Os diques da Região dos Lagos, localizados entre os municípios de Arraial do Cabo, Cabo Frio e Armação dos Búzios (RJ), integram o Enxame de Diques da Serra do Mar (ESM) e apresentam particularidades geoquímicas e geocronológicas que fazem com que seu papel na abertura do Atlântico Sul ainda seja pouco compreendido. Este estudo apresenta os resultados da investigação detalhada sobre a gênese e a idade dessas intrusões, através novas análises de elementos maiores, menores, traços, razões isotópicas (Sr, Nd e Pb) e datações 40Ar/39Ar. Os diques são quimicamente representados por basaltos toleíticos, andesibasaltos toleíticos e basaltos transicionais, com teores de TiO2, em sua maioria, inferiores a 2% (BTi). Os dados de geoquímica elemental permitem identificar dois grupos, um mais primitivo e empobrecido em elementos incompatíveis (grupo A), e outro mais evoluído e enriquecido nesses elementos (grupo B). Os dados sugerem pouca ou nenhuma influência de contaminação crustal durante a evolução e apontam semelhanças do grupo A com os basaltos BTi (Esmeralda) da Província Magmática do Paraná (PMP). O grupo B, por sua vez, apresenta características distintas dos derrames BTi da PMP. O grupo A possui composições isotópicas pouco radiogênicas em Sr e mais radiogênicas em Pb que o grupo B, assemelhando-se àquelas dos diques Horingbaai da Namíbia. As razões isotópicas de Pb sugerem que os dois grupos foram originados por fontes mantélicas distintas, as quais são também menos radiogênicas que os derrames BTi da PMP. Os dados não se adequam à diferenciação por cristalização fracionada com assimilação concomitante ou por mistura envolvendo os reservatórios mantélicos clássicos. Este comportamento pode estar relacionado a heterogeneidades do manto litosférico, causadas por longos processos de subducção durante a amalgamação do Gondwana ocidental. As análises 40Ar/39Ar mostram que a presença de sericitização e albitização nos plagioclásios pode imprimir as idades desses processos nos espectros. Plagioclásios sericitizados do grupo A forneceram idades de 106-108 Ma, e também um provável evento de albitização em 96 Ma. Tais idades discordam tanto das de plagioclásios frescos (idades máximas de 125-140 Ma), afetados por excesso de Ar em decorrência de inclusões de piroxênio e apatita, como daquelas de 132 Ma obtidas em anfibólio-biotita. Estas últimas devem marcar a intrusão dos diques do grupo A, confirmando sua associação com a PMP. A análise em rocha total de um dique do grupo B apresentou idade máxima de cerca de 108 Ma, sugerindo que a intrusão dos grupos A e B podem não ser contemporâneas. A similaridade entre a idade do grupo B e aquela de soerguimento da costa sudeste sugere que estes diques possam ter sido originados durante esse evento, que também teria causado a alteração (sericitização) dos plagioclásios do grupo A. / The Região dos Lagos tholeiitic dykes, located in Rio de Janeiro State, encompass the Arraial do Cabo, Cabo Frio and Armação de Búzios towns and integrate the Serra do Mar Dyke Swarm. Their role in the South Atlantic opening processes is still poorly defined because of their peculiar geochemical and geochronological features. In this work, the petrogenesis and the geochronology of these intrusions were investigated in detail based on new data of elemental (major, minor and trace elements) and isotope (Sr, Nd and Pb) geochemistry along with a careful 40Ar/39Ar dating. The dykes are chemically represented by tholeiitic basalts, andesi tholeiitic basalts and transitional basalts, usually presenting TiO2 contents lower than 2% (LTi). The elemental geochemistry allows the recognition of two magmatic groups; one of them is more primitive and depleted in incompatible elements (group A), whereas the other one is more evolved and enriched in these elements (group B). The data also indicate that crustal assimilation, if existed, had a small role in the magmatic evolution of both groups, and point out similarities between group A and the LTi flows (Esmeralda) from the Paraná Magmatic Province (PMP). Group B, in turn, displays geochemical features very different from those of the LTi basalts from PMP. The Sr isotope compositions of group A are less radiogenic than those of the B one, but the opposite occurs with Pb, which makes the first group similar to the Horingbaai dykes from Namibia. The Pb isotope ratios indicate that A and B were originated from distinct mantle sources, which also differ from those related to PMP LTi flows. The isotope data are not compatible with assimilation-fractional crystallization processes or simple mixtures involving the classic mantle reservoirs. This behavior suggests origin in heterogeneous lithospheric subcontinental mantle, probably affected by long subduction periods during Western Gondwana amalgamation. The 40Ar/39Ar geochronological data point out that the presence of plagioclase sericitization and albitization in their rims may imprint the age of these events in the age spectra. Sericitized plagioclase grains of group A displayed ages of 106-108 Ma, while the albitized fractions provided ages of 96 Ma. Such results disagree with both the fresh plagioclase grains (maximum ages of 125-140 Ma), very affected by excess Ar due to pyroxene and apatite inclusions, and the 132 Ma age of the amphibole-biotite aliquots. This last result very probably corresponds to the dyke emplacement event, confirming the genetic relationship between group A and the PMP. Whole rock dating in a sericite-free group B dyke provided maximum age of 108 Ma, which would imply that A and B groups are not coeval. The similarity between the last age and the uplifting event of Southwestern Brazilian coast suggests that the dykes of group B could have been generated during such process, which also altered (sericitized) the plagioclases of the group A dykes.

