论长英质隐爆角砾岩的气热流体溶浸成矿机制——以赣南6722铀矿床为例   总被引：6，自引：1，他引：6  

章邦桐  饶冰  陈培荣  孔兴功 《矿床地质》2001,20(2):129-136

通过对6722铀矿床地质－地球化学特征及长英质隐爆角砾岩和围岩超微构造研究，结合U，Th等元素溶浸实验结果，得出“隐爆气热流体溶浸成矿富集机制”；来自深部的富含挥发组分（H2O、F、CO2等）的高热安粗岩浆，在早白垩世末（107Ma）沿富城花岗岩体西部蚀变带发育的火山机构中发生隐爆作用，致使围岩发生强烈脆性变形，生成长英质隐爆角砾岩带和震裂花岗岩带；压力、温度降低导致安粗岩浆中挥发组分逸出形成气热流进入稳隐爆裂隙中，并将蚀变花岗岩中的活动性成矿元素（U）浸出转移；成矿物质在物理化学条件（p,t,Eh,pH,化学组分等）急剧变化的部位（长英质隐爆角砾岩及碎裂花岗岩）沉淀富集。  相似文献   

滇西上芒岗红色粘土型金矿床金的特征     

饶文波  高振敏  杨竹森  罗泰义  李红阳 《矿物学报》2001,21(2):259-264

通过化学分析法、X射线衍射和粒度分级、金的浸出实验，对上芒岗红色粘土型金矿床进行研究，发现矿石矿物由褐铁矿、粘土矿物和石英组成，矿石中的金与粗颗粒的多少呈正相关，为微细粒金和游离态金，被吸附于褐铁矿、粘土矿物和石项等矿物表面或裂隙中，在红色粘土剖面中与Mo、Sb、Hg、As等元素紧密共生，金在弱酸-弱碱性条件下活性、迁移，在潜水面附近再沉淀，上芒岗卡林型金矿体为红色粘土型金矿的主要矿源体。  相似文献   

Climatic change due to land surface alterations   总被引：1，自引：0，他引：1  

Sergio H. Franchito  V. Brahmananda Rao 《Climatic change》1992,22(1):1-34

A primitive equations global zonally averaged climate model is developed. The model includes biofeedback mechanisms. For the Northern Hemisphere the parameterization of biofeedback mechanisms is similar to that used by Gutman et al. (1984). For the Southern Hemisphere new parameterizations are derived. The model simulates reasonably well the mean annual zonally averaged climate and geobotanic zones.Deforestation, desertification and irrigation experiments are performed. In the case of deforestation and desertification there is a reduction in the surface net radiation, evaporation and precipitation and an increase in the surface temperature. In the case of irrigation experiment opposite changes occurred. In all the cases considered the changes in evapotranspiration overcome the effect of surface albedo modification. In all the experiments changes are smaller in the Southern Hemisphere.  相似文献   

Comparative study of scintillations at the magnetic equator and at the crest region of the equatorial anomaly in Indian zone     

Boby Mathew  B. M. Pathan  K. N. Iyer  D. R. K. Rao 《Journal of Earth System Science》1991,100(4):331-340

Using simultaneous long-term observations of ionospheric scintillation at equator and anomaly crest region in the same longitude (Indian) zone comparative features of scintillation occurrence are brought out. The salient features are: (a) predominantly pre-midnight occurrence of scintillation at equator during winter and equinox seasons, (b) increase of pre-midnight scintillation occurrence with solar activity (c) shifting of occurrence peak during summer from post-midnight in low to pre-midnight in high solar activity periods (d) similarity of scintillation behaviour at these locations during winter and equinoxes but dissimilarity during summer. The solar activity response and magnetic effects indicate that the scintillations at the anomaly crest region in winter and equinox, particularly during high solar activity periods, are of equatorial origin while the summer events may be of local or mid-latitude origin.  相似文献   

Preliminary results from very long period data collected by a broad band digital seismic station     

C. V. Ramakrishna Rao  V. K. Gaur 《Journal of Earth System Science》1991,100(4):369-378

Preliminary analysis of seismograms recorded by a wide band high dynamic range digital seismograph installed under a collaborative research programme between IPG, Paris and NGRI, Hyderabad, indicates that the crust and upper mantle structure below the Indian continent are characterized by high velocity up to a depth of 500 km. Both the group and phase velocities in the period range of 100–350s are found to be faster by 3–4% and 1–3% respectively compared with global models such as the preliminary reference earth model.  相似文献   

The effect of a lower boundary condition on the boundary-layer structure of an axisymmetric vortex     

