Structural development along the Billefjorden Fault Zone in the area between Kjellströmdalen and Adventdalen/Sassendalen, central Spitsbergen     

PÅL HAREMO  ARILD ANDRESEN  HENNING DYPVIK  JENÖ NAGY  ERS ELVERHøI  TOR ARNE EIKELAND  HALVOR JOHANSEN 《Polar research》1990,8(2):195-216

The Billefjorden Fault Zone represents a major lineament on Spitsbergen with a history of tectonic activity going back into the Devonian and possibly earlier. Recent structural, sedimcntological and stratigraphical investigations indicate that most of the stratigraphic thickness variations within the Mesozoic strata along the Billefjorden Fault Zone south of Isfjordcn are due to Tertiary compressional tectonics related to the transpressive Eocene West-Spitsbergen Orogeny. No convincing evidence of distinct Mesozoic extensional events, as suggested by previous workers, has been recognized. Tertiary compressional tectonics are characterized by a combined thin-skinned/thick-skinned structural style. Decollement zones arc recognized in the Triassic Sassendalen Group (tower Décollement Zone) and in the Jurassic/Cretaceous Janusfjellet Subgroup (Upper Décollement Zone). East-vergent folding and reverse faulting associated with these decollement' zones have resulted in the development of compressional structures, of which the major arc the Skolten and Tronfjellct Anticlines and the Advcntelva Duplex. Movements on one or more high angle east-dipping reverse faults in the pre-Mesozoic basement have resulted in the development of the Juvdalskampcn Monocline, and are responsible for out-of-sequence thrusting and thinning of the Mesozoic sequence across the Billefjorden Fault Zone. Preliminary shortening calculations indicate an eastward displacement of minimum 3-4 km, possibly as much as 10 km for the Lower Cretaceous and younger rocks across the Billefjorden Fault Zone.  相似文献   

IUGS and the State of the Geosciences——Based on a speech delivered at the Opening Ceremony of the 32nd International Geological Congress in Florence, August 2004     

Eduardo F.J. de Mulder 《《幕》》2005,28(3):224-225

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The kinematics of the large western knot in the halo of the young planetary nebula NGC 6543     

Deborah L. Mitchell  M. Bryce  J. Meaburn  J. A. López  M. P. Redman  D. Harman  M. G. Richer  H. Riesgo 《Monthly notices of the Royal Astronomical Society》2005,362(4):1286-1294

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西藏结则茶卡湖岸沉积物中铀系年龄及意义     

杨俊峰  卢书炜  赵虹  崔霄峰  吕宪河 《地球科学与环境学报》2006,28(3):6-10

通过对藏北高原西北部结则茶卡湖泊及其沿岸地质地貌调查,发现其为一个富含硼、锂、钾、锶的封闭型盐湖,沿岸海拔4 850 m拔湖325 m有一条明显的高位湖岸线,该湖岸线到湖面之间有六级湖积阶地发育,六级以上阶地保存零星。沿湖岸不同高度上的湖积物U系年龄分别为(14.2±1.2)ka BP(T2)、(38.0±3.5)ka BP(T4)和(41.6±3.2)ka BP(T5)。湖面下降的幅度是藏北高原迄今所知最大。根据湖面平均下降速度推算高位湖岸线和高位湖积层的形成年龄在(120~90)ka BP,与东部的纳木错和西部的甜水海基本一致,说明藏北高原在晚更新世初期有一个明显的泛湖期。大约100 ka BP结则茶卡湖面开始下降,晚更新世以来湖泊演化是在封闭体系干旱环境下进行的,盐湖形成于14 ka BP左右,藏北高原在晚更新世以来气候变化可能为自西向东逐渐变为干寒。  相似文献   

Compaction-induced inclination shallowing of the post-depositional remanent magnetization in a synthetic sediment     

G. L. Anson  K. P. Kodama 《Geophysical Journal International》1987,88(3):673-692

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Neutron capture measurements on radioactive93Zr     

