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  • 1
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    Volcanic edifice weakening via decarbonation: A self-limiting process? (2012)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The inherent instability of volcanic edifices, and their resultant propensity for catastrophic collapse, is a constant source of volcanic risk. Structural instability of volcanic edifices may be amplified by the presence of carbonate rocks in the sub-volcanic strata, due to the debilitating response of carbonates to thermally-induced alteration. Nonetheless, decarbonation reactions (the primary weakening mechanism), may stall when the system becomes buffered by rising levels of a reaction product, carbon dioxide. Such thermodynamic stalling might be inferred to serve to circumvent the weakness of volcanic structures. However, the present study shows that, even when decarbonation is halted, rock physical properties continue to degrade due to thermal microcracking. Furthermore, as a result, the pathways for the escape of carbon dioxide are numerous within a volcanic edifice. Therefore, in the case of an edifice with a subvolcanic sedimentary basement, the generation of carbon dioxide via decarbonation is unlikely to hinder its impact on instability, and thus potentially devastating flank collapse.
    Description: Published
    Description: L15307
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: restricted
    Keywords: volcanic weakening; decarbonation ; 04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
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    Decarbonation and thermal microcracking under magmatic P-T-fCO2 conditions: the role of skarn substrata in promoting volcanic instability (2014)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: We present a systematic study on the influence of pressure (0.1–600 MPa), temperature (750– 1200 ◦C), carbon dioxide fugacity (logfCO2 = −4.41 to 3.60) and time (2–12 hr) on the chemical and physical properties of carbonate rock. Our experiments aim to reproduce the conditions at the periphery of magma chamber where carbonate host rock is influenced by, but not readily assimilated by, magma. This permits the investigation of the natural conditions at which circulating fluids/gases promote infiltration reactions typical of metasomatic skarns that can involve large volumes of subvolcanic carbonate basements. Results show that, providing that carbon dioxide is retained in the pore space, decarbonation does not proceed at any magmatic pressure and temperature. However, when the carbon dioxide is free to escape, decarbonation can occur rapidly and is not hindered by a low initial porosity or permeability. Together with carbon dioxide and lime, portlandite, a mineral commonly found in voluminous metasomatic skarns, readily forms during carbonate decomposition. Post-experimental analyses highlight that thermal microcracking, a result of the highly anisotropic thermal expansion of calcite, exerts a greater influence on rock physical properties (porosity, ultrasonic wave velocities and elastic moduli) than decarbonation. Our data suggest that this will be especially true at the margins of dykes or magma bodies, where temperatures can reach up to 1200 ◦C. However, rock compressive strength is significantly reduced by both thermal cracking and decarbonation, explained by the relative weakness of lime + portlandite compared to calcite, and an increase in grain size with increasing temperature. Metasomatic skarns, whose petrogenetic reactions may involve a few tens of cubic kilometres, could therefore represent an important source of volcanic instability.
    Description: Published
    Description: 369-380
    Description: 2R. Laboratori sperimentali e analitici
    Description: JCR Journal
    Description: restricted
    Keywords: Volcanic hazards and risks ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    Decarbonation and thermal microcracking under magmatic P-T-f CO2 conditions: the role of skarn substrata in promoting volcanic instability (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-10
    Description: We present a systematic study on the influence of pressure (0.1–600 MPa), temperature (750–1200 °C), carbon dioxide fugacity (log f CO 2  = –4.41 to 3.60) and time (2–12 hr) on the chemical and physical properties of carbonate rock. Our experiments aim to reproduce the conditions at the periphery of magma chamber where carbonate host rock is influenced by, but not readily assimilated by, magma. This permits the investigation of the natural conditions at which circulating fluids/gases promote infiltration reactions typical of metasomatic skarns that can involve large volumes of subvolcanic carbonate basements. Results show that, providing that carbon dioxide is retained in the pore space, decarbonation does not proceed at any magmatic pressure and temperature. However, when the carbon dioxide is free to escape, decarbonation can occur rapidly and is not hindered by a low initial porosity or permeability. Together with carbon dioxide and lime, portlandite, a mineral commonly found in voluminous metasomatic skarns, readily forms during carbonate decomposition. Post-experimental analyses highlight that thermal microcracking, a result of the highly anisotropic thermal expansion of calcite, exerts a greater influence on rock physical properties (porosity, ultrasonic wave velocities and elastic moduli) than decarbonation. Our data suggest that this will be especially true at the margins of dykes or magma bodies, where temperatures can reach up to 1200 °C. However, rock compressive strength is significantly reduced by both thermal cracking and decarbonation, explained by the relative weakness of lime + portlandite compared to calcite, and an increase in grain size with increasing temperature. Metasomatic skarns, whose petrogenetic reactions may involve a few tens of cubic kilometres, could therefore represent an important source of volcanic instability.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 4
