Qinling-Type Lead-Zinc Deposits     

Li Jianzhong  Gansu Institute of Geology for Non-Ferrous Metals  CNNC  Lanzhou  Gansu He Dianren North west Institute of Geology for Non-Ferrous Metals  CNNC  Xi''an  Shaanxi  Wu Jianmin Research Institute of Geology for Mineral Resources  CNNC  Guilin  Guangxi 《《地质学报》英文版》1993,67(1)

Qinling-type Pb-Zn deposits are located in the Qinling fold belt, occurring in the fine-clastic and carbonate rocks of the Devonian marine facies. They are reformed sedimentary deposits originating from hydrothermal waters, and may be subdivided into 2 subtypes: hydrothermal sedimentary deposits (Changba subtype) and reformed hydrothermal sedimentary deposits (Bijiashan-Qiandongshan subtype). In comparison with some of the famous Palaeozoic Pb-Zn deposits in the world, the Qinling-type Pb-Zn deposits constitute an independent type, which possesses some characteristics of both hydrothermal sedimentary deposits (Meggen type) and reformed hydrothermal deposits (Mississippi Valley type).  相似文献   

Sedimentology Review/1     

C. P. North 《Basin Research》1993,5(3):193-194

  相似文献   

A study of abrupt climate change in a simple nonlinear climate model     

R Q Lin  G R North 《Climate Dynamics》1990,4(4):253-261

We use a seasonal energy balance climate model to study the behavior of the snowline cycle as a function of external parameters such as the solar constant. Our studies are confined in this study to cases with zonally symmetric land-sea distributions (bands or caps of land). The model is nonlinear in that the seasonally varying snow/sea ice line modifies the energy receipt through its different albedo from open land or water. The repeating steady-state seasonal cycle of the model is solved by a truncated Fourier series in time. This method is several thousand times faster than a time stepping approach. The results are interesting in that a number of bifurcations in the snowline behavior are found and studied for various geographies. Polar land caps and land bands positioned near the poles exhibit a variety of discontinuous summer snow cover behaviors (abrupt transitions as a parameter such as solar constant is slowly varied), which may be relevant to the inception and decay of continental ice sheets.  相似文献   

Analysis and interpretation of the paleogeographic distribution of marine sedimentary phosphorites     

A. E. Gunter  R. W. Yole  E. Irving  F. K. North  W. Yzerdraat  W. Neely 《Mathematical Geosciences》1983,15(1):225-226

World-wide distribution of marine phosphorite deposits has been plotted on computergenerated paleogeographic maps of specific geologic time intervals in order to determine if and when optimum arrangements of continents and oceans existed for phosphorogenesis. Geographic input data for the program HYPERMAP consists of digitized continental edges and bathymetry and appropriate coordinates for discrete continental structural blocks. Paleopole and block rotation data were used to construct maps for the following time intervals; Recent, 20, 40, 60, 80, 100, 120, 140, 170–190, 250, 280, 325, 350, 375, 400, 450, 500, and 600 Ma. Phosphorite deposits were plotted directly on the appropriate map according to location and age. The major phosphorites have been divided into four types (A, B, C, D)on the basis of the environment of deposition and facies association. A and B types were deposited in water depths of several hundred meters in association with black shales, chert, and dolomite. In terms of reserves of P ₂ O ₅ they show marked distribution peaks in the Lower and Middle Cambrian and the Permian. C and D types were deposited in water depths of tens of meters in association with quartz siltstones, quartz mudstones, and carbonates. Time distribution peaks in the Lower and Middle Cambrian, the Ordovician, Upper Cretaceous-Eocene, and the Miocene are evident for these deposits. The plotted distributions may be related to a recent model of phosphorite deposition (Sheldon, 1980)which suggests that phosphate levels in ocean water have fluctuated with time. Phosphate content built up during times of high-level warm seas was brought into favorable depositional sites by equatorial and tradewind belt upwelling currents. The paleogeographic analysis shows that maximum phosphorite deposition from equatorial upwelling (type C)occurred north and south of narrow constricted equatorial seaways, at times of high-level warm seas. Maximum deposition of phosphorites from tradewind belt upwelling (types A, B, C, D)occurred when polar oceans were wide and there were extensive north-south trending coasts in low latitudes, at times of transition from high-level warm seas to low-level cool seas.  相似文献   

