Brown amphibole as tracer of tectono-magmatic evolution of the Atlantis Bank Oceanic Core Complex (IODP Hole U1473A)

Brown amphibole is a minor but common mineral component in lower oceanic crust. It is generally interpreted as products of migrating SiO2 and H2O-rich fluids or melts, which can be either residual melts from advanced magmatic differentiation of Mid-Ocean Ridge Basalt (MORB), or hydrothermal fluids including a seawater component. Within the lower oceanic crust exhumed at the Atlantis Bank Oceanic Core Complex (OCC), along the ultraslow Southwest Indian Ridge, brown amphibole is ubiquitous in all lithologies from olivine- to oxide-gabbros and diorites, including both undeformed and plastically deformed varieties. We here show the results of a systematic petrological study conceived to unravel the nature of the H2O-rich component recorded in brown amphiboles and document: (i) the evolution of migrating melts during the magmatic stage and (ii) different extents of melt-bearing deformation events recorded throughout the entire crustal transect. The low Cl contents and the light over heavy Rare Earth Elements (LREE/HREE) ratios and high Ti contents in brown amphiboles, indicate they crystallized from melts with a magmatic hydrous component. Consistently, their δ18O values are in equilibrium with MORB composition, except for diorite amphiboles that possibly record the local assimilation of altered minerals. In undeformed olivine gabbros, interstitial pargasite crystallized at hypersolidus conditions (~1000°C) from the melt residual after late stages of MORB differentiation. We speculate that before the olivine gabbro crystal mush reached fully solid state, some aliquots of residual melts were extracted and accumulated within discrete intervals. There, ferrobasaltic melts differentiated through the early crystallization of Fe-Ti oxides and clinopyroxene as liquidus phases, ultimately forming the oxide gabbros. This process promoted rapid Si enrichment and depletion in Fe, Ti, V in the residual melt, later extracted to form the crosscutting diorite veins. The mylonitic olivine gabbros record high-temperature plastic deformation (~900°C ± 50°C) under hypersolidus conditions, involving melts residual from previous crystallization of the gabbroic rock. Further solid-state plastic deformation led to substantial grain-size reduction and, consequently, to an increase in porosity. This created pathways for subsequent melt focussing, which likely represent late-stage differentiated melts migrating throughout the lower crustal section. This study shows that brown amphibole in the Atlantis Bank lower oceanic crust is the crystallization product of melts residual from advanced magmatic differentiation, which are also locally involved in the plastic deformation events during crustal accretion

High‐spatial‐resolution measurements of iron isotopes in pyrites by secondary ion mass spectrometry using the new Hyperion‐II radio‐frequency plasma source

International audienceIron isotopic signatures in pyrites are considered as a good proxy to reconstruct paleoenvironmental and local redox conditions. However, the investigation of micro-pyrites less than 20µm in size has been limited by the evaluable analytical techniques. The development of the new brighter radio-frequency plasma ion source (Hyperion-II source) enhances the spatial resolution by increasing the beam density 10 times compared with the Duoplasmatron source.Here we present high-spatial-resolution measurements of iron isotopes in pyrites using a 3 nA–3 μm primary 16O− beam on two Cameca IMS 1280-HR2 ion microprobe instruments equipped with Hyperion sources at CRPG-IPNT (France) and at SwissSIMS (Switzerland). We tested analytical effects, such as topography and crystal orientation, that could induce analytical biases perceptible through variations of the instrumental mass fractionation (IMF).Results: The δ56Fe reproducibility for the Balmat pyrite standard is ±0.25‰ (2 standard deviations) and the typical individual internal error is ±0.10‰(2 standard errors). The sensitivity on 56Fe+ was 1.2 × 107 cps/nA/ppm or better. Tests on Balmat pyrites revealed that neither the crystal orientation nor channeling effects seem to significantly influence the IMF. Different pyrite standards (Balmat and SpainCR) were used to test the accuracy of the measurements. Indium mounts must be carefully prepared with a sample topography less than 2 μm, which was checked using an interferometric microscope. Such a topography is negligible for introducing change in the IMF. This new source increases the spatial resolution while maintaining the high precision of analyses and the overall stability of the measurements compared with the previous Duoplasmatron source.Conclusions: A reliable method was developed for performing accurate and highresolution measurements of micrometric pyrites. The investigation of sedimentary micro-pyrites will improve our understanding of the processes and environmental conditions during pyrite precipitation, including the contribution of primary (microbial activities or abiotic reactions) and secondary (diagenesis and/or hydrothermal fluid circulation) signatures

