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No description available.

No description available.

Le craton Archéen canadien, en partie situé au Québec, possède plusieurs occurrences de roches mantelliques reliées aux kimberlites, dont les intrusions Le Tac et Lac Shortt situées dans la région de Chibougamau. Les phases minérales dominantes sont l'olivine, la phlogopite et la serpentine. Les minéraux matriciels sont la serpentine, l'apatite, la pérovskite, le diopside et la calcite. Deux générations d'olivine sont observées dans les deux intrusions. La phlogopite possède une composition variable suggérant une interaction chimique avec un magma de type kimberlitique. La composition des intrusions Le Tac et Lac Shortt est similaire aux kimberlites de faciès hypabyssal des Groupes I et II. Les diagrammes des profils des multi-éléments corrèlent avec ceux des kimberlites avec des anomalies négatives en Rb, Sr et K et positives en Nd et La. Le potentiel diamantifère des deux intrusions étudiées est faible, mais cette région peut tout de même être intéressante pour l'exploration diamantifère.

The Lucerne pluton intrudes rocks of the Penobscot formation Ordovician-Silurian (?)), a quartz-rich sulfidic pelite that contains muscovite, biotite, cordierite, andalusite, plagioclase, pyrrhotite and graphite outside the thermal aureole; and the Bucksport formation (=Vassalboro, Silvian-Devonian (?)), a calcareous, quartzofeldspathic pelite that contains chlorite, biotite, celadonitic muscovite, albite, and ilmenite outside the Lucerne aureole. Within the aureole, the Penobscot formation contains K-feldspar plus andalusite as the result of muscovite reaction with quartz. Corundum occurs at the immediate contact of the granite from the. reaction of the remaining muscovite. The Bucksport formation is recrystallized within the aureole to a purple and green gneiss. The gneissic banding is not present in the low grade calcareous rocks, and represents the segregation of biotite-rich and calc-silicate-rich bands. Vertical or sleepy dipping, the banding parallels both the regional strike and the intrusive contact, and is probably the result of both mechanical and chemical effects. The following sequence of assemblages (+ quartz) is found in the calcareous portions of the Bucksport formation as the Lucerne contact is approached: a) chl + bio + musc + cc + albite; b) bio + cc + plag (An₂₅₋₃₃); c) actinolite + cc + K-feldspar + plag (An₄₀); d) diopside + zoisite + sphene +cc+ plag (An₈₅₋₉₀). Interbedded pelites contain biotite + quartz + plagioclase + pyrite with corundum occurring at the igneous contact in quartz free beds. The mineral assemblages in the Lucerne aureole indicate a lithostatic pressure between 1000 and 3000 bars during metamorphism with temperatures between 700°C and 450°C. Isobaric univariant assemblages in the calc-silicate beds indicate buffering of H₂O/CO₂ fluids produced by prograde reactions. H₂O rich fluids that produced zoisite were probably associated with late stage crystallization of the Lucerne. / Master of Science

Interpretation of geophysical data obtained near Lumberton, North Carolina suggests the presence of a granitic pluton buried beneath Slate Belt-like rocks. A 239 m drill core retrieved from a hole 7.5 km southeast of the city of Lumberton consists of interlayered felsic and mafic volcanics of lower amphibolite grade metamorphism. Dipping reflections in a nearby 16. 5 km long seismic reflection line are believed to be from these volcanics, which are interpreted to be 3.5 km or more in thickness. Below these volcanics is an acoustically transparent zone which is interpreted to be caused by a granitic pluton. This hypothesis is supported by gravity data, which show a -35 mgal Bouguer gravity anomaly, and the relatively high heat flow of 63.4±5 mW/m² obtained in the drill hole, both of which are characteristic of Hercynian granitic plutons in the southeastern United States. Gravity modeling suggests that the body is nearly circular in shape, about 45 km in diameter, and nearly 14 km in thickness. Deep, nearly horizontal reflections in the 5 to 7 sec time range are interpreted to be from the base of the granitoid at a depth of about 17 km. One possible explanation for these reflections is that the granitoid is allochthonous; emplaced elsewhere and then transported to its present position along a sole thrust. The high heat flow suggests that the body is unmetamorphosed and the thrusting, which may post-date or be coeval with the intrusion, would thus be late Paleozoic in age. / M.S.