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry     

S. Hubrig  P. North  M. Schller 《Astronomische Nachrichten》2007,328(6):475-490

We re‐discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M_⊙ are concentrated towards the centre of the main‐sequence band. In contrast, stars with masses M > 3 M_⊙ seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M_⊙ and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main‐sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0. in slower rotating stars of mass M > 3 M_⊙ too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M_⊙. The obliquity angle distribution as inferred from the distribution of r ‐values appears random at the time magnetic stars become observable on the H‐R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90. or 0. for M < 3 M_⊙. The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M_⊙, no similar trend is found for stars with M < 3 M_⊙. However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

冷却塔托架约束装置在工程抗震中的应用     

苏远升  孙星武 《华北地震科学》1999,17(4):61-65

阐述了电力系统中冷却塔托架约束装置的结构创新及其在工程抗震上的应用,从而克服了传统托架结构与施工工艺存在的诸多弊端,并大大增强了托架支承系统抗御地震破坏的能力。  相似文献   

Orbital solution and fundamental parameters of σ Scorpii     

J. R. North  J. Davis  P. G. Tuthill  W. J. Tango  J. G. Robertson 《Monthly notices of the Royal Astronomical Society》2007,380(3):1276-1284

The first orbital solution for the spectroscopic pair in the multiple star system σ Scorpii, determined from measurements with the Sydney University Stellar Interferometer, is presented. The primary component is of β Cephei variable type and has been one of the most intensively studied examples of its class. The orbital solution, when combined with radial velocity results found in the literature, yields a distance of  174⁺²³₋₁₈ pc  , which is consistent with, but more accurate than the Hipparcos value. For the primary component we determine  18.4 ± 5.4 M_⊙, −4.12 ± 0.34 mag  and  12.7 ± 1.8 R_⊙  for the mass, absolute visual magnitude and radius, respectively. A B1 dwarf spectral type and luminosity class for the secondary is proposed from the mass determination of  11.9 ± 3.1 M_⊙  and the estimated system age of 10 Myr.  相似文献   

The systemic velocities of four long-period cataclysmic variable stars     

R. C. North  T. R. Marsh  U. Kolb  V. S. Dhillon  C. K. J. Moran 《Monthly notices of the Royal Astronomical Society》2002,337(4):1215-1223

  相似文献   

Erratum to: The carbon balance of reducing wildfire risk and restoring process: an analysis of 10-year post-treatment carbon dynamics in a mixed-conifer forest     

Morgan L. Wiechmann  Matthew D. Hurteau  Malcolm P. North  George W. Koch  Lucie Jerabkova 《Climatic change》2015,132(4):721-722

  相似文献   

赣南大吉山五里亭岩体的锆石ELA-ICP-MS定年及其与钨成矿关系的新认识   总被引：39，自引：3，他引：36  

邱检生  McInnes BIA  徐夕生  Allen C M 《地质论评》2004,50(2):125-133

大吉山是南岭地区一个著名的大型钨多金属矿床,五里亭岩体是矿区出露规模最大的火成岩体,岩性为中粗粒似斑状黑云母二长花岗岩。锆石 ELA-ICP-MS 定年结果表明其形成年龄为 237.5±4.8 Ma,属印支期岩浆活动的产物。与南岭地区典型钨多金属矿床成矿岩体相比,五里亭岩体贫硅,富钙、镁、铁,Rb/Sr、Rb/Ba 和 U/Th 比值低,K/Rb 比值高,铕负异常不显著,分异指数低,尚未达到矿化岩体的分异演化程度,不具备矿化岩体的地球化学特征。元素—同位素综合示踪显示区内白云母碱长花岗岩为五里亭岩体经高度分异演化的产物,它与钨多金属矿成矿直接有关。矿区范围内出露的闪长岩起源于地幔,这一岩浆侵位所引起的高热场环境有利于花岗质岩石的形成与演化,对成矿具有重要的意义。  相似文献