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Saguenay, Canada

The Université du Québec à Chicoutimi is a branch of the Université du Québec founded in 1969 and based in the Chicoutimi borough of Saguenay, Quebec. UQAC has secondary study centers in La Malbaie, Saint-Félicien, Alma and Sept-Îles. In 2003, 6583 students were registered and 209 professors worked for the university, making it the third largest of the ten Université du Québec branches, after UQAM and UQTR. Wikipedia.

Sawyer E.W.,University of Quebec at Chicoutimi
Journal of Metamorphic Geology

The beginning stages of melt segregation and the formation of leucosomes are rarely preserved in migmatites. Most arrays of leucosomes record a more advanced stage where flow dominates over segregation. However, the early stages in the formation of leucosomes and the segregation of melt are preserved in a partially melted meta-argillite from the metatexite zone (>800 °C) of the contact aureole around the Duluth Complex, Minnesota. The rock contains 2.4 modal% leucosome in a matrix consisting of 40.5% in situ neosome and 57.1% cordierite + plagioclase framework. The domainal microstructure in the matrix is a pre-anatectic feature resulting from the bulk composition. Terminal chlorite reactions produced a large volume of cordierite which, with plagioclase, formed a framework that enclosed patches of biotite + quartz + plagioclase ± K-feldspar. Upon melting, these fertile domains became patches of in situ neosome. Plagioclase in the neosome is less sodic than in the leucosome, hence segregation of melt occurred during crystallization, not melting. Segregation was delayed because the cordierite + plagioclase framework was strong enough to resist dilatation and compaction until after crystallization started. The leucosomes are small (i.e. they are microleucosomes) and display a systematic progression in morphology as length and aspect ratio increase from ~1 to 19 mm and from ~2.5 to >30 respectively. Small equant micropores form first, and in places these coalesce into small (~1 mm, aspect ratio ~2.5), isolated, blunt-ended, elliptical microleucosomes. In the next stage, micropores develop ahead of, and at ~45° to the left and right of the blunt tip of a microleucosome; one of these develops into an elliptical leucosome and an en echelon array of either a left- or right-stepping elliptical microleucosome forms. Each elliptical microleucosome in the en echelon arrays is separated by a bridge of matrix. Next, microleucosomes of greater length (>4 mm) and aspect ratio (>5) form when the bridges of cordierite + plagioclase matrix rupture and the elliptical microleucosomes link together to form a zigzag-shaped microleucosome. Finally, still longer microleucosomes with greater aspect ratios (~30) are formed by the joining of zigzag arrays. Such a progression is characteristic of the way ductile fractures grow. The segregation of melt was driven by the pressure gradient between the dilatant fracture and an adjacent in situ neosome, which drew melt to the growing fracture, thereby creating a microleucosome. The microleucosomes are filled arrays of ductile fractures. Melt was contiguous only between microleucosomes and adjacent patches of in situ neosome. The length-scale of segregation was ~5 mm, the size of a typical patch of in situ neosome, and restricted by the surrounding impermeable cordierite + plagioclase framework. The melt in the microleucosome was the most fractionated and the last to crystallize. All microleucosomes contain entrained minerals as a consequence of their mechanism of growth. Rupture of the bridges resulted in the entrainment of pre-anatectic phases. However, microleucosomes that cross patches of in situ neosome are also contaminated with peritectic phases that were transported with the melt. © 2014 John Wiley & Sons Ltd. Source