Depuis le milieu des années 90, la minéralisation in situ du CO2 est envisagée comme une solution durable et efficace pour limiter ses émissions anthropiques vers l'atmosphère. Il s'agit de récupérer le CO2 émis par certaines industries pour le piéger en profondeur sous forme minérale (carbonates) dans les aquifères mafiques et ultramafiques naturels (de type basaltes et péridotites). La carbonatation du CO2 a été largement décrite dans les systèmes naturels où elle apparait à travers une série de réactions chimiques couplées au transport des espèces réactives dans le fluide. Plusieurs expériences en réacteurs fermés ont été menées depuis une quinzaine d'années afin de mieux comprendre les paramètres physico-chimiques contrôlant ces réactions. Mais très peu d'études n'ont encore caractérisé les processus de transport-réactif au cours de l'injection et de la minéralisation in situ du CO2 dans ces roches.Ces travaux visent à répondre à 3 principaux objectifs : (i) caractériser l'évolution des chemins réactifs lors de l'injection de CO2 dans des roches (ultra-)mafiques, (ii) mesurer les effets en retour des réactions sur les propriétés hydrodynamiques du milieu et (iii) quantifier le rendement et la pérennité des processus sur le long terme. Ils s'appuient sur le développement de protocoles expérimentaux pour (i) reproduire l'injection de CO2 dans les roches (ultra-)mafiques et (ii) caractériser les réactions à l'aide d'une série d'outils géochimiques et analytiques de l'échelle atomique à centimétrique. Trois séries d'expériences de percolation réactive ont été réalisé sur des agrégats (ultra-)mafiques relativement simples (olivines de San Carlos et d'Hawaii) et plus complexes (basaltes de Stapafell) dans des conditions de P-T-confinement in situ (Ptot=10-25 MPa ; T=180-185°C;Pconf=15-28 MPa).Les résultats obtenus ont permis de différencier plusieurs chemins réactifs dans ces systèmes en fonction du transport du fluide, de la porosité du milieu, des hétérogénéités locales de la roche, de la minéralogie et/ou des variations locales de la composition chimique du fluide. Les calculs du bilan de masse ont révélé une minéralisation efficace du CO2 contrôlée par les propriétés chimiques et hydrodynamiques du milieu. Mais certaines réactions associées à l'altération des roches (ultra-)mafiques (hydratation) ont des effets en retour négatifs sur les propriétés réservoirs de la roche (porosité, perméabilité) pouvant compromettre la pérennité du stockage du CO2 dans les aquifères naturels sur le long terme.Ces nouvelles données permettront aux modèles numériques de mieux simuler la carbonatation des roches (ultra-)mafiques en connaissant les propriétés hydrodynamiques du milieu et les hétérogénéités structurales du réservoir. Elles suggèrent aussi qu'un meilleur contrôle de certains paramètres d'injection, comme le débit ou la composition du fluide injecté (ex: pCO2), permettrait d'améliorer le taux et le rendement de la carbonatation. / Since the mid-90s, in situ mineralization of CO2 has been considered as a safe and efficient solution to mitigate its anthropogenic emissions to the atmosphere. It is to recover the CO2 emitted by some industries and trap it in the mineral form (carbonates) in mafic and ultramafic aquifers (e.g. basalts and peridotites). The carbonation of CO2 has been widely described in natural systems where it occurs through a series of complex chemical reactions coupled to the transport of reactive species in the fluid. Numerous experiments have been conducted in batch reactors over the past fifteen years to better understand the physico-chemical parameters controlling the carbonation of (ultra-)mafic rocks. But few studies have further characterized the coupling reactive-transport processes during the injection and in situ mineralization of CO2 in these rocks.This work aims to meet 3 main objectives: (i) characterize changes in reaction paths during the injection of CO2 in (ultra-)mafic systems, (ii) measure the feedbacks effects of chemical reactions on the hydrodynamic rock properties and (iii) quantify the efficiency and sustainability of such processes over long time periods. It is based on the development of experimental protocols to (i) reproduce the injection of CO2 into (ultra-)mafic rocks and (ii) characterize the reactions using a series of geochemical and analytical tools from the atomic to the centimetric scale. Three series of reactive percolation experiments have been performed on (ultra-)mafic aggregates