Experimental Constraints on the Ferric Fe Content and Oxygen Fugacity in Subducted Serpentinites

Serpentinites play an important role in the delivery of water into subduction zones. In addition, serpentinites also contain ferric Fe and can transport significant redox potential. We present high-pressure and high-temperature experiments and Mössbauer spectroscopy measurements on natural lizardite and antigorite samples equilibrated at various oxygen fugacities in order to quantify the relationship between the oxygen fugacity f(O2) and the Fe3+/Fetot ratio in these two phases. In antigorite, Fe3+ partitions into the octahedral site and is charge balanced by tetrahedral Al. In lizardite, tetrahedral Fe3+ is observed only at low temperature as well as under high f(O2), whereas Fe3+ prefers the octahedral site at temperatures exceeding 500 °C and at 3 to 5 GPa. Although metastable, lizardite remains in redox equilibrium in our experiments at conditions above the lizardite to antigorite phase transformation at 300 °C and demonstrates a similar stability to antigorite. The Al concentration of lizardite is found to be temperature dependent, and it was possible to reequilibrate the Fe3+/Fetot ratio of lizardite from 0.1 to 0.9 by using redox buffers such as Fe metal, graphite, graphite–calcite, Re–ReO2 and Ru–RuO2. Our experiments on antigorite demonstrate that antigorite does not adjust its Al concentration on experimental time scales. Since Fe3+ is charge balanced by Al, it was also not possible to manipulate the Fe3+/Fetot ratio of antigorite. The coexisting phases, however, show chemical equilibration with this antigorite composition. We have retrieved the standard Gibbs energy for Fe3+- and Al-endmembers of antigorite and lizardite and calculated the metamorphic evolution of subducting serpentinites. The lizardite to antigorite transformation does not cause a decrease in the bulk Fe3+/Fetot ratio under f(O2) buffered conditions, in contrast to observations from some natural settings, but does result in the formation of additional magnetite due to antigorite having a lower Fe3+/Fetot ratio than lizardite at equilibrium. If the f(O2) of antigorite serpentinite is buffered during subduction, such as due to the presence of graphite and carbonate, the bulk Fe3+/Fetot ratio decreases progressively. On the other hand, in a closed system where the bulk serpentinite Fe3+/Fetot ratio remains constant, the f(O2) increases during subduction. In this scenario, the f(O2) of an antigorite serpentinite with a typical Fe3+/Fetot ratio of 0.4 increases from the fayalite–magnetite–quartz to the hematite–magnetite f(O2) buffer during dehydration. These f(O2) results confirm earlier inferences that fluids produced by antigorite dehydration may not contain sufficient oxidised sulphur species to oxidise the mantle wedge. Sufficiently high levels of f(O2) to mobilise oxidised sulphur species may be reached upon antigorite dehydration, however, if closed system behaviour maintains a high bulk redox potential across the lizardite to antigorite phase transformation. Alternatively, oxidation of the mantle wedge might be achieved by oxidising agents from sources in subducted oceanic crust and sediments

Building A Winning NFL Roster: Best Practices For Sustained Success

The purpose of this capstone is to identify and analyze the factors that contribute to team success in the National Football League through a review of relevant literature, a survey of league personnel, and firsthand experience as a football administrator. This project first studies quantitative data regarding player acquisition, specifically the data behind the NFL entry draft. Next, the current literature regarding off the field processes such as leadership, organizational culture and engagement were reviewed and finally, a two-step Delphi method survey was distributed to a panel of current league professionals. This paper aims to find the most efficient and effective way for teams to acquire players and several ways to optimize that talent based on the best practices researched in organizational culture and leadership

Internet gaming disorder and risky behaviours among Czech adolescents: a nationally representative study

