1,721,042 research outputs found
A sabbatical reboot
No full text“Why have I traded my private office for a desk in a shared room?” I wondered. “Will I get any work done?” It was my first day at my new co-working space on the outskirts of town, 10 kilometers from my university. “I'm here on sabbatical,” I announced to my new officemates. They were directors of tech startups, unaccustomed to mingling with geoscientists like me. I desperately needed some breathing space away from the pressures of university life, but I wasn't totally convinced it would work out. I needn't have worried. The co-working space turned out to be the perfect environment for rebooting my flailing research career
Did an asteroid impact cause temporary warming during snowball Earth?
No full textThe ca. 717 Ma low-latitude Sturtian “snowball Earth” glaciation lasted ∼56 Myr. However, sedimentological evidence for transient, open ocean conditions during the glaciation appears to contradict the concept of a global deep freeze. We demonstrate multiple lines of geologic evidence from five continents for a temporary, localized sea-ice retreat during the middle of the Sturtian glaciation, which coincides with one, perhaps two, asteroid impacts, and arguably more terrestrial impacts as inferred from the lunar impact record. The well-dated Jänisjärvi impact (ca. 687 Ma) is synchronous with repeated volcanic ash falls whose deposition is most parsimoniously interpreted to indicate a partially ice-free ocean. Temporary greenhouse warming caused by the vaporization of sea ice can explain localized glacial retreat within restricted seaways between these continents, where ice flow would have been constricted and sea ice thinnest before impact
A viable Labrador Sea rifting origin of the Northern Appalachian and related seismic anomalies
No full textThe Northern Appalachian Anomaly (NAA) is a prominent low-seismic-velocity zone, ∼400 km in diameter, in the asthenosphere beneath New England (northeastern USA). Previous studies interpreted this shallow feature, occurring at a depth of ∼200 km, as a thermal anomaly tied to edge-driven convection along the North American continental margins. Those studies recognized, however, that upwelling here is highly unusual given that the passive margin has been tectonically quiescent for ∼180 m.y. We propose an alternative model, based on geologic observations, geotectonic reconstructions, and geodynamic simulations, that the anomaly instead represents a Rayleigh-Taylor instability linked to the breakup of the distant Labrador Sea continental margin. A Labrador Sea origin at breakup, ca. 85−80 Ma, would imply the migration of a chain of Rayleigh-Taylor instabilities at a rate of ∼22 km/m.y., close to expected rates from geodynamic models. A migrating-instability origin for the anomaly can reconcile its spatial characteristics, depth profile, and position near a long-inactive continental margin. A corollary is that the north-central Greenland anomaly, a mirror-image of the NAA, also potentially originated at the time of breakup. Further, The Central Appalachian Anomaly may fit this model if it represents an early-stage instability linked to rifting onset in the Labrador Sea. The NAA and other associated anomalies viably represent a legacy of continental rifting and breakup along the distant Labrador Sea margins
Triggering of major eruptions recorded by actively forming cumulates
No full textMajor overturn within a magma chamber can bring together felsic and mafic magmas, prompting de-volatilisation and acting as the driver for Plinian eruptions. Until now identification of mixing has been limited to analysis of lavas or individual crystals ejected during eruptions. We have recovered partially developed cumulate material (‘live’ cumulate mush) from pyroclastic deposits of major eruptions on Tenerife. These samples represent “frozen” clumps of diverse crystalline deposits from all levels in the developing reservoir, which are permeated with the final magma immediately before eruptions. Such events therefore record the complete disintegration of the magma chamber, leading to caldera collapse. Chemical variation across developing cumulus crystals records changes in melt composition. Apart from fluctuations reflecting periodic influxes of mafic melt, crystal edges consistently record the presence of more felsic magmas. The prevalence of this felsic liquid implies it was able to infiltrate the entire cumulate pile immediately before each eruption
Evolving mantle convection from bottom-up to top-down
No full textWhen it comes to convection, what goes up must come down. Or is it, what goes down must come up? The truth is it depends. Although convection must be mass balanced, there is no reason that it must be force balanced: the positive and negative buoyancy forces driving convection up and down, respectively, do not necessarily need to be balanced. The balance, or imbalance, all depends on the top and bottom boundary layers. Thus, convection in Earth's mantle depends on the temperature differences across the core-mantle boundary below and the lithosphere-asthenosphere boundary above. Convective asymmetry predominated by positive buoyancy, or bottom-up convection, would be driven by plume ascent, whereas if it were predominated by negative buoyancy, or top-down convection, it would be driven by plate subduction. Symmetric convection would balance plume ascent and plate subduction. Is mantle convection on Earth balanced, dominantly top down or bottom up, or time dependent?</p
