Ordovician K-bentonites in the upper-plate active margin of Western Gondwana, (Famatina Ranges): Stratigraphic and palaeogeographic significance   总被引：1，自引：0，他引：1  

Ricardo A. Astini  Gilda Collo  Federico Martina   《Gondwana Research》2007,11(3):311-325

Numerous, thin-bedded, tabular pale-yellowish clay bands are interlayered with black shales in a biostratigraphically constrained Early Ordovician volcano-sedimentary succession at Famatina, western Argentina. This region was part of a fairly continuous upper-plate, convergent volcanic chain that fringed western Gondwana. Mineralogy on both clay and non-clay fractions, whole rock chemistry and field observations on these distinctive event-beds indicate that they originated as relatively coarse fallout tephras, altered first into bentonites and later, through burial metamorphism, into K-bentonites (metabentonites). These tephras were deposited as single crystals and glassy dust or pumiceous fragments in a restricted subtidal environment. The region of Famatina has previously been inferred as the source of abundant distal K-bentonites recorded in the adjacent lower-plate allochthonous Precordillera terrane. However, these K-bentonites within the proximal arc site were unknown and rather unexpected since they are generally better preserved like distal deposits, associated either with central vent plinian–ultraplinian eruptions or with accompanying co-ignimbrite ash clouds. Their chemistry and comparison with those K-bentonites in the Precordillera allow tracing an evolution from volcanic arcs into continental crust. K-bentonites described in this paper are much older than those recorded in the adjacent Precordillera terrane and seem to be associated with a first eruptive period along western Gondwana that has no counterpart in the Argentine Precordillera, suggesting a significant longitudinal separation between these two regions by the Early Ordovician.  相似文献   

History of subduction and back-arc extension in the Central Mediterranean   总被引：11，自引：0，他引：11  

Claudio Faccenna  Thorsten W. Becker  Francesco Pio Lucente  Laurent Jolivet  Federico Rossetti 《Geophysical Journal International》2001,145(3):809-820

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Elastic modeling of the Alto Tiberina normal fault (central Italy): geometry and lithological stratification influences on the local stress field     

Cristina Pauselli  Costanzo Federico 《Tectonophysics》2003,374(1-2):99-113

Two-dimensional, elastic, plane-strain, finite element models (FEMs) are generated to study the state of stress and failure induced by a low-angle normal fault, the Alto Tiberina Fault of the Northern Apennines (central Italy): it is beyond the scope of the present work to show that slip can occur on such a fault. The numerical study was performed to evaluate the influences on the local stress field of the litho-mechanical stratification of formations surrounding the fault, and those induced by the geometry of the fault. The performed models have shown the important role played by evaporites and basement formations of the Umbria-Marche succession as seismogenetic layers. The model results have also underlined that the flat-ramp geometry of the fault induces high relative concentration of stresses in correspondence with the low-angle, east-dipping, synthetic normal faults observed today in shallow depth near the Alto Tiberina surface trace. The stress regime predicted by the final model, in which the behavior of the Alto Tiberina together with the antithetic normal fault of Gubbio was simulated, reconciles available geological and geophysical observable to a greater extent. The numerical results can assist interpretation of the tectonic evolution of the region.  相似文献   

Isotopic and thermochronologic evidence of extremely cold lithosphere associated with a slab flattening in the Central Andes of Argentina          下载免费PDF全文

Gilda Collo  Federico M. Dávila  Wilson Teixeira  Julieta C. Nóbile  Lucy G. Sant′ Anna  Andrew Carter 《Basin Research》2017,29(1):16-40

