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1.
Paleomagnetic secular variation in a portion of the Bonneville Alloformation is compared with secular variation in lacustrine sediments in the Mono Basin, California, and with secular variation in Lake Lahontan sediments in the northwestern Great Basin. The comparison places an age of about 18,000 yr B.P., and a span of 1000 to 3000 yr, on part of a transgressive stage of Lake Bonneville near Delta, Utah, that is coeval with a wet period in the Lahontan Basin. 相似文献
2.
年纹层发育的湖泊沉积物可以提供独立的、绝对定年的时间标尺,为重建高分辨率的区域古地磁场长期变化主曲线提供了难得的条件;基于长而连续的湖泊沉积物年纹层时间标尺建立的区域磁偏角和磁倾角长期变化参考曲线大大增强了岩芯对比和古地磁定年结果的精确性。此外,满足特定条件的湖泊沉积物还可以提供古地磁场强度长期变化的记录并有助于反映宇宙成因核素(如^14C、^10Be等)产生速率的变化、太阳活动等信息;目前,湖泊沉积物纹层年代学时间标尺及古地磁研究程度较高的主要是瑞典、芬兰和北美一些地区,区域古地磁场长期变化主曲线的地理分布并不均匀,因此在全球范围内寻找长序列的、连续的年纹层发育的湖泊进行古地磁研究可以更好地理解仪器观测记录以前的地磁场行为。 相似文献
3.
Variations of the orbital periods of the eclipsing binaries RY Aur, GG Cas, RS Lep, and RV Tri are analyzed. The period variations in all of these systems can be represented as a superposition of a secular period decrease and cyclic variations that can be explained with the light-time effect due to the presence of a third body in the system. The secular period decrease could be due to magnetic braking.
相似文献4.
A ground geomagnetic survey conducted in peninsular India has demarkated the dip equator for the epoch 1991.0. A well-defined
southward migration in the last two decades is evident. The secular trend in the vertical component and the direction of the
migration in the India zone are shown to be consistent. The migratory movement of the dip equator in different longitude sectors
is compared to highlight the complex nature of the secular trends. 相似文献
5.
Lin-Sen Li 《Astronomy Reports》2008,52(10):806-810
We examine the influence of mass-loss due to stellar wind using the celestial mechanics of variable mass, and derive first-and
second-order solutions, taking into account the decreasing mass due to the stellar wind. The theoretical results show that
the semi-major axis exhibits secular and periodic variations in the first-and second-order theory. The orbital eccentricity
exhibits periodic, but no secular variation or changes. The longitude of periastron exhibits only periodic variations in the
first-order solution, but also secular variations in the second-order solution. The theoretical results are applied to the
binary star HD 698, and variability of the orbital elements of this star due to stellar-wind mass loss calculated.
Published in Russian in Astronomicheskiĭ Zhurnal, 2008, Vol. 85, No. 10, pp. 896–900.
The article was translated by the authors. 相似文献
6.
Tectonomagnetic study in the seismoactive area of Narmada-Son lineament,central India: Preliminary results on repeat field observations 总被引：1，自引：0，他引：1
S. Y. Waghmare S. D. Pimprikar P. B. Gawali L. Carlo A. G. Patil 《Journal of Earth System Science》2009,118(3):261-272
Repeated measurements of the total geomagnetic field on the five profiles have revealed a picture of stress-induced tectonomagnetic
effect in the form of secular variation of the total geomagnetic field in the tectonically and seismically active area of
Jabalpur and adjoining areas of the Narmada-Son lineament (NSL), central India. For this experiment, a reference base station
was established within the study area at Jabalpur. Using proton precession magnetometers with a sensitivity of 0.1 nT, simultaneous
measurements of total geomagnetic field were made annually at the base and all field stations. Five cycles of repeated observations
have been performed between 2003 and 2007. For data analysis, a difference method has been applied and the residuals have
been calculated as secular variations of the total geomagnetic field with values ranging from ±0.1nT to about ±14.6nT/yr over
the different stations. The anomalies in secular variation of the total geomagnetic field may be related to anomalous accumulation
of tectonic stresses and tensions on the deep fault zones and crustal blocks due to recent geodynamic processes and active
geological inhomogeneities in the NSL. 相似文献
7.