Adolescent transport and unintentional injuries: a systematic analysis using the Global Burden of Disease Study 2019

Background: Globally, transport and unintentional injuries persist as leading preventable causes of mortality and morbidity for adolescents. We sought to report comprehensive trends in injury-related mortality and morbidity for adolescents aged 10–24 years during the past three decades. Methods: Using the Global Burden of Disease, Injuries, and Risk Factors 2019 Study, we analysed mortality and disability-adjusted life-years (DALYs) attributed to transport and unintentional injuries for adolescents in 204 countries. Burden is reported in absolute numbers and age-standardised rates per 100 000 population by sex, age group (10–14, 15–19, and 20–24 years), and sociodemographic index (SDI) with 95% uncertainty intervals (UIs). We report percentage changes in deaths and DALYs between 1990 and 2019. Findings: In 2019, 369 061 deaths (of which 214 337 [58%] were transport related) and 31·1 million DALYs (of which 16·2 million [52%] were transport related) among adolescents aged 10–24 years were caused by transport and unintentional injuries combined. If compared with other causes, transport and unintentional injuries combined accounted for 25% of deaths and 14% of DALYs in 2019, and showed little improvement from 1990 when such injuries accounted for 26% of adolescent deaths and 17% of adolescent DALYs. Throughout adolescence, transport and unintentional injury fatality rates increased by age group. The unintentional injury burden was higher among males than females for all injury types, except for injuries related to fire, heat, and hot substances, or to adverse effects of medical treatment. From 1990 to 2019, global mortality rates declined by 34·4% (from 17·5 to 11·5 per 100 000) for transport injuries, and by 47·7% (from 15·9 to 8·3 per 100 000) for unintentional injuries. However, in low-SDI nations the absolute number of deaths increased (by 80·5% to 42 774 for transport injuries and by 39·4% to 31 961 for unintentional injuries). In the high-SDI quintile in 2010–19, the rate per 100 000 of transport injury DALYs was reduced by 16·7%, from 838 in 2010 to 699 in 2019. This was a substantially slower pace of reduction compared with the 48·5% reduction between 1990 and 2010, from 1626 per 100 000 in 1990 to 838 per 100 000 in 2010. Between 2010 and 2019, the rate of unintentional injury DALYs per 100 000 also remained largely unchanged in high-SDI countries (555 in 2010 vs 554 in 2019; 0·2% reduction). The number and rate of adolescent deaths and DALYs owing to environmental heat and cold exposure increased for the high-SDI quintile during 2010–19. Interpretation: As other causes of mortality are addressed, inadequate progress in reducing transport and unintentional injury mortality as a proportion of adolescent deaths becomes apparent. The relative shift in the burden of injury from high-SDI countries to low and low–middle-SDI countries necessitates focused action, including global donor, government, and industry investment in injury prevention. The persisting burden of DALYs related to transport and unintentional injuries indicates a need to prioritise innovative measures for the primary prevention of adolescent injury. Funding: Bill & Melinda Gates Foundation

Global, regional, and national mortality among young people aged 10-24 years, 1950-2019: a systematic analysis for the Global Burden of Disease Study 2019

