Search

Iron oxidation state and environment in magmas afect their phase diagram and their properties, including viscosity and density, which determine magma mobility and eruptive potential. In turn, magma composition, pressure, temperature and oxygen fugacity afect iron oxidation state and coordination, potentially leading to complex feedbacks associated with magma ascent, degassing and eruption. While equilibrium experiments and models have led to a deep understanding of the role of iron in melts, our knowledge of the efects of disequilibrium processes on iron oxidation state and its structural role in lavas and magmas remains limited. Accordingly, we performed a series of dynamic disequilibrium experiments on a natural melt composition (a phonolite lava from Erebus volcano, Antarctica) at atmospheric pressure, in which oxygen fugacity and temperature were controlled and varied. During the experiments, we continuously measured iron oxidation and coordination using Fe K-edge dispersive X-ray Absorption Spectroscopy (XAS). We found that iron oxidation state changes in the phonolite melt are reversible and well reproduced by existing models. Changes in iron oxidation state are driven by joint difusion of alkali cations and oxygen anions at magmatic temperatures (~1000 °C for Erebus phonolite). However, redox difusion timescales are too slow for any signifcant oxygen exchange with the atmosphere at the lava/air interface or via air entrainment. Turning to iron coordination, while Fe2+ and Fe3+ are present mostly in an average fve-fold coordination, complex coordination variations decoupled from redox changes were detected. The data suggest transitions between Fe3+ in four-fold and six-fold coordination prior to reduction or as a consequence of oxidation. This questions the possible implication of Fe coordination changes in triggering crystallisation of magnetite nanolites upon magma ascent, and, through such crystallisation events, in promoting magma explosivity.

PURPOSE: Magmas (mitochondria-associated protein involved in granulocyte-macrophage colony-stimulating factor signal transduction) is a nuclear gene that encodes the mitochondrial import inner membrane translocase subunit Tim16. Magmas is highly conserved, ubiquitously expressed in mammalian cells, and is essential for cell viability. Magmas expression levels are increased in prostate cancers and pituitary adenomas. Moreover, silencing Magmas by RNAi sensitizes pituitary adenoma cells to pro-apoptotic stimuli and induces a G0/G1 accumulation. The aim of this study was to examine whether inhibition of Magmas by small molecule inhibitors could be beneficial for the treatment of malignant gliomas. METHODS: We evaluated the expression of Magmas in patient-derived glioblastoma tissue samples and xenograft models. We studied the feasibility of a small molecule Magmas inhibitor (BT#9) as a therapeutic agent in stable human glioma cell lines and high-grade patient derived glioma stem-like cells. RESULTS: Magmas was overexpressed in tissue sections from glioma patients and xenografts. In vivo studies revealed that BT#9 could cross the blood-brain barrier in the animal model. Magmas inhibition by BT#9 in glioma cell lines significantly decreased cell proliferation, induced apoptosis along with vacuole formation, and blocked migration and invasion. In addition, BT#9 treatment decreased the respiratory function of glioma cells, supporting the role that Magmas serves as a reactive oxygen species regulator. CONCLUSIONS: This is the first study on the role of Magmas in glioma. Our findings suggest that Magmas plays a key role in glioma cell survival and targeting Magmas by small molecule inhibitors may be a therapeutic strategy in gliomas.

The purpose of this article is to analyze the philosophy of values developed by Cornelius Castoriadis from his theory of the imaginary institution of societies. By understanding the emergence of imaginary significations, it is possible to identify their manifestations through the representations, the affects and the intentions of individuals. In this context, values correspond to a series of significations that motivate the conduct of individuals. In fact, in a specific society, individuals believe in symbols that make sense for them. The presentation of the values does not reflect a moral project, but rather a socio-political construction that must be carefully described in order to identify the alteration of values over time. The article explores the way in which Castoriadis poses the problem of the persistence of past values with the risk of depending on established norms without being able to really transform them. In this perspective, Castoriadis refers to a fundamental value which is that of autonomy capable of questioning existing imaginaries.

