<p> The last major episode of deformation occurred in the area studied during the Grenville orogeny (~1000 Ma ago). Deformation of this zone is characterized by a northeast trending penetrative foliation and southeast plunging mineral lineation which increase in intensity and decrease in inclination from northwest to southeast. The deformation was imposed during reverse fault movement in which the southeastern block (the Grenville province) was vertically displaced on the order of 20 kilometers above the adjacent block (the Southern province). The Killarney belt of granites, which separate the Grenville province from the Southern province in this area, are intrusive into the Huronian metasediments and predate the Grenville orogeny. These granites also show evidence of Grenvillian deformation. </p> <p> Paleopiezometry has shown that the differential stress during deformation increases from less than 1 Kbar to more than 6 Kbar from southeast to northwest. The microstructural strain features in quartz and felspar and the mineralogy indicate that a temperature change o£ 400 C is associated with this change in differential stress. Kinematic analysis of mylonites supports the reverse fault model o£ the Grenville Front. </p> / Thesis / Master of Science (MSc)

<p> Amphibolites and gneisses of the "Grenville province" and granitic rocks of the Chief Lake batholith near Sudbury show the effects of several phases of deformation. </p> <p> The first phase of deformation affected previously metamorphosed rocks of the "Grenville province" together with enclosed pegmatite sills, and formed congruous parasitic S- and Z-folds. The rocks were then subjected to faulting and local refolding. About 1, 750 m. y. ago, the Chief Lake batholith was intruded and truncated the previous folds. Finally, all the rocks were subjected to a simultaneous regional metamorphism and strong deformation. </p> <p> During this final deformation, all the previous linear structures were rotated to parallel the strongly-developed regional mineral lineations. The high-grade rocks of high amphibolite facies to the S. E. of the cataclastic zone flowed upwards from a greater depth than the rocks of greenschist facies to the N. E. of the cataclastic zone. The sharp increase in metamorphic grade occurs within the cataclastic zone which is about one mile wide. </p> <p> The final progressive deformation of the rocks is compared with the constant-volume deformation ellipsoid as initiated from the uniaxial prolate type through the constriction type to the plane- strain type; wherein the direction of maximum elongation plunges moderately to the S. S. E. and parallels the regional mineral lineations, the passive fold axes, the elongations of conical folds, and the original flow directions (shown by deformed mineral lineations) of slip folds; while the direction of maximum shortening generally plunges to the N. W. and is normal to the penetrative foliations and the active axial planes of slip folds. </p> / Thesis / Master of Science (MSc)

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)

The Blue Ridge Province of western North Carolina contains a wide variety of metamorphosed igneous and sedimentary rocks that record the tectonic effects of Precambrian and Paleozoic orogenic cycles. Tectonic interpretations of the events that led to the present configuration are varied and often conflicting. This investigation examines metamorphosed mafic rocks that are widely interpreted to have formed during the closure of ocean basins. Metabasites, and specifically eclogites, have a tendency to mark tectonic sutures and frequently preserve pressure (P), temperature (T), and age data (t) that can be gleaned from mineral equilibria and U-Pb isotopic compositions. As such, the examination of the metabasites is considered the key to understanding the orogenic history of the southern Blue Ridge where these metabasites occur. Chapter 2 is an investigation of the retrograde reactions related to the decompression of sodic pyroxenes that react to form diopside-plagioclase-hornblende-quartz symplectites as stability fields are overstepped during isothermal decompression. In Chapter 3 metabasites from the central and eastern Blue Ridge are re-examined and P-T pathways of these lithologies are determined. The argument is made that the Taconic orogeny of the Blue Ridge is the result of a continent-continent collision event that culminated in a mega-mélange that coincides with the Cullowhee terrane and the eastern Blue Ridge mélange of western North Carolina. Chapter 4 contains the results of a geochronological investigation of the Precambrian basement complex of the eastern Great Smoky Mountains. Chapter 5 is a whole rock geochemical study of the same basement complex. In Chapter 6, a potential lithologic correlation between the southern Blue Ridge basement and the Arequipa- Antofalla block of Peru is discussed. The geologic history of western South America from the Mesoproterozoic through Cambrian is summarized, a potential isotope-based lithologic correlation is proposed, and the early tectonic history of the central Blue Ridge is discussed. Chapter 7 contains brief summaries of Chapters 1-6.

