The Fazenda Largo off-craton kimberlites of Piauí State, Brazil     

Felix V. Kaminsky  Sergei M. Sablukov  Ludmila I. Sablukova  Olga D. Zakharchenko 《Journal of South American Earth Sciences》2009,28(3):288-303

In the late 1990s, the Fazenda Largo kimberlite cluster was discovered in the Piauí State of Brazil. As with earlier known kimberlites in this area – Redondão, Santa Filomena-Bom Jesus (Gilbues) and Picos – this cluster is located within the Palaeozoic Parnaiba Sedimentary Basin that separates the São Francisco and the Amazonian Precambrian cratons. Locations of kimberlites are controlled by the ‘Transbrasiliano Lineament’. The Fazenda Largo kimberlites are intensely weathered, almost completely altered rocks with a fine-grained clastic structure, and contain variable amounts of terrigene admixture (quartz sand). These rocks represent near-surface volcano-sedimentary deposits of the crater parts of kimberlite pipes. By petrographic, mineralogical and chemical features, the Fazenda Largo kimberlites are similar to average kimberlite. The composition of the deep-seated material in the Fazenda Largo kimberlites is quite diverse: among mantle microxenoliths are amphibolitised pyrope peridotites, garnetised spinel peridotites, ilmenite peridotites, chromian spinel + chromian diopside + pyrope intergrowths, and large xenoliths of pyrope dunite. High-pressure minerals are predominantly of the ultramafic suite, Cr-association minerals (purplish-red and violet pyrope, chromian spinel, chromian diopside, Cr-pargasite and orthopyroxene). The Ti-association minerals of the ultramafic suite (picroilmenite and orange pyrope), as well as rare grains of orange pyrope-almandine of the eclogite association, are subordinate. Kimberlites from all four pipes contain rare grains of G10 pyrope of the diamond association, but chromian spinel of the diamond association was not encountered. By their tectonic position, by geochemical characteristics, and by the composition of kimberlite indicator minerals, the Fazenda Largo kimberlites, like the others of such type, are unlikely to be economic.  相似文献   

Variations of daytime and nighttime electron temperature and heat flux in the upper ionosphere,topside ionosphere and lower plasmasphere for low and high solar activity     

Vladimir Truhlik  Ludmila Triskova  Dieter Bilitza  Katerina Podolska 《Journal of Atmospheric and Solar》2009,71(17-18):2055-2063

A database of the electron temperature (T_e) comprising of most of the available LEO satellite measurements is used for studying the solar activity variations of T_e. The T_e data are grouped for two levels of solar activity (low LSA and high HSA), five altitude ranges between 350 and 2000 km, and day and night. By fitting a theoretical expression to the T_e values we obtain variation of T_e along magnetic field lines and heat flux for LSA and HSA. We have found that T_e increases with increase in solar activity at low and mid-latitudes during nighttime at all altitudes studied. During daytime the T_e response to solar activity depends on latitude, altitude, and season. This analysis shows existence of anti-correlation between T_e and solar activity at mid-latitudes below 700 km during the equinox and winter day hours. Heat fluxes show small latitudinal dependence for daytime but substantial for nighttime.  相似文献   

Hydrogeochemistry of the permafrost zone in the central part of the Yakutian diamond-bearing province,Russia     

Sergey?V.?AlexeevEmail author  Ludmila?P.?Alexeeva 《Hydrogeology Journal》2003,11(5):574-581

The hydrogeochemical characteristics and zonation of the permafrost zone in the central part of the Yakutian diamond-bearing province formed mainly under the influence of cryogenic processes that occurred in the late Cenozoic. On the basis of field and experimental studies, conclusions were formulated that the perennial cryogenesis of the sedimentary cover in this region resulted in increasing the concentration of carbonate and sulfate compounds in groundwaters as well as increasing the concentration of easily soluble compounds (sodium, magnesium, and calcium chlorides).

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Resumen Las características hidrogeoquímicas y la zonación del permafrost existente en el centro de la provincia de Yakutia, rica en diamantes, se formaron fundamentalmente bajo la influencia de procesos criogénicos durante el tramo final del Cenozoico. Con base en estudios de campo y experimentales, se ha concluido que la criogénesis perenne de la cubierta sedimentaria de la región ha provocado un aumento de la concentración de compuestos de carbonato y sulfato en las aguas subterráneas, además de incrementar la concentración de compuestos solubles, como el sodio, magnesio y cloruros de calcio.