PurposeMagmas (mitochondria-associated protein involved in granulocyte-macrophage colony-stimulating factor signal transduction) is a nuclear gene that encodes the mitochondrial import inner membrane translocase subunit Tim16. Magmas is highly conserved, ubiquitously expressed in mammalian cells, and is essential for cell viability. Magmas expression levels are increased in prostate cancers and pituitary adenomas. Moreover, silencing Magmas by RNAi sensitizes pituitary adenoma cells to pro-apoptotic stimuli and induces a G0/G1 accumulation. The aim of this study was to examine whether inhibition of Magmas by small molecule inhibitors could be beneficial for the treatment of malignant gliomas.MethodsWe evaluated the expression of Magmas in patient-derived glioblastoma tissue samples and xenograft models. We studied the feasibility of a small molecule Magmas inhibitor (BT#9) as a therapeutic agent in stable human glioma cell lines and high-grade patient derived glioma stem-like cells.ResultsMagmas was overexpressed in tissue sections from glioma patients and xenografts. In vivo studies revealed that BT#9 could cross the blood-brain barrier in the animal model. Magmas inhibition by BT#9 in glioma cell lines significantly decreased cell proliferation, induced apoptosis along with vacuole formation, and blocked migration and invasion. In addition, BT#9 treatment decreased the respiratory function of glioma cells, supporting the role that Magmas serves as a reactive oxygen species regulator.ConclusionsThis is the first study on the role of Magmas in glioma. Our findings suggest that Magmas plays a key role in glioma cell survival and targeting Magmas by small molecule inhibitors may be a therapeutic strategy in gliomas.

We develop a theory of split extensions of unitary magmas, which includes defining such extensions and describing them via suitably defined semidirect product, yielding an equivalence between the categories of split extensions and of (suitably defined) actions of unitary magmas on unitary magmas. The class of split extensions is pullback stable but not closed under composition. We introduce two subclasses of it that have both of these properties.

The purpose of this article is to analyze the philosophy of values developed by Cornelius Castoriadis from his theory of the imaginary institution of societies. By understanding the emergence of imaginary significations, it is possible to identify their manifestations through the representations, the affects and the intentions of individuals. In this context, values correspond to a series of significations that motivate the conduct of individuals. In fact, in a specific society, individuals believe in symbols that make sense for them. The presentation of the values does not reflect a moral project, but rather a socio-political construction that must be carefully described in order to identify the alteration of values over time. The article explores the way in which Castoriadis poses the problem of the persistence of past values with the risk of depending on established norms without being able to really transform them. In this perspective, Castoriadis refers to a fundamental value which is that of autonomy capable of questioning existing imaginaries.

The purpose of this article is to analyze the philosophy of values developed by Cornelius Castoriadis from his theory of the imaginary institution of societies. By understanding the emergence of imaginary significations, it is possible to identify their manifestations through the representations, the affects and the intentions of individuals. In this context, values correspond to a series of significations that motivate the conduct of individuals. In fact, in a specific society, individuals believe in symbols that make sense for them. The presentation of the values does not reflect a moral project, but rather a socio-political construction that must be carefully described in order to identify the alteration of values over time. The article explores the way in which Castoriadis poses the problem of the persistence of past values with the risk of depending on established norms without being able to really transform them. In this perspective, Castoriadis refers to a fundamental value which is that of autonomy capable of questioning existing imaginaries.

Magma reservoirs underneath volcanoes grow through episodic emplacement of magma batches. These pulsed magma injections can substantially alter the physical state of the resident magma by changing its temperature, pressure, composition, and volatile content. Here we examine plagioclase phenocrysts in pumice from the 2014 Plinian eruption of Kelud (Indonesia) that record the progressive capture of small melt inclusions within concentric growth zones during crystallization inside a magma reservoir. High-spatial-resolution Raman spectroscopic measurements reveal the concentration of dissolved H2O within the melt inclusions, and provide insights into melt-volatile behavior at the single crystal scale. H2O contents within melt inclusions range from ?0.45 to 2.27 wt% and do not correlate with melt inclusion size or distance from the crystal rim, suggesting that minimal H2O was lost via diffusion. Instead, inclusion H2O contents vary systematically with anorthite content of the host plagioclase (R2 = 0.51), whereby high anorthite content zones are associated with low H2O contents and vice versa. This relationship suggests that injections of hot and H2O-poor magma can increase the reservoir temperature, leading to the dilution of melt H2O contents. In addition to recording hot and H2O-poor conditions after these injections, plagioclase crystals also record relatively cold and H2O-rich conditions such as prior to the explosive 2014 eruption. In this case, the elevated H2O content and increased viscosity may have contributed to the high explosivity of the eruption. The point at which an eruption occurs within such repeating hot and cool cycles may therefore have important implications for explaining alternating eruptive styles.

