Alkaline and ultramafic carbonate lamprophyres in Central Bohemian carboniferous basins,Czech Republic     

Dr. J. Ulrych  Dr. E. Pivec  Dr. K. Zák  Dr. J. Bendl  Dr. P. Bosák 《Mineralogy and Petrology》1993,48(1):65-81

Summary Dykes of alkaline and ultramafic carbonate lamprophyres (monchiquite-ouachitite and aillikite) intrude the Carboniferous sediments of Central Bohemia. Their characteristic feature is the presence of substantial amounts of a sodalite group mineral (presumably haüyne), carbonate and barite. Isotopic compositions of ¹³C (–3.4 to –6.2) and ¹⁸O ( + 13.5 to + 15.9) indicate that the carbonate is of primary magmatic origin and that fluids were formed at temperatures of 500 to 350°C. High contents of CO₂ (3.6 to 17.6 wt.%) and incompatible elements, high LREE/HREE ratios (30.0 to 57.7), and low Rb/Sr (0.025 to 0.078) and⁸⁷Sr/⁸⁶Sr (0.7038 to 0.7042) ratios suggest the ultramafic lamprophyres are related to deep-seated carbonated magmas of mantle origin. Low degree of partial melting ( < 1%) of the mantle peridotite is envisaged, with additional transport of fluids rich in incompatible elements into the crustal chamber. Alkaline lamprophyres are fractionated derivatives which originated from the same source. Magma intrusion from different levels of a magma chamber into fracture zones under horizontal tension without a central intrusion could result in variability in lamprophyre composition (cumulates or evolved derivatives).

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Alkalische und ultramafische Karbonat-Lamprophyre der zentralen böhmischen Karbonbecken, Tschische Republik

Zusammenfassung Alkalische und ultramafische Karbonat-Lamprophyrgänge (Monchiquit-Ouachitit und Aillikit) intrudieren in karbonische Sedimente Zentralböhmens. Sie sind charakterisiert durch das Auftreten von beträchtlichen Mengen an Mineralen der Sodalith-Gruppe (v.a. Haüyn), Karbonaten und Baryt. Ihre Isotopenzusammensetzung von ¹³C (–3.4 bis –6.2) und ¹⁸O (13.5 bis 15.9) zeigt, daß die Karbonate primär magmatischen Ursprungs sind und daß assoziierte Fluide in einem Temperaturbereich von 350 bis 500°C gebildet wurden. Hohe Gehalte an CO₂ (3.6 bis 17.6 Gew. %), inkompatiblen Elementen, hohe LREE/HREE-Verhältnisse (30.0 bis 57.7), sowie niedrige Rb/Sr—(0.025 bis 0.078) und⁸⁷Sr/⁸⁶Sr-(0.7038 bis 0.7042) Verhältnisse lassen vermuten, daß die ultramafischen Lamprophyre mit karbonatischen Magmen des Mantels in Beziehung stehen. Eine niedrige Aufschmelzungsrate ( < 1%) von Mantelperidotit mit zusätzlichem Transport von, an inkompatiblen Elementen angereicherten Fluiden, in die krustale Magmenkammer wird diskutiert. Alkalische Lamprophyre sind als stärker fraktionierte Magmen, die derselben Quelle entstammen, zu verstehen. Die Intrusion der aus verschiedenen Bereichen der Magmenkammer stammenden Magmen in durch horizontale Dehnung verursachte Störungszonen könnte das Fehlen eines zentralen Intrusionskörpers und die unterschiedliche Zusammensetzung der Lamprophyre (Kumulate oder entwickelte Derivate) erklären.

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With 8 Figures  相似文献   

Propagation and absorption of cyclotron maser radiation in solar microwave spike bursts     

Z. Kuncic  P. A. Robinson 《Solar physics》1993,145(2):317-338

It has been argued that the loss-cone-driven electron cyclotron maser instability can account for the properties of millisecond microwave spike bursts observed during some solar flares. However, as it propagates outward from the corona, maser radiation undergoes gyroresonance absorption when its frequency is a harmonic of the local electron-cyclotron frequency. Existing analytical models using slab geometries predict that this absorption should be sufficiently strong to prevent the radiation from being seen at the observed levels, except under highly restrictive conditions or for unrealistic plasma parameters. A more comprehensive analysis is presented here to determine if and when maser radiation can escape to produce microwave spike bursts. This analysis employs numerical raytracing and incorporates propagation and absorption of fundamental maser emission in a realistic model of a coronal flux loop. It is found that ranges of physical conditions do exist under which maser radiation can escape to an observer and that these conditions are much more limiting for fundamental emission in the extraordinary ()-mode than in the ordinary (o)-mode. Detailed investigation implies that escaping radiation in the -mode is highly directional and chiefly observable toward the center of the solar disk, while escapingo-mode radiation is found to emerge from the corona over a much wider range of directions, with some cases corresponding to radiation observable near the solar limb.  相似文献   