Orbital-period variations of the low-mass, semi-detached eclipsing binary RT Per are analyzed. In addition to the secular variation of the orbital period determined by the mass transfer between the components, cyclic variations are also present. Both the light-time effect and magnetic oscillations can describe the cyclic orbital-period variations of RT Per. The secular period increase can be explained by a uniform flow of matter from the lower-mass to the higher-mass component at a rate of 0.60 × 10−8M-/year, with the total angular momentum being conserved. The period variations can be represented equally accurately by either a superposition of two cyclic variations or a superposition of a secular period increase and two cyclic variations. Approximately the same parameters are derived for the lower-period (36.8 year) variations when the times of minima are fitted with a linear or a quadratic formula. For the longer-period variation, a period of 275 years and amplitude of 0.104 days are found using the linear formula, or 89 years and 0.045 days using the quadratic formula.
相似文献8.
Julie Prytulak Tim Elliott Dirk L. Hoffmann Christopher D. Coath 《Geostandards and Geoanalytical Research》2008,32(1):55-63
The accuracy of 231 Pa-235 U measurements can be readily assessed using a secular equilibrium reference material (RM), but a secular equilibrium RM is also required to calibrate the 233 Pa spike used in 231 Pa determinations. The only silicate RM commonly accepted to be in secular equilibrium is Table Mountain Latite (TML) and so an additional reference is required. Our measurements on the widely available USGS BCR-2 (Basalt Columbia River) rock powder yielded (231 Pa/235 U) = 0.997 ± 0.013 2s (n = 10), indicating its value as a secondary reference to test the fidelity of U-Pa determinations. Such a reference material additionally provides a useful check on data reduction, which our literature survey highlights can lead to discrepancies of up to 53% between reported (231 Pa/235 U) activity ratios and corresponding U and Pa concentration data. 相似文献
9.
Magnetic secular variation is recorded as a quasi-rhythmical process of uncertain origin. Rhythmic changes recorded in the Scisti a Fucoidi in the central Apennines of Italy, pelagic sediments of Mid-Cretaceous (Late Albian) age, show strong correspondence to patterns of orbital variation. In the same strata cyclic magnetic variations are found with peaks in the same range (105, 40, 26,19 kyr). These results appear to support earlier suggestions that secular variations may be related to these astronomical patterns. 相似文献
10.
《International Geology Review》2012,54(8):40-51
Increased accuracy and volume of geodetic investigation, particularly precise repeated leveling, has made possible the study of secular land movements, the slow uplift and subsidence of the lithosphere. Many nations have engaged in level-measuring surveys which have resulted in the compilation of maps of contemporary crustal movements. Although many geodesists and geologists maintain that only certain parts of the earth's crust are mobile, there is not a single area of any consequence in which secular movements are absent. Contemporary movements, varying in direction and intensity, occur in mountainous regions, plains, and sea bottoms. These movements influence river patterns, shoreline configurations, and landscape forms in general. With increased precision and number of engineering projects, the consideration of secular movements becomes a necessary element in longterm planning of complex construction such as ports, pipelines, canals, irrigation systems, and hydroelectric stations. -- G. E. Denegar. 相似文献
11.
The latitudes of the zonal boundaries of the global magnetic field of the Sun are determined from the magnetic neutral lines on synoptic Hα maps obtained during 1878–1999. The area of the polar zone occupied by magnetic field of a single polarity at solar minima has doubled over the last 120 years. This provides an explanation for the secular increase in heliospheric characteristics, which differs from the two-fold increase of the magnetic field strength predicted for this period. The temporal variations of the magnetic flux from the polar regions and their role in global changes of the Earth’s climate are discussed in connection with secular variations in the structure of the internal magnetic field of the Sun. 相似文献
12.
