Étude du comportement des éléments hautement sidérophiles et chalcophiles dans les gouttelettes sulfurées de MORB

Les Eléments Hautement Sidérophiles (EHS) et les éléments chalcophiles sont des outils géochimiques essentiels pour la compréhension de processus géologiques tels que la différenciation terrestre et la formation de gisements magmatiques. Cependant, de nombreux aspects de leur comportement restent inconnus dans différents systèmes magmatiques. La distribution des éléments chalcophiles dans le manteau est mal déterminée à cause du manque de données pour les coefficients de partage entre le liquide sulfuré et le liquide silicate. Et le comportement des EHS pendant les premières étapes de la cristallisation du liquide sulfuré n'est pas bien compris, surtout en ce qui concerne le mode de formation de Minéraux du Groupe du Platine (MGP). Dans cette étude nous nous intéressons aux gouttelettes sulfurées trempées dans des verres frais de MORB. Ces gouttelettes représentent un liquide sulfuré qui a été trempé et qui a interagi avec le liquide silicate; ainsi elles sont adéquates pour calculer de nouveaux coefficients de partage et pour étudier la distribution des EHS et des éléments chalcophiles dans des sulfures représentatifs de sulfures magmatiques de hautes températures. Ces gouttelettes sulfurées présentent des textures variant de grains fins à zonées au sein d'un même échantillon ayant subi un refroidissement supposé homogène. Les textures à grains fins sont caractérisées par des intercroissances micrométriques de Solution Solide Monosulfurée (SSM) et d'une Solution Solide Intermédiaire (SSI) avec présence mineure de pentlandite et de magnetite. Les textures zonées sont caractérisées par une SSM massive et par un liquide sulfuré résiduel trempé riche en Cu avec présence d'exsolution de pentlandite et de magnetite automorphe. L'étude pétrographique et les analyses par Microsonde Électronique nous ont permis de déterminer que la taille des gouttelettes est un paramètre contrôlant les textures. Ainsi, les gouttelettes sulfurées de petites tailles (10- 30|im) présentent préférentiellement des textures à grains fins et les gouttelettes de grandes tailles (>50|um) présentent préférentiellement des textures zonées. Nous proposons que les petites gouttelettes sulfurées aient subi un sur-refroidissement plus brutal que les grosses gouttelettes sulfurées dû à une solubilité effective plus élevée. Au moment de l'éruption cette solubilité effective plus élevée retarde la cristallisation des petites gouttelettes sulfurées abaissant ainsi les taux de diffusion et augmentant les taux de nucléation ce qui aboutit à des textures à grains fins. À l'opposé, la cristallisation des grosses gouttelettes n'est pas retardée au moment de l'éruption ce qui permet la différenciation des phases sulfurées. Les analyses par Ablation Laser couplée à un Spectromètre de Masse (LA-ICP-MS) sur les gouttelettes à grains fins et le verre adjacent ont permis de calculer de nouveaux coefficients de partage pour le Co (45), Ni (776), Cu (133), Zn (3.5), Se (323), Ag (1138), Cd (107), Sn (10.8), Te (4791), Pb (57) et le Bi (487). Ces valeurs permettent de déterminer la contribution des sulfures au coefficient de partage général durant la fusion du manteau. Le Cu et le Te se comportent principalement comme des éléments compatibles pendant la fusion du manteau alors que les autres Iéléments chalcophiles sont modérément à fortement incompatibles. De plus, les rapports Cu/Pd des gouttelettes sulfurées suggèrent qu'elles se forment dans la chambre magmatique à Paplomb de la dorsale océanique et ont eu le temps de s'équilibrer avec le liquide silicate. Ni les profils de LA-ICP-MS ni les images de Microscope Electronique à Balayage ne montrent la présence d'inclusions indiquant qu'elles ne contiennent pas de Minéraux du Groupe du Platine (MGP). La répartition des EHS et des éléments chalcophiles dans les gouttelettes sulfurées montre que le Ni, Co, Re et une partie du Pt et du Pd sont intégrés en solution solide dans la SSM. Le Cu, Zn, Ag, Cd, Sn, Te, Bi, Pb et le Pt et le Pd restants sont concentrés dans le liquide sulfuré trempé riche en Cu. Comme pour les autres gouttelettes, les gouttelettes zonées ne contiennent pas de MGP. Le refroidissement subi par les gouttelettes implique que les taux de diffusion étaient trop faibles pour permettre la formation de MGP. Cela indique que l'exsolution est un processus majeur dans la formation des MGP dans les sulfures, qui est commun dans les systèmes refroidis plus lentement

Textural variations in MORB sulfide droplets due to differences in crystallization history

