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91.
The late Hercynian tectonic evolution of the Calabria crust is characterized by peak metamorphic conditions up to 800 °C and 1000 MPa, and coeval mid‐crustal granitoid emplacement at 304–300 Ma. To check if a post‐collisional extensional framework, similar to that of other Hercynian massifs, can explain petrologic data, we model the pressure–temperature evolution of the crust during extension following granitoid emplacement. Model parameters are constrained by petrologic, geochemical and structural data. Computed P–T paths are characterized by nearly isothermal decompression followed by isobaric cooling, which show a good fit to petrologic P–T paths for duration of extension between 5 and 10 Ma. The model results, therefore, support an interpretation of the magmatic and metamorphic evolution of the Calabria crust in terms of the late Hercynian extension. In this framework, slab break‐off is a reasonable explanation for the common evolution of the southern European Hercynian massifs. 相似文献
92.
We modelled thermo-rheological perturbations, related to the emplacement of a magmatic body in the upper crust. This approach was considered relevant for the areas characterized by elevated surface heat flow and chiefly for the geothermal fields. The numerical conductive thermal model applied to the Larderello geothermal area in Tuscany, allowed to constrain size, depth and timing of emplacement of the pluton. We inferred that the emplacement of a magmatic body, at a minimum depth of 3 km, having a horizontal extension of 14 km and a maximum thickness of 8 km, can reasonably reproduce the observed regional surface heat flow anomaly of the Larderello area, when 300 (± 100) kyr are elapsed from the magma emplacement. Even assuming an incremental growth, the first magma injection should not be older than 1 ± 0.3 Ma.
Results of the thermal model were used to set up a rheological model and to simulate the drifting of the brittle-ductile transition during the cooling of the pluton. A comparison with the K-horizon profile, a prominent seismic reflector in the Larderello area, was then performed. It was found that the K-horizon approximately corresponds with the pluton roof and with the current location of the brittle-ductile transition. 相似文献
93.
Design of hysteretic dampers with optimal ductility for the transverse seismic control of cable‐stayed bridges 下载免费PDF全文
Alfredo Camara Roberto Cristantielli Miguel A. Astiz Christian Málaga‐Chuquitaype 《地震工程与结构动力学》2017,46(11):1811-1833
Cable‐stayed bridges require a careful consideration of the lateral force exerted by the deck on the towers under strong earthquakes. This work explores the seismic response of cable‐stayed bridges with yielding metallic dampers composed of triangular plates that connect the deck with the supports in the transverse direction. A design method based on an equivalent single‐degree of freedom approximation is proposed. This is proved valid for conventional cable‐stayed bridges with 200‐ and 400‐m main spans, but not 600 m. The height of the plates is chosen to (1) achieve a yielding capacity that limits the maximum force transmitted from the deck to the towers, and to (2) control the hysteretic energy that the dampers dissipate by defining their design ductility. In order to select the optimal ductility and the damper configuration, a multi‐objective response factor that accounts for the energy dissipation, peak damper displacement and low‐cycle fatigue is introduced. The design method is applied to cable‐stayed bridges with different spans and deck–support connections. The results show that the dissipation by plastic deformation in the dampers prevents significant damage in the towers of the short‐to‐medium‐span bridges under the extreme seismic actions. However, the transverse response of the towers in the bridge with a 600‐m main span is less sensitive to the dampers. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
94.
Sedimentation processes in reservoirs can be studied by performing theoretical analysis laboratory experimentation numerical simulation or a combination of these three methods. Available literature focused on reservoirs is abundant.…… 《国际泥沙研究》2007,22(1):80-86
Sedimentation processes in reservoirs can be studied by performing theoretical analysis, laboratory experimentation, numerical simulation, or a combination of these three methods. Available literature focused on reservoirs is abundant. For instance, the works conducted by Hotchkiss and Parker (1991), Morris and Fan (1997), and De Cesare et al. 相似文献
95.
