Nb-Ta-minerals from the cap de creus pegmatite field,eastern Pyrenees: distribution and geochemical trends   总被引：2，自引：0，他引：2  

P. Alfonso Abella  J. -C. Melgarejo i Draper  M. Corbella i Cordomi 《Mineralogy and Petrology》1995,55(1-3):53-69

Summary Internal structure and mineralogy facilitate distinction of four main pegmatite types at the eastern end of the Pyrenees. Three main trends in compositional variations in Nb-Ta-Sn-REE-Ti minerals have been established: a regional trend, with Ta/(Ta + Nb) ratio increasing towards the more evolved pegmatites, Mn/(Mn + Fe) being relatively low and increasing only slightly; a single-body trend, with similar enrichment toward the late pegmatite units; a single-crystal trend, with zoning related to both Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios and a tendency toward Ta-enrichment in the late growth stages. The regional geochemical enrichment trends in the Mn/(Mn + Fe) ratios and Ta/(Ta + Nb) are those expected for a beryl-columbite pegmatite type. In a single pegmatite, the evolution depends on the simultaneous growth of other mineral species. Three factors seem to control the development of zoning in columbite-tantalite crystals: availability of Mn, Ta, Fe, Nb, significant differences in solubility between mineral group end members and re-equilibria with late pegmatite fluids.

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Nb-Ta-Minerale aus dem Pegmatit-Feld vom Cap de Creus, östliche Pyrenäen: Verteilung und geochemische Trends

Zusammenfassung Am Ostrand der Pyrenäen können anhand des inneren Aufbaus und der Mineralogie vier Haupttypen von Pegmatiten unterschieden werden. Die Zusammensetzungen von Nb-Ta-Sn-SEE-Ti-Mineralen folgen drei Haupttrends: einem regionalen Trend, bei dem das Verhältnis Ta/(Ta + Nb) zu den höher entwickelten Pegmatiten hin zunimmt, während Mn/(Mn + Fe) relativ niedrig ist und nur leicht zunimmt; einem lokalen (auf das jeweilige Vorkommen beschränkten) Trend mit einer ähnlichen Anreicherung zu den spätpegmatitischen Einheiten hin; einem auf Einzelkristalle bezogenen Trend mit Zonierung in bezug auf die Verhältnisse Ta/(Ta + Nb) und Mn/(Mn + Fe) und einer Tendenz zur T a-Anreicherung in den späten Wachstumsphasen. Die regionalen geochemischen Anreicherungstrends in den Mn/(Mn + Fe)- und Ta/(Ta + Nb)-Verhältnissen entsprechen jenen, wie sie für den Beryll-Columbit-Pegmatit-Typ erwartet werden. In einem einzelnen Pegmatit hängt die Entwicklung vom gleichzeitigen Wachstum anderer Mineral-Spezies ab. Drei Faktoren scheinen die Ausbildung einer Zonierung in Columbit-Tantalit-Kristallen zu kontrollieren: das Angebot an Mn, Ta, Fe und Nb, deutliche Unterschiede in der Löslichkeit der Endglieder von Mineralgruppen und die Iteequilibrierung mit spätpegmatitischen Lösungen.

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With 6 Figures  相似文献   

A nocturnal atmospheric loss of CH<Subscript>2</Subscript>I<Subscript>2</Subscript> in the remote marine boundary layer     

Lucy J. Carpenter  Stephen J. Andrews  Richard T. Lidster  Alfonso Saiz-Lopez  Miguel Fernandez-Sanchez  William J. Bloss  Bin Ouyang  Roderic L. Jones 《Journal of Atmospheric Chemistry》2017,74(2):145-156

Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH₂I₂) and chloro-iodomethane (CH₂ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH₂I₂ and CH₂ICl in air and of CH₂I₂ in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH₂I₂ was lower in amplitude than that of CH₂ICl, despite its faster photolysis rate. We speculate that night-time loss of CH₂I₂ occurs due to reaction with NO₃ radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k _CH2I2+NO3 of ≤4 × 10^?13 cm³ molecule^?1 s^?1; a previous kinetic study carried out at ≤100 Torr found k _CH2I2+NO3 of 4 × 10^?13 cm³ molecule^?1 s^?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m^?2 d^?1 for CH₂I₂ and 3.7 +/? 0.8 nmol m^?2 d^?1 for CH₂ICl), we show that the model overestimates night-time CH₂I₂ by >60 % but reaches good agreement with the measurements when the CH₂I₂ + NO₃ reaction is included at 2–4 × 10^?13 cm³ molecule^?1 s^?1. We conclude that the reaction has a significant effect on CH₂I₂ and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.  相似文献   