This paper presents relative secular variations of the total intensity of the geomagnetic field against a background of results of magnetic anomaly interpretation along seismic profile P4. Profile P4 crosses a Variscan folding zone in the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ), and the Polish part of the East European Craton (EEC). Secular geomagnetic field variations
measured in 1966–2000 along a line adjacent to seismic profile P4 were analysed. The study of secular variations, reduced to the base recordings at the Belsk Magnetic Observatory, showed that the growth of geomagnetic field at the East European Craton was slower than in the Trans-European Suture Zone and the Paleozoic Platform.A 2D crustal magnetic model was interpreted as a result of magnetic modelling, in which seismic, geological and geothermal data were also used. The modelling showed that there were significant differences in the magnetic model for geotectonic units, which had been earlier determined based on deep seismic survey data. It should be noted that a fundamental change of trend of the relative secular variations was observed at the slope of the Precambrian Platform. After analysing the geomagnetic field observed along profile P4, the hypothesis that the contact between Phanerozoic and Precambrian Europe lies in Poland's territory can be proven. 相似文献
13.
14.
Astronomy Reports - Two methods have been developed to study secular (apsidal and nodal) orbital precession in circumbinary systems consisting of a binary star and an exoplanet. The first method is... 相似文献
15.
Shale and greywacke compositions from the Archean to Phanerozoic record a secular change in the siliciclastic material that comprises much of Earth's continental margins, past and present. This study explores the metamorphic consequence of these compositional changes, by comparing phase equilibrium models constructed for average Archean, Proterozoic, and Phanerozoic shale and greywacke compositions equilibrated along two Barrovian-type geotherms: 1330℃/GPa(A) and 800 ℃/GPa(B). Our models show that Archean siliciclastic rocks can retain up to 4 vol.% water at middle to lower crustal conditions, nearly twice that of Proterozoic and Phanerozoic compositions. The increased ferromagnesium content of Archean siliciclastic rocks stabilizes chlorite to higher temperatures and results in a biotite-rich assemblage at solidus temperatures. Accordingly, water-absent biotite dehydration melting is predicted to play a greater role in the generation of melt in the metamorphism of Archean aged units,and water-absent muscovite dehydration melting is of increasing importance through the Proterozoic and Phanerozoic. This secular variation in predicted mineral assemblages demonstrates the care with which metamorphic facies diagrams should be applied to Archean compositions. Moreover, secular changes in the composition of shale and greywacke is reflected in the evolution of anatectic melt towards an increasingly less viscous, Ca-rich, and Mg-poor monzogranite. 相似文献
16.
利用青海玉树国家基本气象观测站1961-2010年的总辐射常规观测资料, 分析了玉树地区总辐射的长期变化趋势. 结果表明: 玉树地区总辐射在1961-2010年期间总体呈现减弱趋势, 其变化经历了增强变"亮"-减弱变"暗"-增强变"亮"-震荡回落4个阶段; 春、夏季的总辐射变化趋势对年际变化趋势有主导作用. 小波分析表明, 玉树地区近50 a的总辐射变化过程中, 存在多时间尺度周期的变化特征; 长期变化趋势和国内其他站点的变化趋势相比均表现出减弱的趋势, 但各站点减弱趋势倾向率不同. 最后, 对比分析了总辐射和同期气象要素、MODIS反演的气溶胶AOD之间的关系. 相似文献
17.
胶东地区滑脱构造与金矿成矿浅析 总被引：5，自引：0，他引：5
滑脱构造对超大型金矿床的形成有重要的控制作用。根据对胶江地区蓬家夼、郭城和发云夼金矿的研究,结合国内外有关资料,分析了滑脱构造的地质特征及其所控制的层间滑动角砾岩型金矿的特征,提出了３点新认识：１）滑脱城沉积盆地的不同地域控制着不同的成矿类型,构成了完整的层间滑动角砾岩型金矿成矿系列;２）在伸展环境中形成的,伴有热液沉积矿层的滑脱构造在后期的构造演化过程中,常可复活,叠加后期成矿作用,并被构造推覆 相似文献
18.
