Assessing sulfur redox state and distribution in abyssal serpentinites using XANES spectroscopy

Sulfur is one of the main redox sensitive and volatile elements involved in chemical transfers between earth surface and the deep mantle. At mid-oceanic ridges, sulfur cycle is highly influenced by serpentinite formation which acts as a sink of sulfur under various oxidation states (S 2 − , S − , S 0 and S 6 + ). Sulfur sequestration in serpentinites is usually attributed to the crystallization of secondary minerals, such as sulfides (e.g. pyrite, pyrrhotite) or sulfates (e.g. anhydrite). However, the role of serpentine minerals as potential sulfur carriers is not constrained. We investigate the distribution and redox state of sulfur at micro-scale combining in situ spectroscopic (X-ray absorption near-edge structure: XANES) and geochemical (SIMS) measurements in abyssal serpentinites from the SWIR (South West Indian Ridge), the Rainbow and the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) areas. These serpentinites are formed in different tectono-metamorphic settings and provide a meaningful database to understand the fate of sulfur during seafloor serpentinization. XANES spectra of serpentinite powders show that the sulfur budget of the studied samples is dominated by oxidized sulfur (S 6 + / S = 0.6–1) although sulfate micro- phases, such as barite and anhydrite, are absent. Indeed, μ -XANES analyses of mesh, bastite and antigorite veins in thin sections and of serpentine grains rather suggest the presence of S 6 + ions incorporated into serpentine minerals. The structural incorporation of S in serpentine minerals is also supported by X- ray fluorescence mapping revealing large areas (1600 μm 2 ) of serpentinite where S is homogeneously distributed. Our observations show that serpentine minerals can incorporate high S concentrations, from 140 to 1350 ppm, and that this can account for 60 to 100% of the sulfur budget of abyssal serpentinites. Serpentine minerals thus play an important role in S exchanges between the hydrosphere and the mantle at mid-oceanic ridges and may participate to S recycling in subduction zones.NERC Deep Volatiles Consortium Grant NE/M000303/

Drilling constraints on lithospheric accretion and evolution at Atlantis Massif, Mid-Atlantic Ridge 30°N

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B07103, doi:10.1029/2010JB007931.Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100–220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45° rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises ∼70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge

Mortality and pulmonary complications in patients undergoing surgery with perioperative sars-cov-2 infection: An international cohort study

Background The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (740%) had emergency surgery and 280 (248%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (261%) patients. 30-day mortality was 238% (268 of 1128). Pulmonary complications occurred in 577 (512%) of 1128 patients; 30-day mortality in these patients was 380% (219 of 577), accounting for 817% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 175 [95% CI 128-240], p<00001), age 70 years or older versus younger than 70 years (230 [165-322], p<00001), American Society of Anesthesiologists grades 3-5 versus grades 1-2 (235 [157-353], p<00001), malignant versus benign or obstetric diagnosis (155 [101-239], p=0046), emergency versus elective surgery (167 [106-263], p=0026), and major versus minor surgery (152 [101-231], p=0047). Interpretation Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Evaluation of appendicitis risk prediction models in adults with suspected appendicitis

Background Appendicitis is the most common general surgical emergency worldwide, but its diagnosis remains challenging. The aim of this study was to determine whether existing risk prediction models can reliably identify patients presenting to hospital in the UK with acute right iliac fossa (RIF) pain who are at low risk of appendicitis. Methods A systematic search was completed to identify all existing appendicitis risk prediction models. Models were validated using UK data from an international prospective cohort study that captured consecutive patients aged 16–45 years presenting to hospital with acute RIF in March to June 2017. The main outcome was best achievable model specificity (proportion of patients who did not have appendicitis correctly classified as low risk) whilst maintaining a failure rate below 5 per cent (proportion of patients identified as low risk who actually had appendicitis). Results Some 5345 patients across 154 UK hospitals were identified, of which two‐thirds (3613 of 5345, 67·6 per cent) were women. Women were more than twice as likely to undergo surgery with removal of a histologically normal appendix (272 of 964, 28·2 per cent) than men (120 of 993, 12·1 per cent) (relative risk 2·33, 95 per cent c.i. 1·92 to 2·84; P < 0·001). Of 15 validated risk prediction models, the Adult Appendicitis Score performed best (cut‐off score 8 or less, specificity 63·1 per cent, failure rate 3·7 per cent). The Appendicitis Inflammatory Response Score performed best for men (cut‐off score 2 or less, specificity 24·7 per cent, failure rate 2·4 per cent). Conclusion Women in the UK had a disproportionate risk of admission without surgical intervention and had high rates of normal appendicectomy. Risk prediction models to support shared decision‐making by identifying adults in the UK at low risk of appendicitis were identified

