Petrographic and microthermometrical studies of emeralds in the ‘Garimpo’ of Capoeirana,Nova Era,Minas Gerais State,Brazil     

J. L. de Souza  J. C. Mendes  R. M. da Silveira Bello  D. P. Svisero  J. V. Valarelli 《Mineralium Deposita》1992,27(2):161-168

Petrographic investigations in the area of the Capoeirana emerald deposit, Minas Gerais State, revealed two main lithostructural units. The first unit is comprised of gneissic rocks of granitic composition belonging to the basement complex, and the second is composed of a highly weathered metasedimentary-metavolcanic sequence represented by metapelitic schists, amphibolites, schists derived from ultramafic rocks, and quartzites. Quartz and pegmatoid veins appear near the contacts between the gneissic rocks and the mineralization metasedimentary-metavolcanic sequence. The emerald mineralization is dominantly concentrated within the intercalations of meta-ultramafic schists near the contact of the pegmatoid veins. Microthermometric studies of the fluid inclusions of the emerald grains indicate that crystallization occurred in the pressure and temperature ranges of 2000 to 2750 bar and 450 to 650 °C, respectively. These data suggest that the mineralizing solutions have had a late hydrothermal-pneumatolytic origin characterized by low pressures, suggestive of the paragenesis talc + tremolite + carbonate + biotite-phlogopite + chlorite of the emerald wall rocks.  相似文献   

Direct dating of Plio-Quaternary pumices by Ar/Ar step-heating and single-grain laser fusion methods: the example of the Monts-Dore massif (Massif Central, France)     

Gilbert Fraud  Philippe Lo Bello  Chris M. Hall  Jean-Marie Cantagrel  Derek York  Michel Bernat 《Journal of Volcanology and Geothermal Research》1990,40(1)

K-feldspars separated from Plio-Quaternary pumice flows of the Monts-Dore massif (Massif Central, France) give ⁴⁰Ar/³⁹Ar saddle-shaped age spectra. Laser-probe analysis of hand-picked single grains gives ages in agreement with those of overlying and underlying lava flows previously dated by the conventional K-Ar method. The laser-probe ages are lower than the minimum ages measured on the populations of grains by the step-heating method. As previously suggested by Lo Bello and co-workers for the pumice flow of Neschers belonging to the same volcanic massif, the saddle-shaped age spectra are ascribed to the different Ar-release patterns of two populations of K-feldspars: (1) young sanidine phenocrysts of the pumices; and (2) old K-feldspars plucked from the Hercynian basement during the explosive eruption. Measurements of both the granitic rocks from surrounding areas and the granitic xenoliths included in pumices give ages around 330 Ma and show that most of the xenocrysts included in the pumices did not lose significant amounts of argon during the eruption. With the ⁴⁰Ar/³⁹Ar step-heating method, we were able to detect contamination of Quaternary K-feldspars by Hercynian K-feldspars as low as 0.25. Because pumice flows of the Monts-Dore massif crop out over large areas, these new ages will be useful for establishing a precise stratigraphy of the European Plio-Quaternary.  相似文献   

Lateral variability of flow over a sill in a channel of southern Chile     

Mario Cáceres  Arnoldo Valle-Levinson  Carlos Molinet  Manuel Castillo  Monica Bello  Carlos Moreno 《Ocean Dynamics》2006,56(3-4):352-359

Measurements of velocity and density profiles were used to describe the tidal and mean flow structure across and along a sill in Refugio Channel, a fjord-like inlet in Southern Chile (43.9°S). These are the first oceanographic measurements of any kind effected in Refugio Channel. Current profiles were obtained with a 307.2-kHz acoustic Doppler current profiler during two semidiurnal cycles along a repeated triangular circuit. Two along-channel transects formed the sides of the triangle that crossed the sill and were identified as the western and eastern transects. One cross-channel transect, the base of the triangle, was located on the seaward side of the sill. Density profiles were obtained at the corners of the triangle. The longitudinal mean flow in the western transect showed a two-layer exchange structure over the landward side of the sill. The structure of net seaward flow at the surface and landward flow at depth was disrupted by the sill in such a way that over the seaward side of the sill, only seaward flow was observed throughout the water column. This likely resulted from the blocking of landward net flow by the sill. In the eastern transect, two-layer exchange dominated over most of the transect and was consistent with the observed density profiles. Over the seaward side of the sill, a surface layer, ∼10m deep, flowed landward as a third layer. This feature should have been caused by river input further seaward (to the north) and produced a surface convergence region over the sill. In terms of tidal flows, the greatest tidal current amplitudes were 40cm s⁻¹ over the sill as the flow accelerated through the reduced cross-sectional area of the channel. Near-surface flow convergences were identified over both along-channel transects.  相似文献   