We present results for transport properties (diffusion and viscosity) using computer simulations. Focus is made on a densified binary sodium disilicate 2SiO2-Na2O (NS2) liquid and on multicomponent magmatic liquids (MORB, basalt). In the NS2 liquid, results show that a certain number of anomalies appear when the system is densified: a diffusivity maxima/minima is found for the network-forming ions (Si,O) which bears some striking similarities with the well-known case of water or liquid silica, whereas the sodium atom displays three distinct régimes for diffusion. Some of these features can be correlated with the obtained viscosity anomaly under pressure, the latter being fairly well reproduced from the simulated diffusion constant. In model magmas (MORB liquid), we find a plateau followed by a continuous increase of the viscosity with pressure. Finally, having computed both diffusion and viscosity independently, we can discuss the validity of the Eyring equation for viscosity which relates diffusion and viscosity. It is shown that it can be considered as valid in melts with a high viscosity. On the overall, these results highlight the difficulty of establishing a firm relationship between dynamics, structure and thermodynamics in complex liquids. © 2012 Elsevier B.V.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2011., Cataloged from PDF version of thesis., Includes bibliographical references (p. 191-202)., Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the effects of variable oxygen fugacity (fo₂) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water flow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H₂O saturated conditions at all crustal depths, and a new geobarometer-hygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of mafic enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H₂O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35 km beneath Mt. Shasta., by Michael James Krawczynski., Ph.D.

The most recent volcanism in the Valles caldera is represented by the El Cajete Pyroclastic Beds (ECPB), Battleship Rock Ignimbrite (BRI), and Banco Bonito Flow (BBF) as well as the VC-1 rhyolite, which are collectively known as the East Fork Member (EFM) of the Valles Rhyolite. The EFM was erupted at approximately 55 ka and 40 ka after an approximate 460 ka lull in volcanism. Previous studies suggested a mafic intrusion at depth triggered the eruptions. This thesis represents the first detailed study of the EFM. Crystal assemblages consist of plagioclase, biotite, clinopyroxene, orthopyroxene, amphibole, sanidine, quartz, and oxides. Electron probe microanalysis and detailed petrography indicates that two distinct crystal populations are present in the ECPB, BRI, and BBF. Large (1 mm), typically resorbed or subhedral crystals represent one population, and small (0.5 mm), generally euhedral crystals represent the other. The large resorbed plagioclase crystals typically have rim overgrowths. Both normal and reverse zonation is present. 40Ar/39Ar geochronology performed on euhedral biotite and groundmass glass from the BBF returned isochron ages of 478 ± 27 ka and 575 ± 15 ka and total gas ages of 125.01 ± 1 ka and 129.82 ± 0.80 ka, respectively. High Mg numbers of large euhderal biotite and 40Ar/39Ar ages older than the accepted age range indicate these crystals are xenocrystic. Radiogenic isotopes are consistent with mixing between the mantle and lower crustal reservoirs. General trends are evident between whole-rock major and trace elements with increasing SiO2. In general, incompatible trace elements increase and compatible trace elements decrease. Incompatible trace element ratios indicate the presence of a single magma batch. The heterogeneity in crystal morphology and chemistry can be explained by a model in which partial melting of mid- to deep continental crust occurred due to an intrusion of an intermediate composition magma. Magma mixing and an exchange of

Massive graphite deposition resulting in volumetrically large occurrences in volcanic environments is usually hindered by the low carbon contents of magmas and by the degassing processes occurring during and after magma emplacement. In spite of this, two graphite deposits are known worldwide associated with volcanic settings, at Borrowdale, UK, and Huelma, Spain. As inferred from the Borrowdale deposit, graphite mineralization resulted from the complex interaction of several factors, so it can be considered as an example of self-organized critical systems. These factors, in turn, could be used as potential guides for exploration. The key factors influencing graphite mineralization in volcanic settings are as follows: (1) an unusually high carbon content of the magmas, as a result of the assimilation of carbonaceous metasedimentary rocks; (2) the absence of significant degassing, related to the presence of sub-volcanic rocks or hypabyssal intrusions, acting as barriers to flow; (3) the exsolution of a carbon-bearing aqueous fluid phase; (4) the local structural heterogeneity (represented at Borrowdale by the deep-seated Burtness Comb Fault); (5) the structural control on the deposits, implying an overpressured, fluid-rich regime favouring a focused fluid flow; (6) the temperature changes associated with fluid flow and hydration reactions, resulting in carbon supersaturation in the fluid, and leading to disequilibrium in the system. This disequilibrium is regarded as the driving force for massive graphite precipitation through irreversible mass-transfer reactions. Therefore, the formation of volcanic-hosted graphite deposits can be explained in terms of a self-organized critical system.