R. L. Macklin 《Astrophysics and Space Science》1985,115(1):71-83

Neutron capture measurements made on a sample of fission-product zirconium containing 20%⁹³Zr(t _1/2=1.5×10⁶a) at the Oak Ridge Electron Linear Accelerator time-of-flight facility resulted in the identification of 138 resonance peaks for the⁹³Zr isotope at neutron energies up to 21.5 keV. Average capture cross sections from 20 to 300 keV were derived by subtracting neutron capture yields of the stable zirconium isotopes^{90, 91, 92, 94, 96}Zr and additional backgrounds. The average cross sections found were significantly less than those of JENDL-1. While generally 30% higher than those of ENDF/B —V below 60 keV, the binned data overlapped the smooth ENDF/B —V curve. The average for a Maxwellian neutron spectrum withkT=30 keV is (95±10) mb and the resonance contribution to the capture resonance integral is (15.0±0.5)b.Research sponsored by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-AC05-840R21400 with the Martin Marietta Energy Systems, Inc.  相似文献   

Theoretical properties of radio-galaxies     

L. Zaninetti 《Astrophysics and Space Science》1985,108(2):401-407

A complete sample of symmetric double radio-galaxies has been investigated by inferring the propagation of a jet along the radio-axis and computing velocities with the aid of different models. A best linear fit between radio-luminosity and velocity is proposed in the range 10⁴⁰ ergs s^–145 ergs s^–1.  相似文献   

Monitoring the Microarcsecond Quasar J1819+3845     

J. Dennett-Thorpe  A.G. de Bruyn 《Astrophysics and Space Science》2001,278(1-2):101-104

We present the results of a year-long monitoring campaign on J1819+3845.We interpret the results of this WSRT campaign to infer critical source parameters such as source lifetime and structure on tens of microarcseconds. The long lifetime of the source at such high brightness temperatures requires continuous energy injection or exotic emission processes. We have previously interpreted the extreme scintillation ofJ1819+3845 as due to a relatively nearby (∼ 20 pc) scattering screen. We show this screen has a velocity w.r.t. the LSR of ∼ 25 kms^-1, as measured by the changing scintillation properties throughout the year: the `velocity parallax'. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Dhofar 081: A new lunar highland meteorite     

A. GRESHAKE  R. T. SCHMITT  D. ST FFLER  M. PTSCH  L. SCHULTZ 《Meteoritics & planetary science》2001,36(3):459-470

Abstract— The lunar meteorite Dhofar 081, found as a single fragment of 174 g in the Dhofar region of Oman, is a shocked feldspathic fragmental highland breccia dominated by anorthosite‐rich lithic and mineral clasts embedded into a fine‐grained mostly shock melted clastic matrix. Major mineral phases in the bulk rock are Ca‐rich plagioclase (An_96.5–99.5), pyroxene (FS_21.9–46.2Wo_3.0–41.4), and olivine (Fa_29.3–47.8); accessory phases include Fe‐Ni metal, ilmenite, and Ti‐Cr‐rich spinel. Dhofar 081 contains subordinate crystalline fragments of large anorthosites, intersertal impact‐melt rocks, microporphyritic impact‐melt breccias, dark fine‐grained impact‐melt breccias, large cataclastic feldspars, and irregularly shaped brown glass clasts. Mafic components are rare and no genuine regolith components were found in the sections studied. Minerals in Dhofar 081 show homogeneously distributed shock features: intergranular recrystallization, strong fracturing and mosaicism in feldspar as well as a high density of mostly irregular fractures in pyroxene and olivine. Localized impact melting caused by one or several impacts led to a strong lithification. Based on these effects an equilibration shock pressure of about 15–20 GPa is estimated for the strongest shock event in Dhofar 081. Devitrification of the “glassy” material in the rock indicates thermal annealing after shock melting suggesting that the 15–20 GPa shock event predated the ejection event. According to the concentrations of implanted solar noble gases Dhofar 081 represents a polymict clastic breccia deposit with possibly a minor regolith component. A similar noble gas record of Dhofar 081 and MacAlpine Hills 88104/05 suggests the possibility of a source crater pairing of both meteorites. As indicated by noble gas measurements pairing of Dhofar 081 with the other lunar meteorites found in Oman, Dhofar 025 and Dhofar 026, is unlikely.  相似文献   

Non Gaussian and Non Local Transport in the Earth's Distant Magnetotail     

A. Greco  G. Zimbardo  P. Veltri  A.L. Taktakishvili  L.M. Zelenyi 《Astrophysics and Space Science》2001,277(1-2):35-38

We study the ion dynamics in a magnetic field reversal with a constant electric field and with a model of three dimensional magnetic turbulence. By computing the mean square displacements in the plane of the current sheet we find superdiffusive and superballistic transport regimes. Since velocity increases with the length of the free path, we have accelerated Lévyflights. The possibility to generate power law velocity distribution functions is pointed out, as well as the long memory effects and non local properties of ion transport. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献