A comment on: ‘TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz’, by Jay B. Thomas,E. Bruce Watson,Frank S. Spear,Philip T. Shemella,Saroj K. Nayak and Antonio Lanzirotti     

Colin J. N. Wilson  Terry M. Seward  Aidan S. R. Allan  Bruce L. A. Charlier  Léa Bello 《Contributions to Mineralogy and Petrology》2012,164(2):359-368

Trace concentrations of Ti in quartz are used to indicate the pressure and temperature conditions of crystallization in the ‘TitaniQ’ geothermobarometer of Thomas et al. (Contrib Miner Petrol 160:743–759, 2010). It utilises the partitioning of Ti into quartz as an indicator of the pressures and/or temperatures of crystal growth. For a given value of TiO₂ activity in the system, if temperatures are inferred to ±20 °C, pressure is constrained to ±1 kbar and vice versa. There are significant contrasts, however, between the conclusions from TitaniQ and those for natural quartz (as well as other mineral phases) in volcanic rocks. Application of the TitaniQ model to quartz from the 27 ka Oruanui and 760 ka Bishop high-silica rhyolites, where the values of T, P and TiO₂ activity are constrained by other means (Fe–Ti oxide equilibria, melt inclusion entrapment pressures in gas-saturated melts, melt and amphibole compositions), yields inconsistent results. If realistic values are given to any two of these three parameters, then the value of the third is wholly unrealistic. The model yields growth temperatures at or below the granite solidus, pressures in the lower crust or upper mantle, or TiO₂ activities inconsistent with the mineralogical and chemical compositions of the magmas. CL imagery and measurements of Ti (and other elements) in quartz are of great value in showing the growth histories and changes in conditions experienced by crystals, but direct linkages to P, T conditions during crystal growth cannot be achieved.  相似文献   

The 1.5 meter solar telescope GREGOR     

W. Schmidt  O. von der Lühe  R. Volkmer  C. Denker  S.K. Solanki  H. Balthasar  N. Bello Gonzlez  Th. Berkefeld  M. Collados  A. Fischer  C. Halbgewachs  F. Heidecke  A. Hofmann  F. Kneer  A. Lagg  H. Nicklas  E. Popow  K.G. Puschmann  D. Schmidt  M. Sigwarth  M. Sobotka  D. Soltau  J. Staude  K.G. Strassmeier  T.A. Waldmann 《Astronomische Nachrichten》2012,333(9):796-809

The 1.5 m telescope GREGOR opens a new window to the understanding of solar small‐scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro‐polarimeter for the visible wavelength range, the GRating Infrared Spectro‐polarimeter (GRIS) and the Broad‐Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe’s largest solar telescope and number 3 in the world. Its all‐reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150″. GREGOR is equipped with a high‐order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro‐polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Estimation of thermal inertia of Abeokuta Ogun State,southwestern Nigeria     

H.I. Kuforiji  O.D. Akinyemi  M.A. Busari  R. Bello 《Arabian Journal of Geosciences》2017,10(6):150

Thermal inertia (I) is an important parameter in the Earth’s thermal study. There is no doubt that correct and up-to-date knowledge of thermal inertia particularly as it is affected by the land use/cover will provide good and useful information to agriculturists and environmental scientists. In this work, thermal inertia of Abeokuta City of Ogun State, southwestern Nigeria, was determined. Map of the study area was gridded using 2-min resolution which gave 5 × 5 sampling points from where core samples were collected. Bulk density (ρ _s ), thermal conductivity (λ _s ), and heat capacity (C _s ) of the samples were determined. The pattern of variation of the city view of I (in the order of ×10³ Jm^?2 s^?1/2 K^?1) showed that the main urban built-up part of the study area, Abeokuta South, had the highest I _mean, 0.76160 with standard deviation of 0.032547 and standard error of 0.01455541. The trend also varied along each sampling latitudinal line. It ranges between 0.509 and 0.756 on latitude 7° 14′, 0.557 and 0.768 on latitude 7° 12′, 0.642 and 0.782 on latitude 7° 10′, 0.7 and 0.794 on latitude 7° 08′, and between 0.642 and 0.728 on latitude 7° 06′. Hence, we have estimated thermal inertia of Abeokuta using the thermophysical properties of the study area. Thermal inertia tends to gradually decrease with distance from the city center (Abeokuta South). This result is promising in possible future consideration of urban ground heat energy conversion to other forms of energy.  相似文献   