LiDAR DEM of Boset volcano in Ethiopia
No full textHigh-resolution light detection and ranging (LiDAR) data of Boset volcano in Ethiopia was collected and processed by the Natural Environment Research Council (NERC) Airborne Research and Survey Facility (ARSF). The data was collected in November 2012 and used to create a digital elevation model (DEM) that has 2 m horizontal and 0.2 m vertical resolution. The LiDAR data was recorded within two swaths. The majority of the data is in a NNE striking swath (30 km length, 5.8 km width) parallel to the rift and a second narrow swath (26.5 km length, 0.75 km width) is across the remnant caldera wall of Gudda volcano. The LiDAR data has been geo-referenced by the NERC ARSF using GPS station ground control points located in the towns of Nazret and Wellenchiti. The file is a .dem file, which is a geospatial file format for storing a raster-based digital elevation model. The data is associated to the RiftVolc project, which is a NERC large grant NE/L013932. When using the data please cite Siegburg et al. (2018) https://doi.org/10.1016/j.jvolgeores.2017.12.014
Note: following feedback from users that the original files were unreadable, the datafiles were updated on 31 May 2022</span
Geochemical data to support the Southampton doctoral thesis "The volcanic and geochemical evolution of the Adda’do Magmatic Segment, Southern Afar, Ethiopia [Thesis]"
No full textGeochemical data to support "The volcanic and geochemical evolution of the Adda’do Magmatic Segment, Southern Afar, Ethiopia [Thesis]". Consisting of major element, trace element, and radiogenic isotope data.</span
Greenlandic debris in Iceland likely tied to Bond 1 ice-rafting in the Dark Ages
No full textWe report the discovery of exotic igneous, metamorphic, and sedimentary cobbles in raised beach deposits near Breiðavík, northern Iceland. These deposits consist of alternating cobble-, sand-, and silt-dominated facies. A nearby package of sands and silts, dated to the Late Antique Little Ice Age (LALIA; ca. 536−660 CE), provides age constraints for the raised terraces. While the upper terraces are composed exclusively of local basaltic material, the lowermost terraces (∼2 m above high tide) contain a mix of basaltic and nonbasaltic cobbles, including quartzofeldspathic gneiss, granitoid, rhyolite, sandstone, and serpentinite. U-Pb geochronologic analysis of zircon revealed dominant age modes of ca. 2800, 1150, 500, and 240 Ma with Lu-Hf isotopic compositions suggesting derivation from Greenland’s North Atlantic craton and Caledonian fold belt. The colder conditions of the LALIA, coupled with increased iceberg calving from the Greenland ice sheet, would have led to enhanced ice-rafted debris (IRD) transport to disparate areas south and east of Greenland. The East Greenland and East Iceland currents transported this IRD from Greenland, with deposition occurring along the Icelandic coast as the icebergs melted. This IRD was likely transported across the North Atlantic during Bond event 1. This process, along with those during other transient cooling events, may explain the age discrepancies between local bedrock and detrital zircons in the Arctic
Viability of greenhouse gas removal via artificial addition of volcanic ash to the ocean
No full textMitigating human contributions to climate change is a highly debated topic, as it becomes evident that many nations do not adhere to optional reductions in global emission. Substantial research is taking place into negative carbon technologies that actively reduce the amount of atmospheric carbon dioxide (CO
2) via greenhouse gas removal (GGR). Various GGR methods have been proposed, from reforestation to ocean fertilisation. This article discusses advantages of an approach based on enhanced input of tephra to the ocean, to increase the drawdown of atmospheric CO
2. Natural addition of tephra to the ocean results in preservation of enhanced organic matter in sediment. Hence, augmenting its delivery should raise the level of sequestration. Calculations indicate that offshore tephra addition could sequester 2750 tonnes of CO
2 per 50,000 tonnes of ash delivered (a typical bulk carrier's capacity). The cost is estimated as ∼$55 per tonne of CO
2 sequestered and is an order of magnitude cheaper than many proposed GGR technologies. Further advantages include: tephra addition is simply an augmentation of a natural Earth process, it is a low technology approach that requires few developments, and it may sequester carbon for thousands of years. Hence, offshore tephra addition warrants further investigation to assess its viability.
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