Two independent Fe³⁺ species have been simultaneously introduced into Linde L zeolite. One is an exchanged Fe³⁺ species while the other is the molecular species FeCI₃, By simpIe outgassing at 573°K, the exchanged Fe³⁺ is reduced to Fe²⁺. By sweeping the system at 523°K with H₂, both species are converted to ferrous and, at 573°K, the exchanged species is reduced to Feº and the FeCI₃ is reduced to FeCI₂. Outgassing the latter system at 573°K oxidizes the Feº to Fe₂O₃ while the FeCI₂ remains intact. These valency changes were examined using Mössbauer Spectroscopy and, using this technique, a Morin transition appears to have been detected in the Feº species. / Science, Faculty of / Chemistry, Department of / Graduate

Large δ13C excursions present at the Permian-Triassic boundary are thought to indicate a considerable release of isotopically light carbon into the atmosphere (Retallack and Jahren, 2008). The largest of these excursions (-22.2 ‰) was measured in organic matter from Antarctica (Retallack and Jahren, 2008). Antarctic coals are known to be heavily intruded by Jurassic dikes and sills, and the δ13C values of the organic matter may have been influenced by later thermal alteration. In order to evaluate the influence of rank and maceral content on isotopic composition, a total of 335 samples described as Permian-age "coal" were obtained primarily from the United States Polar Rock Repository. Most of the organic matter from Permian coal seams in Antarctica has been extensively altered after burial by localized high heat flow and, in some cases, contact metamorphism associated with dikes and sills; this thermal alteration has likely changed the δ13C values of the organic matter. The rank of the samples prior to intrusion is estimated to be medium to high volatile bituminous. The majority of the samples analyzed (96%) have been altered to above low volatile bituminous rank based on vitrinite reflectance, most (83%) are semi- to meta-anthracites, and a few have been altered to anisotropic cokes. The samples do not follow the typical burial maturation geochemical track, as they are higher in volatile matter (%, daf) and O (%, dmmf), and lower in H (%, dmmf) than coals of the same rank that have undergone normal burial maturation. Carbon stable isotopic data indicate a weak correlation with coal rank as well as with the amount of pyrolitic carbon. Although the isotopically lightest samples measured in this study are located within what is interpreted to be the Permian-Triassic boundary, the effects of thermal alteration of organic matter on δ13C values must be considered in any interpretation of Permian-Triassic atmospheric conditions.

