40Ar/39Ar age of the Rotoiti Breccia and Rotoehu Ash, Okataina Volcanic Complex, New Zealand, and identification of heterogeneously distributed excess 40Ar in supercooled crystals

Co-magmatic granitoid clasts erupted as part of the Rotoiti Ignimbrite (Rotoehu Tephra) contain euhedral K-feldspar and biotite crystals that protrude into miarolytic cavities and show textural evidence for growth in super-cooled conditions and are thus interpreted as growing during eruption. 40Ar/39Ar stepped heating experiments on single K-feldspar crystals reveal the presence of heterogeneously distributed excess 40Ar, preferentially released at lower temperature steps (most likely from fluid/melt inclusions), which cannot reliably be characterised by, or corrected for using isotope correlation diagrams due to mixing between three reservoirs of 40Ar (radiogenic, atmospheric and excess). This excess 40Ar component is common, but not ubiquitous, and an age population unmixing algorithm applied to single-crystal fusion data identifies a younger group of K-feldspar and biotite crystals that appear to be largely unaffected by excess 40Ar. This population gives a statistically robust weighted mean age of 47.4 ± 1.5 ka (1σ, n = 13) and an indistinguishable inverse isochron age of 50 ± 3 ka for this historically difficult to date eruption. The weighted mean age is significantly younger than previous age estimates of the Rotoiti eruption obtained by K/Ar and 40Ar/39Ar dating of bracketing lavas, but is indistinguishable from recent 14C and (U-Th)/He dates and estimates based on orbital tuning and sedimentation rates constrained by 14C ages

Observation of centimetre-scale argon diffusion in alkali feldspars: implications for ⁴⁰Ar/³⁹Ar thermochronology

New data from a gem-quality feldspar from Itrongay, Madagascar, record naturally occurring 40Ar/39Ar age profiles which can be numerically modelled by invoking a single diffusion mechanism and show that microtexturally simple crystals are capable of recording complex thermal histories. We present the longest directly measured, naturally produced 40Ar*-closure profiles from a single, homogeneous orthoclase feldspar. These data appear to confirm the assumption that laboratory derived diffusion parameters are valid in nature and over geological timescales. Diffusion domains are defined by crystal faces and ancient cracks, thus in gem-quality feldspars the diffusion domain size equates to the physical grain size. The data also illustrate the potential of large, gem-quality feldspars to record detailed thermal histories over tens of millions of years and such samples should be considered for future studies on the slow cooling of continental crust

Spatially heterogeneous argon-isotope systematics and apparent 40Ar/39Ar ages in perlitised obsidian

In situ laser ablation Ar-isotope analyses of variably hydrated and devitrified obsidian from the ~ 27 Ma Cochetopa Dome, San Juan, USA, reveal complex interplay between degassing of initial Ar and absorption of atmospheric Ar. These processes have locally modified the Ar-isotope composition of the obsidian and led to spurious, spatially-heterogeneous Ar-isotope and 40Ar/39Ar age data. Small perlite beads exhibit older apparent Ar-ages at the rims than the cores. This is interpreted as an apparent excess of 40Ar at the rims, produced either by a) diffusion of excess 40Ar into the bead during flushing of the lava with excess 40Ar-bearing volcanic gas, or by b) isotopic fractionation during degassing of initial Ar, causing preferential loss of 36Ar over 40Ar at the bead rims. The second interpretation is favoured by a relative enrichment of 36Ar in the core of a perlite bead along a microlite-free (poorly degassed) flow band, and by a lack of age variation in a larger, fresh, well-degassed perlite bead. These isotopic gradients were later overprinted during glass hydration by absorption of Ar with near-atmospheric composition, resulting in elevated 36Ar and reduced radiogenic 40Ar* yields at the rims of perlite beads. These complex interactions essentially represent the mixing of three distinct Ar reservoirs: initial trapped Ar that may or may not be fractionated, an isotopically atmospheric Ar component introduced during hydration, and radiogenic 40Ar*. Such reservoir mixing is the underlying reason for poor correlations on isotope correlation diagrams and the difficulties in validating the composition of the non-radiogenic Ar component. We thus suggest that high 36Ar yields are a combination of the incomplete degassing of initial (possibly magmatic) Ar and the gain of Ar during interaction between the obsidian and meteoric/atmospheric fluids. Our analyses emphasise the challenging nature of 40Ar/39Ar dating obsidian samples, but also point to possible solutions by careful sample characterisation and selection of highly degassed samples

Spatially heterogeneous argon-isotope systematics and apparent ⁴⁰Ar/³⁹Ar ages in perlitised obsidian