Les microstructures de deformation des serpentines et la partition sismique-asismique: exemple de la Californie

Composition du jury: C. Mével, Rapporteur, D.R CNRS au LGM - Université Paris VI (France) M. Jessell, Rapporteur, Professeur associé à l'Université de Toulouse (France) M. Mellini, Examinateur, Professeur à l'Université de Sienne (Italie) A. Baronnet, Examinateur, Professeur à l'Université d'Aix-Marseille III (France) A-M. Boullier, Directrice de thèse, D.R CNRS au LGIT - Grenoble I (France) J-P. Gratier, Directeur de thèse, Physicien d'observatoire à l'Université Grenoble I (France)Geophysic studies have identified a seismic-aseismic partitioning along california active faults. Mapped serpentinites have been proposed to be a potential cause of aseismic creep. In order to better understand the deformation mechanisms of serpentinites in this context, we have studied, at different scale of observations, the deformation microstructures of serpentines collected in the San Andreas fault system (California). The use of several techniques of observation (petrographic microscope, SEM, TEM) and analysis (electron microprobe, EDS-SEM and TEM) was required in order to preserve information during scale shifts. Outside fault zones, serpentinites show markers of their deformation history before active faulting. Vein study allowed a good characterization of optical textures within these rocks and a better comprehension of the growth mechanisms of serpentine in interstices and open-fractures. Capillary effects could help crystrallisation in micrometer-range interstices by creating and maintenaing a diffusionnal transfer (in aqueous phase) of elements from the matrix to the vein. This continuous or incremental process, has been proposed to explain formation of fibrous veins. In opposition, open-fractures would be fed by an advectif transfer of solutes. Precipitation could occur thanks to a drop of the solute solubility due to a difference of temperature between the matrix (colder) and the fluid (hotter). Growth kinetic appears as a main factor in controlling the relative occurence of the different serpentine types encountered in this study (lizardite and chysotile), compared to classical thermodynamic parameters (pressure and température). Inside natural faults, deformation is very localized on a gouge zone or on a shiny fault plane. It is accommodated, respectively, by a pressure solution creep (stable slip) and by unstable cataclasatic events (low magnitude events, M<0). This leeds to an aseismic behaviour of serpentines at the global scale in faults.Les études géophysiques identifient une partition entre segments à comportement sismique et segments à comportement asismique le long des grandes failles actives californiennes. Il a été proposé que la présence des serpentinites le long de certains segments soit une cause potentielle d'un fluage asismique à ces endroits. Afin d'améliorer nos connaissances sur les mécanismes de déformation des serpentinites dans ce type de contexte, nous avons réalisé une étude des structures de déformation naturelles dans ces roches, collectées dans le réseau de failles actives de San Andreas (Californie). Le couplage de plusieurs techniques (microscope pétrographique, MEB, MET, microsonde) a été nécessaire pour préserver les informations au cours des changements d'échelles d'observations. Les serpentinites hors des zones cisaillées offrent des indices de leur histoire, antérieurement à la tectonique actuelle. L'étude détaillée des veines a permis, d'une part, une bonne caractérisation des textures optiques complexes classiquement rencontrées dans ces roches et, d'autre part, une meilleure compréhension des mécanismes de croissance des serpentines dans les interstices et les fractures ouvertes. Des effets capillaires pourraient faciliter la cristallisation dans des interstices de l'ordre du micron en permettant la mise en place d'un transfert de matière par diffusion en phase aqueuse depuis l'encaissant vers la veine. Ce mécanisme a été proposé pour expliquer la formation de veines fibreuses à ouverture lente ou saccadée (crack-seal). En revanche, les fractures ouvertes seraient nourries grâce à un transport advectif des éléments au sein d'un fluide. La précipitation serait alors permise par la chute de la solubilité du soluté au contact d'un encaissant relativement plus froid. La cinétique de croissance apparaît comme un facteur déterminant sur les conditions d'occurrence relative des différents types de serpentines représentés (lizardite et chrysotile), ce qui relativise le rôle des facteurs thermodynamiques classiques (pression et température). La déformation des serpentinites dans les failles naturelles, caractérisées par un taux de déformation lent et la présence de fluides, est très localisée, soit dans une zone de gouge, soit sur un plan de faille brillant. La déformation y est accommodée, respectivement, par un mécanisme de fluage par dissolution-cristallisation (glissement stable) et des épisodes de glissement fragiles instables (magnitudes faibles, M<0). Cela aboutit à un comportement globalement asismique des serpentines à l'échelle des failles actives