Intrinsic sample methods for mineral exploration and resource assessment     

DeVerle Harris  Guocheng Pan 《Natural Resources Research》1993,2(2):113-121

We report on an objective methodology, referred to as intrinsic sample methodology, for the delineation of exploration target areas or resource areas for assessment. Important features of the methodology include (1) identification of recognition criteria for critical genetic factors, (2) synthesis of new variables from enhanced geodata, (3) estimation of logit probability models, and (4) cutting of estimated logit probabilities to delineate exploration targets or resource areas. The methodology is demonstrated on the Walker Lake quadrangle of Nevada and California.  相似文献   

流体在岩浆型铬铁矿和铂族元素成矿过程中的作用及意义     

苏本勋  刘霞  袁庆晗  罗扬  潘旗旗  白洋  崔梦萌  肖燕  唐冬梅 《地质学报》2022,96(12):4091-4100

镁铁- 超镁铁岩是揭示地幔物质组成和壳幔相互作用的重要窗口，也是Ni- Cu- PGE- Cr等金属矿产资源的重要载体。不同的镁铁- 超镁铁岩体赋矿特征明显不同：蛇绿岩以产出铬铁矿床为特征，阿拉斯加型岩体主要赋含铂族元素(PGE)矿床，大型层状岩体则可同时产出铬铁矿床、PGE矿床和Cu- Ni硫化物矿床。这种成矿差异显然与赋矿岩体形成的构造背景、母岩浆经历的岩浆演化过程有关，但缺少关键控制因素的研究。前人对上述不同种类矿床的研究工作主要集中于地幔源区的部分熔融、上升过程中或岩浆房内的围岩混染和结晶分异等岩浆过程，而极少关注流体作用。近年来，实验岩石学和岩石地球化学的研究均表明幔源岩浆演化过程中的流体活动可能对成矿元素的富集迁移起到至关重要的作用，同时这些成矿元素的赋存状态和分配系数也在不断更新。厘清Cr和PGE在熔体演化——尤其是流体出溶过程中的地球化学行为，刻画并揭示其迁移富集、分离和再富集的成矿过程及控制因素，已成为当前岩浆矿床研究的热点。本文围绕富水流体与铬铁矿和PGE成矿关系的科学问题，总结了不同镁铁- 超镁铁岩体的成矿差异以及铬铁矿和PGE矿床成矿过程中的流体活动记录，提出流体性质和组分对铬铁矿和PGE迁移富集的控制作用，强调有必要开展蛇绿岩、大型层状镁铁- 超镁铁岩体和阿拉斯加型岩体的对比研究。  相似文献   

五大连池火山群新期火山渣丘成因的探讨     

潘玉林  杨森林 《东北地震研究》1997,13(3):66-71

火山渣丘,是火山区内的一种特殊的地质现象,以前地其成因国内外尚无详细探讨和描述,有的学者曾经统称为副火山。笔者通过实地调查,对这一结论提出新的见解,认为火山渣丘的形成是一复杂的地质现象,其成因具有多元性。这对探讨火山喷发规律,对火山地质地貌的准确描述与具有积极作用。  相似文献   

含煤层地质环境下地震波场的数值模拟   总被引：3，自引：2，他引：1  

潘冬明  杨顶辉 《地球物理学进展》1997,12(1):74-83

本文对含低速煤层地质环境下弹性波场多波多分量地震资料进行了二维数值模拟研究,对人工边界反射进行了有效处理,频散效应得到了有效的压制,对几种不同激发与观测排列方式下的弹性波资料进行了模型计算与分析。  相似文献   

A note on the performance of the multiply-upstream semi-Lagrangian advection schemes for one-dimensional nonlinear momentum conservation equation     

