e.g., deep water passive margin. </p> <p> North of the field area a lobe of Archean crust extends into the Grenville Province, anchored by the Pontiac Group on the northern margin of the Grenville Front (GF), and consisting in part of the parautocthonous Red Cedar Lake Gneiss south of the GF. The full expression of the Archean lobe within the Grenville Province and north of the North Bay Temiscaming field area is unknown, however, preliminary results from Nd isotopic mapping suggest that Archean crust between the suture and the Grenville Front Tectonic Zone (GFTZ) may be part of, or, derived from this Archean parautocthonous lobe. Archean provenance crust north of the field area defines a relatively homogeneous belt of crust with ca 2.72 Ga model ages and a whole rock Sm-Nd isochron age of 2.77 Ga. This is in sharp contrast to the heterogeneity of model ages displayed by Archean crust further west, between the suture (French River area) and the Grenville Front near Sudbury, Ontario (Dickin et al., 1989). Here, the Archean foreland may owe its peculiar heterogeneity to mixing between 2. 72 Ga crust and 2. 4 Ga Huronian volcanics andjor 1. 7 Ga Kilarnian juvenile crust (Dickin et al., 1990). Evidence for the presence of these crustal endmembers in the North Bay Temiscaming area is lacking. </p> <p> Finally, the presence of a suture zone consisting of mixed provenance metasediments is the best evidence yet in support of the suture hypothesis explanation for the model age transition as opposed to juxtaposition of two crustal age domains by Grenville thrusting. </p> / Thesis / Bachelor of Science (BSc)