Sulfide droplets from fresh Mid-Ocean-Ridge Basalt (MORB) glasses show different textures. Some are fine-grained droplets consist of Monosulfide Solid Solution (Mss) and Intermediate Solid Solution (Iss) micrometric intergrowths with pentlandite at the Mss-Iss interface and disseminated Fe-oxide grains; other droplets display a characteristic “zoned” texture consisting of segregated massive grains of Mss and Iss, with euhedral Fe-oxides and pentlandite occuring as equant grains and as flame-shaped domains in the Mss formed by exsolutions. The difference in the textures implies a difference in the crystallization history of the sulfide droplets. These different textures are observed in droplets that are only millimeters apart in the same sample, and thus had an identical cooling history. Therefore, some other factors controlled the textural development. There is relationship between the size and the texture of the droplets. The larger sulfide droplets tend to have zoned textures and the smaller ones fine-grained textures. We propose that the latter have experienced greater undercooling before crystallization. The reason for the delay in crystallization could be that, in the small sulfide droplets, large stable grains with low surface to volume ratio cannot form, which results in higher effective solubility of the Mss. Due to the high degree of undercooling in the small droplets, there were numerous nucleation sites and the diffusion rates of the crystal components in the liquid were lower, leading to fine-grained Mss-Iss intergrowths. In contrast, larger droplets with lower effective solubility of Mss began to crystallize at higher temperature, and thus had fewer nucleation sites, higher diffusion rates, and more time for sulfide differentiation

Whole-genome sequencing of chronic lymphocytic leukemia identifies subgroups with distinct biological and clinical features

The value of genome-wide over targeted driver analyses for predicting clinical outcomes of cancer patients is debated. Here, we report the whole-genome sequencing of 485 chronic lymphocytic leukemia patients enrolled in clinical trials as part of the United Kingdom’s 100,000 Genomes Project. We identify an extended catalog of recurrent coding and noncoding genetic mutations that represents a source for future studies and provide the most complete high-resolution map of structural variants, copy number changes and global genome features including telomere length, mutational signatures and genomic complexity. We demonstrate the relationship of these features with clinical outcome and show that integration of 186 distinct recurrent genomic alterations defines five genomic subgroups that associate with response to therapy, refining conventional outcome prediction. While requiring independent validation, our findings highlight the potential of whole-genome sequencing to inform future risk stratification in chronic lymphocytic leukemia

Dimethyl fumarate in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial

Dimethyl fumarate (DMF) inhibits inflammasome-mediated inflammation and has been proposed as a treatment for patients hospitalised with COVID-19. This randomised, controlled, open-label platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing multiple treatments in patients hospitalised for COVID-19 (NCT04381936, ISRCTN50189673). In this assessment of DMF performed at 27 UK hospitals, adults were randomly allocated (1:1) to either usual standard of care alone or usual standard of care plus DMF. The primary outcome was clinical status on day 5 measured on a seven-point ordinal scale. Secondary outcomes were time to sustained improvement in clinical status, time to discharge, day 5 peripheral blood oxygenation, day 5 C-reactive protein, and improvement in day 10 clinical status. Between 2 March 2021 and 18 November 2021, 713 patients were enroled in the DMF evaluation, of whom 356 were randomly allocated to receive usual care plus DMF, and 357 to usual care alone. 95% of patients received corticosteroids as part of routine care. There was no evidence of a beneficial effect of DMF on clinical status at day 5 (common odds ratio of unfavourable outcome 1.12; 95% CI 0.86-1.47; p = 0.40). There was no significant effect of DMF on any secondary outcome

Dimethyl fumarate in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial

Dimethyl fumarate (DMF) inhibits inflammasome-mediated inflammation and has been proposed as a treatment for patients hospitalised with COVID-19. This randomised, controlled, open-label platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing multiple treatments in patients hospitalised for COVID-19 (NCT04381936, ISRCTN50189673). In this assessment of DMF performed at 27 UK hospitals, adults were randomly allocated (1:1) to either usual standard of care alone or usual standard of care plus DMF. The primary outcome was clinical status on day 5 measured on a seven-point ordinal scale. Secondary outcomes were time to sustained improvement in clinical status, time to discharge, day 5 peripheral blood oxygenation, day 5 C-reactive protein, and improvement in day 10 clinical status. Between 2 March 2021 and 18 November 2021, 713 patients were enroled in the DMF evaluation, of whom 356 were randomly allocated to receive usual care plus DMF, and 357 to usual care alone. 95% of patients received corticosteroids as part of routine care. There was no evidence of a beneficial effect of DMF on clinical status at day 5 (common odds ratio of unfavourable outcome 1.12; 95% CI 0.86-1.47; p = 0.40). There was no significant effect of DMF on any secondary outcome

