Understanding the degassing of young volcanic systems using noble gases

Incompatible inert trace elements He, Ne and Ar are widely used to characterize magmatic reservoirs and to study volcanic processes. Their isotopic signature and fractionation (e.g. 4He/40Ar ratio) provide useful information on magma source, magma differentiation and contamination. Several studies have investigated sources, reservoirs and chemical controls of noble gases, but few efforts have been made to study which factors control noble gas incorporation and release during degassing episodes. The aim of this research is to identify these factors and to test how they influence noble gas behaviour in volcanic rocks with different degassing histories. This will help improve our understanding of how noble gases are recycled into the atmosphere during volcanism. Particular attention will be given to the behaviour of Ar because of its use in 40Ar/39Ar dating. A better knowledge of how Ar is trapped and released from volcanic rocks will help find a solution to the ‘excess argon problem’: the presence of an excess portion of Ar inside rocks that is not related to atmospheric Ar nor to the radiogenic decay of 40K, complicates 40Ar/39Ar age dating. Younger volcanic rocks are more affected by this problem due to their lower concentrations of radiogenic Ar with respect to non-radiogenic Ar. In this study, samples from 0 to 2 Ma are used to study rocks with different proportion of radiogenic and excess Ar. A variety of materials (pumice, ash, non-vesicular glass, crystals) and deposit types (pyroclastic fall, ignimbrites, lavas, and Pele’s hair) from Tenerife (Spain), Etna (Italy) and Masaya (Nicaragua), will be used to test how noble gases vary in response of cooling rate (Pele’s hairs vs. lavas vs. mode of pyroclastic emplacement), depositional environment (distal vs. proximal) and physical characteristics of the deposit (grain size, crystals vs. bubbles, rock porosity). Petrographic, SEM and XRF analysis will be conducted to characterise mineral assemblages, textures and chemistry of the samples; noble gas concentration and distribution will be determined by laser ablation mass spectrometry; the internal structure and topology (e.g. form, distribution and connectivity of vesicles) will be quantified using X-ray microtomography in order to identify fast-pathways for the release of noble gases from volcanic materials during degassing episodes

Noble gases: A tool to track the degassing of active volcanic systems

He, Ne and Ar are widely used to characterize magmatic reservoirs and to study volcanic processes. Their isotopic signature and fractionation (e.g. 4He/40Ar ratio) provide information on magma source, differentiation, contamination and degassing. Several studies have investigated sources, reservoirs and chemical controls of noble gases, but few efforts have been made to study which factors control noble gas incorporation, partition and release during degassing episodes. The aim of this research is to identify these factors and to test how they influence noble gas behaviour in volcanic rocks with different degassing histories. This will help improve our understanding of how noble gases are recycled into the atmosphere during volcanism. Particular attention will be given to the behaviour of Ar because of its use in 40Ar/39Ardating. A better knowledge of how Ar is trapped and released from volcanic rocks will help find a solution to the 'excess argon problem': the presence of an excess portion of 40Ar inside rocks that is not related to atmospheric Ar nor to the radiogenic decay of 40K, which complicates 40Ar/39Ar age dating. Younger volcanic rocks are more affected by this problem due to their lower concentrations of radiogenic 40Ar with respect to non-radiogenic Ar. Samples from 0 to 1 Ma are used to study rocks with different proportion of radiogenic and excess 40Ar. A variety of materials (pumice, ash, non-vesicular glass, crystals) and deposit types (pyroclastic fall, ignimbrites, lavas, and Pele's hairs) from Tenerife (Spain), Etna (Italy) and Masaya (Nicaragua), will be used to test how noble gases vary in response of cooling rate (Pele's hairs vs. lavas vs. mode of pyroclastic emplacement) and physical characteristics of the deposit (crystals vs. bubbles, rock porosity). Noble gas mass spectrometry results from Pele's hairs/tears collected in 2015-2016 at Masaya Volcano, a persistent degassing system, show an inverse degassing trend with 2016 samples less degassed (low 4He/40Ar ratio) than 2015 samples (high 4He/40Ar ratio). Causes and factors controlling this trend have been investigated. Mineral assemblages and sample textures have been characterised by petrographic analysis; samples chemistry have been determined by electron-probe and NANO-SIMS analysis; further studies on the internal structure of the considered material will help to understand the role of bubbles in noble gas distribution and release during degassing episodes