Patrick F. Dobson Teamrat A. Ghezzehei Paul J. Cook J. Alfredo Rodríguez-Pineda Lourdes Villalba Rodrigo De la Garza 《Hydrogeology Journal》2012,20(1):155-166
A study of seepage occurring in an adit at the Nopal I uranium mine in Chihuahua, Mexico, was conducted as part of an integrated natural analogue study to evaluate the effects of infiltration and seepage on the mobilization and transport of radionuclides. An instrumented seepage collection system and local automated weather station permit direct correlation between local precipitation events and seepage. Field observations recorded between April 2005 and December 2006 indicate that seepage is highly heterogeneous with respect to time, location, and quantity. Seepage, precipitation, and fracture data were used to test two hypotheses: (1) that fast flow seepage is triggered by large precipitation events, and (2) that an increased abundance of fractures and/or fracture intersections leads to higher seepage volumes. A few zones in the back adit recorded elevated seepage volumes immediately following large (>20 mm/day) precipitation events, with transit times of less than 4 h through the 8-m thick rock mass. In most locations, there is a 1?C6 month time lag between the onset of the rainy season and seepage, with longer times observed for the front adit. There is a less clear-cut relation between fracture abundance and seepage volume; processes such as evaporation and surface flow along the ceiling may also influence seepage. 相似文献
96.
Samuel Angiboust Mostafa Fayek Ian M. Power Alfredo Camacho Georges Calas Gordon Southam 《Mineralium Deposita》2012,47(8):859-874
Epithermal uranium deposits of the Sierra Pe?a Blanca are classic examples of volcanic-hosted deposits and have been used as natural analogs for radionuclide migration in volcanic settings. We present a new genetic model that incorporates both geochemical and tectonic features of these deposits, including one of the few documented cases of a geochemical signature of biogenic reducing conditions favoring uranium mineralization in an epithermal deposit. Four tectono-magmatic faulting events affected the volcanic pile. Uranium occurrences are associated with breccia zones at the intersection of fault systems. Periodic reactivation of these structures associated with Basin and Range and Rio Grande tectonic events resulted in the mobilization of U and other elements by meteoric fluids heated by geothermal activity. Focused along breccia zones, these fluids precipitated under reducing conditions several generations of pyrite and uraninite together with kaolinite. Oxygen isotopic data indicate a low formation temperature of uraninite, 45–55°C for the uraninite from the ore body and ~20°C for late uraninite hosted by the underlying conglomerate. There is geochemical evidence for biological activity being at the origin of these reducing conditions, as shown by low δ34S values (~?24.5‰) in pyrites and the presence of low δ13C (~?24‰) values in microbial patches intimately associated with uraninite. These data show that tectonic activity coupled with microbial activity can play a major role in the formation of epithermal uranium deposits in unusual near-surface environments. 相似文献
97.
Alfredo E. Zurita Alfredo A. Carlini David Gillette Rodolfo Sánchez 《Journal of South American Earth Sciences》2011,31(2-3):178-185
Knowledge of the main aspects of the Great American Biotic Interchange (GABI) concerning the glyptodontine Glyptodontidae (Xenarthra) is very scarce. A bidirectional dispersal process was recently proposed for this clade, with the presence of the North American genus Glyptotherium Osborn recognized in latest Pleistocene sediments of northern South America (Venezuela and Brazil). However, the earliest stages of this paleobiogeographical process remain poorly understood, mainly because of the limited fossil record on this clade in late Pliocene sediments. The goals of this contribution are: a) to present and describe the first record of a glyptodontine glyptodontid from the late Pliocene of northern South America, tentatively assigned to a new species of Boreostemma Carlini et al. (Boreostemma? sp. nov); and b) to analyze its paleobiogeographical implications with respect to the GABI. This new material was recovered from the San Gregorio Formation (late Pliocene, prior the GABI) in northern Venezuela, where it is represented by several osteoderms of the dorsal carapace. A comparison among the three known late Pliocene glyptodontine glyptodontids of a) southern South America (Paraglyptodon), b) northern South America (Boreostemma), and c) southern North America ("Glyptotherium"), reveals a series of shared characters between (b) and (c), not present in (a). The most important of these shared characters in (b) and (c) are: all the osteoderms present a great development of the central figure, which is always larger than the peripherals; the sulcus that delimits the central and peripheral figures is narrower and shallower; and all the osteoderms present are relatively thin. This evidence suggests that the lineage of Glyptodontinae which participated in the GABI and subsequently diversified in North America originated in northern South America. Moreover, the evident morphological differences between these glyptodontines with respect to the southern South American forms show a significant separation of both lineages since at least latest Miocene-early Pliocene. 相似文献
98.