from relatively simple (olivines from San Carlos and Hawaii) to more complex samples (basalts from Stapafell) under in situ P-T-containment conditions (Ptot=10-25 MPa; T=180-185°C; Pcont=15-28 MPa).The results allowed us to differentiate several reactions paths in these systems depending on the fluid transport, rock porosity, local hydrodynamic properties, mineralogy and/or local changes in the fluid composition. Mass balance calculations have revealed an efficient mineralization of CO2 in the samples. It is controlled by the chemical and the hydrodynamic properties of the rock at the pore scale. But some reactions associated with the alteration of (ultra-)mafic rocks (e.g. hydration) have negative feedbacks effects on the reservoir rock properties (porosity and permeability) that may compromise the sustainability of CO2 storage in natural aquifers in the long term.These new supporting data will allow numerical models to better simulate the carbonation of (ultra-)mafic rocks knowing the hydrodynamic properties and the structural heterogeneities of the reservoir. They also suggest that a better control of some injection parameters, such as the flow injection rate and the injected fluid composition (e.g. pCO2), would improve the rate and yield of CO2 mineralization in these systems.

Comprehension of eruptive histories is critical in understanding the evolution of magmatic systems at arc volcanoes and may supply evidence to the petrogenesis of intermediate and evolved magmas. Within the 300 ka eruptive history of Mount St. Helens, Washington, the Kalama Eruptive Period, 1479- ~1750 CE was bracketed by interludes of quiescence (Hoblitt et al., 1980) and thus likely represents an entire eruptive cycle within a span of 300 years. Study of the magmatic evolution during this short time period provides key information regarding inputs and the plumbing system of Mount St. Helens. This research aims to enhance comprehension of processes leading to the petrogenesis of intermediate magmas by providing whole rock and phase geochemical data of an eruptive cycle, thereby providing constraints on the magmatic evolution of the Kalama Eruptive Period. The eruptive sequence is divided into early, middle and late subperiods. The early Kalama began with two dacitic plinian eruptions and continued with smaller eruptions of dacite domes (64.4-66.5 wt% SiO₂) that included quenched mafic inclusions (53.7-57.7 wt% SiO₂). The middle Kalama signified the onset of basaltic andesite and andesite eruptions ranging between 55.5-58.5 wt % SiO₂. Subsequently, summit domes that began as felsic andesite (61-62.5 wt% SiO₂) and transitioned to dacite (62.5-64.6 wt% SiO₂) dominated the late Kalama. Previous work on Kalama-aged rocks suggests magma mixing is an integral process in their production. Compositions and textures of crystal phases, in addition to the presence of xenocrysts in middle and late Kalama rocks, confirm mechanical mixing of magmas likely produced many of the sampled compositions. New petrographic observations were integrated with new whole rock and phase EMP and LA-ICP-MS data and the known stratigraphy in order to constrain the magmatic and crustal components active during the Kalama Eruptive Period. New findings include: 1. Two populations of quenched mafic inclusions, one olivine-rich and one olivine-poor, are identified from the early Kalama based on mineralogy, textures, and major and trace element chemistry. Major element modeling shows crustal anatexis of plutonic inclusions found in early Kalama dacites could produce the felsic magma source of the olivine-poor population. The olivine-rich population incorporated cumulate material. 2. Four distinct lava populations erupted during the early part of the middle Kalama (X lavas), including two found exclusively in lahar deposits: M-type lahars are the most mafic, B-type lahars are more mixed, the Two Finger Flow was previously grouped with other middle Kalama-age lavas, and the X lava (in situ) has unique geochemical and textural character. X tephras likely correlate with the lavas. 3. There were at least three mafic source contributions at Mount St. Helens during the eruptive period: the parent to the X deposits, the cumulate material in the olivine-rich QMIs, and the calc-alkaline parent to the MKLV and SDO. The magma reservoir at Mount St. Helens has been modeled as a single, elongate chamber (Pallister et al., 1992). Multiple coeval basaltic or basaltic andesite parents fluxing into the magmatic system beneath the volcano could indicate a more complex magma chamber structure. / Graduation date: 2011