De nombreux travaux expérimentaux ont été effectués, au cours des dernières décennies pour recréer des magmas anatectiques felsiques à partir de la fusion par déshydratation de différents types de roches tels que des métasédiments ou des roches ignées. Cependant, les granites naturels de type S sont beaucoup plus enrichis en fer et magnésium que tous les liquides felsiques qui ont pu être obtenus expérimentalement. De plus, des analyses de liquides felsiques en inclusion dans les minéraux métamorphiques ont montré les mêmes résultats que les travaux expérimentaux. Récemment, Pentrainement de phases péritectiques lors de l'extraction du liquide a été démontré comme étant l'un des processus responsables de ces enrichissements. Seulement, un certain nombre des granites de type S riches en fer et en magnésium ne contiennent pas de minéraux tels que le grenat ou la cordiérite mais seulement un fort enrichissement enbiotite. L'hypothèse testée au cours de ce doctorat est que le processus responsable de l'enrichissement en FeO* (tout le fer est considéré comme étant du Fe2+) et MgO est l'incorporation et la désagrégation de matériel riche en FeO* et MgO lors de l'extraction et de la mise en place du granite et, que les réactions de ce matériel avec le magma entraînent la formation de biotite. Pour se faire, une étude de terrain, pétrologique et géochimique ainsi qu'une modélisation à l'aide du logiciel THERMOCALC, ont été effectuées sur un pluton granitique de croûte profonde : Le granite de Wuluma en Australie Centrale. Cette étude a permis de montrer que les enrichissements en FeO* et MgO dans le granite de Wuluma venaient principalement d'enrichissements en biotite, sous forme de schlieren, d'agrégats, ou bien dans la matrice. L'origine de trois types de schlieren a été déterminée. Les schleiren associés aux enclaves et les schleiren longs proviennent de la désagrégation et retirement d'enclaves et de lambeaux de roches encaissantes (pris entre les différents dykes de m

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011, Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the e ects of variable oxygen fugacity (fO2) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water ow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H2O saturated conditions at all crustal depths, and a new geobarometerhygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of ma c enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H2O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35km beneath Mt. Shasta.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011, Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the e ects of variable oxygen fugacity (fO2) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water ow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H2O saturated conditions at all crustal depths, and a new geobarometerhygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of ma c enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H2O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35km beneath Mt. Shasta.

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011, Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the e ects of variable oxygen fugacity (fO2) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water ow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H2O saturated conditions at all crustal depths, and a new geobarometerhygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of ma c enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H2O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35km beneath Mt. Shasta.

Melting and crystallization processes on the Earth and Moon are explored in this thesis, and the topics of melt generation, transport, and crystallization are discussed in three distinct geologic environments: the Moon's mantle, the Greenland ice sheet, and the Earth's crust. Experiments have been conducted to determine the conditions of origin for two high-titanium magmas from the Moon. The lunar experiments (Chapter 2) were designed to explore the e ects of variable oxygen fugacity (fO2) on the high pressure and high temperature crystallization of olivine and orthopyroxene in high-Ti magmas. The results of these experiments showed that the source regions for the high-Ti lunar magmas are distributed both laterally and vertically within the lunar mantle, and that it is critical to estimate the pre-eruptive oxygen fugacity in order to determine true depth of origin for these magmas within the lunar mantle. Chapter 3 models the behavior of water ow through the Greenland ice sheet driven by hydrofracture of water through ice. The results show that melt water in the ablation zone of Greenland has almost immediate access to the base of the ice sheet in areas with up two kilometers of ice. Chapter 4 is an experimental study of two hydrous high-silica mantle melts from the Mt. Shasta, CA region. Crystallization is simulated at H2O saturated conditions at all crustal depths, and a new geobarometerhygrometer based on amphibole magnesium number is calibrated. In Chapter 5 I use the new barometer to study a suite of ma c enclaves from the Mt. Shasta region, and apply it to amphiboles in these enclaves. Evidence for pre-eruptive H2O contents of up to 14 wt% is presented, and bulk chemical analyses of the inclusions are used to show that extensive magma mixing has occurred at all crustal depths up to 35km beneath Mt. Shasta.

We present new U-series disequilibrium and radiogenic isotope data for 7 mafic lavas from the Lesser Antilles arc. These are combined with published data in an internally consistent model that quantitatively estimates the amount of sediment and fluid added to the source of the Lesser Antilles arc system. Some lavas form an array consistent with bulk sediment addition (0.2–2%) whereas others appear to require addition of 0.4–2% sediment melt, particularly in the south of the arc. Evidence for both bulk sediment and sediment melt addition can be found within both the northern and central sections of the arc suggesting a thermal structure whereby the upper portions of the subducted sediment pile lie close to their solidus beneath much of the arc. Addition of up to 5% fluid derived from altered oceanic crust to these sediment enriched mantle wedge source regions can simulate the majority of the lavas on a plot of 207Pb/204Pb versus Ce/Pb. By taking into account the range in calculated wedge compositions and allowing for some mobility of Th in the fluid, the same model can also account for much of the observed range of U–Th–Ra disequilibria, especially if the eclogitic residue contains trace amounts of rutile. The implication of this more complex model is that the time scales for fluid addition and differentiation could be significantly shorter than those estimated in some previous studies.

