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  • 1
    Electronic Resource
    Electronic Resource
    Purine alkaloid formation in buds and developing leaflets of Coffea arabica: Expression of an optimal defence strategy?
    Amsterdam : Elsevier
    Phytochemistry 25 (1986), S. 613-616 
    Details
    ISSN: 0031-9422
    Keywords: Coffea arabica ; Rubiaceae ; alkaloids ; caffeine. ; chemical defence ; coffee ; developmental physiology ; theobromine
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0031-9422(86)88009-8
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  • 2
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    Eruption of Shallow Crystal Cumulates during Explosive Phonolitic Eruptions on Tenerife, Canary Islands (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-25
    Description: The recent eruptive history on the island of Tenerife is characterized in part by the presence of zoned phonolitic ignimbrites, some of which prominently display two types of juvenile clasts (i.e. light-colored, aphyric pumices alongside darker, more crystal-rich pumices, here dubbed ‘crystal-poor’ and ‘crystal-rich’, respectively). Petrographic observation of the crystal-rich pumices reveals intensely resorbed and intergrown mineral textures, consistent with the system reaching a high crystallinity, followed by perturbation and remobilization prior to eruption. Some trace elements show anomalous concentrations in such crystal-rich pumices (e.g. bulk Ba 〉 2000 ppm alongside low Zr and a positive Eu anomaly) indicative of crystal accumulation (of feldspar ± biotite). Many biotite and feldspar crystals are reversely zoned, with rim concentrations that are high in Ba but low in Sr, implying crystallization from an ‘enriched’ melt, potentially derived from remobilization by partial melting of the aforementioned cumulate zones. Given (1) the presence of cumulates in the eruptive record on Tenerife and a bimodality of pumice textures, (2) the presence of three dominant compositions (basanite, phonotephrite, phonolite, separated by compositional gaps) in the volcanic record, and (3) abundant support for crystal fractionation as the dominant drive for magmatic evolution in Tenerife, it is hypothesized that crystal-poor magmas are extracted from mushy reservoirs in both the lower and upper crust. The thermodynamic software MELTS is used to test a polybaric differentiation model whereby phonolites ( sensu lato ) are generated by extraction of residual liquids from an intermediate-crystallinity phonotephritic mush in the upper crust, which is in turn generated from the residual liquids of an intermediate-crystallinity basanitic mush at deeper levels. Latent heat spikes following crystallization of successive phases in the upper crustal reservoir provide a thermal buffering mechanism to slow down cooling and crystallization, permitting enhanced melt extraction at a particular crystallinity interval (mostly ~40–60 vol. % crystals). MELTS modeling typically fits the observed chemical data adequately, although some major elements (mostly Al 2 O 3 ) also indicate partial ‘cannibalization’ of feldspar along with some magma mixing (and potentially minor crustal contamination).
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 3
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    Rift-Related Transition from Andesite to Rhyolite Volcanism in the Taupo Volcanic Zone (New Zealand) Controlled by Crystal-melt Dynamics in Mush Zones with Variable Mineral Assemblages (2011)
    Oxford University Press
    Details
    Publication Date: 2011-11-01
    Description: The Taupo Volcanic Zone (TVZ), located in the North Island of New Zealand, represents part of a magmatic arc that is at present undergoing active extension. Around 0·9 Myr ago, an acceleration in rifting was followed by a progressive transition in the composition of volcanic products (until ~0·7 Ma) from typical arc-type andesite into overwhelmingly large, caldera-forming rhyolitic eruptions with subordinate basalt and dacite in the Central TVZ. Despite an obvious compositional gap in the erupted products in the Central TVZ within the last 0·7 Myr (little to no erupted products with SiO 2 contents between 55 and 65 wt %), phenocryst minerals (plagioclase, amphibole, pyroxene) show an uninterrupted compositional record that suggests crystallization from a continuum of melt compositions. Coupled with radiogenic isotope evidence, the whole-rock and mineral chemistry data are consistent with magmatic differentiation controlled by crystal fractionation of primary mantle-derived magmas accompanied by some assimilation of local wall-rocks. In the Southern TVZ and in the early part of the Central TVZ, magmatic differentiation was dominated by the lower crustal evolution of relatively dry (~1 wt % H 2 O) arc basalts, crystallizing a pyroxene–plagioclase-dominated assemblage. However, the conditions of crystallization in the lower crust appear to have changed within the last million years in the Central TVZ, with amphibole and oxides appearing earlier in the crystallization sequence. In this framework and using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs, we show that melts extracted from crystal mushes within an optimal ‘extraction window’ (~50 and 80 vol. % crystals) match those erupted at the surface. Lower crustal mushes fed by basalt with 1 wt % H 2 O (dominated by a pyroxene–plagioclase assemblage) release andesitic melts at the extraction window. These melts then erupt at the surface to form the observed andesitic part of the arc. With a slightly higher water content (~2 wt %) in the basalt, the melt composition at the extraction window from lower crustal mushes is dacitic rather than andesitic. Although some dacitic melts will reach the surface, most will be trapped in the upper crust and crystallize to form a silicic mush. Extraction of the interstitial liquid after 〉50% crystallization from this upper crustal reservoir produces the large volumes of rhyolitic magma erupted over the past 0·7 Myr (〉4000 km 3 from ignimbrite-forming eruptions).