Os diques da Região dos Lagos, localizados entre os municípios de Arraial do Cabo, Cabo Frio e Armação dos Búzios (RJ), integram o Enxame de Diques da Serra do Mar (ESM) e apresentam particularidades geoquímicas e geocronológicas que fazem com que seu papel na abertura do Atlântico Sul ainda seja pouco compreendido. Este estudo apresenta os resultados da investigação detalhada sobre a gênese e a idade dessas intrusões, através novas análises de elementos maiores, menores, traços, razões isotópicas (Sr, Nd e Pb) e datações 40Ar/39Ar. Os diques são quimicamente representados por basaltos toleíticos, andesibasaltos toleíticos e basaltos transicionais, com teores de TiO2, em sua maioria, inferiores a 2% (BTi). Os dados de geoquímica elemental permitem identificar dois grupos, um mais primitivo e empobrecido em elementos incompatíveis (grupo A), e outro mais evoluído e enriquecido nesses elementos (grupo B). Os dados sugerem pouca ou nenhuma influência de contaminação crustal durante a evolução e apontam semelhanças do grupo A com os basaltos BTi (Esmeralda) da Província Magmática do Paraná (PMP). O grupo B, por sua vez, apresenta características distintas dos derrames BTi da PMP. O grupo A possui composições isotópicas pouco radiogênicas em Sr e mais radiogênicas em Pb que o grupo B, assemelhando-se àquelas dos diques Horingbaai da Namíbia. As razões isotópicas de Pb sugerem que os dois grupos foram originados por fontes mantélicas distintas, as quais são também menos radiogênicas que os derrames BTi da PMP. Os dados não se adequam à diferenciação por cristalização fracionada com assimilação concomitante ou por mistura envolvendo os reservatórios mantélicos clássicos. Este comportamento pode estar relacionado a heterogeneidades do manto litosférico, causadas por longos processos de subducção durante a amalgamação do Gondwana ocidental. As análises 40Ar/39Ar mostram que a presença de sericitização e albitização nos plagioclásios pode imprimir as idades desses processos nos espectros. Plagioclásios sericitizados do grupo A forneceram idades de 106-108 Ma, e também um provável evento de albitização em 96 Ma. Tais idades discordam tanto das de plagioclásios frescos (idades máximas de 125-140 Ma), afetados por excesso de Ar em decorrência de inclusões de piroxênio e apatita, como daquelas de 132 Ma obtidas em anfibólio-biotita. Estas últimas devem marcar a intrusão dos diques do grupo A, confirmando sua associação com a PMP. A análise em rocha total de um dique do grupo B apresentou idade máxima de cerca de 108 Ma, sugerindo que a intrusão dos grupos A e B podem não ser contemporâneas. A similaridade entre a idade do grupo B e aquela de soerguimento da costa sudeste sugere que estes diques possam ter sido originados durante esse evento, que também teria causado a alteração (sericitização) dos plagioclásios do grupo A. / The Região dos Lagos tholeiitic dykes, located in Rio de Janeiro State, encompass the Arraial do Cabo, Cabo Frio and Armação de Búzios towns and integrate the Serra do Mar Dyke Swarm. Their role in the South Atlantic opening processes is still poorly defined because of their peculiar geochemical and geochronological features. In this work, the petrogenesis and the geochronology of these intrusions were investigated in detail based on new data of elemental (major, minor and trace elements) and isotope (Sr, Nd and Pb) geochemistry along with a careful 40Ar/39Ar dating. The dykes are chemically represented by tholeiitic basalts, andesi tholeiitic basalts and transitional basalts, usually presenting TiO2 contents lower than 2% (LTi). The elemental geochemistry allows the recognition of two magmatic groups; one of them is more primitive and depleted in incompatible elements (group A), whereas the other one is more evolved and enriched in these elements (group B). The data also indicate that crustal assimilation, if existed, had a small role in the magmatic evolution of both groups, and point out similarities between group A and the LTi flows (Esmeralda) from the Paraná Magmatic Province (PMP). Group B, in turn, displays geochemical features very different from those of the LTi basalts from PMP. The Sr isotope compositions of group A are less radiogenic than those of the B one, but the opposite occurs with Pb, which makes the first group similar to the Horingbaai dykes from Namibia. The Pb isotope ratios indicate