We present new U-series disequilibrium and radiogenic isotope data for 7 mafic lavas from the Lesser Antilles arc. These are combined with published data in an internally consistent model that quantitatively estimates the amount of sediment and fluid added to the source of the Lesser Antilles arc system. Some lavas form an array consistent with bulk sediment addition (0.2–2%) whereas others appear to require addition of 0.4–2% sediment melt, particularly in the south of the arc. Evidence for both bulk sediment and sediment melt addition can be found within both the northern and central sections of the arc suggesting a thermal structure whereby the upper portions of the subducted sediment pile lie close to their solidus beneath much of the arc. Addition of up to 5% fluid derived from altered oceanic crust to these sediment enriched mantle wedge source regions can simulate the majority of the lavas on a plot of 207Pb/204Pb versus Ce/Pb. By taking into account the range in calculated wedge compositions and allowing for some mobility of Th in the fluid, the same model can also account for much of the observed range of U–Th–Ra disequilibria, especially if the eclogitic residue contains trace amounts of rutile. The implication of this more complex model is that the time scales for fluid addition and differentiation could be significantly shorter than those estimated in some previous studies.

We present new U-series disequilibrium and radiogenic isotope data for 7 mafic lavas from the Lesser Antilles arc. These are combined with published data in an internally consistent model that quantitatively estimates the amount of sediment and fluid added to the source of the Lesser Antilles arc system. Some lavas form an array consistent with bulk sediment addition (0.2–2%) whereas others appear to require addition of 0.4–2% sediment melt, particularly in the south of the arc. Evidence for both bulk sediment and sediment melt addition can be found within both the northern and central sections of the arc suggesting a thermal structure whereby the upper portions of the subducted sediment pile lie close to their solidus beneath much of the arc. Addition of up to 5% fluid derived from altered oceanic crust to these sediment enriched mantle wedge source regions can simulate the majority of the lavas on a plot of 207Pb/204Pb versus Ce/Pb. By taking into account the range in calculated wedge compositions and allowing for some mobility of Th in the fluid, the same model can also account for much of the observed range of U–Th–Ra disequilibria, especially if the eclogitic residue contains trace amounts of rutile. The implication of this more complex model is that the time scales for fluid addition and differentiation could be significantly shorter than those estimated in some previous studies.

[ES] Los magmas se generan en cuatro ambientes geodinámicos diferentes: a) en los márgenes de placa constructivos, en los que se incluyen las dorsales centro-oceánicas y las cuencas tras-arco; b) en los márgenes de placa destructivos, como los arcos-isla y los márgenes continentales activos; c) en zonas de intraplaca oceánica, y d) en zonas de intraplaca continental. En las dorsales, en los arcos-isla intraoceánicos y en las islas oceánicas los magmas sólo se pueden generar en el manto superior, ya que en estas áreas no existe corteza continental, pero en los márgenes continentales activos y en las áreas de intraplaca continental la corteza puede jugar un papel más o menos importante. A su vez, las dos zonas del manto superior en las que potencialmente se pueden originar magmas son la litosfera y la astenosfera. El mecanismo por el que se originan los magmas en cada uno de estos ambientes geodinámicos es diferente. En los márgenes de placa constructivos la astenosfera asciende adiabáticamente y funde. En los márgenes destructivos la generación de magmas está relacionada con la subducción. Finalmente, en áreas de intraplaca continental el magmatismo está asociado a fenómenos de extensión producidos por fenómenos tales como la indentación y la delaminación o bien está relacionado con plumas mantélicas, como ocurre en general en áreas de intraplaca oceánica. El tipo de erupción depende de la composición del magma, y sobre todo de su temperatura, viscosidad y contenido en gases. En general, los magmas basálticos (que tienen contenidos en SiO2 comprendidos entre 45 y 52%, temperaturas de 1.000-1.200 °C, viscosidades del orden de 10-102 Pa·s y baja abundancia de gases) extruyen de forma tranquila o moderadamente explosiva, dando lugar a erupciones de tipo hawaiano o estromboliano. Por el contrario, los magmas ácidos (que tienen contenidos en SiO2 superiores al 63%, temperaturas de 700 a 900 °C, viscosidades entre 106 y 108 Pa·s y elevado contenido en gases) y los traquíti, [EN] Magmas are generated in four well-defined geodynamic settings: a) constructive plate margins, including mid-ocean ridges and back-arc basins; b) destructive plate margins, such as island arcs and active continental margins; c) oceanic intraplate areas, and d) continental intraplate areas. In mid-ocean ridges, intraoceanic island-arcs and oceanic islands, magmas can only be generated at the upper mantle due to the absence of continental crust. On the contrary, the crust can play an important role in continental settings. Additionally, the generation of magma in the upper mantle can be located in the asthenosphere and the lithosphere. The mechanisms of magma generation in each geodynamic setting is different. In constructive plate margins, the asthenosphere rises adiabatically and melts. In destructive margins, melting is linked to subduction. Finally, in continental intraplate areas melting is associated to extensional processes, which can be linked to various phenomena such as indentation, delamination or mantle plumes, as in the case of oceanic intraplate settings. The eruptive mode depends strongly on the magma composition, and more precisely of its temperature, viscosity and gas content. In general, basaltic magmas (characterised by SiO2 abundances between 45 to 52%, temperatures of 1.000-1.200 °C, viscosities of 10-102 Pa·s and low gas content) erupt in a quiet or moderately explosive way, producing hawaiian- or strombolian-type eruptions. On the other hand, acid magmas (with SiO2 higher than 53%, temperatures of 700-900 °C, viscosities between 106 and 108 Pa·s and high gas contents) are characterised by explosive, vulcanian- to plinian-type eruptions. At global scale, the volcanic eruptions and their associated phenomena are less frequent and involve less victims and damage than other natural disasters. According to the recent database by Witham (2005), from the 176 considered volcanoes and volcanic areas, only a half are related to more than one incident