Long-Term Profiles of Wind and Weibull Distribution Parameters up to 600 m in a Rural Coastal and an Inland Suburban Area 总被引:1,自引:1,他引:0
Sven-Erik Gryning Ekaterina Batchvarova Rogier Floors Alfredo Peña Burghard Brümmer Andrea N. Hahmann Torben Mikkelsen 《Boundary-Layer Meteorology》2014,150(2):167-184
An investigation of the long-term variability of wind profiles for wind energy applications is presented. The observations consists of wind measurements obtained from a ground-based wind lidar at heights between 100 and 600 m, in combination with measurements from tall meteorological towers at a flat rural coastal site in western Denmark and at an inland suburban area near Hamburg in Germany. Simulations with the weather research and forecasting numerical model were carried out in both forecast and analysis configurations. The scatter between measured and modelled wind speeds expressed by the root-mean-square error was about 10 % lower for the analysis compared to the forecast simulations. At the rural coastal site, the observed mean wind speeds above 60 m were underestimated by both the analysis and forecast model runs. For the inland suburban area, the mean wind speed is overestimated by both types of the simulations below 500 m. When studying the wind-speed variability with the Weibull distribution, the shape parameter was always underestimated by the forecast compared to both analysis simulations and measurements. At the rural coastal site although the measured and modelled Weibull distributions are different their variances are nearly the same. It is suggested to use the shape parameter for climatological mesoscale model evaluation. Based on the new measurements, a parametrization of the shape parameter for practical applications is suggested. 相似文献
99.
An approach to analyze regime change in spatial time series datasets is followed and extended to jointly analyze a dynamical
model depicting regime shift and observational data informing the same process. We analyze changes in the joint model–data
regime and covariability within each regime. The method is applied to two observational datasets of equatorial sea surface
temperature (TAO/TRITON array and satellite) and compared with the predicted data by the ECCO-JPL modeling system. 相似文献
100.
Juana Vegas Blanca Ruiz‐Zapata José E. Ortiz Luis Galán Trinidad Torres Ángel García‐Cortés María J. Gil‐García Alfredo Pérez‐González José L. Gallardo‐Millán 《第四纪科学杂志》2010,25(7):1051-1062
Geochemical (element analysis, molecular analysis of organic compounds), physical, palynological, mineralogical and sedimentary facies analysis were performed to characterise the sedimentary record in Fuentillejo maar‐lake in the Central Spanish Volcanic Field of Campo de Calatrava, in order to reconstruct the palaeoenvironmental and palaeoclimatic processes which controlled vegetation patterns and deposition of different sedimentary facies. The upper 20 m of core FUENT‐1 show variations in clastic input, water chemistry, vegetation and organic fraction sources in the lake throughout the Late Pleistocene and Holocene. The temporal framework provided by 14C accelerator mass spectrometry dating allows assigning the sequence to the last 50 cal. ka BP. Arid phases identified in the FUENT‐1 sequence are correlated to Heinrich events (HE) and to stadials of the Dansgaard/Oeschger (D/O) cycles. Siliciclastic facies with high magnetic susceptibility values, high Juniperus pollen content, a low Paq index (aquatic macrophysics proxy index), a decrease in the relative percentage of the n‐C27 and an increase in the n‐C31 alkanes are indicative of arid and colder climatic events related to HE 2, HE 1 and the Younger Dryas (YD). Similar short cold and arid phases during the Holocene were identified at 9.2–8.6, 7.5–7 and 5.5–5 cal. ka BP. In dolomite–mud facies, the pollen data show an increase in the herbs component, mainly – Chenopodiaceae, Artemisia and Ephedra – steppe taxa; a low Paq index, a decrease in the relative percentage of the n‐C27 alkane and an increase in the n‐C31 alkane are also observed. This facies was probably the result of lower lake levels and more saline–alkaline conditions, which can be interpreted as linked to arid–warm periods. These warm and arid phases were more frequent during Marine Isotope Stage (MIS) 3 and the interstadials of MIS 2. HE 4, HE 2, HE 1 and the YD in core FUENT‐1 were immediately followed by increases of warm steppe pollen assemblages that document rapid warming similar to the D/O cycles but do not imply increasing humidity in the area. Fuentillejo hydrology is controlled by changes in the atmospheric and oceanic systems that operated on the North Atlantic region at millennial scale during the last 50 cal. ka BP. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献