The Appalachian National Scenic Trail is a unit of the National Park System created by the National Trails Act of 1968. Commonly referred to as the Appalachian Trail, or the AT, this National Park has some of the longest boundaries of any park. The AT is routed more than 2000 miles along the mountains of the eastern United States. The land purchased for the protection of the AT creates a separate boundary on each side of the trail. Monitoring these boundaries for intrusions or encroachments is a difficult and time-consuming task when done totally by field methods. This thesis presents a more efficient and consistent monitoring process using remote sensing data and change detection algorithms. Using Landsat TM images, Normalized Difference Vegetation Index (NDVI), and image difference change detection, this research shows that major boundary encroachments can be detected. Detection of sub-pixel vegetation index decreases identifies specific locations for field inspection. Assuming low cost multispectral Landsat imagery is available, simple NDVI difference calculation allows this technique to be applied to the entire AT one or more times per year. This procedure would improve the response time for encroachment mediation. The producer's accuracy for finding possible encroachments was 100 percent and the consumer's accuracy for possible encroachments indicated was 78.3 percent. Due to limited image availability, this study only examines change between one pair of Landsat images. Further refinement of these techniques should investigate other Landsat images at other times. Use of other remote sensing systems and change detection algorithms could be the focus of further research. / Master of Science

M.S.

The Clarno Formation is a series of volcanic, volcaniclastic, and related intrusive rocks located in central Oregon. It is the westernmost extent of a broader Eocene magmatic belt that covers much the western United States. The magmatic belt stretches eastward from Oregon to western South Dakota, and from the Canadian Yukon to northern Nevada. While once attributed to subduction of the Farallon Plate under North America, more recent work suggests that a more complex tectonic regime involving extension was in place during the early Cenozoic. In the vicinity of Mitchell, Oregon, the Clarno Formation is well represented along with Mesozoic metamorphic and sedimentary units, and younger Tertiary volcanic and volcaniclastic units. In this area, Clarno volcanic activity occurred from ~52-42 Ma, producing mostly andesites and related volcaniclastic rocks. The Mitchell area is also underlain by related intrusive bodies ranging from basalt to rhyolite in composition. The Clarno was most active at ~49 Ma, and is dominantly calcalkaline. In addition, there are several coeval alkaline and peraluminous intrusives also scattered throughout the Clamo Formation. While these suites are less voluminous than the calc-alkaline magmatism, they offer insight into the tectonic and magmatic processes at work in this area during the Eocene. Whereas silicic intrusions are common in the Clarno, the high-silica rhyolite dike on the south face of Scott Butte is unusual due to its large garnet phenocrysts. The existence of primary garnet in rhyolitic magmas precludes middle to upper crustal genesis, a common source for silicic magmas. ⁴⁰Ar/³⁹Ar age determinations of the biotite indicate an age of ~51 Ma. This is after andesitic volcanism had commenced, but prior to the most active period of extrusion. The presence of the almandine garnet indicates that the dike represents partial melting of lower crustal (18-25 km) material. The presence of a high field strength element (HFSE) depletion commonly associated with subduction are magmatism indicates that either the source material had previously been metasomatised, or that some subduction melts/fluids (heat source) mixed with the crustal melt. Two alkaline suites, a high-K calc-alkaline basanite (Marshall and Corporate Buttes) and alkaline minette/kersantite lamprophyres (near Black Butte and Mud Creek), were emplaced ~49 Ma, during the height of calc-alkaline activity. The basanite lacks the HFSE depletion common in the other Clarno rocks. Instead it has a HIMU-type (eg. St Helena) ocean island basalt affinity, resulting from partial melting of enriched asthenospheric mantle. In contrast, the lamprophyres represent hydrous partial melts of metasomatized litho spheric mantle veins and bodies. Alkaline magmatism was not limited to the most active periods of calc-alkaline activity. The emplacement of an alkali basalt (Hudspeth Mill intrusion) at ~45 Ma occurred four million years after the largest pulse of volcanism, but still during calcalkaline activity. This alkali basalt represents partial melting of metasomatized lithospheric mantle. The occurrence of these alkaline suites coeval with the calc-alkaline activity is significant in that it disputes prior subduction theories for the broader Eocene magmatism that are based on spatial and temporal variations from calc-alkaline to alkaline magmatism. These suites also give further insight into the complex tectonic regime that existed in Oregon during the Eocene. The occurrence of asthenospheric melts not caused by fluid fluxing, along with lower lithospheric alkaline melts, are normally associated with extension. Extension provides these magmas with both the mechanism for melting, and the ability to reach shallow crust with little or no contamination. Extension is in agreement with both White and Robinson's (1992) interpretation that most Clarno Formation deposition occurred in extensional basins, and with other provinces in the broader Eocene magmatic belt. / Graduation date: 2002

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy