The emergence of magnetic flux   总被引：1，自引：0，他引：1  

Cornelis Zwaan 《Solar physics》1985,100(1-2):397-414

This paper first summarizes the morphology and dynamics of emerging flux regions and arch filament systems and then discusses detailed observations of a particular active region with emerging magnetic flux.The central part of the growing active region shows abnormal granulation and a weak magnetic field that, locally, is transverse. In the border zone, strong downward flows occur in the chromopshere and photosphere (small features with strong magnetic fields (faculae, pores) are formed here.) Near the leading and following edge, sunspots are formed by the coalescence of such small magnetic elements.The observational data are interpreted by means of a heuristic model of an emergent magnetic loop-shaped bundle consisting of many flux tubes. In this model we incorporate the theory of convective collapse and the buoyancy of flux tubes. The observed complexity in the structure and dynamics, including strong transverse fields and velocity shear, is attributed to the emergence of several flux regions within the active region at different orientations.  相似文献   

Assessment of sandstone deterioration at Ta Keo temple (Angkor): first results and future prospects     

Marie-Françoise André  Samuel Etienne  Denis Mercier  Franck Vautier  Olivier Voldoire 《Environmental Geology》2008,56(3-4):677-688

A first application of geomorphological methods to the assessment of sandstone deterioration at Angkor is presented. Damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1,000 year-old Ta Keo temple. Methods combine field observations and measurements at 230 sampling points, high-resolution lasergrammetry and stereophotogrammetry on a 2-m² test zone, and SEM observations. The first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution, and exhibits a high spatial variability. Percentages of deteriorated surfaces vary from 17.6 to 93.8%, and average stone recession values from 0.00 to 2.71 cm (minimum) and 0.34 to 5.49 cm (maximum). On the test-zone, stereophotogrammetry and 3D-mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963. On the whole, the amount of deteriorated surfaces more than tripled between 1963 and 2008. The degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite (CaCO3), with secondary importance of barite (BaSO4) and gypsum (CaSO₄·2H₂O). Future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s.  相似文献   

Leaching mechanisms of oxyanionic metalloid and metal species in alkaline solid wastes: A review     

Geert Cornelis  C. Anette Johnson  Tom Van Gerven  Carlo Vandecasteele 《Applied Geochemistry》2008

An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility.  相似文献   

Tying seismic data to geologic information from core data: an example from ODP Leg 177     

Etienne Wildeboer Schut  Gabriele Uenzelmann-Neben 《Geo-Marine Letters》2006,26(4):235-248

The integration of seismic data with core data should provide ground-truth to a structural interpretation of seismic data. The main difficulty in such an integration effort is the correct translation of physical property measurements on cores to a form which can be used in seismostratigraphic interpretation. In the absence of down-hole well data and check-shots, required knowledge of the velocity structure at the drilling locations can be obtained directly from measurements of the physical properties of core samples. This involves upscaling of the data from physical properties of cores to the sample interval used in the seismic data. In the present study, three of the seven drill-sites of ODP (Ocean Drilling Program) Leg 177 in 1997/1998, located on the Agulhas Ridge in the south-eastern Atlantic (sites 1088–1090), were connected with eight seismic profiles. Physical properties data measured on the cores from the various holes at each site were combined to create a single continuous log and used to construct synthetic seismograms. The synthetics generally show a good agreement with real seismic data in terms of amplitude and waveform. Some reflections in these generated traces may have a time-shift due to sections with incomplete or spurious P-wave velocity measurements in the ODP datasets. The main reflectors identified in the real seismic data correspond to hiatuses or periods of reduced sedimentation rates, and correlate well with density variations. One particular hiatus, clearly observable in the real seismic data, was not unequivocally identifiable in the various types of core data, and tying core data to seismic data can confirm its existence in the core data, showing the benefit of including seismic data in an interpretation of core log data. On the other hand, core data provide a calibration tool for the geological timescale of seismic data and information about the lithology, needed in the interpretation of seismic data.  相似文献   

Gravity Anomaly and Tectonics in the Northern Part of the North Fiji Basin - Preliminary Result of the 1994 NOFI Cruise under the NEW STARMER Programme     

Matsumoto  Takeshi  Goslin  Jean  Lagabrielle  Yves  Ruellan  Etienne  Tanahashi  Manabu 《Marine Geophysical Researches》1997,19(1):37-53

A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications. The former is supported by a restoring force of an imaginary elastic plate in the crust and the latter by the Airy type isostasy. These characteristics can be derived from the difference in magmatic activity, as influenced by the difference in lithospheric structure. The latter is characterised by greater active magmatism and hydrothermalism underneath the ridge than the former. Such a difference in the magmatic activity and the horizontal scale of the shallow subsurface structure is derived from the difference in the stiffness or viscosity of the lithosphere beneath the two ridges.  相似文献   

Active spreading and hydrothermalism in North Fiji Basin (SW Pacific). Results of Japanese French Cruise Kaiyo 87     