Background Documentation of patterns and long-term trends in mortality in young people, which reflect huge changes in demographic and social determinants of adolescent health, enables identification of global investment priorities for this age group. We aimed to analyse data on the number of deaths, years of life lost, and mortality rates by sex and age group in people aged 10-24 years in 204 countries and territories from 1950 to 2019 by use of estimates from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. Methods We report trends in estimated total numbers of deaths and mortality rate per 100 000 population in young people aged 10-24 years by age group (10-14 years, 15-19 years, and 20-24 years) and sex in 204 countries and territories between 1950 and 2019 for all causes, and between 1980 and 2019 by cause of death. We analyse variation in outcomes by region, age group, and sex, and compare annual rate of change in mortality in young people aged 10-24 years with that in children aged 0-9 years from 1990 to 2019. We then analyse the association between mortality in people aged 10-24 years and socioeconomic development using the GBD Socio-demographic Index (SDI), a composite measure based on average national educational attainment in people older than 15 years, total fertility rate in people younger than 25 years, and income per capita. We assess the association between SDI and all-cause mortality in 2019, and analyse the ratio of observed to expected mortality by SDI using the most recent available data release (2017). Findings In 2019 there were 1.49 million deaths (95% uncertainty interval 1.39-1.59) worldwide in people aged 10-24 years, of which 61% occurred in males. 32.7% of all adolescent deaths were due to transport injuries, unintentional injuries, or interpersonal violence and conflict; 32.1% were due to communicable, nutritional, or maternal causes; 27.0% were due to non-communicable diseases; and 8.2% were due to self-harm. Since 1950, deaths in this age group decreased by 30.0% in females and 15.3% in males, and sex-based differences in mortality rate have widened in most regions of the world. Geographical variation has also increased, particularly in people aged 10-14 years. Since 1980, communicable and maternal causes of death have decreased sharply as a proportion of total deaths in most GBD super-regions, but remain some of the most common causes in sub-Saharan Africa and south Asia, where more than half of all adolescent deaths occur. Annual percentage decrease in all-cause mortality rate since 1990 in adolescents aged 15-19 years was 1.3% in males and 1.6% in females, almost half that of males aged 1-4 years (2.4%), and around a third less than in females aged 1-4 years (2.5%). The proportion of global deaths in people aged 0-24 years that occurred in people aged 10-24 years more than doubled between 1950 and 2019, from 9.5% to 21.6%. Interpretation Variation in adolescent mortality between countries and by sex is widening, driven by poor progress in reducing deaths in males and older adolescents. Improving global adolescent mortality will require action to address the specific vulnerabilities of this age group, which are being overlooked. Furthermore, indirect effects of the COVID-19 pandemic are likely to jeopardise efforts to improve health outcomes including mortality in young people aged 10-24 years. There is an urgent need to respond to the changing global burden of adolescent mortality, address inequities where they occur, and improve the availability and quality of primary mortality data in this age group. Copyright (C) 2021 The Author(s). Published by Elsevier Ltd