Mapping groundwater storage variations with GRACE: a case study in Alberta,Canada     

Jianliang Huang  Goran Pavlic  Alfonso Rivera  Dan Palombi  Brian Smerdon 《Hydrogeology Journal》2016,24(7):1663-1680

The applicability of the Gravity Recovery and Climate Experiment (GRACE) to adequately represent broad-scale patterns of groundwater storage (GWS) variations and observed trends in groundwater-monitoring well levels (GWWL) is examined in the Canadian province of Alberta. GWS variations are derived over Alberta for the period 2002–2014 using the Release 05 (RL05) monthly GRACE gravity models and the Global Land Data Assimilation System (GLDAS) land-surface models. Twelve mean monthly GWS variation maps are generated from the 139 monthly GWS variation grids to characterize the annual GWS variation pattern. These maps show that, overall, GWS increases from February to June, and decreases from July to October, and slightly increases from November to December. For 2002–2014, the GWS showed a positive trend which increases from west to east with a mean value of 12 mm/year over the province. The resulting GWS variations are validated using GWWLs in the province. For the purpose of validation, a GRACE total water storage (TWS)-based correlation criterion is introduced to identify groundwater wells which adequately represent the regional GWS variations. GWWLs at 36 wells were found to correlate with both the GRACE TWS and GWS variations. A factor f is defined to up-scale the GWWL variations at the identified wells to the GRACE-scale GWS variations. It is concluded that the GWS variations can be mapped by GRACE and the GLDAS models in some situations, thus demonstrating the conditions where GWS variations can be detected by GRACE in Alberta.  相似文献   

A unified hydrogeological conceptual model of the Milk River transboundary aquifer,traversing Alberta (Canada) and Montana (USA)     

Marie-Amélie Pétré  Alfonso Rivera  René Lefebvre  M. Jim Hendry  Attila J. B. Folnagy 《Hydrogeology Journal》2016,24(7):1847-1871

A conceptual model of the transboundary Milk River Aquifer (MRA), extending across the Canada–USA border, was developed based on literature, focused fieldwork and a three-dimensional geological model. The MRA corresponds to the Virgelle Member of the Milk River Formation (Eagle Formation in Montana, USA) and it is an important groundwater resource over a large area (25,000 km²). The Virgelle outcrops near the international border and along the Sweet Grass Arch in Montana. The down-gradient limit of the MRA is the unconformity separating the Virgelle from the gas-bearing sandy shale of the Alderson Member. The MRA is confined above by the Pakowki/Claggett Formations aquitards and below by the Colorado Group aquitard. The MRA contains higher transmissivity areas resulting in preferential flowpaths, confirmed by natural geochemical tracers. Tritium and ¹⁴C delineate restricted recharge areas along the outcrops on both sides of the international border. Drastic decreases in horizontal hydraulic gradients indicate that the Milk River intercepts a large proportion of groundwater flowing to the north from the recharge area. Downgradient of the Milk River, groundwater movement is slow, as shown by ³⁶Cl residence times exceeding 1 Ma. These slow velocities imply that groundwater discharge downgradient of the Milk River is via vertical leakage through the Colorado Group and upward along buried valleys, which act as drains and correspond to artesian areas. When confined, the MRA contains a fossil groundwater resource, not significantly renewed by modern recharge. Groundwater exploitation thus far exceeds recharge, a situation requiring properly managed MRA groundwater depletion.  相似文献   

The K-band Hubble diagram for the brightest cluster galaxies: a test of hierarchical galaxy formation models     

Alfonso Aragón-Salamanca  Carlton M. Baugh  & Guinevere Kauffmann 《Monthly notices of the Royal Astronomical Society》1998,297(2):427-434

