Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

No description available.

This study is a detailed investigation concerning the construction of granite plutons by the incremental emplacement of granitic sheets. The modem consensus is that sheeted plutons are often controlled by tectonic structures such shear zones. The Main Donegal Granite (MDG), NW Ireland forms the basis to this study. This pluton is the largest presently exposed member of the Caledonian Donegal Batholith (~405 Ma). Field evidence from this highly deformed pluton, attest to emplacement along the long-axis of a sinistral transcurrent shear zone. The presence of long and persistent xenolith "trains" within the pluton has been taken as evidence of an overall sheeted structure; however detailed maps have not been available to test this hypothesis. Two earlier members of the Donegal Batholith, the Ardara and Thorr plutons, whilst having their main outcrops outside the MDG, also occur as xenoliths within the main body. It can be demonstrated in a number of critical situations that these xenoliths are commonly more deformed than the host MDG facies. Furthermore the presence of original country rock contacts implies these xenoliths were originally in situ. These features imply that the shear zone was active prior to the emplacement of the MDG, with it controlling the emplacement of substantial parts of these earlier plutons. Further evidence from the study of parts of the petrographically similar and younger Trawenagh Bay Granite implies the sinistral shear zone was still operational after the majority of the MDG had crystallised. New, detailed (scale 1:250) and reconnaissance mapping of the MDG, reveals its hitherto unrecognised heterogeneity. At least seven major plutonic zones or packages have been identified. All these units have an NE -SW elongate form parallel to the long axis of the pluton and are often, but not always, separated by extensive "raft-trains" of country rock and older plutons. The major packages in the central regions of the pluton are often complex and are composed of three main granitoid phases, ranging in composition form early granodiorites and tonalites to latest porphyritic and to lesser extent equigranular, monzogranites. The early granodiorite and tonalite sheets are now only preserved as xenolithic rafts within the later monzogranites. The broad range in composition/chemistry together allied with field observations implies a complex intrusion history, with these granitoid packages representing sites of long-standing intrusion within the pluton. In contrast, towards the more marginal areas of the pluton there are large units of monzogranite which are characterised by general homogeneity, but in reality are believed to consist of relatively small compostionally similar sheets. On all scales, either meta-sediments, older plutonic material, or early MDG facies are found to lie along the boundaries of younger intrusive units. This implies the pluton is primarily sheeted in character and that the "raft-trains" are partially disrupted, in situ roof material which has been wedged apart during the intrusion of the sheets. The appearance of sheets within the field is dependent on the rheology of the material into which the granitic material was intruded into, i.e. to what extent has the host was crystallised. The degree of crystallisation in the host is related to how fast later sheets were being intruded, i.e. the rate of emplacement. The field relationships, in the central regions of the pluton, between the granodiorites tonalites and the later monzogranites, are interpreted as representing zones of episodic-to slow emplacement, where earlier phases had become essentially competent by the time later units were intruded (i.e. capable of fracture). These earlier phases may be preserved as angular rafts within later sheets. At moderate emplacement rates earlier sheets may still be crystallising but sufficiently viscous to prevent mixing, except at their immediate boundaries with transitional contacts developing. The more homogeneous zones are believed to be related to rapid emplacement with original contacts between pulses being destroyed at the level of emplacement due to homogenisation of pulses which had similar viscosities and hence allowed mixing. The emplacement of granitic melts within active shear zones can lead to the development of a self- perpetuating situation, where melts in a shear zone will enhance deformation rates and cause greater displacements subsequently allowing more melt to enter the shear zone promoting even greater displacement rates. This process is only halted when melts within the source regions are drained; hence the rate of pluton construction and appearance of sheets within plutons is ultimately related to how fast granitic melts are being generated within the source regions.

N/A / Thesis / Bachelor of Science (BSc)

