The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps   总被引：1，自引：0，他引：1  

Giovanni Grieco  Alfredo Ferrario  Edmond A. Mathez 《Ore Geology Reviews》2004,24(3-4):299

The magmatic metasomatism that was responsible for producing chromitite–dunite bodies in the unusual phlogopite peridotite of the Finero Complex in Permian to Triassic times also influenced the Cr-platinum group elements (PGE) mineralization. At least the end stages of this metasomatism are recorded in compositional zoning of chromite grains in the podiform chromitite. Metasomatic melt, with or without vapor, reacted with chromite to produce core-to-rim Cr enrichment of extant chromite grains and was concurrent with pyroxene crystallization. Under conditions of lower melt/rock ratio, metasomatism resulted in core-to-rim Al enrichment in chromite and crystallization of amphibole between chromite and clinopyroxene. This early, high-temperature metasomatism is unrelated to the later and pervasive K-metasomatism that crystallized phlogopite and was associated with the intrusion of clinopyroxenite dikes that cut the peridotite. Much later, serpentinization of olivine locally depleted chromite in Al and enriched it in Fe and formed minor amounts of magnetite.The PGE, which are present mainly as laurite inclusions in chromite, were remobilized by the early metasomatism. This resulted in substantial variation in the PGE contents of chromitites and imposed a characteristic PGE pattern in which chondrite-normalized Os, Ir, Ru and Rh contents are high but Pt and Pd contents are low. The slopes of PGE chondrite-normalized concentration patterns are systematically related to absolute PGE abundance and to rock mode. Chromitites with low modal orthopyroxene, clinopyroxene, and amphibole exhibit negative PGE slopes and contain relatively high PGE concentrations, whereas chromitites rich in these silicate minerals have positive slopes and low PGE contents.  相似文献   

Detection of displacements on Tenerife Island, Canaries, using radar interferometry   总被引：1，自引：0，他引：1  

José Fernández  Rosana Romero  Daniel Carrasco  Kristy F. Tiampo  Gema Rodríguez-Velasco  Alfredo Aparicio  Vicente Araña  F. J. González-Matesanz 《Geophysical Journal International》2005,160(1):33-45

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Life‐cycle cost analysis based on a renewal model of earthquake occurrences     

Yuji Takahashi  Armen Der Kiureghian  Alfredo H‐S. Ang 《地震工程与结构动力学》2004,33(7):859-880

A decision methodology for the management of seismic risk of a single building is presented. The decision criterion aims at minimizing the expected life‐cycle cost, including the initial cost of the design and the expected cost of damage due to future earthquakes. The expected life‐cycle cost of each design alternative is formulated using a renewal model for the occurrence of earthquakes in a seismic source, which accounts for the temporal dependence between the occurrence of ‘characteristic’ earthquakes. The formulation involves the expected damage cost from an earthquake of specified magnitude in a given source. This term is estimated by simulating the processes of fault rupture, elastic wave propagation, surface soil amplification, dynamic structural response and generation of damage costs. As an example, the methodology is applied to an actual office building in Tokyo. A simple decision problem between two design alternatives is set: a bare steel moment frame, and the same frame equipped with oil dampers. Through this case study, the installation of the oil dampers is demonstrated to be effective in reducing the life‐cycle cost of the building under consideration. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Hydrogeology and Paleohydrology of Ancient Machu Picchu   总被引：1，自引：0，他引：1  

Kenneth R. Wright  Gary D. Witt  Alfredo Valencia Zegarra 《Ground water》1997,35(4):660-666

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Lifeline response to spatially variable ground motions     

Aspasia Zerva  Alfredo H-S. Ang  Y. K. Wen 《地震工程与结构动力学》1988,16(3):361-379

Lifeline systems have been heavily damaged during past earthquakes; this has often been attributed to the effect of differential ground motion at the supports of these long structures. Based on a stochastic model for the ground excitation the responses of pipelines and bridges of various span lengths subjected to either perfectly or partially correlated random input motions in the axial, lateral (i.e. transverse horizontal) and vertical directions are investigated and the significance of the spatial variation of ground motion is examined.  相似文献   

Iron,manganese and trace metal concentrations in seaweeds from the central west coast of the Gulf of California     

Miguel Angel Huerta-Diaz  Francisco de León-Chavira  María Lucila Lares  Alfredo Chee-Barragán  Arturo Siqueiros-Valencia 《Applied Geochemistry》2007

Concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn in four macroalgae species (Ulva lactuca, Chondracanthus squarrulosus, Sargassum sinicola and Gracilariopsis lemaneiformis) were obtained for the first time from the central part of the west coast of the Gulf of California. Generally, no differences in metal concentrations were found among the different seaweed species, although spatial differences were apparent. Iron, Mn and Cu exhibited higher concentrations at the stations located in front of Angel de la Guarda Island, probably because of high vertical mixing processes present in the zone. The results were compared with dissolved metal concentrations reported for the Gulf of California (Cd, Mn and Fe) and the North Pacific Ocean. The resulting linear regression of the results vs. North Pacific Ocean concentrations indicated that the levels of Cu, Ni and Zn measured in this study were within its 95% confidence level. Furthermore, this comparison was capable of detecting dissolved Fe and Mn enrichments in Gulf of California waters relative to the North Pacific Ocean concentrations. Calculations of total masses of metals associated with algal biomass on the west coast of the Gulf of California indicated that the lowest masses were represented by Cu (108 ± 25 kg) and Ni (184 ± 52 kg), whereas Pb (1.1 ± 0.6 ton) and Fe (10.9 ± 8.5 ton) were the elements with the highest associated masses.  相似文献   

Pressure–temperature evolution of the late Hercynian Calabria continental crust: compatibility with post‐collisional extensional tectonics     

Alfredo Caggianelli  Domenico Liotta  Giacomo Prosser  Giorgio Ranalli 《地学学报》2007,19(6):502-514

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   

Regional thermo-rheological field related to granite emplacement in the upper crust: implications for the Larderello area (Tuscany,Italy)     

Federica Rochira  Alfredo Caggianelli  Salvatore de Lorenzo 《Geodinamica Acta》2018,30(1):225-240

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   

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   

DISCUSSION ON ＂NUMERICAL SIMULATION OF SEDIMENT RELEASE FROM RESERVOIRS＂ （No. 1, 2006） BY KHOSROWNEJAD A. AND NEISHABORI A.     

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