The Opatica Subprovince in the Canadian Shield is a late Archaean (2761-2702 Ma) plutonic arc formed above a north-dipping subduction zone. Anatexis (2690-2677 Ma) of leucogranodiorite and leucotonalite orthogneisses in the Opatica generated migmatites in an area of north-vergent back thrusts visible at the surface and in L. ithoprobe seismic profile 48. Schollen diatexite migmatites occur in the thrusts and metatexite migmatites between them.The modal mineralogy, microstructure, and whole rock major, trace and oxygen isotope compositions of the protolith and migmatites were investigated to; 1) determine the melting reaction, 2) find microstructural criteria for identifying residual rocks in leucocratic systems where there is no melanosome, and 3) to determine the source of the fluid involved in anatexis.Partial melting of the protolith did not change the mineral assemblage, but the abundance of quartz and microcline both declined and plagioclase and biotite increased in the residual rocks. Quartz, plagioclase and microcline show evidence for dissolution and biotite does not. Thus, water-fluxed melting of quartz. +. plagioclase. +. microcline occurred. A mass balance indicates 25-30% partial melting. The melting reaction consumed the microcline and created essentially monomineralic domains of plagioclase. Extraction of 80-90% of the melt left a thin film of melt on the grain boundaries, and crystallization of these in the plagioclase domains created diagnostic microstructures. Microcline fills the last remaining pore space and forms high-aspect ratio crystals between plagioclases or triangular crystals at grain junctions. Quartz shows a range of morphologies, from high-aspect ratio films through the "string of beads" to isolated rounded grains, as the microstructure progressively equilibrated after crystallisation.Most accessory phases, including zircon, remained in the residuum. However, almost all the schollen migmatites have high contents of Th, U, Nb, Ta and REE relative to the protolith, due to contamination by accessory phases derived from mafic rocks. Disaggregation of the mafic rocks may have been facilitated by the high strain in the back thrusts where the schollen diatexites formed.Average whole rock δ18O for the protolith and migmatites are similar (ca 8.2%), and the small difference between melt-rich (8.6%) and residuum-rich rocks (8.0%) is consistent with fractionation. Thus, the fluid that caused melting was probably of metamorphic origin with δ18O similar to the protolith. The seismic profile shows several reflectors extending to a present depth of 20 km (ca. 40 km in the late Archaean) under the migmatites; these are the paths along which the metamorphic fluid migrated and generated the migmatites now at the surface. A new type of neosome reported in this study may have formed along fractures that the fluids migrated along, however, these are peripheral pathways in the metatexites adjacent to the back thrusts and schollen diatexites. © 2009 Elsevier B.V. Source

The origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous-pyritic sedimentary rocks as the source for orogenic gold mineralization. Fluid inclusions from selected deposits were analyzed by solid-probe mass spectrometry. Fluids are mostly aqueous-carbonic, with variable amounts of N2, CH4, C2H6, Ar, H2S, H2 and He. For fluids with CH4 and C2H6, their ratios (C1/C2) range from 2.6 to 25.5, indicating that C2H6 is sourced from thermally degraded organic matter. Proportions of CO2, CH4, C2H6 and H2 are highly variable and can be explained by hydrothermal reactions where C2H6 is degraded to CO2 by water consumption. Such reactions may account for the problematic CO2-rich, H2O-poor fluids associated with some of the richest gold districts. Conditions needed for C2H6 degradation are also fundamental for forming gold deposits, such as HS--enriched fluids for carrying gold and local weakly oxidizing conditions for promoting gold precipitation. The C2H6 content is recorded in fluids from Mesoarchean to Cretaceous gold deposits, providing support for a general model where fluids and gold were sourced from deeply buried, carbonrich, and pyrite-gold-bearing sedimentary rocks. © 2013 Geological Society of America. Source

Higgins M.D.,University of Quebec at Chicoutimi
International Geology Review

The initial growth of crystals in magma is driven by kinetic forces, and the resulting textures can be preserved in rapidly cooled igneous rocks. However, crystals in such rocks have a high surface area with respect to their volume, and hence an excess surface energy. This energy can be dissipated by textural equilibration. At advanced stages, this is represented by textural coarsening, in which smaller crystals dissolve simultaneously with the growth of larger crystals. These textural changes occur commonly in slowly cooled plutonic rocks and may be important for the development of some volcanic rocks as well. Textural coarsening is clearly an important petrologic process, but may not have received the attention it deserves inasmuch as it does not change the chemical composition of the rock, and hence cannot be quantified by the geochemical methods that currently dominate petrology. © 2011 Taylor & Francis. Source

Higgins M.D.,University of Quebec at Chicoutimi
Contributions to Mineralogy and Petrology

K-feldspar megacrysts are common in granitoids, but relatively rare in chemically equivalent volcanic rocks. Dacites from Taapaca volcano have euhedral sanidine megacrysts up to 5 cm long. Small crystals, where present, are rounded. Growth of the megacrysts engulfed plagioclase and amphibole crystals. Crystal size distributions (CSD) of sanidine megacrysts are hump shaped. All these data show that megacrysts developed from the host magma by coarsening: this was enabled by the cycling of magma temperature around the sanidine liquidus temperature in response to injections of more mafic magma and subsequent magmatic overturns. Plagioclase crystals enclosed in the megacrysts are small and have short, steep, straight CSDs, which contrasts with the CSDs of plagioclase in the groundmass which are shallower and extend to larger sizes. This shows that plagioclase was also coarsened approximately synchronously with sanidine, in response to the same temperature conditions. © 2011 Springer-Verlag. Source

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