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 4
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    Hot clasts and cold blasts: thermal heterogeneity in boiling-over pyroclastic density currents (2015)
    Geological Society (of London)
    Details
    Publication Date: 2015-01-09
    Description: Partial thermal remanent magnetization data from clasts in pyroclastic density current (PDC) deposits provide information on the emplacement temperatures of both lithic and juvenile magmatic clasts contained in the deposits. We collected palaeomagnetic data from clasts in PDC deposits emplaced during historical eruptions of two volcanoes in Ecuador, the 2006 eruption at Tungurahua and the 1877 eruption at Cotopaxi. These eruptions were characterized by emplacement of PDCs mainly related to boiling-over activity. The deposits of these eruptions are similar and are characterized by cauliflower-textured juvenile scoria clasts up to 1 m in diameter and a diverse assemblage of lithic clasts surrounded by an unwelded ashy matrix. On the basis of progressive thermal demagnetization experiments, we infer that emplacement temperatures for most of the lithic clasts in PDC deposits are below 90 °C. In contrast, palaeomagnetic data from juvenile clasts from the same deposits provide emplacement temperatures higher than 540 °C. These data indicate the PDC were thermally heterogeneous over short length scales (decimetres) also after deposition. We hypothesize that PDCs emplaced by the boiling-over mechanism cool quickly owing to atmosphere entrainment, causing the juvenile clasts to form a rind that retains heat and that also prevents lithic clasts from appreciable heating. Several deposits on Cotopaxi, despite being morphologically similar to the PDC deposits, contain both cold lithic and juvenile clasts, which we interpret to be lahar deposits formed by PDCs travelling across glacial ice and snow. Rare deposits containing both hot lithic and hot juvenile clasts are classified as well-mixed, hot PDCs, and were erupted during a more energetic phase at Tungurahua.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 5
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    Ina pit crater on the Moon: Extrusion of waning-stage lava lake magmatic foam results in extremely young crater retention ages (2017)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2017-04-12
    Description: The enigmatic Ina feature on the Moon was recently interpreted to represent extrusive basaltic volcanic activity within the past 100 m.y. of lunar history, an extremely young age for volcanism on the Moon. Ina is a 2 x 3 km D-shaped depression that consists of a host of unusual bleb-like mounds surrounded by a relatively optically fresh hummocky and blocky floor. Documentation of magmatic-volcanic processes from shield volcano summit pit craters in Hawai’i and new insights into shield-building and dike evolution processes on the Moon provide important perspectives on the origin of Ina. We show that the size, location, morphology, topography, and optical maturity of Ina are consistent with an origin as a subsided summit pit crater lava lake on top of a broad ~22-km-diameter, ~3.5-b.y.-old shield volcano. New theoretical treatments of lunar shield-building magmatic dike events predict that waning-stage summit activity was characterized by the production of magmatic foam in the dike and lake; the final stages of dike stress relaxation and closure cause the magmatic foam to extrude to the surface through cracks in the lava lake crust to produce the mounds. The high porosity of the extruded foams (〉75%) altered the nature of subsequent impact craters (the aerogel effect), causing them to be significantly smaller in diameter, which could bias the crater-derived model ages. Accounting for this effect allows for significantly older model ages, to ~3.5 b.y., contemporaneous with the underlying shield volcano. Thus extremely young volcanic eruptions are not required to explain the unusual nature of Ina.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 6
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    Inferring Compressible Fluid Dynamics From Vent Discharges During Volcanic Eruptions (2018)
    American Geophysical Union
    Details
    Publication Date: 2018-07-28