We analyse the K -band Hubble diagram for a sample of brightest cluster galaxies (BCGs) in the redshift range 0< z <1. In good agreement with earlier studies, we confirm that the scatter in the absolute magnitudes of the galaxies is small (0.3 mag). The BCGs exhibit very little luminosity evolution in this redshift range: if q ₀=0.0, we detect no luminosity evolution; for q ₀=0.5, we measure a small negative evolution (i.e., BCGs were about 0.5 mag fainter at z =1 than today). If the mass in stars of these galaxies had remained constant over this period of time, substantial positive luminosity evolution would be expected: BCGs should have been brighter in the past, since their stars were younger. A likely explanation for the observed zero or negative evolution is that the stellar mass of the BCGs has been assembled over time through merging and accretion, as expected in hierarchical models of galaxy formation. The colour evolution of the BCGs is consistent with that of an old stellar population ( z _for>2) that is evolving passively. We can thus use evolutionary population synthesis models to estimate the rate of growth in stellar mass for these systems. We find that the stellar mass in a typical BCG has grown by a factor ≃2 since z ≃1 if q ₀=0.0, or by factor ≃4 if q ₀=0.5. These results are in good agreement with the predictions of semi-analytic models of galaxy formation and evolution set in the context of a hierarchical scenario for structure formation. The models predict a scatter in the luminosities of the BCGs that is somewhat larger than the observed one, but that depends on the criterion used to select the model clusters.  相似文献   

Littoral benthos of the saline crater lakes of the basin of Oriental, Mexico   总被引：2，自引：0，他引：2  

Javier Alcocer  Elva Escobar  Alfonso Lugo  Laura Peralta 《International Journal of Salt Lake Research》1998,7(2):87-108

Two saline crater lakes in the basin of Oriental, Puebla-Tlaxcala-Veracruz, were investigated for littoral benthic macroinvertebrates. Fifty taxa were identified with the oligochaetes, amphipods, chironomids and leeches the dominant organisms. These four taxa made up to 99 per cent in both number and biomass.Limnodrilus hoffmeisteri, Hyalella azteca, Tanypus (Apelopia) sp. andStictochironomus sp. were the most abundant organisms. Unlike other saline lakes which have a littoral benthos dominated by chironomids, Alchichica and Atexcac were dominated by oligochaetes (70–73 per cent). The gastropod,Physa sp., was found up to a salinity of 8 g L⁻¹; in other studies, it has been found in lower salinities.L. hoffmeisteri is also a typical inhabitant of freshwater lakes, particularly of deep waters. It was dominant in the shallow, saline waters of the two lakes studied. Salinity did not affect species richness. Alchichica, the most saline of the six crater lakes of Puebla (salinity, 7.4 g L⁻¹), had 30 per cent more species than the freshwater lakes, and double the species number of Atexcac. It seems the main factor controlling species richness and the density and biomass of organisms in Alchichica and Atexcac is the presence of aquatic vegetation. It does this by increasing habitat heterogeneity and providing food and protection against predators.  相似文献   

The macrobenthic fauna of a former perennial and now episodically filled mexican saline lake     

Javier Alcocer  Alfonso Lugo  Elva Escobar  Malinali Sánchez 《International Journal of Salt Lake Research》1996,5(3):261-274

Totolcingo (El Carmen), a large and now episodically filled playa lake in the east-ernmost portion of the Mexican Plateau, filled with water in 1993. Water persisted for just one month (May). Alkaline (pH 10), saline (K₂₅ up to 30,000S/cm) waters, dominated by NaHCO₃ and Na₂CO₃, characterized the lake. The fauna was depauperate. The components of the fauna wereEphydra (Hydropyrus)hians Say (ephydrid),Limnodrilus hoffmeisteri Claparède (tubificid), andBerosus sp. (Coleoptera). The species in the lake were widely dispersed and typical inhabitants of saline lakes. Possible reasons for the depauperate fauna include (a) overall physical and chemical conditions, (b) unpredictable hydrology, and (c) the short (one month) inundation period prevented colonization.  相似文献   

Hydrochemistry of waters from five cenotes and evaluation of their suitability for drinking-water supplies, northeastern Yucatan, Mexico     

Javier Alcocer  Alfonso Lugo  Luis E. Marín  Elva Escobar 《Hydrogeology Journal》1998,6(2):293-301