G. V. Rao  W. H. Raymond 《Boundary-Layer Meteorology》1978,14(4):525-541

The effect of an injection of specific momentum at the bottom boundary of an axisymmetric, quasisteady maintained vortex is studied by extending the earlier investigation of Kuo (1971). Non-zero vertical velocities at the top of the surface layer representing the lower extremity of a vortex are prescribed. Positive values of the superimposed vertical velocity signified pumping; negative, sucking. The two second-order ordinary differential equations governing the tangential and radial velocities of the vortex are solved by employing Newton's iterative method.The result, viz., that pumping produces a deeper inflow layer and destabilizes the motion while suction depresses the inflow layer and produces stability confirmed an earlier finding of certain fluid dynamicists. Modifications of the boundary-layer structure produced by spatially varying the angular momentum distribution of a vortex are analogous to those caused by the imposition of the Taylor boundary condition at the lower extremity of the vortex. They are also similar to those rendered by varying pumping or suction. The latter result is believed to be new while the former simply agrees with an earlier theoretical deduction.  相似文献   

Cavity radius estimation for contained peaceful nuclear explosions—An analytic approach     

M P Ranga Rao  S K Sikka 《Journal of Earth System Science》1978,87(3):13-21

An analytical method based on Penny-Taylor model has been modified and applied for the estimation of the final cavity radius for contained peaceful nuclear explosions. The calculated cavity radii for some nuclear explosions in granite, alluvium and sandstone rocks are in good agreement with measured values.  相似文献   

U/Pb Systematics of zircons during dynamic metamorphism     

A. Krishna Sinha  Lynn Glover III 《Contributions to Mineralogy and Petrology》1978,66(3):305-310

Eight zircon fractions from the Henderson Gneiss were analyzed from the Brevard mylonites and adjacent Inner Piedmont rocks near Rosman, North Carolina, to determine variations of U/Pb systematics of zircons in a pressure-dominated metamorphism. Substantial uranium gain occurred during zircon recrystallization and size reduction.At Rosman, the Henderson Gneiss zircons probably formed about 600 m.y. ago and now show evidence of being binary mixtures. They experienced mylonitization at about 450 m.y. ago during Taconic deformation and metamorphism in the almandine amphibolite facies. The lower intensity, upper greenschist or greenschist-amphibolite Acadian (360–390 m.y.) metamorphism and mylonitization (recrystallization) had little effect on the zircons but disturbed Rb/Sr systems.The ages of dynamic metamorphism and thrusting (450, 360–390) in the Piedmont and Blue Ridge near and along the Brevard zone at Rosman, North Carolina, agree well with the tectonic interpretations of the Valley and Ridge Taconic (ca. 470-400 m.y.) and Acadian (ca. 375-330 m.y.) clastic wedges. Intermittent thrusting, folding, and uplift rather than continuous secular uplift of the crystalline terrane seems indicated.  相似文献   

Ionization effects from cosmic sources of x-rays in the lower atmosphere     

D P Sharma  U R Rao  K Kasturirangan 《Journal of Earth System Science》1978,87(7):155-163

Detectable ionization effects in the ionosphericD-region from individual, strong and steady x-ray sources such as Sco X-1 and transient x-ray sources such as Cet X-2 have been reported by us and many others previously based on the field strength and phase variations of the VLF data. As a follow up to these investigations, we have examined the integrated effects of many of the known x-ray sources discovered by UHURU, ANS, Ariel V and SAS-3 satellites, in order to understand the totality of their effects. These effects are examined in the present paper for 0° and +38° geographic latitudes corresponding to midnight conditions and for different times of the year. Such effects are compared, in turn, with those of the known steady sources responsible forD-region ionization such as Lyman-alpha and galactic cosmic radiations. The results are presented as profiles of electron production rates as a function of height. Our study leads to the conclusion that there should be detectable annual variations of the electron density which are pronounced around May-August. Further, the results of the computations on electron production rates corresponding to the spectacular x-ray nova A0620-00 are also included in the present paper.  相似文献   

A nonstationary nocturnal drainage flow model     

K. S. Rao  H. F. Snodgrass 《Boundary-Layer Meteorology》1981,20(3):309-320

The evolution and structure of the steady state of an idealized nocturnal drainage flow over a large uniformly-sloping surface are studied using a nonstationary model with a height-dependent eddy diffusivity profile and a specified surface cooling rate. The predicted mean velocity and temperature profiles are compared with Prandtl's stationary analytical solutions based on the assumption of a constant eddy diffusivity in the drainage layer. The effects of important physical parameters, such as the slope angle, surface cooling, atmospheric stability, and surface roughness, on the steady drainage flow are investigated.Affiliated with Oak Ridge Associated Universities (ORAU).  相似文献