In situ laser ablation Ar-isotope analyses of variably hydrated and devitrified obsidian from the ~ 27 Ma Cochetopa Dome, San Juan, USA, reveal complex interplay between degassing of initial Ar and absorption of atmospheric Ar. These processes have locally modified the Ar-isotope composition of the obsidian and led to spurious, spatially-heterogeneous Ar-isotope and 40Ar/39Ar age data. Small perlite beads exhibit older apparent Ar-ages at the rims than the cores. This is interpreted as an apparent excess of 40Ar at the rims, produced either by a) diffusion of excess 40Ar into the bead during flushing of the lava with excess 40Ar-bearing volcanic gas, or by b) isotopic fractionation during degassing of initial Ar, causing preferential loss of 36Ar over 40Ar at the bead rims. The second interpretation is favoured by a relative enrichment of 36Ar in the core of a perlite bead along a microlite-free (poorly degassed) flow band, and by a lack of age variation in a larger, fresh, well-degassed perlite bead. These isotopic gradients were later overprinted during glass hydration by absorption of Ar with near-atmospheric composition, resulting in elevated 36Ar and reduced radiogenic 40Ar* yields at the rims of perlite beads. These complex interactions essentially represent the mixing of three distinct Ar reservoirs: initial trapped Ar that may or may not be fractionated, an isotopically atmospheric Ar component introduced during hydration, and radiogenic 40Ar*. Such reservoir mixing is the underlying reason for poor correlations on isotope correlation diagrams and the difficulties in validating the composition of the non-radiogenic Ar component. We thus suggest that high 36Ar yields are a combination of the incomplete degassing of initial (possibly magmatic) Ar and the gain of Ar during interaction between the obsidian and meteoric/atmospheric fluids. Our analyses emphasise the challenging nature of 40Ar/39Ar dating obsidian samples, but also point to possible solutions by careful sample characterisation and selection of highly degassed samples

Inherent tracers for carbon capture and storage in sedimentary formations: composition and applications

Inherent tracers - the “natural” isotopic and trace gas composition of captured CO₂ streams – are potentially powerful tracers for use in CCS technology. This review outlines for the first time the expected carbon isotope and noble gas compositions of captured CO₂ streams from a range of feedstocks, CO₂-generating processes and carbon capture techniques. The C-isotope composition of captured CO₂ will be most strongly controlled by the feedstock, but significant isotope fractionation is possible during capture; noble gas concentrations will be controlled by the capture technique employed. Comparison with likely baseline data suggests that CO₂ generated from fossil fuel feedstocks will often have δ13C distinguishable from storage reservoir CO₂. Noble gases in amine-captured CO₂ streams are likely to be low concentration, with isotopic ratios dependant on the feedstock, but CO₂ captured from oxyfuel plants may be strongly enriched in Kr and Xe which are potentially valuable subsurface tracers. CO₂ streams derived from fossil fuels will have noble gas isotope ratios reflecting a radiogenic component that will be difficult to distinguish in the storage reservoir, but inheritance of radiogenic components will provide an easily recognisable signature in the case of any unplanned migration into shallow aquifers or to the surface

Application of benchtop micro-XRF to geological materials

Recent developments in X-ray optics have allowed the development of a range of commercially available benchtop micro-XRF (μ-XRF) instruments that can produce X-ray spot sizes of 20-30 μm on the sample, allowing major- and trace-element analysis on a range of sample types and sizes with minimal sample preparation. Such instruments offer quantitative analysis using fundamental parameter based 'standardless' quantification algorithms. The accuracy and precision of this quantitative analysis on geological materials, and application of micro-XRF to wider geological problems is assessed using a single benchtop micro-XRF instrument. Quantitative analysis of internal reference materials and international standards shows that such instruments can provide highly reproducible data but that, for many silicate materials, standardless quantification is not accurate. Accuracy can be improved, however, by using a simple type-calibration against a reference material of similar matrix and composition. Qualitative analysis with micro-XRF can simplify and streamline sample characterization and processing for subsequent geochemical and isotopic analysis

Carbon capture and storage at the end of a lost decade

Following the landmark 2015 United Nations Paris Agreement, a growing number of countries are committing to the transition to net-zero emissions. Carbon capture and storage (CCS) has been consistently heralded to directly address emissions from the energy and industrial sectors and forms a significant component of plans to reach net-zero. However, despite the critical importance of the technology and substantial research and development to date, CCS deployment has been slow. This review examines deployment efforts over the last decade. We reveal that facility deployment must increase dramatically from current levels, and much work remains to maximize storage of CO2 in vast subsurface reserves. Using current rates of deployment, CO2 storage capacity by 2050 is projected to be around 700 million tons per year, just 10% of what is required. Meeting the net-zero targets via CCS ambitions seems unlikely unless worldwide coordinated efforts and rapid changes in policy take place

Noble gases confirm plume related mantle degassing beneath Southern Africa

Southern Africa is characterised by unusually elevated topography and abnormal heat flow. This can be explained by thermal perturbation of the mantle, but the origin of this is unclear. Geophysics has not detected a thermal anomaly in the upper mantle and there is no geochemical evidence of an asthenosphere mantle contribution to the Cenozoic volcanic record of the region. Here we show that natural CO2 seeps along the Ntlakwe-Bongwan fault within KwaZulu-Natal, South Africa, have C-He isotope systematics that support an origin from degassing mantle melts. Neon isotopes indicate that the melts originate from a deep mantle source that is similar to the mantle plume beneath Réunion, rather than the convecting upper mantle or sub-continental lithosphere. This confirms the existence of the Quathlamba mantle plume and importantly provides the first evidence in support of upwelling deep mantle beneath Southern Africa, helping to explain the regions elevation and abnormal heat flow