A series of 1 atm experiments has been performed to test the influence of iron content and oxidation state on the saturation of phosphate minerals in magmatic systems. Four bulk compositions of different iron content have been studied. The experiments cover a range of temperature from 1030 to 1070 degrees C and oxygen fugacity from 1.5 log units below to 1.5 log units above the Fayalite-Magnetite-Quartz buffer. The results demonstrate that neither iron content of the liquid nor oxidation state play a significant role on phosphate saturation. On the other hand, SiO (sub 2) and CaO contents of the liquid strongly influence the appearance of a crystalline phosphate. Our results are combined with data from the literature to define an equation which predicts the P (sub 2) O (sub 5) content of silicate liquids saturated in either whitlockite or fluorapatite: M (sub P2O5) (super liq-sat) = exp[T(-0.8579/139.00-M (sub SiO2) (super liq) + 0.0165)-3.3333 ln (M (sub CaO) (super liq) 0], where M represents the molar percentage of the relevant oxides and T is temperature in K. This equation is valid over extremely wide ranges of liquid composition and temperature (e.g., M SiO (sub 2) from 10% to 80%), including peraluminous liquids. The equation is used to illustrate the relative effects of melt chemistry and temperature on phosphate saturation, both in general terms and in particular for the case of ferrobasaltic differentiation relevant to the late stage differentiation of mafic layered intrusions. It is concluded that magmatic liquids may reach high concentrations in both iron and phosphorus, not through direct association of P (super 5+) and Fe (super 3+), but rather as a consequence of the variations of CaO and SiO (sub 2) content of the liquid. These results may help explain the petrogenesis of certain enigmatic rock types dominated by association of apatite and iron-titanium oxides, such as nelsonites.

La région de Tadoussac est située dans la partie est-centrale de la province de Grenville entre les rivières Saguenay et Saint-Laurent. Les principaux types de roches sont, 1) Orthogneiss gris granodioritiques, 2) Métasédiments incluant des métapelites métamorphisé au faciès amphibolitique supérieur, 3) Gneiss mafiques et 4) Les granites alcalins. Le pluton granitique a été injecté dans une faille de décrochement active pendant la mise en place du magma. À l'échelle de l'affleurement, du coté sud-ouest, ce pluton est en contacte intrusif avec les gneiss mafiques à intermédiaires, et recoupe la foliation générale ainsi que les dykes de granites et des pegmatites associés. Ces roches mafiques à intermédiaires se trouvent dans la faille en décrochement dextre, elles enregistrent une foliation importante et hébergent des veines de ségrégation du matériel leucocrate parallèle à la foliation ainsi que des structures extensionnelles, qui ressemble amplement a des leucosomes d'une migmatite, en plus, il y a des zones ou les amphiboles sont transformées en biotite évoquant un patron de fractures. Sur une base pétrographique, on note que les ségrégations dans les roches mafiques présentent des microstructures magmatiques. L'absence de paragenèse minéralogique qui peut suggérer des réactions anatectiques favorise l'interprétation selon laquelle, les roches mafiques dérivent du magma mafique injecté et cristallisé dans la faille active. Les évidences géochimiques montrent que les unités mafiques sont tholéiitiques et alcalines, ces caractères proviendraient d'une source magmatique enrichie en alcalins, ce qui met à l'évidence un processus de contamination crûstale du magma. La composition des ségrégations dans les roches mafiques peut être expliqué plutôt par une ségrégation de liquide résiduel que par une fusion partielle faute d'existence de liquide anatectique. Donc, l'interprétation est celle de deux magma alcalins, l'un felsique l'autre mafique qui s'injectent en même temp