Terrane discrimination in polycyclic continental basement rocks is challenging due to high-grade metamorphism and intense deformation. Based on early USGS mapping the Blue Ridge basement in the Dellwood quadrangle of the eastern Great Smoky Mountains was proposed to consist of augen orthogneisses of Laurentian (Grenvillian) affinity interfolded with migmatitic hornblende and biotite paragneisses (“Carolina Gneiss”) and amphibolites of uncertain affinity. However, detailed study reveals that the hornblende gneiss of Hadley and Goldsmith (1963) is a heterogeneous map unit consisting of (1)metaplutonic rocks; (2) variably foliated and folded felsic orthogneisses; (3) strongly migmatitic, folded Hbl+Bt-bearing gneisses; (4) foliated and lineated garnet amphibolites Field relations, petrology, and geochemistry demonstrate that felsic orthogneisses are related to metaplutonic rocks via (post-Taconian) progressive deformation and reconstitution. Whole rock XRF geochemistry reveals likely protoliths of Hbl gneiss and Bt gneiss are geochemically similar and have common sources. U-Pb zircon geochronology and field relationships suggest felsic orthogneisses (1050 Ma,1150-1190 Ma, 1250-1300 Ma) are components of the Mesoproterozoic Grenville basement, and not part of a metamorphosed Neoproterozoic syn-rift Laurentian margin cover sequence. A previously unknown age mode for Mesoproterozoic plutonism in the southern Appalachians was discovered (~1250-1300 Ma) suggesting the presence of a component exotic to pre-Grenvillian Laurentia (Amazonia?).

A scapolite-hornblende-biotite schist from the Grenville province of the Canadian Shield has been analysed for Tl by an atomic absorption technique with a high sensitivity. K, Rb and some major oxides were determined by wet chemistry. Tl, K/Rb, K/Tl and Tl/Rb were compared to several other rocks and for this report were found to be 432ppb, 429, 4.85x10³ and 88.4x10⁻³ respectively. These values are similar to those quoted for other rocks. / Thesis / Bachelor of Science (BSc)

<p> Approximately eighty new neodymium model ages were determined on grey orthogneisses in the Mattawa region of Ontario and were used to develop a Grenvillian tectonic model in the region. A residual-magnetic field map developed from aeromagnetic data provides an additional constraint on the terranes mapped based on Nd-model ages. The field area was divided into three sections: the northern section, the Mattawa klippe, and the southern section. </p> <p> The objectives of mapping in the northern section were two-fold: 1) to map the location of erosional remnants of the allochthon boundary thrust (ABT) and 2) to test the hypothesis that northwestward thrusting of the ABT over the parautochthonous belt caused decollement of a magmatically reworked Archean terrane, creating a duplex thrust sheet and consequent northwestward thrusting of the magmatically reworked Archean parautochthon. </p> <p> Two allochthonous units previously mapped in this region are the Lac Watson nappe and the Lac Booth klippe. These allochthonous units, characterized by Nd-model ages <1.8 Ga are bound by a magmatically reworked Archean terrane (referred to as the reworked Archean parautochthon) with a Nd-model age range of 1.9-2.6 Ga. Likewise, the perimeter of the reworked Archean parautochthon is truncated by a pristine Archean terrane which exclusively hosts Nd-model ages> 2.6 Ga, indicating that there are three crustal stacking levels in the northern section. </p> <p> Nd-model age mapping was employed in the Mattawa klippe region with the same objectives as in the northern section and additionally to provide constraints on the methodology that is to be used when mapping first-order tectonic boundaries such as the ABT. Ketchum and Davidson (2000) suggested that the ABT trended northward in this region based on the presence of 1.16 Ga coronitic metagabbros which Ketchum (1994) concluded were exclusively confined to the allochthonous polycyclic belt (APB). It was detennined here that although the metagabbros are confined to allochthonous crust, based on Nd-model ages, they are contained within an allochthonous klippe (Mattawa klippe) overlying the reworked Archean parautochthon, that transported the coronitic metagabbros northwestward. Therefore, this klippe represents an erosional remnant ofthe APB but the main ABT is located further south. </p> Nd-model age mapping in the southern region identified three distinct crustal terranes. The Mattawa fault was detennined to be a brittle fault following approximately along a pre-Grenvillian suture. This separates the reworked Archean parautochthon from the Paleoproterozoic parautochthon, which had a Nd-model age range from 1.8-1.9 Ga The Paleoproterozoic parautochthon was found to be truncated by the main body of the APB, containing Nd-model ages < 1.8 Ga. The boundary between the Paleoproterozoic parautochthon and the APB was interpreted as the location of the main ABT. </p> <p> Based on the distnbution of Nd-model ages in the region, four distinct crustal terranes were identified representing two thrusting events. Initially the ABT was overthrust on the parautochthonous belt causing decollement of the reworked Archean parautochthon. The entrainment of the reworked Archean parautochthon under the APB generated a duplex thrust sheet, which resulted in the consequent northwestward thrusting of the reworked Archean parautochthon over the pristine Archean terrane. Finally, the ABT was offset by post-Grenvillian normal faulting associated with Ottawa-Bonnechere graben. </p> / Thesis / Master of Science (MSc)

