Thesis (M.Sc.)--Memorial University of Newfoundland, 1982. / Bibliography : leaves 338-346. Also available online.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Six maps and diagrams on folded leaves in pocket. Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 380-389).

Benjamin Lake map-area lies within the Archaean Slave province of the Canadian Shields. It is underlain by metamorphosed volcanic and sedimentary rocks of the Yellowknife Group that are tightly folded and have been intruded by a series of granodiorite plutons. Assessment of the relations between metamorphism and intrusion is based mainly on field observations, on the results of a petrographic study of over 300 thin sections of the metasedimentary and granitic rocks, and on mineral compositions determined by optical methods. The reactions that produced the various metamorphic minerals are discussed. Regional metamorphic grade in the metasediments ranges from the upper part of the greenschist facies to the middle part of the cordierite-amphibolite facies of the low pressure andalusite-sillimanite facies series. Pelites and semipelites of amphibolite grade are knotted schists characterized by large porphyroblasts of cordierite and andalusite. Metamorphism, in part synkinematic, has outlasted regional deformation. Increase in the andalusite content of the knotted schists towards the east-southeast is considered to have been controlled by conditions of metamorphism rather than by changes in rock composition. Stability relations of observed minerals and their assemblages lead to estimates of conditions during regional metamorphism between 450° and 600°C at between 2 and 3½ Kb. Both pressure and temperature increased in an east-southeasterly direction. The cordierite isograd represents an isothermal surface of about 525°C. Granodioritic magma invaded the metasediments during the later stage of tectonism. Time relations between the resultant plutons have been established. The earliest plutons were emplaced during regional metamorphism and involved the bordering metasediments in the formation of migmatites. Later intrusions have sharp contacts and display a range in form from narrow, dike-like stocks to plutons with oval plan. The latter appear to have developed from the former by swelling in place and have accommodated themselves by pushing aside the previously deformed metasediments. Later still are larger plutons that are concordant in parts and discordant in others. Introduction of pegmatites preceded this latest phase of intrusion but succeeded the earlier phases. The plutonic series shows a gross compositional change with time from equigranular hornblende-biotite quartz diorite through biotite granodiorite to porphyritic granodiorite and quartz monzonite with megacrysts of K-feldspar. Some stocks of granodiorite show a certain amount of internal differentiation, with the K-feldspar content increasing from margin to core. Granodiorite stocks are surrounded by narrow aureoles in which the rocks are characterized by higher proportion of biotite and andalusite than in the regional knotted schists. Pressure-temperature relations between cordierite-muscovite and biotite-andalusite assemblages suggest that pressures in the aureoles of the stocks were slightly higher than those that prevailed during regional metamorphism, which in turn suggests forceful intrusion. The presence of high quartz pseudomorphs in some granodiorites places an upper pressure limit of about 4 Kb on granodiorite crystallization. / Arts, Faculty of / Philosophy, Department of / Graduate

<p> Separated minerals From 18 different rock samples were available. These came From various locations in the Grenville province. OF these samples, there were 44 minerals which had at least one coexisting mineral phase. These were all analysed For boron by thermal neutron irradiation using the Prompt Gamma Neutron Activation Analysis at McMaster University Nuclear Reactor. There was a preferential boron partition determined For the samples originating From an igneous source, and a numerical value of 0.7 was determined for k-Feldspar/Biotite. There was no Preferential boron partition among the coexisting phases that originated From a metamorphic source. Sphene and Fluorite contained much less boron than other minerals that coexisted with them. </p> / Thesis / Bachelor of Science (BSc)

<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)

A brief description of a low grade regionally metamorphosed region in the Madoc area in Southern Ontario is given. Plagioclase compositions from metamorphosed basic rocks of this region were studied with the intention of finding co-existing plagioclases in the region of peristerite solvus. X-ray diffraction was found useful in determining the presence of two co-existing plagioclase feldspars. Two peaks occurred in the region of the 131 and 131 peaks if this was the case. Compositional determinations for albitic feldspars were found inaccurate as the angular separation (Δ29) between the 131 and 131 peaks was apparently reduced indicating plagioclase composition less than An0. For anorthite rich feldspars the angular separation between 131 and 131 gave relatively accurate compositions. The electron microprobe was used·to determine the plagioclase compositions of samples from the Madoc area. Results compared well for anorthite rich feldspars determined by both X-ray diffraction and. electron microprobe techniques. Only one rock was found to contain two plgioclases related to a peristerite solvus. A zoned nature appears to exist. Albite and oligoclase coexist, the oligoclase grading into andesine. Also, albitic plagioclase is associated with epidote inclusions; a diffusion relationship probably existing between the two. With increased metamorphic grade, epidote disappears and the anorthite content of plagioclase increases. / Thesis / Bachelor of Science (BSc)

No description available.

No description available.