Background and aims: The aim of the present study was to estimate the complex association between Internet Gaming Disorder (IGD), substance use, and other risky behaviours in Czech adolescents whilst providing prevalence estimates of IGD and psychometric information regarding the Czech Internet Gaming Disorder Scale–Short-Form (IGDS9-SF). Methods: A representative sample of 3,950 Czech adolescents was recruited through stratified random sampling in the school setting. Results: Disordered gamers showed frequent use of specific substances such as pharmaceuticals, methylenedioxymethamphetamine, and lysergic acid diethylamide. In contrast, non-gamers had higher prevalence of alcohol, cigarettes, sedatives and tranquillisers, and marijuana use. A logistic regression, utilising IGDS9-SF raw scores and average daily gaming time, revealed a U-shaped relationship between gaming and both alcohol and cigarette use. Additionally, conduct problems such as bullying, and risky in-game behaviours were more prevalent among disordered gamers, with the exception of forging parents' signatures. The overall prevalence of IGD was 3.62% (95% CI = [3.1%, 4.3%]), with higher rates in males (5.89%; 95% CI = [4.9%, 7.0%]) than in females (1.45%; 95% CI = [1.0%, 2.1%]). Discussion and conclusions: The Czech IGDS9-SF used in the present study showed adequate psychometric properties. The association between gaming and substance use behaviours may be specific and multifaceted depending on the severity of the gaming-related problems. Furthermore, disordered gamers may become more vulnerable due to a higher incidence of conduct problems, bullying (victimisation), and in-game risky behaviours such as engagement with microtransactions mechanics (e.g., loot box) within video games

Mathematical modelling of clostridial acetone-butanol-ethanol fermentation

Clostridial acetone-butanol-ethanol (ABE) fermentation features a remarkable shift in the cellular metabolic activity from acid formation, acidogenesis, to the production of industrial-relevant solvents, solventogensis. In recent decades, mathematical models have been employed to elucidate the complex interlinked regulation and conditions that determine these two distinct metabolic states and govern the transition between them. In this review, we discuss these models with a focus on the mechanisms controlling intra- and extracellular changes between acidogenesis and solventogenesis. In particular, we critically evaluate underlying model assumptions and predictions in the light of current experimental knowledge. Towards this end, we briefly introduce key ideas and assumptions applied in the discussed modelling approaches, but waive a comprehensive mathematical presentation. We distinguish between structural and dynamical models, which will be discussed in their chronological order to illustrate how new biological information facilitates the ‘evolution’ of mathematical models. Mathematical models and their analysis have significantly contributed to our knowledge of ABE fermentation and the underlying regulatory network which spans all levels of biological organization. However, the ties between the different levels of cellular regulation are not well understood. Furthermore, contradictory experimental and theoretical results challenge our current notion of ABE metabolic network structure. Thus, clostridial ABE fermentation still poses theoretical as well as experimental challenges which are best approached in close collaboration between modellers and experimentalists

Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C, O, 87Sr/86Sr) data from Kangankunde, Malawi

This is the final version of the article. Available from Springer Verlag via the DOI in this record.Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and 87Sr/86Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8–15 wt% REE2O3, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The 87Sr/86Sr values (0.70302–0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C (δ18O + 3 to + 5‰VSMOW and δ13C − 3.5 to − 3.2‰VPDB). In contrast, dolomite in the same samples has similar δ13C values but much higher δ18O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar δ18O and 87Sr/86Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: δ18O + 7.7 to + 10.3‰ and δ13C −5.2 to −6.0‰; 87Sr/86Sr 0.70296–0.70298) is not directly linked with the REE mineralisation.This project was funded by the UK Natural Environment Research Council (NERC) SoS RARE project (NE/M011429/1) and by NIGL (NERC Isotope Geoscience Laboratory) Project number 20135

Foreword to the thematic set on ‘Mineral deposits and ore-forming processes in spatial, temporal and geodynamic context (a special issue in honor of Professor Zdeněk Pouba)’