<p> The Hawke River Terrane of the Grenville Province in eastern Labrador is dominated by a coronitic gabbronorite to anorthosite body plus associated amphibolitic to granodioritic bodies known as the White Bear Arm Complex (WBAC). Petrographic and geochemical evidence supports a constant volume sub-solidus diffusion origin for double coronas of orthopyroxene and amphibole around olivine. Geochemical evidence suggests that corona formation was not completely isochemical, requiring an influx of potassium, iron and magnesium, but on a whole-rock scale was probably closed to the latter two elements. Nd and Sr isotopic evidence indicates that the coronas did not form as a response to a much later (eg. Grenville aged) metamorphic event, and probably. developed during post-crystallisational cooling or during a metamorphism shortly thereafter. </p> <p> The WBAC is cut by a monzonitic to granodioritic body mineralogically and chemically similar to the WBAC 'monzonite', known as the Paradise Arm Pluton (PAP). Petrographic, geochemical, and field relationship evidence indicates an igneous origin for the PAP and the WBAC monzonite. Both of these units have been subjected to low grade (greenschist facies) metamorphism. The WBAC and the PAP are hosted by the Paradise Metasedimentary Gneiss Belt, an aluminous paragneiss which has been raised to middle to upper amphibolite grade metamorphism, except immediately adjacent to the contact with the WBAC, where granulite grade has been obtained, forming high-temperature aluminosilicates such as osumilite and sapphirine. The contact zone has also been contaminated by fluids from the gabbronorites, reflected by petrography, elemental and isotopic geochemistry. </p> <p> Field relationships and geochemistry are ambiguous regarding whether the monzonitic units were derived by fractional crystallisation of the gabbronorite or partial melting of the paragneisses, but trace element variation favours the latter model. The PAP is a product of physical, geochemical and Sr isotopic mixing between a granodioritic end-member and a paragneissic one. </p> <p> Sm-Nd isotope systematics on whole-rocks do not provide a precise emplacement age for the WBAC gabbronorite, but indicate a Labradorian age (ca. 1.65 Ga old). Rb-Sr wholerock systematics show a Labradorian-aged trend and a steeply sloping trend interpreted as a mixing line with an unspecified crustal component, possibly corresponding to the potassium metasomatism indicated earlier. Rb-Sr on minerals from two rocks produces a precise age of 1675 ± 15 Ma and a similar, imprecise age. </p> <p> The WBAC monzonite and the Paradise Arm Pluton give Rb-Sr ages of 1621 ± 11 Ma CMSWD=24) and 1573 % 18 Ma (MSWD=9) respectively, with low initial 87Sr/ 86Sr ratios around 0.7040. These are interpreted as a minimum emplacement age and a mixing line, respectively. The PMGB paragneisses give a Rb-Sr age of 1630 ± 16 Ma CMSWD=35), with an initial 87Sr/ 86Sr composition around 0.704. All ages are equal within expanded 2σ error of each other (ie. MSWD=1), and give Labradorian ages. There is no evidence of Grenville-aged (ca. 1.0 Ga old) metamorphism. </p> <p> Rb-Sr isotopic and E Nd -E Br variations suggest crustal contamination of the gabbronorites, although the contaminant cannot be identified. Two separate mechanisms are required to generate the observed trends: a fluid metasomatism and a bulk-rock crustal contamination, or else contamination by currently unidentified low Sr crustal material. The WBAC gabbronorites provide evidence for 'extra'-LREE-depleted mantle beneath eastern Labrador at 1.65 Ga, with E Nd of at least +7.6. </p> / Thesis / Master of Science (MSc)