Very high temperature (>900 °C) contact metamorphism and metasomatism of aluminous schist xenoliths in the mafic to ultramafic Cortlandt Complex, New York, resulted in formation of bodies of unusual Fe- and Al-oxide-rich rock called emery. During contact heating, disequilibrium thermal decomposition of the protolith schists in one closely examined xenolith produced two end-member materials: a quartzo-feldspathic water-undersaturated melt which partitioned much of the silica and calcium and all of the alkalis of the original schist; and a highly aluminous fine-grained emery residuum which contained spinel, magnetite, ilmenohematite, sillimanite, and sporadically corundum. During cooling, melt within the xenoliths was injected as cm-scale veinlets into the silica-poor solid residuum. Local increase in silica activity resulted in progressive silication reactions of spinel-rich residuum to several silicates. A simple model of progressive silication would require that reactions should occur from lower to higher silica content of product silicates in stages, e.g., spinel – sapphirine (Si/O=0.10), sapphirine – garnet (0.25), garnet – orthopyroxene (0.28), rather than directly from spinel to higher-silica minerals which would overstep intermediate reaction steps. However, observed reaction textures indicate the latter more complex behavior in which spinel may have reaction rims of, or occur as inclusions within, any of the three silicate minerals. Statistical analysis of several samples has shown the mode to be the spinel-orthopyroxene reaction rim boundary although orthopyroxene is the highest-silica product mineral, based on Si/O ratio. Chi-square test results are significant and show that the textural relations observed among spinel, sapphirine, garnet, and orthopyroxene are dependent. Increased silica activity therefore cannot be the only factor controlling the reaction sequence. Microprobe data has been collected in an attempt to correlate mineral compositions with the different textural occurrences. The effects of local equilibria appear to be the dominant factors in the overstepping of sequential reactions. Qualitative activity-activity diagrams proved useful for examining the effects of bulk composition on the relative stabilities of spinel and the three silicates, including variations in Fe/(Fe+Mg), bulk Mn and Zn contents, and minor local variation in oxygen fugacity. Matrix spinel compositions (i.e., those not modified by reaction to silicates) fall into two groups: a more magnesian one containing spinels with average Fe/(Fe+Mg) (Fe#) of 0.49 and a less magnesian one, average Fe# of 0.67. With regard to this bulk compositional effect, the more magnesian composition should reduce garnet stability due to the strong fractionation of Fe into garnet, thus favoring the reaction of spinel to orthopyroxene within silica-rich areas. In more aluminous areas, spinel will react to form sapphirine, then garnet, then possibly orthopyroxene. A less magnesian composition would expand the stability of garnet at the expense of sapphirine and, to a lesser extent, orthopyroxene. Zinc has a subtle effect on mineral stabilities. Because Zn is strongly partitioned into spinel, higher zinc contents (concentrations in some spinels are as high as 14.9 mol% gahnite) may expand the stability of that mineral considerably. Consequently, spinel stability may increase relative to the three silicates, but this may be quite variable due to variable reaction stoichiometry and different reaction-boundary slopes in the activity-activity diagram. In general, spinels with the highest Zn content occur next to orthopyroxene (ave. 4.9 mol% gahnite in spinels) for which the stability appears to be only slightly affected by this increase in Zn. The greatest decrease in silicate stability is observed in sapphirine. Spinels adjacent to sapphirine contain no more than 1.3 mol% gahnite. The effects of manganese and oxygen fugacity were also examined. Mn increases the stability of garnet due to strong partitioning of Mn into this mineral. It can be inferred using statistical and chemical data that this has some bearing on textural relations in garnet-bearing samples, but the lack of obvious Mn fractionation by other minerals examined makes it impossible to interpret the effects of Mn in the garnet-free samples. Calculated ferric-ferrous ratios in analyzed minerals were examined in an attempt to study the effect of oxygen fugacity on the stabilities of minerals. In the more magnesian compositions, which may correlate with slightly higher fO2 during reactions, spinels should react to form sapphirine, then possibly garnet or orthopyroxene with further silica activity increase. In lower-fO2 environments (perhaps those with higher bulk Fe#), spinel should react directly to form orthopyroxene. The coexistence of magnetite and ilmenohematite dictates T-fO2 conditions very nearly at those of the Hematite-Magnetite buffer. Minor fO2 variations that might have had an effect on silicate-forming reactions would only be recorded by small variations in magnetite and ilmenohematite solid solutions (ulvospinel and ilmenite contents, respectively). These data were not acquired in this study, however, so no definite conclusions could be made. / Master of Science

This geothermobarometric investigation of St Persholmen, Utö, in the south central part of Sweden presents an attempt at determining the metamorphic conditions of this important part of the Svecofennian province. Belonging to the geology of the Bergslagen area, Utö historically represent part of Sweden’s vast ore resources with concentrations of iron, copper and sulfides. Rock types from this area are around 1.91-1.89 Ga old (Stephens et al. 2009) and as such Paleoproterozoic in age. The rocks on Utö are considered representative of Bergslagen and record the closing of an ocean starting with subduction followed by volcanic episodes and orogeny (Talbot 2008). The bedrock we observe at Persholmen is thought to represent the remains of the aforementioned orogeny where greywackes from the oceanic stage have been preserved at the base of the mountain range (Stålhös 1982). The two rock types of interest at Persholmen which have been evaluated in this study are 1) normal greywackes and 2) greywackes which have been migmatised either because of the influence of fluids, reworking in an accretionary prism or melted at the base of a mountain range. In this project the area of study has been mapped and samples have been retrieved in order to distinguish the mineralogy and metamorphic history of the bedrock. After petrographic analysis I have determined mineral chemistry by the use of a SEM (Scanning Electron Microscope). These chemical data have then been entered into the computer programs AX and THERMOCALC for determination of temperature and pressure. For the normal/migmatised greywackes a temperature of 538 ±36/756±133°C and a pressure of 3.1±1.3/3.8±3.2 kbars respectively have been estimated. Two generations of muscovite provide evidence of fluid-rock interactions and at the north coast of Persholmen the occurrence of sillimanite indicates a high grade of metamorphism.