Formation of chondrules : precursors and chronology

Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température, sont les constituants majeurs des météorites primitives. Ils présentent d'importantes variabilités texturales et chimiques révélatrices d'une histoire complexe. Cette thèse s'est intéressée à la chronologie de formation des chondres et de leurs précurseurs à deux échelles de temps distinctes aux moyens de deux approches complémentaires : la géochimie isotopique via le chronomètre isotopique à courte période ²⁶lAl-²⁶Mg et la pétrologie expérimentale. Le développement au cours de cette thèse d'un protocole analytique innovant de mesure in situ de haute précision par sonde ionique des compositions isotopiques du Mg et Al, a permis de démontrer l'homogénéité de la distribution de l'²⁶Al dans le disque d'accrétion, ce qui présente d'importantes implications sur la chronologie relative et les processus de formation des chondres, mais aussi sur l'origine de l'²⁶Al dans le Système Solaire. L'application de ce protocole analytique aux olivines reliques des chondres permet de préciser leur origine, ainsi que leur chronologie et leur processus de formation. Les expérimentations permettent de montrer qu'il est aisé de former des analogues de chondres de type II PO à partir de chondres de type I PO. Un tel processus de formation des chondres implique l'application de régimes thermiques isothermes suivis d'une trempe rapide, incompatibles avec les mécanismes classiques d'ondes de choc. D'autre part, nous montrons que les compositions chimiques en éléments majeurs et traces des différents types de chondres porphyriques peuvent être reproduites par le mélange de trois phases réfractaires solides héritées des précurseurs des chondres (olivine réfractaire, liquide réfractaire et métal) et d'une phase gazeuse riche en éléments volatils et modérément volatils. Ces résultats nous ont conduit à proposer un modèle de filiation entre les chondresChondrules are the major constituent of primitive meteorites. The large variability of textures and chemical compositions within chondrules is indicative of a complex history. This work is focused on the chronology of formation of chondrules and of their precursors by using two complementary tools: the short-lived radio-isotopes ²⁶Al-²⁶Mg and the experimental petrology.The development of a high precision analytical methodology for in situ measurements of the Mg and Al isotopic compositions by ion probe allows to demonstrate that the distribution of ²⁶Al was homogeneous within the accretion disk. This result has important implications for the chronology and process of chondrule formation and also for the origin of ²⁶Al in the Solar System. By using the same methodology with relict olivines in chondrules, we were able to constrain their origin and their formation process.From experimental petrology studies, we show that it was easy to form type II PO chondrules analogues from type I PO analogues. Such a process for chondrules formation implies an isothermal heating followed by a quick quench which is incompatible with the classical shock-waves model. Moreover, we show that the chemical compositions for major and trace elements of the different types of porphyritic chondrules can be easily reproduced by a mixing model composed of three refractory phases inherited from chondrules precursors (refractory olivine, refractory liquid and iron metal) and a gas phase enriched in volatile and moderately volatile elements. Finally, we propose a model of genetic linkage between the different types of porphyritic chondrule

Formation des chondres : Précurseurs et Chronologie

Chondrules are the major constituent of primitive meteorites. The large variability of textures and chemical compositions within chondrules is indicative of a complex history. This work is focused on the chronology of formation of chondrules and of their precursors by using two complementary tools: the short-lived radio-isotopes 26Al-26Mg and the experimental petrology. The development of a high precision analytical methodology for in situ measurements of the Mg and Al isotopic compositions by ion probe allows to demonstrate that the distribution of 26Al was homogeneous within the accretion disk. This result has important implications for the chronology and process of chondrule formation and also for the origin of 26Al in the Solar System. By using the same methodology with relict olivines in chondrules, we were able to constrain their origin and their formation process. From experimental petrology studies, we show that it was easy to form type II PO chondrules analogues from type I PO analogues. Such a process for chondrules formation implies an isothermal heating followed by a quick quench which is incompatible with the classical shock-waves model. Moreover, we show that the chemical compositions for major and trace elements of the different types of porphyritic chondrules can be easily reproduced by a mixing model composed of three refractory phases inherited from chondrules precursors (refractory olivine, refractory liquid and iron metal) and a gas phase enriched in volatile and moderately volatile elements. Finally, we propose a model of genetic linkage between the different types of porphyritic chondrules.Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température, sont les constituants majeurs des météorites primitives. Ils présentent d'importantes variabilités texturales et chimiques révélatrices d'une histoire complexe. Cette thèse s'est intéressée à la chronologie de formation des chondres et de leurs précurseurs à deux échelles de temps distinctes aux moyens de deux approches complémentaires : la géochimie isotopique via le chronomètre isotopique à courte période 26Al-26Mg et la pétrologie expérimentale. Le développement au cours de cette thèse d'un protocole analytique innovant de mesure in situ de haute précision par sonde ionique des compositions isotopiques du Mg et Al, a permis de démontrer l'homogénéité de la distribution de l'26Al dans le disque d'accrétion, ce qui présente d'importantes implications sur la chronologie relative et les processus de formation des chondres, mais aussi sur l'origine de l'26Al dans le Système Solaire. L'application de ce protocole analytique aux olivines reliques des chondres permet de préciser leur origine, ainsi que leur chronologie et leur processus de formation. Les expérimentations permettent de montrer qu'il est aisé de former des analogues de chondres de type II PO à partir de chondres de type I PO. Un tel processus de formation des chondres implique l'application de régimes thermiques isothermes suivis d'une trempe rapide, incompatibles avec les mécanismes classiques d'ondes de choc. D'autre part, nous montrons que les compositions chimiques en éléments majeurs et traces des différents types de chondres porphyriques peuvent être reproduites par le mélange de trois phases réfractaires solides héritées des précurseurs des chondres (olivine réfractaire, liquide réfractaire et métal) et d'une phase gazeuse riche en éléments volatils et modérément volatils. Ces résultats nous ont conduit à proposer un modèle de filiation entre les chondres