Jean-Marie Auzende  Eiichi Honza  Xavier Boespflug  Satendra Deo  Jean-Philippe Eissen  Jun Hashimoto  Philippe Huchon  Junichiro Ishibashi  Yo Iwabuchi  Philip Jarvis  Masato Joshima  Kiyoyuki Kisimoto  Yasuto Kuwahara  Yves Lafoy  Tsuyoshi Matsumoto  Jean-Pierre Maze  Kiyohiko Mitsuzawa  Hiroyasu Monma  Takeshi Naganuma  Yukihiro Nojiri  Suguru Ohta  Kiyoshi Otsuka  Yoshihisa Okuda  Hélène Ondreas  Akira Otsuki  Etienne Ruellan  Myriam Sibuet  Manabu Tanahashi  Takeo Tanaka  Tetsuro Urabe 《Marine Geophysical Researches》1990,12(4):269-283

The aim of the Japanese-French Kaiyo 87 cruise was the study of the spreading axis in the North Fiji Basin (SW Pacific). A Seabeam and geophysical survey allowed us to define the detailed structure of the active NS spreading axis between 16° and 22° S and its relationships with the left lateral motion of the North Fiji Fracture Zone. Between 21° S and 18°10′ S, the spreading axis trends NS. From 18°10 S to 16°40 S the orientation of the spreading axis changes from NS to 015°. North of 16°40′ S the spreading axis trends 160°. These two 015° and 160° branches converge with the left lateral North Fiji fracture zone around 16°40′ S to define an RRFZ triple junction. Water sampling, dredging and photo TV deep towing give new information concerning the hydrothermal activity along the spreading axis. The discovery of hydrothermal deposits associated with living communities confirms this activity.  相似文献   

Editorial     

Cornelis De Jager  Zdeněk Švestka 《Solar physics》1978,56(1):3-4

  相似文献   

Diachronous evolution of volcano-sedimentary basins north of the Congo craton: Insights from U–Pb ion microprobe dating of zircons from the Poli, Lom and Yaoundé Groups (Cameroon)   总被引：1，自引：0，他引：1  

Sadrack Flix Toteu  Joseph Penaye  Etienne Deloule  William Randall Van Schmus  Rigobert Tchameni 《Journal of African Earth Sciences》2006,44(4-5):428

Ion microprobe U–Pb dating of zircons from Neoproterozoic volcano-sedimentary sequences in Cameroon north of the Congo craton is presented. For the Poli basin, the depositional age is constrained between 700–665 Ma; detrital sources comprise ca. 920, 830, 780 and 736 Ma magmatic zircons. In the Lom basin, the depositional age is constrained between 613 and 600 Ma, and detrital sources include Archaean to Palaeoproterozoic, late Mesoproterozoic to early Neoproterozoic (1100–950 Ma), and Neoproterozoic (735, 644 and 613 Ma) zircons. The Yaoundé Group is probably younger than 625 Ma, and detrital sources include Palaeoproterozoic and Neoproterozoic zircons. The depositional age of the Mahan metavolcano-sedimentary sequence is post-820 Ma, and detrital sources include late Mesoproterozoic (1070 Ma) and early Neoproterozoic volcanic rocks (824 Ma). The following conclusions can be made from these data. (1) The three basins evolved during the Pan-African event but are significantly different in age and tectonic setting; the Poli is a pre- to syn-collisional basin developed upon, or in the vicinity of young magmatic arcs; the Lom basin is post-collisional and intracontinental and developed on old crust; the tectono-metamorphic evolution of the Yaoundé Group resulted from rapid tectonic burial and subsequent collision between the Congo craton and the Adamawa–Yade block. (2) Late Mesoproterozoic to early Neoproterozoic inheritance reflects the presence of magmatic event(s) of this age in west–central Africa.  相似文献   

GGR Critical Review of Analytical Developments in 2004–2005     

Janet M. Hergt  L. Paul Bédard  Etienne Deloule  Klaus Peter Jochum  Kathryn L. Linge  Paul J. Sylvester  Matthias Willbold  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2006,30(3):141-142

In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields.  相似文献   

2004–2005 Analytical Developments in Secondary Ion Mass Spectrometry     

Etienne Deloule 《Geostandards and Geoanalytical Research》2006,30(3):175-182

This review of the literature from 2004 and 2005 concerning secondary ion mass spectrometry (SIMS) highlights the contribution the technique has made in the fields of petrology, geochronology, cosmochemistry and material sciences. In petrology, much research was devoted to the measurement of stable isotopes and trace elements by developments in multicollection acquisition, with emphasis on low atomic mass number elements. Elements studied in particular were S (in sulfides), O (in garnets), C (in sedimentary organic matter), Cl (in glasses) and Si. Novel applications of SIMS to geochronology have included the measurement of young zircon grains by the U-Pb and U-Th decay methods. An increasing number of studies have combined U-Pb geochronology with the measurement of trace elements or stable isotopes in zircon.  相似文献