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    Reconstructing magma failure and the degassing network of dome-building eruptions (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-03-22
    Description: Volcanic eruptions are regulated by the rheology of magmas and their ability to degas. Both detail the evolution of stresses within ascending subvolcanic magma. But as magma is forced through the ductile-brittle transition, new pathways emerge as cracks nucleate, propagate, and coalesce, constructing a permeable network. Current analyses of magma dynamics center on models of the glass transition, neglecting important aspects such as incremental strain accommodation and (the key monitoring tool of) seismicity. Here, in a combined-methods study, we report the first high-resolution (20 μm) neutron-computed tomography and microseismic monitoring of magma failure under controlled experimental conditions. The data reconstruction reveals that a competition between extensional and shear fracturing modes controls the total magnitude of strain-to-failure and importantly, the geometry and efficiency of the permeable fracture network that regulates degassing events. Extrapolation of our findings yields magma ascent via strain localization along conduit margins, thereby providing an explanation for gas-and-ash explosions along arcuate fractures at active lava domes. We conclude that a coupled deformation-seismicity analysis holds a derivation of fracture mechanisms and network, and thus holds potential application in forecasting technologies.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 5
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    The viscous-brittle transition of crystal-bearing silicic melt: Direct observation of magma rupture and healing (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-07-01
    Description: Magmas may flow or break depending on their deformation rate. The transition between such viscous and brittle behavior controls the style of volcanic eruptions. While the brittle failure of silicate melts is reasonably well characterized, the effect of crystals on the viscous-brittle transition has not yet been constrained. Here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures (600–900 °C), strain rates (10−4–10−1 s−1), and confining pressures (200–300 MPa) relevant for volcanic systems. We present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction. Furthermore, the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present. The fractures formed during brittle failure of crystal-bearing magma originate in the melt phase, which enables gas to escape, and hence to reduce gas overpressure. These degassing pathways heal on relatively short time scales owing to the high confining pressure at depth, highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing.
    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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    Advances in high-resolution neutron computed tomography: Adapted to the earth sciences (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-12-01
    Description: The application of state-of-the-art detector systems at the Advanced Neutron Tomography and Radiography Experimental System (ANTARES; Munich, Germany) has led to significant improvements in spatial resolution and contrast for geomaterial imaging. Resolutions of ~16–100 µm are now possible with fields of view of 33–205 mm, a level now comparable with X-ray computed tomography (XCT), for which a micro-XCT at the Institute for Mineralogy, Crystallography and Material Science at the University of Leipzig was used. Fine pixel resolution comes at the cost of image quality and increased exposure time, so that the optimum configuration for each sample must be determined on a case by case basis. Our interdisciplinary approach has yielded an efficient system of data acquisition, processing, and quantification that is well suited for geomaterial imaging. We expect to find applications in a much wider spectrum of geomaterial research, including the formation of natural glasses, the characterization of limited and/or precious samples such as scientific drill cores, and biomineralization studies.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 7
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    How tough is tuff in the event of fire? (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-04-01
    Description: Tuff has been extensively used as a building material in volcanically and tectonically active areas over many centuries, despite its inherent low strength. A common and unfortunate secondary hazard accompanying both major volcanic eruptions and tectonic earthquakes is the initiation of catastrophic fires. Here we report new experimental results on the influence of high temperatures on the strength of three tuffs that are commonly used for building in the Neapolitan region of Italy. Our results show that a reduction in strength was only observed for one tuff; the other two were unaffected by high temperatures. The cause of this strength discrepancy was found to be a product of the initial mineralogical composition, or more specifically, the presence of thermally unstable zeolites within the initial rock matrix. The implications of these data are that, in the event of fire, only the stability of buildings or structures built from tuff containing thermally unstable zeolites will be reduced. Unfortunately, this includes the most widespread dimension stone in Neapolitan architecture. We recommend that this knowledge should be considered during fire hazard mitigation in the Neapolitan area and that other tuffs used in construction worldwide should be tested in a similar way to assess their fire resistance.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Volcanic glass and its suitability to recover the ancient geomagnetic field strength (2014)