Mobility of gold and other metals during alteration of the oceanic crust : Implications for the formation of VMS deposits

Tremendous physical and chemical exchanges occur along oceanic ridges between the lithosphere, the hydrosphere and the biosphere. During these exchanges important mobilisation of metals by hydrothermal fluid circulation takes place within the oceanic crust. Volcanogenic massive sulphide (VMS) deposits are hydrothermal ore deposits rich in Cu-Zn-Pb bearing sulphide minerals that form during submarine venting of these hydrothermal fluids near the seafloor. A proportion of the metals enriched in these deposits are mobilised from deeper crustal levels during high-temperature hydrothermal alteration. Gold-rich VMS deposits represent an important sub-set of VMS deposits that are enriched in Au and related elements such as As, Sb, Se and Te. The processes that form Au-rich VMS are still debated, due in part to our lack of understanding of the behaviour of these elements during formation and alteration of the oceanic crust. In this thesis we carry out a systematic investigation into the behaviour of Au, As, Sb, Se and Te during evolution of the oceanic crust. Three localities are studied: the Ocean Drilling Program (ODP) Hole 1256D in the Cocos plate, the Troodos ophiolite in Cyprus and the ODP Hole 786B in the Izu-Bonin forearc. The investigation has been carried out using cutting-edge analytical techniques including ultra-low detection limit analyses of Au and other metals in rock samples. The objectives of the thesis are 1) to quantify the mobilisation of metals including Au, related elements As, Sb, Se and Te and base metals during the alteration of the oceanic crust; 2) to determine the mineral reactions which promote this mobilisation; 3) to investigate the variability in metal mobility in different tectonic settings in the oceanic crust and 4) to investigate the extent to which the composition of  “source area” oceanic crust controls the composition of VMS deposits in different tectonic settings. The main outcomes of this study are fourfold. 1) The distribution of Au and related elements in primary crust varies considerably between different tectonic settings. Sulphide minerals play an important role in the behaviour of Au, Se and Cu during magmatic differentiation and hydrothermal alteration, but have a lesser influence on other metals. The oxidation state of the primary crust controls whether sulphide minerals are present, and thus is an important control on the budget and mobility of strongly chalcophile metals during hydrothermal alteration. 2) Large masses of Au and related elements are mobilised from the sheeted dyke complex in mid-oceanic ridge (MOR) and ophiolite settings. Significantly more metals are mobilised from the source areas than are trapped in the VMS deposits observed in these settings. Therefore, most of the metals mobilised from the source areas are lost, either during transport, venting, sedimentation or late fluid mobilisation. 3) Insufficient Au is mobilised from MOR settings at ODP Hole 1256D to form Au-rich VMS deposits. The quantity of Au mobilised from the Troodos ophiolite could potentially lead to Au-rich VMS formation but additional processes such as vapour separation by sub-seafloor boiling or magmatic volatile input would be required to increase the Au : base metal ratio. The lack of evidence for these processes in Troodos implies that Au-rich VMS deposits are not likely to be abundant in this area. 4) Isotopic and trace element evidence supports magmatic input in the hydrothermal system at ODP Hole 786B, implying that magmatic fluid input into hydrothermal systems leaves a specific signature which can be tracked.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.</p

Concentration of chalcophile and siderophile elements in MORB sulphide droplets : new sulphide melt-silicate melt partition coefficients

We have determined the concentrations of chalcophile and siderophile elements by LA-ICP-MS from sulphide droplets and fresh glass in contact with them from MORB pillow rims. MORBs play an important role in the understanding of mantle petrogenesis, providing information on chemical fractionation of elements in the mantle. However, chalcophile element behaviour is not completely understood, partly due to the lack of data for partition coefficients between sulphide and silicate melts. Some droplets present homogenous textures and others portions rich in monosulphide solid solution (Mss) and intermediate solid solution (Iss) indicating that they have undergone crystal fractionation. For homogenous droplets, concentrations of Ni and Cu are 10 to 1%; Co and Zn 1000 to 100 ppm; Se, Te, Ag and Pb 100 to 10 ppm; Cd, Sn, Pd, Bi and Pt 10 to 1 ppm; Au, Ru and Re 1 to 0.1 ppm. For some of these elements it was also possible to obtain data in fresh glass allowing the calculation of partition coefficients. These were calculated for Ni (745± 252), Cu (1219 ± 381), Co (42 ± 5.5), Zn (3.4 ± 0.9), Sn (10.4 ± 1.8) and Pb (55.6 ± 9.3). Values for Ni, Cu and Co are in agreement with literature [1], suggesting that values for Zn, Sn and Pb are realistic