 Waters from five cenotes that are currently being used for aquatic recreational activities and that lie along the Cancun–Tulum touristic corridor, Mexico, were evaluated hydrochemically to determine whether the cenotes may be considered as potential drinking-water sources. Several parameters exceed the Mexican Drinking Water Standards (MDWS), but since they do not pose a significant health threat, four of the five cenotes may be used as drinking-water sources. The common contaminants in the Yucatan Peninsula, fecal coliforms and nitrate, are in most cases below the MDWS (0–460 MPN/100 ml and 0.31–1.18 mg/L, respectively). Although these four cenotes meet the MDWS, a careful groundwater management policy needs to be developed to avoid contamination (fecal and nitrates) and salt-water intrusion. Received, October 1996 Revised, June 1997; March 1998 Accepted, July 1997  相似文献   

The Hyblean xenolith suite (Sicily): an unexpected legacy of the Ionian–Tethys realm     

Fabio Carmelo Manuella  Vittorio Scribano  Serafina Carbone  Alfonso Brancato 《International Journal of Earth Sciences》2015,104(5):1317-1336

The extensive study of a great number of deep-seated xenoliths from Tortonian tuff-breccia pipes in the Hyblean area (Sicily) revealed the following fundamental evidence: (1) typical continental crust rocks are completely absent in the entire xenolith suite; (2) mantle ultramafics are more abundant than gabbroids; (3) sheared oxide–gabbros, closely resembling those from oceanic fracture zones, are relatively common; (4) secondary mineral assemblages, compatible with alteration processes in serpentinite-hosted hydrothermal systems, occur both in peridotites and gabbros. Among the products of this hydrothermal activity, organic compounds, having abiotic origin via Fischer–Tropsch synthesis, occur in some hydrothermally altered gabbro and ultramafic xenoliths, as well as in hydrothermal clays. Moreover, the U–Pb dating of hydrothermal zircon grains, hosted in a xenolith of metasomatized tectonic breccia, indicated an Early–Middle Triassic age of the fossil hydrothermal system. Another line of evidence for the oceanic nature of the Hyblean–Pelagian basement is the complete absence of continental crust lithologies (granites, felsic metaigneous, and metasedimentary rocks) in outcrops and in boreholes, and the oceanic affinity of the Tertiary volcanic rocks from the Hyblean Plateau and the Sicily Channel (Pantelleria and Linosa Islands), which lack of any geochemical signature for continental crust contamination. A reappraisal of existing geophysical data pointed out that serpentinites form the dominant lithologies in the lithospheric basement of the Hyblean–Pelagian area down to a mean depth of 19 km, which represents the regional Moho considered as the serpentinization front, marking the transition from serpentinites to unaltered peridotites. On these grounds, we confirm that Hyblean xenoliths contain mineralogical, compositional, and textural evidence for tectonic, magmatic, and hydrothermal processes indicating the existence of fossil oceanic core complexes, in the geotectonic framework of the Paleo–Mesozoic, ultra-slow spreading, Ionian–Tethys Ocean forming the present Ionian–Hyblean–Pelagian domain.  相似文献   

Equivalent viscous damping for displacement-based seismic design of hysteretic damped braces for retrofitting framed buildings   总被引：2，自引：2，他引：0  

Fabio Mazza  Alfonso Vulcano 《Bulletin of Earthquake Engineering》2014,12(6):2797-2819

A displacement-based design (DBD) procedure aiming to proportion hysteretic damped braces (HYDBs) in order to attain, for a specific level of seismic intensity, a designated performance level of a structure is proposed for the retrofitting of framed buildings. A key step for the reliability of the DBD procedure is the selection of the equivalent viscous damping in order to account for the energy dissipated by the damped braced frame. In this paper, expressions of the equivalent damping are obtained considering the energy dissipated by the HYDBs and the framed structure. To this end, dynamic analyses of an equivalent single degree of freedom system, whose response is idealized by a trilinear model, are carried out considering real accelerograms matching, on the average, Eurocode 8 (EC8) response spectrum for a medium subsoil class. Then, a three-storey reinforced concrete (r.c.) framed structure of a school building, designed in a medium-risk seismic region according to the Italian code in force in 1975, is supposed as retrofitted as if in a high-risk seismic region of the current seismic code (NTC08) by the insertion of HYDBs. Nonlinear static analyses are carried out to evaluate the vulnerability of the primary structure, characterized by the lack of interior girders along the floor slab direction, and to select optimal properties of the HYDBs. The effectiveness of the retrofitting solutions is checked referring to nonlinear dynamic analyses, considering artificially generated accelerograms whose response spectra match those adopted by NTC08 for the earthquake design levels corresponding to the serviceability and ultimate limit states.  相似文献