Silicon isotopic compositions of chondrule silicates in carbonaceous chondrites and the formation of primordial solids in the accretion disk

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Excess water storage induced by viscous strain localization during high-pressure shear experiment

International audienceStrain localization in viscously deformed rocks commonly results in fine-grained shear zones where massive fluid circulation is regularly observed. Recently attributed to strain-induced pumping, this phenomenon may have major implications for the distribution of ores deposits and rock rheology. However, although grain size reduction and/or creep cavitation have been proposed as important processes, the source mechanism of fluid concentration remains unresolved, particularly at high pressure. Here we use secondary ion mass spectrometry to document the H 2 O content of fine-grained olivine across an experimental shear zone, which developed with grain size reduction during a H 2 o-saturated shear experiment at 1.2 GPa and 900 °C. Through data interpolation, the olivine matrix reveals high fluid concentrations where shear strain is localized. These concentrations far exceed the predicted amount of H 2 o that grain boundaries can contain, excluding grain size reduction as a unique source of water storage. Instead, we show that H 2 o increases per unit of grain boundary across the shear zone, suggesting that cavitation and "healing" processes compete with each other to produce a larger pore volume with increasing strain rate. This provides an alternative process for fluids to be collected where strain rate is the highest in deep shear zones. On Earth, both the crust and mantle incorporate aqueous fluids that interact with solid rock materials in many ways. Commonly referred to as fluid-rock interactions, they strongly affect rock deformation and petrogenetic processes, giving rise, for instance, to hydrolytic weakening, pressure-solution creep or metamorphic reactions , including partial melting. During strain localization, this type of interactions may involve one or several chemo-physical processes that help to channelize fluid flow in ductile shear zones where grain size is substantially reduced. When rocks deform by sub-solidus viscous creep, strain indeed partitions into fine-grained shear bands that recurrently develop in the presence of massive fluid circulation, as revealed by the enrichment of hydrous phases 1-4 in the shear zones. Although the source process of such fluid flow localization is unknown at present, it may have critical implications for rock mechanics and distribution of ore deposits in deep Earth environments 5. Primarily attributed to seismic pumping of a pre-existing fault 1 , fluid infiltration is commonly inferred using evidence for dissolution-precipitation, which suggests a long-term process rather than a co-seismic one 3,5-7. Rutter and Brodie 8 and Wark and Watson 9 proposed that high fluid contents could occur in ductile shear zones as a result of fluid permeation in response to grain size reduction; because of high pressure and high temperature, supercritical fluids may distribute along grain boundaries as a uniform boundary film 9. However, recent observations of syn-tectonic water accumulation along mantle shear bands 4 do not support such a "passive" process for attracting fluids towards ductile shear zones. Instead, they suggest that fluids are dynamically driven by the deformation itself. There is abundant documentation of micro-pores produced during deformation of fine-grained material, including within natural shear zones in the middle/lower crust 5,7,10-15 and during deformation experiments on ceramics, metals and natural rocks 16-20. Also referred to as creep cavitation, the production of these micro-pores results either from grain boundary sliding (GBS) or, in a minor extent, from Zener-Stroh cracking if dislocations interact with grain boundaries 17. In both cases, the micro-cavities arise from limitations of the material to flow, particularly when diffusive mass transfer is slow at low temperature. This led several authors to propose tha