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Résumé Les caractéristiques hydrogéochimiques et la zonation de la région de permafrost dans la partie centrale de la province diamantifère de Yakoutie ont été acquises principalement sous l'influence des processus cryogéniques qui existent depuis la fin du Tertiaire. Sur la base d'études expérimentales et de terrain, on conclut que la cryogenèse permanente de la couverture sédimentaire de cette région a provoqué un accroissement de la concentration des composés carbonatés et sulfatés dans les eaux souterraines, en même temps que celui de composés facilement solubles, comme les chlorures de sodium, de magnésium et de calcium.

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Statistical aspects of eliminating systematic effects     

Lubomír Kubáček  Ludmila Kubáčková  Reviewer F. Štulajter  Reviewer G. Siráň 《Studia Geophysica et Geodaetica》1986,30(1):1-12

Summary A procedure for processing measurements subject to systematic effects is derived such that it ensures their optimum elimination in the results of the processing. It is proved that no other method of eliminating systematic effects yields better results.

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The use of the discrete surface fourier analysis of anomalous fields for resolving them     

Ludmila Kubáčková  Reviewer O. Šefl 《Studia Geophysica et Geodaetica》1973,17(2):106-110

Summary The subject of this paper is one method of numerical computing of the resolution of a summary anomalous field into its components, a method which respects the spectral approach to this problem.Dedicated to 90th Birthday of Professor Frantiek Fiala  相似文献   

Late orogenic, large-scale rotations in the Tien Shan and adjacent mobile belts in Kyrgyzstan and Kazakhstan   总被引：6，自引：1，他引：5  

Rob Van der Voo  Natalia M. Levashova  Ludmila I. Skrinnik  Taras V. Kara  Mikhail L. Bazhenov   《Tectonophysics》2006,426(3-4):335-360

Most of Kazakhstan belongs to the central part of the Eurasian Paleozoic mobile belts for which previously proposed tectonic scenarios have been rather disparate. Of particular interest is the origin of strongly curved Middle and Late Paleozoic volcanic belts of island-arc and Andean-arc affinities that dominate the structure of Kazakhstan. We undertook a paleomagnetic study of Carboniferous to Upper Permian volcanics and sediments from several localities in the Ili River basin between the Tien Shan and the Junggar–Alatau ranges in southeast Kazakhstan. Our main goal was to investigate the Permian kinematic evolution of these belts, particularly in terms of rotations about vertical axes, in the hope of deciphering the dynamics that played a role during the latest Paleozoic deformation in this area. This deformation, in turn, can then be related to the amalgamation of this area with Baltica, Siberia, and Tarim in the expanding Eurasian supercontinent. Thermal demagnetization revealed that most Permian rocks retained a pretilting and likely primary component, which is of reversed polarity at three localities and normal at the fourth. In contrast, most Carboniferous rocks are dominated by postfolding reversed overprints of probably “mid-Permian” age, whereas presumably primary components are isolated from a few sites at two localities. Mean inclinations of primary components generally agree with coeval reference values extrapolated from Baltica, whereas declinations from primary as well as secondary components are deflected counterclockwise (ccw) by up to  90°. Such ccw rotated directions have previously also been observed in other Tien Shan sampling areas and in the adjacent Tarim Block to the south. However, two other areas in Kazakhstan show clockwise (cw) rotations of Permian magnetization directions. One area is located in the Kendyktas block about 300 km to the west of the Ili River valley, and the other is found in the Chingiz Range, to the north of Lake Balkhash and about 400 km to the north of the Ili River valley. The timing of the ccw as well as cw rotations is clearly later than the disappearance of any marine basins from northern Tarim, the Tien Shan and eastern Kazakhstan, so that the rotations cannot be attributed to island-arc or Andean-margin plate settings — instead we attribute the rotations to large-scale, east–west (present-day coordinates), sinistral wrenching in an intracontinental setting, related to convergence between Siberia and Baltica, as recently proposed by Natal'in and Şengör [Natal'in, B.A., and Şengör, A.M.C., 2005. Late Palaeozoic to Triassic evolution of the Turan and Scythian platforms: the pre-history of the palaeo-Tethyan closure, Tectonophysics, 404, 175–202.]. Our previous work in the Chingiz and North Tien Shan areas on Ordovician and Silurian rocks suggested relative rotations of  180°, whereas the Permian declination differences are of the order of 90° between the two areas. Thus, we assume that about 50% of the total post-Ordovician rotations are of pre-Late Permian age, with the other half of Late Permian–earliest Mesozoic age. The pre-Late Permian rotations are likely related to oroclinal bending during plate boundary evolution in a supra-subduction setting, given the calc-alkaline character of nearly all of the pre-Late Permian volcanics in the strongly curved belts.  相似文献