Prof. Z. I. Janjić 《Meteorology and Atmospheric Physics》1995,55(1-2):1-16

Summary Two-time-level multiply-upstream semi-Lagrangian schemes were examined in the case of the self-advecting, one-dimensional nonlinear momentum conservation equation. The shock formation process was analyzed. It is pointed out that the shocks cannot be created in the truncated systems satisfying the Pudykiewicz, Benoit and Staniforth criterion.The numerical integrations were restricted to 12 h. It was shown that, at least in the sub-CFL range, increased complexity of the scheme can compensate reduced horizontal resolution. A considerable sensitivity of the schemes with respect to the time step was detected. In the super-CFL mode, several windows on various time scales were found within which the Pudykiewicz, Benoit and Staniforth criterion was satisfied. The time step of 1.44 times the maximum time step allowed by the CFL criterion was used in the semi-Lagrangian runs.The super-CFL, semi-Lagrangian solutions were diverging progressively from the sub-CFL ones as the forecasts advanced. This was also reflected in the energy spectra.Unacceptably large energy losses were encountered in the super-CFL, semi-Lagrangian runs. Most of these losses could be explained by the reduced mean wind speed, i.e., the amplitude of the zero wavenumber wave. At the same time, the energy content in the shorter waves increased. In a more complex model, such a situation would resemble a loss of zonal, and an increase of transient eddy kinetic energy.A trajectory error measure was defined as the maximum absolute value of the distance between the actual arriving point of the particle originating at the estimated departure point, and the grid point assumed to be the arrival point in the semi-Lagrangian procedure. In contrast to the sub-CFL regime, this measure could reach a considerable fraction of the grid distance in the computations with the super-CFL time steps.In the physical system considered, the trajectories are determined only by the velocities at the departure points. With the semi-Lagrangian schemes the distances traveled by the particles are estimated on the basis of the velocities at the points downstream with respect to the departure points. Thus, unless the solution is smooth (in space and time) on the scales of the extrapolation distances/times, the upstream extrapolation does not promise the convergence of the solution.With 16 Figures  相似文献   

湘中“桃江式”锰矿含锰岩系的定量研究及其找矿意义          下载免费PDF全文

潘汉军  侯景儒  张廷勋 《地质找矿论丛》1995,10(2):16-27

本文从分析地质体数学特征的思想出发,来研究“桃江式”锰矿的含矿母岩－“含锰岩系”的数学特征。含锰岩系主要由五种岩石组成：粘土岩、黑色页岩、条带状页岩、含锰灰岩和碳酸锰矿层,其数学特征研究包括其统计特征分析、结构特征分析和空间特征分析。文最后讨论了这些数学特征在寻找同类锰矿中的意义。  相似文献   

The effect of an optically thin region on stability of an accretion disk around a supermassive black hole     

B. F. Liu  G. Z. Xie  K. F. Ji 《Astrophysics and Space Science》1995,225(2):299-314

We analyse conditions of the innermost portion of an accretion disk and establish a set of equations for this region. A stable innermost region may exist, which can probably explain the observed UV and X-ray spectra, avoiding the unstable emission. We then discuss the detailed radial structure of a disk around a black hole for typical AGN parameters and obtain different kinds of- relationships for different regions of a disk. On the basis of this, we discuss the stability. A new type of cycle is present, which we call a double S shaped cycle. In this cycle, the extent of accretion rate variability is much larger than that in dwarf nova cycles. This probably solves the problem of violent variability of AGN. In the meantime, the very high accretion rate at the hottest state in limit cycles in the unstable region may provide continuous injection of matter to the jet and power the relativistic motion of the jet.  相似文献   

On the internal structure and magnetic fields of     

C. Z. Zhang  K. Zhang 《Earth, Moon, and Planets》1995,69(3):237-247

First, a sequence of four-zone models for the interior of Venus is constructed under the assumption of hydrostatic equilibrium. While the equation of state for each zone is taken to be the Bullen's relation with its coefficients consistent with the PREM Earth model (Dziewonski and Anderson, 1981), the position of core-mantle boundary is determined by matching solutions of the Emden's equation in different regions. The results of hydrostatic models indicate the presence of a reasonably large molten iron core in Venus, broadly similar to the Earth. It is also found that the position of the core-mantle interface is nearly model-independent. Second, we focus on the question why Venus does not possess a significant global magnetic field and on what we can learn from this fact. Solutions of magnetohydrodynamic equations appropriate for the molten core of Venus are discussed. It is argued that, because the Elsasser number measuring the relative importance of Coriolis and Lorentz forces satisfies 1, equations for the problem of thermal convection in the Venusian fluid core must be nearly uncoupled with the dynamo equation. The existence of a global magnetic field, though small, then suggests that the size of the magnetic Reynolds numberR _m must beR _m =O(10), sustaining a dynamo action near its marginal state but not an active dynamo in the Venusian molten core. On the basis of asymptotic relations for finite amplitude convection, a useful constraint on important physical parameters for the liquid core of Venus is derived and discussed.  相似文献