E. N. Vinyaikin 《Astronomy Reports》2014,58(9):626-639
Many-year measurements of the radio flux of the young supernova remnant Cassiopeia A relative to the radio galaxy Cygnus A were continued at 290 and 151.5 MHz. The new data are used together with previously published observations carried out at decameter, meter, centimeter, and millimeter wavelengths to derive the frequency dependence of the secular variation of the radio flux density of Cas A: $d_\nu [\% year^{ - 1} ] = - (0.63 \pm 0.02) + (0.04 \pm 0.01)\ln \nu [GHz] + (1.51 \pm 0.16) \times 10^{ - 5} (\nu [GHz])^{ - 2.1} $ . The observed slowing of the secular variations with decreasing frequency at decameter wavelengths can be explained by a decrease in the optical depth of a remnant HII zone around Cas A with time due to recombination of hydrogen atoms. The new derived frequency dependence for the rate of the secular decrease, absolute and relative measurements of the radio flux density of Cas A carried out over the last 25 years, and the absolute spectrum of Cyg A are used to construct the spectrum of Cas A in the range 5–250 000 MHz predicted for epoch 2015.5. 相似文献
19.
A. M. Cherepashchuk V. F. Esipov A. V. Dodin V. V. Davydov A. A. Belinskii 《Astronomy Reports》2018,62(11):747-763
Spectroscopic monitoring of SS 433 was performed during the 11 years between 2007 and 2017. Shifts of the moving Hα emission lines are analyzed and corresponding radial velocity curves plotted. All published spectroscopic data on SS 433 are used to search for secular variations of the parameters of the kinematic model. Deviations of the model parameters from their mean values are observed during relatively short time intervals (several years), but no secular changes have been detected. The presence of a component varying periodically with the orbital period is confirmed for the velocity variations for the matter in the relativistic jets, possibly indicating that the orbit of SS 433 is slightly elliptical. The stability of the parameters of the kinematic model testifies that a model with a slaved accretion disk that follows the precession of the optical star’s rotation axis is very suitable for the supercritical accretion disk in the SS 433 system. 相似文献
20.
Secular evolution of the lithosphere beneath the eastern North China Craton: evidence from Mesozoic basalts and high-Mg andesites 总被引：6，自引：0，他引：6
Hong-Fu Zhang Min Sun Mei-Fu Zhou Jian-Ping Zheng 《Geochimica et cosmochimica acta》2003,67(22):4373-4387
Geochemical and isotopic data from Mesozoic lavas from the Jianguo, Niutoushan, Wulahada, and Guancaishan volcanic fields on the northern margin of the North China Craton provide evidence for secular lithospheric evolution of the region. Jianguo lavas are alkaline basalts with LILE- and LREE-enrichment ((La/Yb)N=12.2-13.2) and MORB-like Sr-Nd-Pb isotopic ratios ((87Sr/86Sr)i<0.704; εNd=3.9-4.8; (206Pb/204Pb)i≈18). Niutoushan basalts are similar but show evidence of olivine fractionation. Wulahada lavas are high-Mg andesites (Mg#∼67) with EM1 Sr-Nd-Pb isotopic signatures. Geochemical data suggest that the basalts originated from MORB-type asthenosphere whereas the high-Mg andesites were derived an EM1 mantle source, i.e., a refractory lithospheric mantle modified by a previously subducted slab. The result, combined with the available data of the Mesozoic basalts from the southern portion of the NCC (Zhang et al., 2002), manifests a vast secular evolution of the lithospheric mantle beneath the eastern NCC from the Paleozoic refractory continental lithosphere to this Mesozoic modified lithosphere. Compared with the cratonic margin, the lithospheric mantle beneath the center of the craton was less extensively modified, implying the secular evolution was related to the subduction processes surrounding the NCC. Therefore, we suggest that the interaction of the slab-derived silicic melt with the old refractory lithospheric mantle converted the Paleozoic cratonic lithospheric mantle into the late Mesozoic fertile mantle, which was also different from the Cenozoic counterpart. A geodynamic model is proposed to illustrate such a secular lithosphere evolution. 相似文献