Le Complexe intrusif de Matamec (1.38-1.35 Ga) se situe en Moyenne-Côte-Nord, dans le centre-est de la Province géologique de Grenville au Québec. I1 représente une intrusion mafique-felsique en feuillets d'envergure régionale (80 x 40 km) chevauchée sur les gneiss migmatisés du Complexe de Manitou lors de l'orogénie grenvillienne. Les gabbronorites massifs y dominent et y sont intercalés avec des lambeaux de paragneiss et des feuillets massifs à foliés de mangérites, de monzonites et de granites porphyriques, communément à texture rapakivi. Des zones de mélange de magmas, contenant des enclaves gabbronoritiques microgrenues incluses dans des phases monzonitiques ou monzodioritiques hybrides, sont communes dans le Complexe et reflètent une mise en place contemporaine des magnas mafiques et felsiques. La structure des enclaves comporte tous les intermédiaires entre des enclaves amiboïdes et massives et des enclaves allongées, qui définissent une foliation magmatique et, par endroits, des plis d'écoulement. Certaines enclaves sub-verticales, situées de part et d'autre du Complexe, présentent des critères de polarité à leur base structurale (e.g., empreintes de charge, skuctures de flamme, veines granitiques ascendantese t moulage de phénocristaux), qui témoignent d'une mise en place et d'une cristallisation à l'horizontale des feuillets. Des faciès intermédiaires et hybrides issus d'un mélange entre des magmas mafiques et felsiques affleurent sporadiquement à l'intérieur du Complexe et ont été identifiés comme des monzodiorites quartzifères. Ces roches comportent des xénocristaux de quartz et de feldspath potassique baignant dans une matrice dioritique à grain fin. Les textures de type rapakivi et les mégacristaux de quartz présents dans les monzonites et les monzodiorites, ainsi que la présence de zonations oscillatoires dans les zircons et localement dans le plagioclase, témoignent de conditions d'instabilité lors de la cristallisation de ces magmas. Ces textures se

Concentrations of platinum-group elements and sulphides in the Pyroxenite Marker of the upper Main Zone are variable, but generally low (up to 100 ppb PGE and 0.2 weight % S). The metal patterns may mostly be explained by sulphide segregation from PGE depleted residual Upper Critical Zone magma, but they are inconsistent with sulphide segregation from a replenishing influx of undepleted Critical Zone magma. Instead, we favour a model whereby a relatively cool and dense Main Zone crystal mush intruded the Bushveld chamber during the later stages of the deposition of the Upper Critical Zone and displaced warmer and lighter residual magma depleted in chalcophile metals (Sharpe, 1985). Based on the metal contents and textural evidence such as the occurrence of ophitic textures, we hypothesize that the Pyroxenite Marker formed in response to localized supercooling and the suppression of plagioclase crystallization. The model implies that the layer represents a poor target for PGE mineralization in the upper portions of the Bushveld Complex.

Mafic-ultramafic sills of up to 450m in thickness occur near the contact between sedimentary and volcanic rocks of the Silverton Formation, Transvaal Supergroup, on the farms Blaauwboschkraal, Zwartkopje and Waterval, some 10km north of Waterval Boven in the Mpumalanga Province. The sills consist of peridotite, harzburgite, pyroxenite and gabbro, and may locally contain up to about 10% Ni-Cu-PGE sulphides. Metal contents of the rocks reach 0.7% Cu, 0.8% Ni, and 2 ppm PGE. Sulphides are found at variable levels within the intrusions and are interpreted to have precipitated from distinct surges of magma streaming through a conduit. This model is analogous to that proposed for the Uitkomst Complex, which hosts sulphides of broadly similar composition to the present bodies and which consists of broadly similar lithologies, apart from the presence of chromitite in the latter. The lithological and compositional similarities between the intrusions raise the possibility of undiscovered economic sulphide concentrations in the present bodies. However, olivines in most of the ultramafic rocks are undepleted in Ni, suggesting that either sulphide segregation was minor and localized, or that any metal-depleted magmas were flushed out of the conduit by undepleted magma.