Diversity and dynamics of ultramafic-hosted hydrothermal activity at mid-ocean ridges : first results from the Arc-en-Sub oceanographic cruise, Rainbow Massif, 36°14’N MAR

The ultramafic Rainbow Massif hosts the high-temperature (HT) Rainbow hydrothermal site, venting H2, CH4 and Fe-rich fluids that support unique macro- and microbial ecosystems. This Massif also sustained low-temperature (LT) hydrothermal circulation associated to fossil bivalve communities, identified at two sites, Clamstone and Ghost City, with 14C and U-Th dates of 25.5 and 110 kyrs, respectively. Furthermore, the Massif is also underlain by seismic reflectors interpreted as stacked melt lenses, the potential heat source for fossil and active hydrothermal outflows. To understand the diversity, controls, and history of ultramafic-related hydrothermal circulation, and how these different systems are sustained over time, the Arc-en-Sub cruise (May 2022) conducted (1) a compliance experiment to determine if deep-seated reflectors are melt-bearing at depth, (2) extensive bathymetric mapping (70 km2) and magnetic surveying with the Autonomous Underwater Vehicle (AUV) IdefX, and (3) extensive geological observations, sampling, and seafloor imaging (3D and photomosaicing) with the Remotely Operated Vehicle (ROV) Victor, along ~100 km of bottom tracks.Preliminary cruise results reveal corrugated detachment fault surfaces along its western flank, and confirm that the massif is associated with a detachment system rooting westwards, along the S-AMAR ridge segment. The AUV microbathymetry also shows a complex tectonic history of oblique high-angle normal faulting, small-scale detachment faulting, and late strike-slip deformation, with temporal changes yet to be analyzed.ROV observations and sampling confirmed the dominance of ultramafic rocks in the massif substrate, and revealed previously unknown hydrothermal sites, both active and fossil. First, in addition to Rainbow, we have identified several active sites of a new type, with LT fluids venting at temperatures from a few degrees above ambient seawater, and up to 70&#176;C. This discovery significantly extends the style and areal exposures of present-day activity well beyond the HT Rainbow hydrothermal field (> 10 km2). Second, we have identified numerous fossil carbonate and sulfide hydrothermal chimneys at various locations on the massif that are sometimes in close spatial association, suggesting a temporal evolution of local hydrothermal style. Third, fossil bivalve communities are found over much broader areas than previously described (hundreds of m2), extending along the summit of the Massif and its western flank, demonstrating an extensive, and pervasive diffuse flow in the past. Dating of these sites within a detailed structural framework will constrain the timing and duration of these different hydrothermal events to better evaluate their relationships and their links to the magmatic and structural evolution of the massif. These preliminary cruise results already show complex spatio-temporal dynamics of fluid flow, resulting in a far more varied and widespread hydrothermal activity than expected on ultramafic-hosted environment along mid-ocean ridges. These results also provoke further consideration of the impact of ultramafic hydrothermal systems on thermal and chemical ocean-lithosphere exchanges.&#160

Les microstructures de déformation des serpentines et la partition sismique-asismique (exemple de la Californie)

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Formation of clay minerals and exhumation of lower-crustal rocks at Atlantis Massif, Mid-Atlantic Ridge

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