International audienceThe need of human society for mineral resources and the quest for origin of their anomalous accumulations have been stimuli of geological research since its early days. Our knowledge of ore deposits has rapidly accelerated due to ever-growing exploration for non-traditional and high-tech materials to satisfy current technological advances. At the same time, scientific understanding of ore-forming processes has dramatically benefited from expansion and application of novel microanalytical, experimental and computational techniques. This special issue presents recent scientific advances and emerging issues in these fields of economic geology. We are pleased to dedicate this thematic set to honor the 90 th birthday of the late Zdeněk Pouba (1922-2011), professor emeritus of economic geology at the Charles University and a prominent geologist. Zdeněk Pouba was born in Zvolen (Slovakia), entered the Charles University in Prague in 1945 and remained associated with his alma mater for more than sixty years. He held a research fellowship at the Carnegie Institution of Washington, was one of the founding members of the International Association on Genesis of Ore Deposits (IAGOD) and maintained strong involvement in international research programs with leading scientists. His research activities ranged from regional and structural geology of ore and nonmetallic resources to relationships between volcanic and hydrothermal activity and its microbiota-his last research projects. The present issue covers a wide range of topics ranging from isotopic and geochemical to mineralogical and ore-deposit case studies, while highlighting diversity of analytical techniques and scientific approaches. In the first contribution, Pašava et al. identify principal carriers of Pt-group elements (PGE) in metal-rich black shales, using the Zuniy region in the Guizhou province of south China as model example. The anomalously high concentrations of PGE (~ 1 ppm) are hosted in pyrite and nickel sulfides such as millerite and gersdorffite, but PGE compounds are absent. The second paper by Kapsiotis addresses the origin of mantle peridotites in the Vourinos ophiolite complex, Greece, using morphological and compositional variations of chromian spinel. The data indicate coeval formation of chromitites and dunites followed by percolation of residual boninitic melts in a fore-arc setting. The ore-forming potential of ultramafic intrusions in a fossil island arc is further discussed in two studies of Han et al. devoted to Cu-Ni-Co sulfide deposit at Hulu and surrounding mafic-ultramafic complexes in the Central Asian orogenic belt in Eastern Tianshan. The U-Pb zircon dating in combination with Lu-Hf and Re-Os isotopic and whole-rock geochemical analyses reveal derivation of parental magma from a depleted asthenospheric mantle followed by contamination by lower crustal material during Permian plate convergence. Since an arc-related setting is unexpected for this mineralization style, this finding opens new prospects for base-metal mineral exploration. The subsequent contribution by Kohút et al. uses the Re-Os age dating to unravel the multistage history of peculiar U-Mo mineralization at Kurišková in the Western Carpathians (Slovakia). The primary vein mineralization formed by precipitation from magmatic-hydrothermal fluids during Late Permian, but was remobilized by Triassic-Jurassic meteoric fluids to produce a shear zone-related stockwork. This study underpins superposition of volcanic and hydrothermal activity and near-surface fluid flow to produce significant U-Mo enrichment within a volcaniclastic sequence. The issue closes with a case study by Velebil and Zachariáš focused on mercury mineralization at Horní Luby in the Saxothuringian Zone of the Bohemian Massif (Czech Republic). Detailed investigation of fluid-inclusion populations revealed the presence of H 2 O-CO 2 mixtures during metamorphic quartz veining and secretion, with repeated fluid unmixing and precipitation of cinnabar, pyrite and siderite down to 150 °C. The cinnabar composition as well as minute occurrences of mercurian sphalerite indicate a more complex precursor of the mineralization, which has been remobilized during vanning stages of the Variscan orogeny. The special issue provides a selection of diverse mineralization styles occurring in Phanerozoic orogens of Europe and Asia. We hope that the breadth and multitude of approaches presented in the following papers will stimulate new studies and applications of state-of-the-art analytical techniques to further enhance our understanding of ore-forming processes. Finally, we wish to thank all authors contributing to this special issue in honor of Professor Zdeněk Pouba and express our sincere gratitude to reviewers, who frequently supplied high-quality reviews and constructive comments on a tight schedule