Les pegmatites à éléments rares de type LCT sont depuis longtemps étudiées et exploitées pour leurs gemmes et les métaux rares qu’elles contiennent. Malgré de nombreuses études réalisées sur les processus d’enrichissement en éléments rares, ou les mécanismes à l’origine de leurs textures, très peu d’études ont été dédiées aux mécanismes de mise en place des pegmatites et à leur répartition spatiale à l’échelle du champ. Afin de déterminer les mécanismes moteurs à l’origine de l’ascension de ces magmas, une étude multidisciplinaire a été menée sur 3 champs de pegmatites à éléments rares, répartis à l’échelle de la chaîne Varisque. Les résultats démontrent la proximité entre la localisation des pegmatites minéralisées et l’intensité de la déformation encaissante. De plus, la mise en place de ces magmas semble facilitée par un certain mode de fracturation. La modélisation numérique de la mise en place des magmas dans ces zones crustales fragilisées indique que l’ascension est facilitée par leurs faibles viscosité et densité, mais aussi par des perméabilités crustales très élevées (> 10⁻¹² m²), à des profondeurs de l’ordre de 10 km. Enfin, d’après les signatures isotopiques du Li mesurées sur des micas pegmatitiques, le lithium ne fractionne pas depuis le granite voisin, jusqu’aux pegmatites les plus différenciées, puisque les valeurs δ⁷Li (‰) sont toutes comprises dans une gamme de - 2 à + 2 ‰, similaire à celle rencontrée dans les granites orogéniques. Nous suggérons donc que la genèse des magmas pegmatitiques est commune à celle des granites hyperalumineux. Les mécanismes de fracturation et d’attraction (« magma-pumping ») sont envisagés pour avoir favorisé l’ascension de ces magmas résiduels, enrichis en éléments rares, de faibles volumes, au cours de transitions brutales et de courtes durées (~ 10³ ans), de la perméabilité. L’ensemble de ces résultats permet de remettre en question le modèle du granite parent classiquement utilisé pour la prospection de ces gisements, et de proposer un modèle revisité couplant la genèse et la mise en place de ces magmas. / LCT-type rare-element pegmatites have long been studied and exploited for their gems and rare metals they contain. Despite many studies about the rare-element enrichment, or about the mechanisms leading their exotic textures, very few studies have been dedicated to the mechanisms controlling their emplacement and their spatial distribution at the scale of the pegmatite field. To better investigate the origin of ascent-driving mechanisms of these magmas, a multidisciplinary study was conducted on 3 rare-element pegmatite fields across the Variscan belt. The results demonstrate the spatial proximity of the rare-metals-rich pegmatites with the intensity of deformation of the hosting rocks. In addition, spatial statistical analyses suggest that the emplacement of such magmas has been facilitated by fracture-controlled model. According to numerical models, the rise of these pegmatite-forming melts along weakened crustal zones would be facilitated by their peculiar physico-chemical properties (low viscosity and density), but also by very high crustal permeability (> 10⁻¹² m²) at depths around 10 km. Finally, accordingly to Li isotope signatures measured on pegmatitic micas, lithium does not fractionate from neighbouring granite up to the more differentiated pegmatites, since all δ⁷Li (‰) fall within a range of - 2 to + 2 ‰, as for orogenic granites. Therefore, we suggest that the genesis these pegmatite-forming melts is common to that of peraluminous granites. Mechanisms of fracturation and magma-pumping may have favoured the rise of these low volumes of residual melts, enriched in rare-elements, during short periods (~ 10³ yrs) of strong permeability increase. These results question the granitic model commonly used for the exploration of this type of mineral deposits. We suggest a revisited model accounting for both genesis and emplacement controlling mechanisms of the pegmatite-forming melts.

The production of hydrogen (H2) and methane (CH4) related to olivine hydration (i.e. serpentinization) is considered a major contributor to abiotic hydrocarbon synthesis on Earth. Recent discoveries have highlighted the importance of low temperature (<100oC) serpentinization at continental peridotite outcrops. Such sites produce substantial fluxes of abiotic CH4 from gas seeps and/or springs. A limited number of studies in the southern hemisphere offer research on low temperature abiotic hydrocarbon synthesis in natural ultramafic environments, though large areas of exposed ophiolite are prevalent. This study assesses the origin and flux of CH4 and related water-rock interactions from a previously undiscovered site in the Dun Mountain Ophiolite Belt (DMOB), located at Red Hills, New Zealand. Methane emissions from a hyper-alkaline (pH >11.6) and reduced spring of calcium hydroxide (Ca2+-OH-) type waters near the Maitlands Fault were between 730 to 17,000 mg m 2day 1. The δ13C and δD values of CH4 emitting from this spring are consistent with CH4 of abiotic origin (δ13C: 32.7 ‰ VPDB, δD: 363 ‰ V SMOW). Hyper-alkaline fluids emitting from the spring are concentrated in dissolved CH4 (2.2 mg/L) and H2 (0.7 mg/L) and display δ13CCH4 signatures consistent with other sites worldwide. Extensive and localised carbonate precipitation occurs at the hyper-alkaline Ca-rich spring. Isotopic evaluation of carbonate nodules are kinetically fractionated with 13C and 18O depletions up to 30.8 ‰ and 9.3 ‰, respectively. This disequilibrium between the mineralogy and interacting fluids and gases represents a potential habitable environment for microorganisms. Porous, layered carbonates located on the outer edges of the hyper-alkaline spring are the result of atmospheric CO2 interaction with magnesium bicarbonate (Mg2+-HCO3) and Ca2+-OH- hyper-alkaline waters. The precipitation of these carbonates offers potential insight towards low temperature CO2 sequestration. Additionally, various forms of Fe-rich amorphous material precipitate in association with Mg2+-HCO3 type waters at the Red Hills. The identification of bacteria and diatoms within this material offers supporting information regarding microbial survival in metal-rich, reduced environments. This multidisciplinary study demonstrates the interconnected nature of geological, biological and atmospheric interactions in ultramafic environments at low temperature on Earth.