    Geological Society (of London)
    Details
    Publication Date: 2014-09-04
    Description: The determination of the past ancient magnetic field intensity is typically very difficult and error prone. Fresh volcanic glass has been suggested to be an ideal material for obtaining direction and strength of the magnetic field. Domain state bias is generally absent, thermal alteration is normally negligible and, as demonstrated in this study, cooling-rate differences can be corrected for. Major issues remaining include alteration and the origin of the remanence: that is, whether it is a true thermo-, a thermochemical or, for altered samples, a chemical remanence. Hydration, devitrification and perlitization lead to incorrect estimates of the palaeointensity, which are very difficult to recognize as the palaeointensity analysis does not easily expose these biasing effects and points towards ‘reliable’ results. Particular care on sampling and/or volatile measurements are necessary to overcome these drawbacks.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 9
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    Experiments and models on H2O retrograde solubility in volcanic systems (2015)
    Mineralogical Society of America
    Details
    Publication Date: 2015-04-02
    Description: We present a suite of 36 high-temperature (900–1100 °C) experiments performed on 10 x 10 mm unjacketed cores of rhyolitic obsidian from Hrafntinnuhryggur, Krafla, Iceland, under atmospheric pressure. The obsidian is bubble- and crystal-free with an H 2 O content of 0.11(4) wt%. The obsidian cores were heated above the glass transition temperature ( T g ), held for 0.25–24 h, then quenched. During each experiment the volume of the samples increased as H 2 O vapor-filled bubbles nucleated and expanded. Uniquely, the bubbles did not nucleate on the surface of the core, nor escape, conserving mass during all experiments. Within each isothermal experimental suite, the cores increased in volume with time until they reached a maximum, after which continued heating caused no change in volume (measured by He-pycnometry). We interpret these T - t conditions as representing thermochemical equilibrium between the melt and exsolved vapor. These experiments are modeled to recover the 1-atm, temperature-dependent solubility of water in the rhyolite melt. Our results define the magnitude of retrograde solubility (–7.1 x 10 –3 wt% H 2 O per 100 °C) and provide estimates of the enthalpy and entropy of the H 2 O exsolution reaction [ H ° = 17.8 kJ/mol, S ° = 107 J/(K·mol)]. We conclude by modeling the implications of retrograde solubility for the glass transition temperatures ( T g ) of cooling volcanic systems at pressures relevant to volcanic conduits and the Earth’s surface. All volcanic systems cool; the effects of retrograde solubility are to allow melts to rehydrate by H 2 O dissolution as they cool isobarically, thereby depressing T g and expanding the melt window. Ultimately, the melt is quenched at higher H 2 O contents and lower temperatures where the isobaric retrograde solubility curve "catches" the evolving T g .
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 10
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    An advanced rotational rheometer system for extremely fluid liquids up to 1273 K and applications to alkali carbonate meltsk (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-04-02
    Description: A high-temperature rheometer equipped with a graphite furnace, characterized by an air-bearing-supported synchronous motor, has been enhanced by a custom-made Pt-Au concentric cylinder assembly. With this adaptation, viscosity measurements of highly fluid melts can be achieved at high temperatures, up to 1273 K. Due to the air-bearing-supported motor, this apparatus can perform measurements of extremely low torque ranging between 0.01 μNm and 230 mNm (resolution of 0.1 nNm), extending the typical range of viscosity measurements accessible in the present configuration to 10 –3.5 –10 3.5 Pa·s and shear rates up to 10 2 of s –1 . We calibrated the system with distilled water, silicone oils, and the DGG-1 standard glass. We further present new data for the viscosity of Na 2 CO 3 , K 2 CO 3 , and Li 2 CO 3 liquids. Finally, a comparison between our results and literature data is provided, to illustrate the effect of chemical composition and oxygen fugacity on the viscosity of alkali carbonate melts, which serve as analogs for both carbonatitic melts and molten carbonates of industrial relevance. This study substantially improves the database of alkali carbonate melts and dramatically increases the accuracy with respect to previous measurement attempts. The very low viscosity range data and their temperature dependence also helps to constrain very well the activation energy of these highly fluid systems and confirms the estimate of a universal pre-exponential factor for non-Arrhenian viscosity-temperature relationships.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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