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301.
Elena Boari Riccardo Avanzinelli Leone Melluso Guido Giordano Massimo Mattei Arnaldo A. De Benedetti Vincenzo Morra Sandro Conticelli 《Bulletin of Volcanology》2009,71(9):977-1005
The “Colli Albani” composite volcano is made up of strongly silica-undersaturated leucite-bearing rocks. Magmas were erupted during three main periods, but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs. The most alkali-rich magmas, restricted to the caldera-forming period (pre-caldera), are extremely enriched in incompatible trace elements and display more radiogenic Sr (87Sr/86Sr?=?0.71057–0.71067), with slightly less radiogenic Pb with respect to those of the post-caldera period. Post-caldera volcanic activity was concentrated in three different volcanic environments: external to the caldera, along the caldera edge and within the caldera. The post-caldera magmas produced melilite- to leucitite-bearing, plagioclase-free leucitites. In contrast to the pre-caldera lavas, they are characterised by lower incompatible trace element abundances and less radiogenic Sr (87Sr/86Sr?=?0.71006–0.71039). Magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre-caldera period. The multiple caldera collapses dissected and partially obliterated the early magma chamber. During the post-caldera stage, magmas were channelled through several pathways and multiple shallow-level magma reservoirs were established. A lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab-derived component is suggested as the mantle source of Colli Albani parental magmas. Two different parental magmas are recognised for the pre- and post-caldera stages. The differences may be related to the interplay between smaller degrees of melting for the pre-caldera magmas and more carbonate-rich recycled subducted lithologies in the post-caldera magmas. 相似文献
302.
Massimo Zecchin Giuliano Brancolini Luigi Tosi Federica Rizzetto Mauro Caffau Luca Baradello 《Continental Shelf Research》2009
The southern portion of the Venice lagoon contains a relatively thick (up to 20 m) Holocene sedimentary body that represents a detailed record of the formation and evolution of the lagoon. New very high-resolution (VHR) seismic profiles provided a detailed investigation on depositional geometries, internal bounding surfaces and stratal relationships. These informations, combined with core analysis, allowed the identification of large- to medium-scale sedimentary structures (e.g. dunes, point bars), the corresponding sedimentary environment, and of retrogradational and progradational trends. In addition, the availability of dense seismic network produced a 3D reconstruction of the southern lagoon and the recognition of the along-strike and dip variability of the stratal architecture. 相似文献
303.
304.
The aim of the paper is to explore the possibilities offered by SAP2000® v.10, a software package with user‐friendly interface widely used by practising engineers, for seismic analyses of masonry buildings. The reliability of the code was first investigated by carrying out static push‐over (SPO) analyses of two walls, already analysed by other researchers using advanced programs. The equivalent frame modelling was employed in all analyses carried out. The code was then used to investigate the seismic performance of an existing two‐storey building typical of the north‐east of Italy, with the walls being made of roughly squared stones. An SPO analysis was performed first on the most significant wall, followed by a number of time‐history analyses aimed to evaluate the dynamic push‐over curves. Finally, the seismic fragility curves were derived, considering the seismic input as a random variable. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
305.
Massimo D'Orazio 《Geostandards and Geoanalytical Research》1999,23(1):21-29
The concentration of boron was determined in twenty one geochemical reference materials (silicate rocks) by isotope dilution inductively coupled plasma-mass spectrometry. Boron was extracted from the rocks using HF digestion, suppressing boron volatilisation through boron-mannitol complexation. Sample solutions, in a diluted HCl matrix, were analysed by ICP-MS without any separation of boron from the matrix elements. The results obtained were in agreement with the literature data and indicate that using the described procedure, trace amounts of boron can be very easily determined in complex matrices with rapidity and precision. With the instrumentation and reagents used in this study, this procedure can be used for the determination of 0.5 μg g−1 boron in a 15 0 mg silicate rock sample. Replicate analyses of the twenty one geochemical reference materials (GRM), ranging in boron concentration from 1.35 to 15 7 μg g−1 , yielded precisions (relative standard deviation) varying between 0.9 and 9.8%. 相似文献
306.