that A and B were originated from distinct mantle sources, which also differ from those related to PMP LTi flows. The isotope data are not compatible with assimilation-fractional crystallization processes or simple mixtures involving the classic mantle reservoirs. This behavior suggests origin in heterogeneous lithospheric subcontinental mantle, probably affected by long subduction periods during Western Gondwana amalgamation. The 40Ar/39Ar geochronological data point out that the presence of plagioclase sericitization and albitization in their rims may imprint the age of these events in the age spectra. Sericitized plagioclase grains of group A displayed ages of 106-108 Ma, while the albitized fractions provided ages of 96 Ma. Such results disagree with both the fresh plagioclase grains (maximum ages of 125-140 Ma), very affected by excess Ar due to pyroxene and apatite inclusions, and the 132 Ma age of the amphibole-biotite aliquots. This last result very probably corresponds to the dyke emplacement event, confirming the genetic relationship between group A and the PMP. Whole rock dating in a sericite-free group B dyke provided maximum age of 108 Ma, which would imply that A and B groups are not coeval. The similarity between the last age and the uplifting event of Southwestern Brazilian coast suggests that the dykes of group B could have been generated during such process, which also altered (sericitized) the plagioclases of the group A dykes.

La plupart des gisements de Ni-Cu sont issus de magmas komatiitique ou tholéiitique associés à des panaches mantelliques. Leur genèse fait intervenir l’exsolution d’un liquide sulfuré immiscible, l’interaction entre les liquides silicaté et sulfuré afin de concentrer ce-dernier en éléments chalcophiles, et l’accumulation du liquide sulfuré en quantités économiques. La saturation en sulfure est généralement atteinte en réduisant la solubilité des sulfures. Celle-ci se fait par assimilation de roches encaissantes siliceuses et/ou sulfurés.Le dyke d’Älgliden de la ceinture de Skellefte, en Suède, contient des sulfures de Cu et Ni dont les quantités ne sont actuellement pas économiques. La minéralisation d’Älgliden est atypique dans la mesure où elle contient d’importantes teneurs en Au, elle a un faible rapport Ni/Cu et enfin est formé dans un contexte de subduction. Le dyke recoupe un gisement porphyrique à Cu-Au contenant des sulfures ce qui laisse suggérer que la minéralisation d’Älgliden est formée par assimilation.Les objectifs de ce projet de recherche étaient d’examiner les processus de formation de la minéralisation d’Älgliden et son potentiel minier ainsi que de mieux comprendre la formation des gisements à Ni-Cu en contexte de subduction. Ce travail inclut l’étude pétrologique du minerai et de ses roches hôtes, la détermination de compositions minérales, l’analyse des éléments majeurs et traces sur roche totale et enfin des analyses des isotopes du soufre. Ce projet a été financé par la compagnie Boliden qui détient le gisement d’Älgliden.Le dyke est composé en majeure partie de norite à olivines, et minoritairement de leucogabbros. Les compositions sur roches totales, les textures magmatiques et les compositions minérales suggèrent que les norites à olivine se sont formées par accumulation d’olivine tandis que les leucogabbros représentent des liquides résiduels avec ou sans cristaux cumulus de plagioclase ± orthopyroxene. Les norites sont interprétées comme étant formées par une ou deux injections de bouillie cristalline suivie de cristallisation fractionnée. Le magma parent des roches d’Älgliden était un basalte hydraté et évolué dont la teneur en MgO est estimé à 6%.Le minerai sulfuré est principalement disséminé à travers l’ensemble de l’intrusion d’Älgliden. Quelques concentrations modérées de minerai se présentent sous la forme de sulfures en réseaux, de veines de sulfures et de sulfures massifs, lesquelles sont spatialement associées aux leucogabbros et aux xénolites de l’encaissant. L’association entre les leucogabbros et les concentrations en sulfures, leur faible teneur en métaux et leur faible rapport Ni/Cu suggèrent que la phase sulfuré s’est exsolvée tardivement au cours de la différentiation magmatique. Ce timing semble défavorable pour la minéralisation d’Älgliden puisqu’il inhibe à la fois l’interaction entre les liquides silicaté et sulfuré et l’accumulation du liquide sulfuré.La contamination du magma d’Älgliden par son encaissant n’est pas corroboré par