Partition coefficients (D) for Ni, Cu, and platinum-group elements (PGE) between monosulphide solid solution (mss) and Fe-sulphide liquid (liq) have been determined experimentally using an electron microprobe (EMP) to analyze experimental run products. The EMP detection limit is approximately 0.05 weight per cent for the PGE, consequently few results were obtained for Pt and Ir and the precision for Pd and Rh at low concentrations was poor. These run products have been reanalyzed using a proton microprobe (PMP), which has a detection limit between 10 and 50 ppm for these elements. It is now clear that Dmss/liquid for all the elements show a strong dependence on the S content of the run in S-undersaturated and S-saturated runs. However, in S-oversaturated runs the S content of the run does not appear to influence Dmss/liq. The greater precision of the PMP data establishes that in S-oversaturated runs Dmss/liq at 1000°C are consistently higher than those at 1100°C. In contrast, Dmss/liq in the S-undersaturated and S-saturated runs are similar at both temperatures. This difference in behaviour is thought to arise because in the S-undersaturated and S-saturated runs the amount of S in the mss is controlled by the S content of the run. As the S content in the mss increases, the number of vacancies in the structure of the mss also increases, and Dmss/liq rises. In contrast, in S-oversaturated runs the mss has absorbed the maximum amount of S and thus the S content of the run no longer influences the structure of the mss and hence does not control Dmss/liq. Thus, the effect of temperature on Dmss/liqonly becomes apparent in the S-oversaturated runs. The tendency for Os, Ir, Ru and Rh to partition into mss and the exclusion of Cu, Pt and Pd from mss maybe used to explain a number of phenomena; the zonation of massive sulphide bodies, the tendency for Os, Ir, Ru and to a lesser extent Rh to be enriched in cumulates with minor sulphides, and the presence of two types of sulph

Le lien entre la source du magma dans la croûte moyenne à profonde et son site d'accumulation dans la croûte supérieure, est illustré par le massif du Mont Hay, lequel représente une portion de la Croûte moyenne à profonde protérozoïque constituée de roches supracrustales felsiques et mafiques de composition MORB (Middle Ocean Ridge Basalt) et MORB contaminée. Selon des calculs basés sur la composition des roches résiduelles et des fondus solidifiés, la contamination du N-MORB (Normal Middle Ocean Ridge Basalt) par les éléments lithophiles serait en effet le résultat de 82% de magma mafique N-MORB contaminé par 18 % de métasédiments. Le massif du Mont Hay représente une zone de transfert optimale exhumée pour les magmas produits in situ et/ou injectés, qui ont pu être transférés et se mélanger dans un milieu suffisamment chaud pour éviter leur solidification. La caractérisation et le transfert de ces magmas felsiques dans la croûte sont orchestrés par la tectonique et le métamorphisme. Ainsi, le massif du Mont Hay subit une première hybridation lors de la formation du protolithe igné vers 1820 Ma (phase prédéformationnelle) puis une seconde hybridation pendant la déformation subséquente vers 1770 Ma (phase syndéformationnelle). L'hybride prédéformationnel est le résultat du système d'intrusions mafiques et felsiques litées (MASLI) qui se développe à P< 2kbar par infusion de magma mafique dans la croûte amincie du bassin d'arrière-arc en extension. Lors du mélange, les ions sont échangés entre les magmas et la perte de ÏCO et Rb du magma felsique induit un gain de Na pour l'hybride modifiant alors la composition des feldspaths. La fermeture du bassin d'arrière-arc marque le début d'un événement contractionnel qui commence au nord et induit le métamorphisme et l'anatexie du protolithe au faciès granulitique à 825-875 °C et 6-7 kbar. La fusion partielle in situ de la granulite mafique produit les leucosomes tonalitiques (cm) qui correspondent à la source 1 de fondu, ta

Most major magmatic Cu-Ni-PGE sulphide deposits are thought to have formed by segregation of an immiscible sulphide melt from a silicate host magma, in response to processes such as magma mixing, rapid cooling, differentiation, and contamination. The metal content of the sulphides is governed by the concentration of the metals in the silicate host magma, the sulphide melt/silicate melt partition coefficients (D values) of the metals, and the R-factor during sulphide segregation. Fractionation between the metals occurs during partial melting of the upper mantle source, crystallization of oxides, platinum-group minerals (PGM), and silicates (mainly olivine and less so orthopyroxene), segregation of sulphide melt, and crystallization of the sulphide melt. The latter process may yield zoned ore bodies consisting of Os, Ir, Ru, Rh, Fe, (Ni)-rich monosulphide solid solution (mss) cumulate ore and fractionated sulphide ore rich in Cu, Pt, and Pd. It is possible to model these processes and thereby to estimate the potential of a magmatic body to host economic Cu-Ni-PGE sulphide deposits. The location of Cu-Ni-PGE sulphide ores may be facilitated by applying a number of geochemical tools. PGE-rich horizons within layered intrusions are particularly difficult to locate because the ore zones are generally thin compared to the thickness of the intrusions. Variation in Cu/Pd ratios of the silicate rocks may delineate the position of some of these horizons, since the strongly chalcophile Pd is preferentially depleted during sulphide segregation, resulting in an increase in Cu/Pd of the subsequently crystallizing overlying cumulates. Cu/Pd ratios may also be applied in sill-like bodies such as the Uitkomst intrusion, Mpumalanga, to estimate the potential for conduit-type deposits, and in lavas where they may help to locate possible Noril'sk-type mineralized feeder zones to basalt flows. Other methods of determining whether igneous bodies have experienced magma mixing and sulphide