The largest structural trend of the major lithotectonic boundaries in the Grenville Province is located in Ontario where all lithotectonic belts are deflected around Georgian Bay, termed the Big Bend. The thesis will explore some questions related to the formation of this structural feature such as; how the geometry of Grenville aged thrusting contributed to the Big Bend and what conditions led to the formation of the pre-Grenvillian Central Metasedimentary Belt whose geometrical shape may have controlled the development of the Big Bend. First, the geometrical properties of the major lithotectonic boundaries are explored using a three-dimensional model in SketchUp. SketchUp was designed to visualize three-dimensional 1:1 scale real-world structures in Cartesian space. By utilizing refined isotope and geologic surface boundaries accompanied with seismic surveys a three-dimensional tectonic framework of the SW Grenville Province has been constructed. The three-dimensional model of the Grenville Front, Allochthon Boundary Thrust and Central Metasedimentary Belt boundary provides a visual understanding of how the thrust geometry was superimposed from the top-down, eventually producing the Big Bend. Second, 60 new Nd isotope analyses are presented for plutonic orthogneisses from the Central Metasedimentary Belt (CMB), Grenville Province. The CMB has been identified as a back-arc aulacogen with blocks of rifted crustal basement (>1.35GaTDM) in a juvenile matrix of lavas, intrusions and supracrustal sequences (1.35GaTDM). The Grimsthorpe domain is located in the center of the CMB in Ontario and contains large batholiths that exhibit older crustal formation ages known as the Weslemkoon and Elzevir batholiths. The presented Nd isotope analyses identify domains with older crustal formation ages separated by thin salients with younger crustal formation ages inside the Weslemkoon batholith. The intricate geometry of the isotope boundaries within the Weslemkoon batholith suggest that the Laurentian crustal basement was incorporated in the rift and later broken-up by rift related transtension. Continental rift and rifted-arc settings of the Danakil Depression and Gulf of California are explored as modern analogues along with rifted continental fragments known as the Danakil block and Isla Tiburon respectively. Last, the Queensborough mafic-ultramafic complex (QC) is reviewed. The QC is located at the southern end of the Elzevir batholith. The QC was interpreted as a back-arc ophiolite based on REE ratios and MORB normalized spidergrams which were argued to be comparable to modern back-arc basalts. Upon review of the published major and trace element ratios there is a mantle component that is problematical to explain with a back-arc tectonic scenario. The geochemistry suggests that the QC could be partially derived from a mantle plume. The current tectonic models contend this part of Laurentia formed only from subduction related magmatism but based on the trace element data a plume may have been involved as well. The evidence presented supports the identification of the CMB as a failed continental rift and that the failed continental rift created an embayment in Laurentia which governed ductile deformation during Grenvillian orogenic events leading to the formation of the Big Bend. / Thesis / Master of Science (MSc)

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Gneiss domes are structural features associated with orogens worldwide. This study provides a structural analysis of the domes of the Harvey Cardiff Domain, associated with the Grenville Orogeny. Structural data and oriented samples were collected during field work in the summer of 2012. These were used in combination with published and unpublished foliation and lineation data to analyze structural patterns and determine a mechanism of formation for the domes. The end member scenarios for dome formation were taken from the gneiss dome classification scheme devised by Yin (2004). Most of these mechanisms were eliminated based on a lack of necessary large scale geologic features in the region of the study area. An analysis of the foliation pattern of the Cheddar and Cardiff domes was most consistent with formation by diapirism. However, the foliation patterns of the domes differ from the expected diapiric pattern, and seems to represent a non-horizontal slice through a diapir, cutting through a diapir neck in the north and a diapir hat in the south. This pattern can also be explained by rotation of diapiric foliation due to strain induced by the main orogenic event. This hypothesis was tested using COMSOL, a finite elastic strain model, and found to be realistic. With the methods used in this study it is not possible to tell whether this rotation occurred after or during dome emplacement.

The accretionary Mesoproterozoic Grenville Orogeny (ca. 1300 – 980 Ma) involving the Central Metasedimentary Belt is a key building block of the eastern Laurentian margin. A petrographic, mineralogical, geochemical and geochronological study of the migmatite complex in Otter Lake (QC) within the Marble Domain is used to resolve regional metamorphic and magmatic events primarily recorded in the leucosome accessory minerals (i.e. monazite). The relationship between the different stages of monazite and garnet growth and dissolution during the tectonic evolution of the orogenic history for the interpreted metasomatic (injected) and anatectic (in situ) monazite-bearing neosomes from this study supports published thermochronological work in the area and challenges the claim that the Central Metasedimentary Belt was not heated above 500 °C during the Ottawan phase. Instead, the region shows Grenville magmatic and anatectic events were overprinted by high-temperature, fluid-rich Ottawan-phase metamorphism recorded within both injected (monazite-bearing) and in situ (monazite- and garnet-bearing) neosomes.