The Coastal Batholith of central Chile preserves structures that record the concentration, migration, transportation, and emplacement of magma during the progressive construction of a sheeted dike complex. This sheeted dike complex is divided into three main structural-geographic domains. The northwestern domain contains an abundance of deformed microgranitoid enclaves that host features that facilitated the concentration of melt during crystallization. The formation of interconnected dilational sites produced an array of lecocratic zones that may have formed larger dike networks that facilitated the transportation of melt-rich magma producing new magmatic units of similar mineralogy. The central domain is characterized by the presence of two tonalitic units that contain enclave swarms distinguished by their general packing arrangement and degree of elongation. Di erences in the fabric architecture of these enclave swarms are displayed by two separate three-dimensional fabric analyses using the Rf/ method, which indicates an abrupt transition from low-distortion oblate fabrics to more distorted prolate geometries. These changes are compared to the statistical alignment of feldspar phenocrysts that indicate general attening in both units with a higher degree of alignment within the XZ fabric plane for the younger tonalite. The third (southeastern) domain is distinguished by meter-scale, compositionally and texturally diverse sheeted dikes intercalated with biotite-rich migmatite screens of the host gneiss along the pluton margin. The need to process large quantities of fabric data from central Chile presented the opportunity to establish a comprehensive method for the quanti cation of three-dimensional rock fabrics following the Rf/ and Fry methods. In order to test the utility of this procedure, a three-dimensional synthetic model of known strain shape, magnitude, and orientation was processed. The results of this assessment indicate that the procedure accurately calculated the expected state of strain within a small margin of error. Finally, a natural example is presented to test the method's ability to quantify the fabrics of deformed rocks. This example is a \lineation much greater than foliation" (L>>S) metagranite augen gneiss from the Coastal Batholith of central Chile. This analysis resulted in calculated fabric ellipsoids from both the Rf/ and Fry methods that clearly display signi cantly prolate geometries at moderate distortions. The development of the three-dimensional rock fabric quanti cation procedure highlighted the need to teach analytical strain techniques in three-dimensions. To allow for this application, an interactive R script (FRY3D) was created speci cally to aid in the instruction and visualization of three-dimensional strain calculation at the advanced undergraduate and graduate levels. This tutorial was presented to a structural geology course of 20 students at the undergraduate level with a two part semi-quantitative concept assessment before and after the presentation. The results of this assessment indicate a positive increase in student's understanding of three-dimensional nite strain. Finally, a simple examination of analytical error associated with the Panozzo projection technique for strain analysis is presented and indicates relationships among population size, strain magnitude, and initial fabric. My results suggest that this method is most robust when applied to sections containing greater than approximately 125 lines. Moreover, the magnitude-dependent error indicates that the method may be better suited for rocks deformed at low to moderate strains. I recommend an adaption to the initial conditional assumptions for this method that lines exhibit an initial radial symmetry when recentered to a common point.

see document / Master of Science

No description available.

No description available.

This dissertation, Reading, Writing, Rhetoric: A Rhetorically Emplaced Study of an Appalachian Region, explores the themes of ideology, stereotypes, and rhetorical emplacement through a study of education in Southwest Virginia. In this project, I used two methods of data collection: historical research and interviewing. These two methodologies employed together construct a sweeping scope of Appalachian Virginia's experiences with rhetorical emplacement in relation to educational practices and ideologies by encountering some of the earliest stories told about the region and contemporary accounts of teachers who currently work in Appalachian Virginia. My main research questions ask how stories told about Appalachia have affected educational practices within the region, and to answer that question I sought out the history of the stories told about Appalachia through historical research, then, in order to attend to the present realities of the region, I interviewed high school English teachers who identify as Appalachian and work in Appalachian Virginia high schools. The historical and ethnographic methods I employed in this dissertation study allowed me to understand the circulation and variances of particular stories placed onto and developed within (Hsiung) the Appalachian region by first examining the historical interaction of the region with the stories about the region and then understanding how those narratives exist in the world today. By using grounded qualitative coding, I created codes from the historical data set—the codes were: isolation, language, education, expectations, culture, and literacy—and compared them to the interview transcripts, I conclude that while illiteracy has long been a stereotype of the region and one that Appalachians will likely combat for the foreseeable future, the teachers in my study build their pedagogies to support rhetorical thinking and rhetorical situation. / Doctor of Philosophy / This dissertation, Reading, Writing, Rhetoric: A Rhetorically Emplaced Study of an Appalachian Region, explores themes of ideology, stereotypes, and place through a study of writing education in Southwest Virginia. In this project, I used two methods of data collection: historical research and interviewing. These two methods construct a sweeping scope of Appalachian Virginian's experiences with stereotypes that are tied to place by encountering some of the earliest stories told about the region and contemporary accounts of teachers who currently work in Appalachian Virginia. My main research questions ask how stories told about Appalachia have affected educational practices within the region, and to answer that question I sought out the history of the stories told about Appalachia through historical research, then, in order to attend to the present realities of the region, I interviewed high school English teachers who identify as Appalachian and work in Appalachian Virginia high schools. The historical and ethnographic methods I employed in this dissertation study allowed me to understand the circulation and variances of particular stories placed onto and developed within the Appalachian region by first examining the historical interaction of the region with the stories about the region and then understanding how those narratives exist in the world today. I conclude that while illiteracy has long been a stereotype of the region and one that Appalachians will likely combat for the foreseeable future, the teachers in my study shape their classrooms to support students in combatting stereotypes of Appalachia by employing critical thinking activities in their classrooms.