Distinct site preferences for heavy and light REE in amphibole and the prediction of Amph/LDREE 总被引:1,自引:0,他引:1
P. Bottazzi M. Tiepolo R. Vannucci A. Zanetti R. Brumm S. F. Foley R. Oberti 《Contributions to Mineralogy and Petrology》1999,137(1-2):36-45
New experimental amphibole/melt partition coefficients from a variety of geologically relevant amphibole (pargasite, kaersutite,
and K-richterite) and melt compositions obtained under conditions of interest to upper-mantle studies are combined with the
results of X-ray single-crystal structure refinement. The ideal cation radii (r0), calculated using the lattice-site elastic-strain model of Blundy and Wood (1994) under the hypothesis of complete REE (rare
earth elements) ordering at [8]M4, mostly differ significantly from those obtained from both the structure refinement and the ionic radius of [8]Ca2+. Heavier REE may also strongly deviate from the parabolic trends defined by the other REE. On the basis of the crystal-chemical
knowledge of major-element site-preference in amphibole and the occurrence of two sites with different co-ordination within
the M4 cavity (M4 for Ca and Na, M4′ for Fe2+ and Mg), we propose a new model for REE incorporation. LREE order at the [8]M4 site, whereas HREE prefer the M4′ site with lower co-ordination in amphiboles with a significant cummingtonite component,
and may also enter the M2 octahedron, at least in richterite. This more complex model is consistent with the observed Amph/LD, and drops the usual assumption that REE behave as a homogeneous group and order at the M4 site. The availability of multiple
crystal-chemical mechanisms for REE3+ incorporation explains why measured and estimated Amph/LDHREE may differ by up to one order of magnitude. When REE enter two different sites within the same cavity, a fit performed on
the basis of a single curve may appear correct, but the values obtained for r0 are biased towards those of the dominant site, and the Young's modulus is underestimated. When REE are incorporated in multiple
sites in different cavities, the observed pattern cannot be reduced to a single curve, and the partition coefficients of heavy
REE would be strongly underestimated by a single-site fit. The simplistic assumption that REE occupy a single site within
the amphibole structure can thus substantially bias predictive models based on the elastic-strain theory. Our combined approach
allows linkage between fine-scale site preference and the macroscopic properties of minerals and provides more reliable predictive
models for mineral/melt partitioning. After the possible site-assignments have been identified, the shape of the Onuma curves
constructed from accurately determined Amph/LDREE now allows the active mechanisms for REE incorporation in amphiboles to be recognised even where site populations are not
available. The REE preference for polyhedra with smaller size and lower co-ordination than those occupied by Ca invalidates
the general idea that Ca acts as a “carrier” for REE.
Received: 17 March 1999 / Accepted: 11 June 1999 相似文献
307.
Rodolfo Console Massimo Chiappini Liliana Minelli Fabio Speranza Roberto Carluccio Michele Greco 《Acta Geophysica》2018,66(5):931-943
The application of a newly developed physics-based earthquake simulator to the active faults inferred by aeromagnetism in southern Calabria has produced a synthetic catalog lasting 100 ky including more than 18,000 earthquakes of magnitude ≥?4.0. This catalog exhibits temporal, spatial and magnitude features, which resemble those of the observed seismicity. As an example of the potential use of synthetic catalogs, a map of the peak ground acceleration (PGA) for a given exceedance probability on the territory under investigation has been produced by means of a simple attenuation law applied to all the events reported in the synthetic catalog. This map was compared with the existing hazard map that is presently used in the national seismic building regulations. The comparison supports a strong similarity of our results with the values given in the present Italian seismic building code, despite the latter being based on a different methodology. The same similarity cannot be recognized for the comparison of our present study with the results obtained from a previous study based on our same methodology but with a different geological model. 相似文献
308.