Sn-polymetallic greisen-type deposits associated with late-stage rapakivi granites, Brazil: fluid inclusion and stable isotope characteristics   总被引：3，自引：0，他引：3  

Jorge S. Bettencourt  Washington B. Leite Jr.  Claudio L. Goraieb  Irena Sparrenberger  Rosa M.S. Bello  Bruno L. Payolla 《Lithos》2005,80(1-4):363-386

Tin-polymetallic greisen-type deposits in the Itu Rapakivi Province and Rondônia Tin Province, Brazil are associated with late-stage rapakivi fluorine-rich peraluminous alkali-feldspar granites. These granites contain topaz and/or muscovite or zinnwaldite and have geochemical characteristics comparable to the low-P sub-type topaz-bearing granites. Stockworks and veins are common in Oriente Novo (Rondônia Tin Province) and Correas (Itu Rapakivi Province) deposits, but in the Santa Bárbara deposit (Rondônia Tin Province) a preserved cupola with associated bed-like greisen is predominant. The contrasting mineralization styles reflect different depths of formation, spatial relationship to tin granites, and different wall rock/fluid proportions. The deposits contain a similar rare-metal suite that includes Sn (±W, ±Ta, ±Nb), and base-metal suite (Zn–Cu–Pb) is present only in Correas deposit. The early fluid inclusions of the Correas and Oriente Novo deposits are (1) low to moderate-salinity (0–19 wt.% NaCl eq.) CO₂-bearing aqueous fluids homogenizing at 245–450 °C, and (2) aqueous solutions with low CO₂, low to moderate salinity (0–14 wt.% NaCl eq.), which homogenize between 100 and 340 °C. In the Santa Bárbara deposit, the early inclusions are represented by (1) low-salinity (5–12 wt.% NaCl eq.) aqueous fluids with variable CO₂ contents, homogenizing at 340 to 390 °C, and (2) low-salinity (0–3 wt.% NaCl eq.) aqueous fluid inclusions, which homogenize at 320–380 °C. Cassiterite, wolframite, columbite–tantalite, scheelite, and sulfide assemblages accompany these fluids. The late fluid in the Oriente Novo and Correas deposit was a low-salinity (0–6 wt.% NaCl eq.) CO₂-free aqueous solution, which homogenizes at (100–260 °C) and characterizes the sulfide–fluorite–sericite association in the Correas deposit. The late fluid in the Santa Bárbara deposit has lower salinity (0–3 wt.% NaCl eq.) and characterizes the late-barren-quartz, muscovite and kaolinite veins. Oxygen isotope thermometry coupled with fluid inclusion data suggest hydrothermal activity at 240–450 °C, and 1.0–2.6 kbar fluid pressure at Correas and Oriente Novo. The hydrogen isotope composition of breccia-greisen, stockwork, and vein fluids (δ¹⁸O_quartz from 9.9‰ to 10.9‰, δD_H2O from 4.13‰ to 6.95‰) is consistent with a fluid that was in equilibrium with granite at temperatures from 450 to 240 °C. In the Santa Bárbara deposit, the inferred temperatures for quartz-pods and bed-like greisens are much higher (570 and 500 °C, respectively), and that for the cassiterite-quartz-veins is 415 °C. The oxygen and hydrogen isotope composition of greisen and quartz-pods fluids (δ¹⁸O_qtz-H2O=5.5–6.1‰) indicate that the fluid equilibrated with the albite granite, consistent with a magmatic origin. The values for mica (δ¹⁸O_mica-H2O=3.3–9.8‰) suggest mixing with meteoric water. Late muscovite veins (δ¹⁸O_qtz-H2O=−6.4‰) and late quartz (δ¹⁸O_mica-H2O=−3.8‰) indicate involvement of a meteoric fluid. Overall, the stable isotope and fluid inclusion data imply three fluid types: (1) an early orthomagmatic fluid, which equilibrated with granite; (2) a mixed orthomagmatic-meteoric fluid; and (3) a late hydrothermal meteoric fluid. The first two were responsible for cassiterite, wolframite, and minor columbite–tantalite precipitation. Change in the redox conditions related to mixing of magmatic and meteoric fluids favored important sulfide mineralization in the Correas deposit.  相似文献   