The RESET project: constructing a European tephra lattice for refined synchronisation of environmental and archaeological events during the last c. 100 ka

This paper introduces the aims and scope of the RESET project (. RESponse of humans to abrupt Environmental Transitions), a programme of research funded by the Natural Environment Research Council (UK) between 2008 and 2013; it also provides the context and rationale for papers included in a special volume of Quaternary Science Reviews that report some of the project's findings. RESET examined the chronological and correlation methods employed to establish causal links between the timing of abrupt environmental transitions (AETs) on the one hand, and of human dispersal and development on the other, with a focus on the Middle and Upper Palaeolithic periods. The period of interest is the Last Glacial cycle and the early Holocene (c. 100-8 ka), during which time a number of pronounced AETs occurred. A long-running topic of debate is the degree to which human history in Europe and the Mediterranean region during the Palaeolithic was shaped by these AETs, but this has proved difficult to assess because of poor dating control. In an attempt to move the science forward, RESET examined the potential that tephra isochrons, and in particular non-visible ash layers (cryptotephras), might offer for synchronising palaeo-records with a greater degree of finesse. New tephrostratigraphical data generated by the project augment previously-established tephra frameworks for the region, and underpin a more evolved tephra 'lattice' that links palaeo-records between Greenland, the European mainland, sub-marine sequences in the Mediterranean and North Africa. The paper also outlines the significance of other contributions to this special volume: collectively, these illustrate how the lattice was constructed, how it links with cognate tephra research in Europe and elsewhere, and how the evidence of tephra isochrons is beginning to challenge long-held views about the impacts of environmental change on humans during the Palaeolithic. © 2015 Elsevier Ltd.RESET was funded through Consortium Grants awarded by the Natural Environment Research Council, UK, to a collaborating team drawn from four institutions: Royal Holloway University of London (grant reference NE/E015905/1), the Natural History Museum, London (NE/E015913/1), Oxford University (NE/E015670/1) and the University of Southampton, including the National Oceanography Centre (NE/01531X/1). The authors also wish to record their deep gratitude to four members of the scientific community who formed a consultative advisory panel during the lifetime of the RESET project: Professor Barbara Wohlfarth (Stockholm University), Professor Jørgen Peder Steffensen (Niels Bohr Institute, Copenhagen), Dr. Martin Street (Romisch-Germanisches Zentralmuseum, Neuwied) and Professor Clive Oppenheimer (Cambridge University). They provided excellent advice at key stages of the work, which we greatly valued. We also thank Jenny Kynaston (Geography Department, Royal Holloway) for construction of several of the figures in this paper, and Debbie Barrett (Elsevier) and Colin Murray Wallace (Editor-in-Chief, QSR) for their considerable assistance in the production of this special volume.Peer Reviewe

Fusion Learning Colloquium 2022 - Proceedings

This is the proceedings of the 2022 Fusion Learning Colloquium held at Bournemouth University in the UK

An investigation of depositional mechanisms of pyroclastic density currents using anisotropy of magnetic susceptibility (AMS) and a detailed stratigraphic study of the La Caleta Formation, Tenerife

This thesis describes La Caleta Formation and its eruptive history interpreted using sedimentary logs, isopach and isopleth data, granulometry and geochemical studies. The formation has been subdivided into six members, which were emplaced during five eruptive phases. The eruption commenced with fallout from a Plinian eruption column that collapsed, generating a rapid succession of short-lived pyroclastic density currents that deposited extensive ignimbrites and co-ignimbrite ash layers, culminating in a more sustained pyroclastic current that deposited a thick, predominantly massive ignimbrite, capped with a lithic breccia interpreted to represent caldera collapse. Fine ash layers can be deposited by ashfall or pyroclastic density currents and their fine grain size coupled with poor exposure, can hinder interpretations of their depositional origin, which is vital if using ash layers for hazard assessment. A new method of discriminating between these two types of deposit is presented in this thesis. Samples of unequivocal depositional origin were collected from formations within the Bandas del Sur Group and their fabrics, analysed using Anisotropy of Magnetic Susceptibility (AMS). This revealed differences in the distribution of susceptibility axes, the imbrication of the magnetic foliation and the strength and shape of the anisotropy between the two types of deposit. However the discrimination using the traditional AMS plots was found to be equivocal in some instance, so a new discriminant plot has been devised, which can successfully discriminate between the two types of ash layer. AMS has been used to categorise cross-stratified, stratified, diffusely bedded and massive lithofacies, and to interpret flow-boundary conditions and depositional mechanisms. Samples were collected from ignimbrites and ash layers from the Bandas del Sur Group and their AMS fabrics compared. The distribution of the magnetic susceptibility axes on the stereonets has been used to infer flow-boundary conditions; girdle distributions represent more tractional processes, whereas well-grouped distributions represent more granular processes and random distributions represent fluid escape dominated flow-boundary zones. The most significant outcome was the recognition of different types of massive deposit, based on variations in the distribution of the susceptibility axes, which are interpreted to have been deposited at a fluid-escape dominated flow-boundary influenced by other processes (traction and/or granular shear). This indicates that not all massive deposits are emplaced in the same way.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The emplacement and deformation of high-temperature tuffs : a structural analysis of the Grey’s Landing ignimbrite, Snake River Plain, Idaho