    Description: Observations at numerous volcanoes reveal that eruptions are often accompanied by continual radio frequency (CRF) emissions. The source of this radiation, however, has remained elusive until now. Through experiments and the analysis of field data, we show that CRF originates from proximal discharges driven by the compressible fluid dynamics associated with individual volcanic explosions. Blasts produce flows that expand supersonically, generating regions of weakened dielectric strength in close proximity to the vent. As erupted material—charged through fragmentation, friction, or other electrification process—transits through such a region, pyroclasts remove charge from their surfaces in the form of small interparticle spark discharges or corona discharge. Discharge is maintained as long as overpressured conditions at the vent remain. Beyond describing the mechanism underlying CRF, we demonstrate that the magnitude of the overpressure at the vent as well as the structure of the supersonic jet can be inferred in real time by detecting and locating CRF sources. ©2018. The Authors.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 7
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    An experimental evaluation of ash aggregation in explosive volcanic eruptions (2012)
    Elsevier
    Details
    Publication Date: 2012-01-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 8
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    Transient two-dimensional dynamics in the upper conduit of a rhyolitic eruption: A comparison of closure models for the granular stress (2005)
    Elsevier
    Details
    Publication Date: 2005-05-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 9
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    Continuum Modeling of Pressure‐Balanced and Fluidized Granular Flows in 2‐D: Comparison With Glass Bead Experiments and Implications for Concentrated Pyroclastic Density Currents (2019)
    American Geophysical Union
    Details
    Publication Date: 2019-06-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 10
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    Regional radiative impact of volcanic aerosol from the 2009 eruption of Mt. Redoubt (2012)
    Copernicus
    Details
    Publication Date: 2012-04-24
    Description: High northern latitude eruptions have the potential to release volcanic aerosol into the Arctic environment, perturbing the Arctic's climate system. We present assessments of shortwave (SW), longwave (LW) and net direct aerosol radiative forcing efficiencies and atmospheric heating/cooling rates caused by volcanic aerosol from the 2009 eruption of Mt. Redoubt by performing radiative transfer modeling constrained by NASA A-Train satellite data. The optical properties of volcanic aerosol were calculated by introducing a compositionally resolved microphysical model developed for both ash and sulfates. Two compositions of volcanic aerosol were considered in order to examine a fresh, ash rich plume and an older, ash poor plume. Optical models were incorporated into a modified version of the SBDART radiative transfer model. Our results indicate that environmental conditions, such as surface albedo and solar zenith angle (SZA), can influence the sign and the magnitude of the radiative forcing at the top of the atmosphere (TOA) and at the surface and the magnitude of the forcing in the aerosol layer. We find that a fresh, thin plume (~2.5–7 km) at an AOD (550 nm) range of 0.18–0.58 and SZA = 55° over snow cools the surface and warms the TOA, but the opposite effect is seen for TOA by the same layer over ocean. The layer over snow also warms by 64 W m−2AOD−1 more than the same plume over seawater. The layer over snow at SZA = 75° warms the TOA 96 W m−2AOD−1 less than it would at SZA = 55° over snow, and there is instead warming at the surface. We also find that plume aging can alter the magnitude of the radiative forcing. An aged plume over snow at SZA = 55° would warm the TOA and layer by 146 and 143 W m−2AOD−1 less than the fresh plume, while the aging plume cools the surface 3 W m−2AOD−1 more. Comparing results for the thin plume to those for a thick plume (~3–20 km), we find that the fresh, thick plume with AOD(550 nm) = 3, over seawater, and SZA = 55° heats the upper part of the plume in the SW ~28 K day−1 more and cools in the LW by ~6.3 K day−1 more than a fresh, thin plume under the same environmental conditions. We compare our assessments with those reported for other aerosols typical to the Arctic environment (smoke from wildfires, Arctic haze, and dust) to demonstrate the importance of volcanic aerosols.
    Print ISSN: 1680-7316
    Electronic ISSN: 1680-7324
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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