A simplified framework and performance analysis for while-drilling telemetry systems in underbalanced drilling operations     

Opeyemi Bello  Nelson Perozo  Parvin Huseynov  Oscar Grijalva-Meza  Arash Asgharzadeh  Javier Holzmann  Joachim Oppelt 《Environmental Earth Sciences》2018,77(13):512

As it stands, underbalanced drilling (UBD) operation has been beneficial in the exploration of hydrocarbons and production, with advantages like faster drilling control of lost circulation, stuck pipe situations, minimal or less formation damages and an enhanced ability to expedite development of brown fields. In spite of its edge over conventional drilling, the techniques can be more complex as well. Thus, a telemetry system is required to link downhole and surface while-drilling components transmitting and providing useful information under the real-time condition to the driller during drilling operations for more precise wellbore placement to ensure maximum reservoir exposure, ultimate production increment and monitoring conditions. A novel and systematic decision support system model based on distance-based approach has been developed for performance evaluation and optimal selection of while-drilling telemetry systems for the potential development of a depleted reservoir field. The proposed methodology attests to the need for the relative importance of criteria for a given application, without which inter-criterion comparison could not be accomplished. It requires a set of model selection criteria, along with available telemetry techniques and their level of criteria for optimal selection; and it successfully presents the results in terms of a merit value which is used to rank the while-drilling telemetry systems. This aims at delivering reliable drilling performance resulting to deliverable of real-time downhole data collection and most importantly places the matured well with minimal non-productive time during UBD operations. The scientific value of this study is the development of a simplified user-friendly decision support system for telemetry systems performance evaluation and selection optimization. The proposed framework was being validated and applied to a matured reservoir for an optimum selection of telemetry techniques in the UBD operation. The result of computations displayed similar results obtained by expert judgment demonstrating the significance effect and need for telemetry systems.  相似文献   

Robust Statistical Methods to Discriminate Extreme Events in Geoelectrical Precursory Signals: Implications with Earthquake Prediction     

Cuomo  V.  Di Bello  G.  Lapenna  V.  Piscitelli  S.  Telesca  I.  Macchiato  M.  Serio  C. 《Natural Hazards》2000,21(2-3):247-261

In this study, we propose a robuststatistical method to discern anomalous patternsin geoelectrical time series measured in a seismicarea of the Southern Apennine chain. First, a filteringprocedure to remove seasonal effects related tometeo-climatic fluctuations was carried out.Then, we selected an autoregressive model able todescribe the time fluctuations of geoelectricalsignals and propose a method to obtain an objectiveestimate of probability of occurrence for each extremeevent detected in the time series. Our applications inSouthern Italy allow us to hypothesize that theambiguity of short-term prediction is within thecomplicated dynamics of the physical processresponsible for electrical anomalies observed on theearth's surface.  相似文献   

The role of emerging bipoles in the formation of a sunspot penumbra     

R. Schlichenmaier  N. Bello Gonzlez  R. Rezaei  T.A. Waldmann 《Astronomische Nachrichten》2010,331(6):563-566

The generation of magnetic flux in the solar interior and its transport from the convection zone into the photosphere, the chromosphere, and the corona will be in the focus of solar physics research for the next decades. With 4 m class telescopes, one plans to measure essential processes of radiative magneto‐hydrodynamics that are needed to understand the nature of solar magnetic fields. One key‐ingredient to understand the behavior of solar magnetic field is the process of flux emergence into the solar photosphere, and how the magnetic flux reorganizes to form the magnetic phenomena of active regions like sunspots and pores. Here, we present a spectropolarimetric and imaging data set from a region of emerging magnetic flux, in which a proto‐spot without penumbra forms a penumbra. During the formation of the penumbra the area and the magnetic flux of the spot increases. First results of our data analysis demonstrate that the additional magnetic flux, which contributes to the increasing area of the penumbra, is supplied by the region of emerging magnetic flux. We observe emerging bipoles that are aligned such that the spot polarity is closer to the spot. As an emerging bipole separates, the pole of the spot polarity migrates towards the spot, and finally merges with it. We speculate that this is a fundamental process, which makes the sunspot accumulate magnetic flux. As more and more flux is accumulated a penumbra forms and transforms the proto‐spot into a full‐fledged sunspot (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献