The Grenville Province and adjacent Makkovik Province represent two long-lived ancient orogenic belts that contain remnants of Paleoproterozoic crust accreted to the southeastern Laurentian margin during the Great Proterozoic Accretionary Orogen (GPAO). However, the addition of juvenile Paleoproterozoic crust to the Archean craton during this period was followed by a span of intermittent ensialic arc magmatism and high-grade metamorphism that overprinted much of the early- to mid- Proterozoic geologic history of the region. As a result, these ancient orogenic belts contain cryptic terrane boundaries that require extensive geochronologic mapping in order to reconstruct the accretionary and collisional growth of the southeastern Canadian Shield. Accreted Proterozoic terranes in the Grenville and Makkovik Provinces have been previously mapped using Nd isotopes in order to determine their crustal formation ages and the boundaries between them. Since the U-Pb isotope system has completely different chemical behaviour to the Sm-Nd system, whole-rock Pb isotope analysis provides an independent method to test the results of Nd isotope analysis. Likewise, Pb isotope mapping acts as a useful tool for determining the exhumation of highly metamorphosed crust, as uranium is preferentially transported from lower crustal levels into the upper crust during regional metamorphism. Therefore, whole-rock Pb isotope analysis was performed on over 200 Archean and Proterozoic gneisses from the SW Grenville Province and Makkovik Province in order to 1) differentiate areas of accreted Paleoproterozoic crust from the reworked Archean margin, 2) test the location of the Archean-Proterozoic suture previously mapped in both regions by Nd model ages, and 3) investigate the variable degrees of crustal burial-uplift within the Archean foreland of the SW Grenville Province that was exhumed during the Grenville orogeny. In the Makkovik Province, whole-rock Pb isotope data from the Cape Harrison domain are comparable with published Pb data from the central Ketilidian mobile belt of southern Greenland. The similarity in Pb signatures between the two belts points to a crustal component in the Cape Harrison domain that was derived from a Proterozoic mantle-derived source with minimal input from older Archean crust. This is largely different from published Pb signatures for the Aillik domain in southeastern Labrador and border zone in southern Greenland that suggests a crustal component comprised of reworked Archean crust analogous to the pre-Makkovikian Laurentian foreland. Comparison of new and published Pb data from the Makkovik Province and southern Greenland in turn helps to constrain a revised single arc accretionary model for the Makkovik Province. Previous Nd isotope mapping in the SW Grenville Province revels a break in model ages inferred by authors as a cryptic collisional suture between the reworked Archean foreland and an accreted Paleoproterozoic arc. However, some workers have suggested that this terrane actually consists of Archean crust that was magmatically reworked in the Mesoproterozoic. Whole-rock Pb isotope data presented in this study points to a crustal component south of the proposed suture in Ontario that was derived from a Paleoproterozoic mantle source and subsequently reworked by ensialic arc magmatism during the Mesoproterozoic. North of the suture, Pb data reveals an Archean crustal component analogous to reworked Superior basement that was exhumed from different crustal levels during the Grenville orogeny. Here, regions of anomalously radiogenic and unradiogenic Pb signatures differentiate the Archean-Proterozoic suture in Ontario from a tectonic duplex in western Quebec. / Thesis / Master of Science (MSc)

No description available.