The Round Lake Batholith is a composite granitic intrusion into the Archean metavolcanics of the Abitibi Greenstone Belt, Superior Province. The mafic metavolcanics are mainly high iron tholeiitic basalts of ocean floor origin. The intrusion of the batholith has metamorphosed the metavolcanics to amphibolite grade. Moving towards the contact there is no change in the metavolcanics grain size, but mineralogy changes quickly from the actinolite zone with relict pumpellyite to the hornblende zone. Field evidence as well as thin section and chemical analyses have shown that the dioritic appearing hybrid rock, near the contact, is a product of the mafic meta volcanics assimilation into the batholith. / 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.

>Magister Scientiae - MSc / The late− to post−collisional Cape Granite Suite (CGS) located in the southwest of South Africa is comprised of S−, I−, and A−type granites, mafic intrusives, and volcanic flows. The CGS is interpreted to have formed during the closing of the Adamastor Ocean during the Late−Proterozoic to Early−Cambrian. Recently, the S−type granites have received much attention concerning their petrogenesis and sources. However, the I− and A−type granites remain poorly understood and little studied. Therefore, with new geochemical and isotopic data the petrogenesis, sources, and tectonic settings of I− (Vredenburg Batholith) and A−type (Cape Columbine) granites of the CGS form the focus for this study. The major and trace element data presented in this thesis show that the granites from the Vredenburg Batholith are weakly peraluminous to metaluminous, ferroan, and alkali−calcic. Associated with the granites are metaluminous, magnesian, and calc−alkalic igneous enclaves. Formerly, the granites have been interpreted to have formed by fractionation. However, with new geochemical analyses and reassessment of such models, it can be shown that such processes are incompatible with accounting for the chemical variation displayed by the granites and their enclaves. Moreover, the I−type granites and enclaves exhibit positive linear trends between whole−rock major and trace elements vs. maficity (Fe + Mg), which can be explained by co−entrainment of peritectic and accessory phases. The lithogeochemical characteristics of the enclaves and host granite reflect melting of a heterogeneous source. Moreover, the granite and enclave's εNd(t) values reflect melting of Paleoproterozoic-aged crustal sources. Finally, with tectonomagmatic discrimination diagrams, it can be shown that the tectonic setting of the granites indicates a transition from a collisional to extensional regime which corroborates the inferences of previous studies. The Cape Columbine Granites lithogeochemical characteristics are ferroan, calc−alkalic and weakly peraluminous. They show typical A−type granite characteristics in having high silica content, high Na + K values, REE enrichment as compared to S− and I−type granites and strong negative Eu anomalies. For this thesis, it can be shown that anatexis of quartzofeldspathic protolith in an extensional regime produced the chemical variation of the Cape Columbine Granite. Moreover, their isotope ratios are typically radiogenic, indicative of a crustal origin. With this new geochemical data evidence is provided against and in support of previous inferences made about the petrogenesis of the I− and A−type granites of the CGS. This also betters our understanding of the magmatic processes involved in the construction of the CGS over time.

Archean greenstone belts typically form narrow sheared basins separating bulbous tonalo-trondjhemo-granodioritic (TTG) batholiths. The role played by gravity in the development of such dome-and-keel structures is a key question in Archean tectonics. The Pukaskwa batholith - Hemlo shear zone (HSZ) is a representative example of the dome-and-keel structures that are common in Archean terrains. This region has received considerable attention because the HSZ hosts several major gold deposits that are currently being mined. Late dextral strike-slip kinematics of the HSZ are well recorded by abundant strain markers in greenstone rocks, whereas the quartzofeldspathic coarse-grained rocks of the Pukaskwa batholith bear no macroscopically visible fabric. The goal of this study is to understand the structural history of this greenstone belt-batholith system. The Pukaskwa batholith is a heterogeneous assemblage of TTG gneisses bounded by the Hemlo greenstone belt to the north. The density of the Pukaskwa batholith rocks (density = 2700 kg/m3) is on average less than that of the Hemlo greenstone rocks (density = 3000 kg/m3). Since Archean geotherms were considered higher than modern equivalents, the effective viscosity of the TTG rocks might have been sufficiently low to allow their diapiric ascent through denser greenstone rocks. Alternatively, the emplacement of the TTG batholith might have been driven primarily by transpressive tectonics. The anisotropy of magnetic susceptibility (AMS) provides valuable information on the internal fabric of the Pukaskwa batholith. This study provides the kinematic information needed to support either the diapiric or the transpressive tectonic model. AMS recorded east-west trending prolate and plano-linear fabrics across the northern section along the contact, suggesting that transpressional forces from the Hemlo shear zone affected the emplacement of the Pukaskwa batholith. Away from the contact, fabrics are generally flattened, indicative of doming through diapiric processes. Also, in order to fully evaluate the diapiric hypothesis, it is necessary to obtain reliable data on rock densities across the Pukaskwa batholith. The density of about 360 representative specimens from the Pukaskwa batholith has been measured and will constitute a valuable database for future gravimetric investigations by mining companies. The significant degree of correlation between high-field magnetic susceptibility and density in the Pukaskwa batholith should be taken into account in geophysical exploration in Archean terrains, only as a proxy for iron content.

No description available.

The Dumper Dew is a newly discovered pegmatite located on the eastfacing slope of Uncle Tom Mountain in Oxford County, Maine. It is a geochemically evolved LCT-type pegmatite petrogenetically linked to the middle Paleozoic Sebago batholith. Shallow emplacement of the Dumper Dew is evidenced by abundant miarolitic cavities found in the pegmatite. The sheet-like structure of the pegmatite coupled with its intrusion in lowmetamorphic grade country rock suggests rapid crystallization. Northern portions of the wall zone and intermediate zones have undergone hydrothermal alteration by the migration of late-stage fluids. The pegmatite hosts a diverse assemblage of rare-element mineral phases due to its high degree of geochemical fractionation. Trends of geochemical fractionation of individual mineral phases such as K-feldspar, muscovite, garnet, apatite, beryl, spodumene, triphylite-lithiophilite, tourmaline, cassiterite, and columbite-tantalite were attained via instrumentation assay. These trends illustrate an enhanced degree of magmatic differentiation relative to other pegmatites in the area.

Subvolcanically emplaced granitic, miarolitic pegmatites associated with the White Mountain Igneous Province (WMIP), New Hampshire, were sampled and analyzed using modern analytical techniques including X-ray fluorescence, electron microprobe, scanning electron microscopy, and direct-coupled plasma spectrophotometry. Analytical results suggest that all the sampled miarolitic pegmatites from this study are petrogenetically related to the same intrusive suite, the WMIP. Based on the geochemical data, all the samples formed in an anorogenic tectonic setting and are rift-related. They are classified as NYF-type and plot in the “within plate granite” field on tectonic discrimination diagrams. The majority of the samples are peraluminous, A1-type granites. The trace element abundances on the spider diagram and chondrite-normalized diagram, which include a pronounced negative Eu anomaly and REE enrichments, are consistent with these miarolitic pegmatites resulting from a strongly fractionated granitic parental melts, but less fractionated than the classic NYF-systems such as South Platte (Simmons et al. 1987) and the Wausau Syenite Complex (Meyers et al. 1984).

Thesis (M.S.)--University of Montana, 2008. / Title from title screen. Description based on contents viewed Aug. 26, 2008. Includes bibliographical references (p. 64-69).

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 155-177). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Universiẗat, Diss., 2005--München.