Understanding mass fluvial erosion along a bank profile: using PEEP technology for quantifying retreat lengths and identifying event timing 下载免费PDF全文
A. N. Thanos Papanicolaou Christopher G. Wilson Achilles G. Tsakiris Tommy E. Sutarto Fabienne Bertrand Massimo Rinaldi Subhasish Dey Eddy Langendoen 《地球表面变化过程与地形》2017,42(11):1717-1732
This study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses. We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion. We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows. The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
309.
Comparing Beerkan infiltration tests with rainfall simulation experiments for hydraulic characterization of a sandy‐loam soil 下载免费PDF全文
Simone Di Prima Vincenzo Bagarello Laurent Lassabatere Rafael Angulo‐Jaramillo Inmaculada Bautista Maria Burguet Artemi Cerdà Massimo Iovino Massimo Prosdocimi 《水文研究》2017,31(20):3520-3532
Saturated soil hydraulic conductivity, K s , data collected by ponding infiltrometer methods and usual experimental procedures could be unusable for interpreting field hydrological processes and particularly rainfall infiltration. The K s values determined by an infiltrometer experiment carried out by applying water at a relatively large distance from the soil surface could however be more appropriate to explain surface runoff generation phenomena during intense rainfall events. In this study, a link between rainfall simulation and ponding infiltrometer experiments was established for a sandy‐loam soil. The height of water pouring for the infiltrometer run was chosen, establishing a similarity between the gravitational potential energy of the applied water, E p , and the rainfall kinetic energy, E k . To test the soundness of this procedure, the soil was sampled with the Beerkan estimation of soil transfer parameters procedure of soil hydraulic characterization and two heights of water pouring (0.03 m, i.e., usual procedure, and 0.34 m, yielding E p = E k ). Then, a comparison between experimental steady‐state infiltration rates, i sR , measured with rainfall simulation experiments determining runoff production and K s values for the two water pouring heights was carried out in order to discriminate between theoretically possible (i sR ≥ K s ) and impossible (i sR < K s ) situations. Physically possible K s values were only obtained by applying water at a relatively large distance from the soil surface, because i sR was equal to 20.0 mm h?1 and K s values were 146.2–163.9 and 15.2–18.7 mm h?1 for a height of water pouring of 0.03 and 0.34 m, respectively. This result suggested the consistency between Beerkan runs with a high height of water pouring and rainfall simulator experiments. Soil compaction and mechanical aggregate breakdown were the most plausible physical mechanisms determining reduction of K s with height. This study demonstrated that the height from which water is poured onto the soil surface is a key parameter in infiltrometer experiments and can be adapted to mimic the effect of high intensity rain on soil hydraulic properties. 相似文献
310.
Michael Jakob Gunnar Luderer Jan Steckel Massimo Tavoni Stephanie Monjon 《Climatic change》2012,114(1):79-99
This paper compares the results of the three state of the art climate-energy-economy models IMACLIM-R, ReMIND-R, and WITCH to assess the costs of climate change mitigation in scenarios in which the implementation of a global climate agreement is delayed or major emitters decide to participate in the agreement at a later stage only. We find that for stabilizing atmospheric GHG concentrations at 450?ppm CO2-only, postponing a global agreement to 2020 raises global mitigation costs by at least about half and a delay to 2030 renders ambitious climate targets infeasible to achieve. In the standard policy scenario??in which allocation of emission permits is aimed at equal per-capita levels in the year 2050??regions with above average emissions (such as the EU and the US alongside the rest of Annex-I countries) incur lower mitigation costs by taking early action, even if mitigation efforts in the rest of the world experience a delay. However, regions with low per-capita emissions which are net exporters of emission permits (such as India) can possibly benefit from higher future carbon prices resulting from a delay. We illustrate the economic mechanism behind these observations and analyze how (1) lock-in of carbon intensive infrastructure, (2) differences in global carbon prices, and (3) changes in reduction commitments resulting from delayed action influence mitigation costs. 相似文献