We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous levels from the Bermejo and Vinchina basins – both foreland depocentres of the Central Andes of Argentina – that define a low‐temperature regime for the crust akin to a slab shallowing and flattening process. The contents of illite in illite/smectite interstratified (I/S) show a progressive illitization into the deeper parts of both basins. The distribution of I/S is compatible with theoretical simulations and predicted heat flow values of ca. 26 mW m^?2 in the 8–3.4 Ma interval for the Vinchina Basin and ca. 42 mW m^?2 since 9 Ma for the Bermejo Basin. The latter shows heat flow values that are comparable to those reported by magnetotelluric analysis (36–40 mW m^?2) in agreement with previously published heat flow calculations along the modern Andean foreland. The Rb–Sr isochrones in psammopelites (<2 μm fractions) show ages between 125 and 165 Ma, whereas the K–Ar ages decrease as the grain size is smaller (136–224 Ma for 1–2 μm, 112–159 Ma for 0.2–1 μm, 76–116 Ma for <0.2 μ and 39.3–42 Ma for <0.1 μm). These ages are significantly older than the sedimentation in the basins (ca. 16 Ma for the Vinchina Basin; U–Pb age), and can be explained by the presence of a significant amount of detrital components, mainly illite, even in the finer fractions. The preservation of detrital ages is consistent with the shallow diagenesis related to a low‐temperature regime, proposed here for the basins. Younger K–Ar ages (21.3–12 Ma) were obtained for a basal tuffaceous level. Clay mineralogy and R0 ordering in the deepest part of the Vinchina Basin, together with the evolution model of I/S with depth, suggest that the burial temperatures would have not exceeded ca. 100°C in agreement with (U–Th)/He analyses performed on apatite extracted from two tuffaceous units. Thermal indicators from both studied basins confirm the existence of a low‐temperature regime during flat subduction.  相似文献   

The participation of core stakeholders in the design of,and challenges to,the US Clean Power Plan     

Ramiro Berardo  Federico Holm 《Climate Policy》2018,18(9):1152-1164

We examine the participation of stakeholders in the rule-making process leading to the design of the US Clean Power Plan (CPP), which was the cornerstone regulation developed during the Obama administration to lower GHG emissions from power plants in the US. Using publicly available information, we identify the core stakeholders that participated in the different stages of the rulemaking process, from the early draft of the rule to its publication in final form, and examine variables that could help explain their decisions to litigate, either against or in favour of the final version of the rule. We show that the ‘pro-CPP’ stakeholders were (a) more likely to participate during the early stages of the rule-making process, attending meetings with the Environmental Protection Agency (EPA) staff to discuss rule content, and (b) less likely to get involved during the litigation process. ‘Anti-CPP’ stakeholders, on the other hand, did the opposite, being in general less active during the rulemaking stages, and more active during the litigation stage. However, we also find that the ‘anti-CPP’ stakeholders were more tightly organized as a coalition when compared to the ‘pro-CPP’ stakeholders throughout the process (even in the early stages when they participated less). Our results shed new light on the way advocacy coalitions operate in the climate policy subsystem in the US, and help inform debates about the likelihood of conflict and cooperation across a variety of environmental policy topics.

Key policy insights

• The design of the Clean Power Plan was a long and contentious process in which ‘Pro’ and ‘Anti-CPP’ coalitions operated to support and undermine the rule, respectively.

• ‘Pro-CPP’ stakeholders were more active in meetings organized to discuss the CPP with EPA staff, and in submitting written comments.

• ‘Anti-CPP’ stakeholders were more active during litigation, in response to perceived EPA overreach in designing the rule and negative financial impacts on states’ economies.

• Joint participation by ‘Anti-CPP’ stakeholders in meetings conveyed by the EPA to discuss the potential content of the rule helps explain their joint litigation efforts, which hints at their considerable capacity to self-organize as a coalition throughout the process.

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On the formation and stability of Uranus' rings     

Paolo Farinella  Paolo Paolicchi  Federico Ferrini  Anna M. Nobili 《Earth, Moon, and Planets》1980,22(1):103-111

We discuss the possibility of outlining a global model of formation and evolution for the Uranian rings with the minimum allowance for arbitrary assumptions. A condition for the stability of the -ring against differential precession is derived and compared with the similar results by Goldreich and Tremaine (1979). We discuss the problem of the long-term stability of the rings against collisional broadening, showing that the assumption of a confinement due only to self-gravitation requires the presence of a large amount of mass in the rings (10²²–10²³ g for the -ring). This latter hypothesis seems difficult to accept both for observational and for theoretical reasons, so that we suggest that some other confining mechanism (even if more peculiar) should work for this system. Finally we describe a possible scenario for the formation of the rings based on the idea of the break-up at the Roche limit of a tidally evolved satellite: we assume a sequence of events which appears, at least qualitatively, adequate to account for the observational evidence and endowed with a low degree of arbitrarity.Paper presented at the European Workshop on Planetary Sciences, organised by the Laboratorio di Astrofisica Spaziale di Frascati, and held between April 23–27, 1979, at the Accademia Nazionale del Lincei in Rome, Italy.  相似文献   