Towards a Digital Twin of the Earth System: Geo-Soft-CoRe, a Geoscientific Software & Code Repository

[Abstract] The immense advances in computer power achieved in the last decades have had a significant impact in Earth science, providing valuable research outputs that allow the simulation of complex natural processes and systems, and generating improved forecasts. The development and implementation of innovative geoscientific software is currently evolving towards a sustainable and efficient development by integrating models of different aspects of the Earth system. This will set the foundation for a future digital twin of the Earth. The codification and update of this software require great effort from research groups and therefore, it needs to be preserved for its reuse by future generations of geoscientists. Here, we report on Geo-Soft-CoRe, a Geoscientific Software & Code Repository, hosted at the archive DIGITAL.CSIC. This is an open source, multidisciplinary and multiscale collection of software and code developed to analyze different aspects of the Earth system, encompassing tools to: 1) analyze climate variability; 2) assess hazards, and 3) characterize the structure and dynamics of the solid Earth. Due to the broad range of applications of these software packages, this collection is useful not only for basic research in Earth science, but also for applied research and educational purposes, reducing the gap between the geosciences and the society. By providing each software and code with a permanent identifier (DOI), we ensure its self-sustainability and accomplish the FAIR (Findable, Accessible, Interoperable and Reusable) principles. Therefore, we aim for a more transparent science, transferring knowledge in an easier way to the geoscience community, and encouraging an integrated use of computational infrastructure.This research has been funded by the Projects EPOS IP 676564, EPOS SP 871121, SERA 730900, GeoCAM (PGC2018-095154-B-I00, Spanish Government) and the Center of Excellence for Exascale in Solid Earth (ChEESE) under the Grant Agreement 823844. IDF was funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). JA and M-GL are funded by the Spanish Ministry of Science and Innovation through the Juan de la Cierva fellowship (IJC 2018-036074-I and IJC 2018-036826-I, respectively), funded by MCIN/AEI /10.13039/501100011033. AH is grateful for his Ramón y Cajal contract (RYC 2020-029253-I). Additional funding was provided by the Spanish Ministry of Science and Innovation (RTI 2018-095594-B-I00, PGC 2018-095154-B-100) and the Generalitat de Catalunya (AGAUR, 2017SGR1022). AP’s work was supported by: a Science Foundation Ireland Career Development Award (17/CDA/4695); an investigator award (16/IA/4520); a Marine Research Programme funded by the Irish Government, co-financed by the European Regional Development Fund (Grant-Aid Agreement No. PBA/CC/18/01); European Union’s Horizon 2020 research and innovation programme InnoVar under grant agreement No 818144; SFI Centre for Research Training in Foundations of Data Science 18/CRT/6049, and SFI Research Centre awards I-Form 16/RC/3872 and Insight 12/RC/2289_P2. AH and SG thank the Spanish research project PaleoModes (CGL2016-75281-C2-1-R) which provided some of their financial support. JF is supported by an Atracción de Talento senior fellowship (2018-T1/AMB/11493) funded by Comunidad Autonoma de Madrid (Spain), and a project funded by the Spanish Ministry of Science and Innovation (PID2020-114854GB-C22)Junta de Castilla y León; SA0084P20Generalitat de Catalunya; 2017SGR1022Science Foundation Ireland; 17/CDA/4695Science Foundation Ireland; 16/IA/4520Ireland. Marine Institute; PBA/CC/18/01Science Foundation Ireland; 18/CRT/6049Science Foundation Ireland; 16/RC/3872Science Foundation Ireland; 12/RC/2289_P2Comunidad Autonoma de Madrid; 2018-T1/AMB/1149

Age and context of the oldest known hominin fossils from Flores

Recent excavations at the early Middle Pleistocene site of Mata Menge in the So\u27a Basin of central Flores, Indonesia, have yielded hominin fossils1 attributed to a population ancestral to Late Pleistocene Homo floresiensis2. Here we describe the age and context of the Mata Menge hominin specimens and associated archaeological findings. The fluvial sandstone layer from which the in situ fossils were excavated in 2014 was deposited in a small valley stream around 700 thousand years ago, as indicated by 40Ar/39Ar and fission track dates on stratigraphically bracketing volcanic ash and pyroclastic density current deposits, in combination with coupled uranium-series and electron spin resonance dating of fossil teeth. Palaeoenvironmental data indicate a relatively dry climate in the So\u27a Basin during the early Middle Pleistocene, while various lines of evidence suggest the hominins inhabited a savannah-like open grassland habitat with a wetland component. The hominin fossils occur alongside the remains of an insular fauna and a simple stone technology that is markedly similar to that associated with Late Pleistocene H. floresiensis