les concentrations en élément trace et les compositions isotopiques du soufre. En revanche, ces données indiquent que le magma d’Älgliden s’est mis en place dans une zone de subduction où l’on pense que la saturation en sulfure a été atteinte par réduction d’un magma oxydé et riche en élément volatiles, via la cristallisation de magnétite et/ou dégazage. Les valeurs positives de δ34S suggèrent que l’apport de matériel dérivé du slab est responsable du caractère oxydé du magma d’Älgliden.L’état d’oxydation des magmas d’arc leur permet de dissoudre de grandes quantités de S et d’Au. Leur caractère évolué est responsable de leur fortes concentrations relatives en Au et leur faible rapport Ni/Cu. Ainsi, en contexte subduction les sulfures magmatiques sont susceptibles d’avoir ces caractéristiques, et si l’exsolution du liquide sulfuré a lieu plus tôt que dans le cas d’Älgliden cela pourrait conduire à la formation de gisements économiques. / Most major sulfide Ni-Cu deposits originated from komatiitic or tholeiitic magmas that formed in association with mantle plumes. Their genesis involves the segregation of a immiscible sulfide liquid, reaction of the sulfide liquid with silicate melt to upgrade the sulfide in chalcophile elements, and the concentration of the sulfide liquid in economic amounts. Saturation in sulfide is commonly achieved by lowering the sulfide solubility via assimilation of siliceous wall rock or by increasing the S content by adding S-bearing materials.The Älgliden dike in the Skellefte Belt in Sweden contains currently uneconomic Ni-Cu sulfide mineralization. The Älgliden mineralization is atypical insofar as it contains a significant amount of Au, has a low Ni/Cu ratio and formed in a subduction-related geodynamic setting. The host intrusion intrudes sulfide-bearing Cu-Au porphyry mineralization which led to the suggestion that the Älgliden Ni-Cu-Au mineralization was linked to the assimilation of sulfide-bearing wall rocks.The goals of this research project were to investigate the ore forming processes of the Älgliden mineralization and its ore potential, as well as to improve our understanding of the genesis of Ni-Cu deposits in subduction zones. The work is based on a petrological study of the ore and its host rocks, determination of mineral compositions, analyses of major and trace elements in bulk rocks, and sulfur isotope analyses. This was supported by the Boliden company which owns the deposit.The dike is composed mainly of olivine norites with minor leucogabbros. Bulk rock compositions, magmatic textures and mineral compositions suggest that the olivine norites formed by accumulation of olivine and that the leucogabbros represent residual melts with or without cumulus plagioclase ± orthopyroxene. The norites are interpreted to form by one or two injections of an olivine-rich crystal mush and subsequent fractional crystallization. The parental melt of the Älgliden rocks was a hydrous and evolved basalt estimated to contain ≈6 wt.% MgO.The sulfide ore is mainly disseminated throughout the whole Älgliden intrusion. Some weak ore concentrations occur as network to vein and massive sulfides that are spatially associated with the leucogabbros and wallrock xenoliths. The association between the leucogabbros and the concentrations of sulfide, their low ore grade and Ni/Cu ratio suggest that the sulfide segregated late in the differentiation process. This timing appears unfavorable for the Älgliden mineralization because it inhibited both sulfide-silicate liquid interaction and the accumulation of sulfide.Contamination of the Älgliden magma by its wall rocks is not supported by trace element data and S isotope compositions. Instead these data indicate that the Älgliden magma was emplaced above a subduction zone where the sulfide saturation is thought to occur by reduction of the oxidized and volatile-rich magma by magnetite fractionation and/or by degassing. Positive δ34S values suggest addition of slab-derived material which is thought to be responsible for the oxidized character of the Älgliden magma.The oxidation state of arc magmas allows them to carry large amounts of S and Au. Their evolved character is also responsible for their relatively high Au contents and low Ni/Cu. Such characteristics are likely to occur in magmatic sulfide mineralization in subduction zone settings, and if sulfide liquid segregation had occurred earlier than at Älgliden the process may have produced economic sulfide deposits.