Mutual phenomena of Jupiter's satellites     

Zulema Abraham  Federico M. Strauss 《Icarus》1979,37(1):264-271

Observations of an occultation of Europa by Io are fitted by a model light curve. The model has five free parameters, namely the radius of Europa, the impact parameter, the brightness ratio of the satellites, the time of midevent and the mean relative velocity. The model assumes a fixed value for the radius of Io and for the solar phase angle α, and that Europa has a uniform surface brightness. The OC residuals of the best fitting light curve are very small (～0.002 mag) and of a purely random nature; there is no evidence of albedo features. Taking α = 0 does not affect significantly the quality of the fit. Six mutual eclipses were also observed, and their times of minima agree well with the predictions of Aksnes Icarus21 (1974). For two events these predictions differ by about 20 min from those of Brinkmann and Millis Sky & Telescope45 (1973).  相似文献   

An explanation for the light curve of Jupiter's and Saturn's satellites     

Paolo Farinella  Paolo Paolicchi  Federico Ferrini  Anna M. Nobili 《Earth, Moon, and Planets》1979,20(4):385-395

Several satellites of Jupiter and Saturn show an asymmetric reflectance between the leading hemisphere (which is generally brighter for the inner satellites of both systems) and the trailing one (which is brighter for the outer satellites Callisto and Iapetus). In order to seek a unified explantation of these observational data we assume that, during the final phase of the satellite accumulation process, the surfaces were subjected to a heavy meteoroidal bombardment by the residual bodies in the circumplanetary protosatellite swarms. With suitable hypotheses about the orbital elements of these bodies, the resulting collision rate is anisotropic in an opposite way for inner and outer satellites, with a difference between the two hemispheres of the order of 10–20% for all satellites except Iapetus (for which the anisotropy is larger). We conclude that the model can qualitatively account for the observed effect, even if it is difficult to propose a detailed mechanism for changing the albedo properties of the satellite surfaces by means of meteoroidal collisions.  相似文献   

Recruitment indices of European hake, Merluccius merluccius (Linnaeus 1758), in the Northwest Mediterranean based on landings from bottom-trawl multispecies fisheries     

Goni  Raquel; Adlerstein  Sara; Alvarez  Federico; Garcia  Mariano; Sanchez  Pilar; Sbrana  Mario; Maynou  Francesc; Viva  Claudio 《ICES Journal of Marine Science》2004,61(5):760-773

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PCBs and PAHs in surficial sediments from aquatic environments of Mexico City and the coastal states of Sonora,Sinaloa, Oaxaca and Veracruz (Mexico)     

Rossano Piazza  Ana Carolina Ruiz-Fernández  Mauro Frignani  Roberta Zangrando  Luca Giorgio Bellucci  Ivo Moret  Federico Páez-Osuna 《Environmental Geology》2008,54(7):1537-1545

Concentrations of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were measured in 13 surficial sediment samples collected at three lacustrine locations in the surroundings of Mexico City and four coastal areas of the States of Sinaloa, Sonora, Oaxaca and Veracruz. Total PCB concentrations span the interval 3.18–621 ng g⁻¹. The highest values (63.7–621 ng g⁻¹) were found in Mexico City, which is a highly anthropogenically impacted area, whereas low concentrations (3.18–12.9 ng g⁻¹) were characteristic of seven places, some of them subject to intense hydrodynamics. In these latter cases, values increase by 18–73 times if normalised against the fine fraction (silt plus clay) content in sediment. Two samples from Mexico City exceed the ERM (Effect Range Median) guidelines and are likely to cause adverse effects. Samples contain only lower chlorinated PCBs (mainly 2-, 3- and 4-CB), thus suggesting that the most used PCB commercial mixture was Aroclor 1242. The homologue composition of the sample taken close to the nuclear power plant of Laguna Verde is identical to this commercial mixture. PAHs in the same samples have relatively low concentrations (14.9–287 ng g⁻¹), well below ERL (Effect Range Low) guidelines. The composition of PAH mixtures accounts for the influence of both petrogenic and pyrolitic sources, with these latter prevailing at some places in Mexico City.  相似文献