Hafnium isotopic variations in East Atlantic intraplate volcanism

The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), 176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic Hf isotopic compositions (176Hf/177Hfm up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend on the Nd vs. Hf isotope diagram (stretching over >10 εHf units) between a depleted N-MORB-like endmember and a moderately enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed "C" mantle component of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between (1) a low Hf isotope HIMUlike endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic. Both domains, however, seem to share a common, moderately enriched endmember that has "C"-like isotope compositions and is believed to represent subducted, =1 Ga

Titanite Mineralization of Microbial Bioalteration Textures in Jurassic Volcanic Glass, Coast Range Ophiolite, California

Volcanic glasses are rarely preserved in the rock record, and the quality of preservation generally declines with increasing age. Records preserved in ancient basaltic glasses therefore provide important links between processes operating in the distant past, and those that are active on the Earth today. Microbial colonization has been linked to the formation of characteristic structures in basaltic glass, including tubules and granule-filled tubules, which are thought to be produced by microbially mediated glass dissolution. Structures of similar occurrence and morphology but filled almost entirely with fine-grained titanite have been documented in some ancient metabasalts. It has been suggested that the ancient titanite-mineralized structures are mineralized equivalents of hollow tubules in modern glassy basaltic rocks, but a direct link has not been firmly established. We report the discovery of tubular bioalteration structures in fresh and minimally altered basaltic glasses of middle Jurassic (164 Ma) age from the Stonyford Volcanic Complex (SFVC), Coast Range Ophiolite, California. Tubular structures hosted in unaltered basaltic glass are typically hollow, whilst those in zones of zeolitic alteration are mineralized by titanite. Tubules are continuous across zeolite-glass interfaces, which mark an abrupt change from titanite-filled to hollow tubules, demonstrating that titanite growth occurs preferentially within pre-existing tubular structures. Titanite mineralization in the SFVC represent a link between tubular structures in modern basaltic glass and titanite-mineralized features of similar morphology and spatial distribution in ancient metabasalts. Our observations support a link between textures in modern glassy basaltic rocks and some of the oldest-known putative ichnofossils

Morphological and geochemical variations along the eastern Galapagos Spreading Center

[1] As the eastern Galápagos Spreading Center (GSC) shallows westward toward the Galápagos Archipelago, axial morphology evolves from a low-relief, valley-and-ridge terrain to an increasingly prominent axial ridge, closely mirroring the western GSC. Between the Inca Transform (∼85.5°W) and its western termination near 91°W, the eastern GSC comprises seven morphological segments, separated by five morphological discontinuities and the eastward propagating 87°W overlapping spreading center. Combined morphologic and geochemical data divide the eastern GSC into two domains independent of the fine-scale morphologic segmentation. The western domain is defined by its axial ridge morphology and highly variable lava population. Elemental data define steep along-axis gradients, reflecting a complex source that includes one or more hot spot–related components in addition to a highly depleted component. The eastern domain is defined by transitional, valley-and-ridge morphologies and a surprisingly invariant lava population. This population is dominated by shallow crystal fractionation processes and displays significantly less variability attributable to multiple source components. The Galápagos hot spot has long been known to have a symmetrical, long-wavelength influence on crustal accretion along the GSC. Existing isotopic and new elemental data define twin “geochemical peaks” that we interpret as loci for transfer of distinct source components from the Galápagos plume to the GSC. Although Na8 and Fe8 values lie within the negatively correlated global array, Na8 increases with decreasing axial depth, contrary to global trends and consistent with emerging deep, hydrous melting models that predict decreasing overall extent of melting despite increasing melt production. Support for hydrous melting comes from decreasing heavy REE, increasing La/Sm and La/Yb, and the systematics of decreasing FeO and increasing CaO and Al2O3 with decreasing distance to the hot spot. Overall, an enriched, deep melt component appears to coexist in the shallow mantle with a ubiquitous, depleted primitive melt component, consistent with new models for channelized melt flow connecting a deep hydrous melt regime with the dry shallow mantle. Nevertheless, an absence of low-Fe lavas suggests that hydrous melting is strictly limited beneath the eastern GSC, becoming dominant only near the western geochemical peak where input from a hydrous “Northern” or “Wolf-Darwin” plume component is inferred

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