The Grey’s Landing ignimbrite is an exceptionally well-preserved and well-exposed lava-like ignimbrite in the Snake River Plain volcanic province of southern Idaho, USA. High-grade tuffs are typically intensely welded and rheomorphic, preserving evidence of syn- and post-depositional ductile flow. The Grey’s Landing ignimbrite underwent two distinct phases of rheomorphism: (1) syn-depositional welding and rheomorphism as the deposit aggraded, producing a penetrative, mylonite-like L > S fabric including sheath folds, a strong elongation lineation, and shear-sense indicators; and (2) post-depositional, en masse, gravity-driven flow of parts of the deposit down palaeo-slopes, producing a fold-dominated deformation characterised by large-scale folds of the upper surface of the ignimbrite. Thermal and rheological modelling suggest that the original magma was hot (~ 950 °C), volatile-rich (≤ 5 wt % fluorine), and low viscosity (≥ 106 Pa.s-1). Syn-depositional rheomorphism had a strain rate of ~ 10-5 s-1 and deformed ignimbrite with a viscosity similar to the original magma. Postdepositional rheomorphism was limited to 6 months at the upper surface and ≤ 16 years in the centre of the thickest ignimbrite, at a strain rate of ~ 10-6 s-1.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Postoperative continuous positive airway pressure to prevent pneumonia, re-intubation, and death after major abdominal surgery (PRISM): a multicentre, open-label, randomised, phase 3 trial

Background: Respiratory complications are an important cause of postoperative morbidity. We aimed to investigate whether continuous positive airway pressure (CPAP) administered immediately after major abdominal surgery could prevent postoperative morbidity. Methods: PRISM was an open-label, randomised, phase 3 trial done at 70 hospitals across six countries. Patients aged 50 years or older who were undergoing elective major open abdominal surgery were randomly assigned (1:1) to receive CPAP within 4 h of the end of surgery or usual postoperative care. Patients were randomly assigned using a computer-generated minimisation algorithm with inbuilt concealment. The primary outcome was a composite of pneumonia, endotracheal re-intubation, or death within 30 days after randomisation, assessed in the intention-to-treat population. Safety was assessed in all patients who received CPAP. The trial is registered with the ISRCTN registry, ISRCTN56012545. Findings: Between Feb 8, 2016, and Nov 11, 2019, 4806 patients were randomly assigned (2405 to the CPAP group and 2401 to the usual care group), of whom 4793 were included in the primary analysis (2396 in the CPAP group and 2397 in the usual care group). 195 (8\ub71%) of 2396 patients in the CPAP group and 197 (8\ub72%) of 2397 patients in the usual care group met the composite primary outcome (adjusted odds ratio 1\ub701 [95% CI 0\ub781-1\ub724]; p=0\ub795). 200 (8\ub79%) of 2241 patients in the CPAP group had adverse events. The most common adverse events were claustrophobia (78 [3\ub75%] of 2241 patients), oronasal dryness (43 [1\ub79%]), excessive air leak (36 [1\ub76%]), vomiting (26 [1\ub72%]), and pain (24 [1\ub71%]). There were two serious adverse events: one patient had significant hearing loss and one patient had obstruction of their venous catheter caused by a CPAP hood, which resulted in transient haemodynamic instability. Interpretation: In this large clinical effectiveness trial, CPAP did not reduce the incidence of pneumonia, endotracheal re-intubation, or death after major abdominal surgery. Although CPAP has an important role in the treatment of respiratory failure after surgery, routine use of prophylactic post-operative CPAP is not recommended