The Station Creek Igneous Complex (SCIC) is one of the largest Middle-Late Triassic plutonic bodies in the northern New England Orogen of Eastern Australia. The igneous complex comprises of five plutons - the Woonga Granodiorite (237 Ma), Woolooga Granodiorite (234 Ma), Rush Creek Granodiorites (231 Ma) and Gibraltar Quartz Monzodiorite and Mount Mucki Diorite (227 Ma respectively), emplaced as high-level or epizonal bodies within the Devonian-Carboniferous subduction complex that resulted from a westward subduction along the east Australian margin. Composition of the SCIC ranges from monzogabbro to monzogranite, and includes diorite, monzodiorite, quartz monzodiorite and granodiorite. The SCIC has the typical I-type granitoid mineralogy, geochemistry and isotopic compositions. Its geochemistry is characteristics of continental arc magma, and has a depleted-upper mantle signature with up to 14 wt% supracrustal components (87Sr/86Srinitial = 0.70312 to 0.70391; Nd = +1.35 to +4.9; high CaO, Sr, MgO; and low Ni, Cr, Ba, Rb, Zr, Nb, Ga and Y). The SCIC (SiO2 47%-76%) has similar Nd and Sr isotopic values to island-arc and continentalised island-arc basalts, which suggests major involvement of upper mantle sourced melts in its petrogenesis. SCIC comprises of two geochemical groups - the Woolooga-Rush Greek Granodiorite group (W-RC) and the Mount Mucki Diorite-Gibraltar Quartz Monzodiorite group (MMD-GQM). The W-RC Group is high-potassium, calc-alkalic and metaluminous, whereas the MMD-GQM Group is medium to high potassium, transitional calc-alkalic to tholeiitic and metaluminous. The two geochemical groups of the SCIC magmas are generated from at least two distinct sources - an isotopically evolved Neoproterozoic mantle-derived source with greater supracrustal component (10-14 wt%), and an isotopically primitive mafic source with upper mantle affinity. Petrogenetic modeling using both major and trace elements established that the variations within respective geochemical group resulted from fractional crystallisation of clinopyroxene, amphibole and plagioclase from mafic magma, and late fractionation of alkalic and albitic plagioclase in the more evolved magma. Volcanic rocks associated with SCIC are the North Arm Volcanics (232 Ma), and the Neara Volcanics (241-242 Ma) of the Toogoolawah Group. The major and trace element geochemistry of the North Arm Volcanics is similar to the SCIC, suggesting possible co-magmatic relationship between the SCIC and the volcanic rock. The age of the North Arm Volcanics matches the age of the fractionated Rush Creek Granodiorite, and xenoliths of the pluton are found within epiclastic flows of the volcanic unit. The Neara Volcanics (87Sr/86Sr= 0.70152-0.70330, 143Nd/144Nd = 0.51253-0.51259) differs isotopically from the SCIC, indicating a source region within the HIMU mantle reservoir (commonly associated with contaminated upper mantle by altered oceanic crust). The Neara Volcanics is not co-magmatic to the SCIC and is derived from partial melting upper-mantle with additional components from the subducting oceanic plate. The high levels emplacement of an isotopically primitive mantle-derived magma of the SCIC suggest periods of extension during the waning stage of convergence associated with the Hunter Bowen Orogeny in the northern New England Orogen. The geochemical change between 237 to 227 Ma from a depleted-mantle source with diminishing crustal components, to depleted-mantle fractionate, reflects a fundamental change in the source region that can be related to the tectonic styles. The decreasing amount of supracrustal component suggests either thinning of the subduction complex due to crustal attenuation, leading to the late Triassic extension that enables mantle melts to reach subcrustal levels.