金矿床的热液流体特征研究     

王建国  孙丽娜  赵玉山  侯根群  赵纯福 《国土资源》1993,(4)

通过对中国东部金成矿区域地质特征的分析,根据氢氧同位素及流体包裹体数据特征,表明中国东部金矿床成矿流体主要来自大气降水,其次为变质作用过程释放的水和岩浆分异水;成矿金属组分主要来自太古宙变质岩系。  相似文献   

⁴⁰Ar/³⁹Ar and oxygen isotope studies of polymetamorphism from Tinos Island, Cycladic blueschist belt, Greece     

M. BRÖCKER  H. KREUZER  A. MATTHEWS  M. OKRUSCH 《Journal of Metamorphic Geology》1993,11(2):223-240

Abstract Petrological, oxygen isotope and ⁴⁰Ar/³⁹Ar studies were used to constrain the Tertiary metamorphic evolution of the lower tectonic unit of the Cyclades on Tinos. Polyphase high-pressure metamorphism reached pressures in excess of 15 kbar, based on measurements of the Si content in potassic white mica. Temperatures of 450–500° C at the thermal peak of high-pressure metamorphism were estimated from critical metamorphic assemblages, the validity of which is confirmed by a quartz–magnetite oxygen isotope temperature of 470° C. Some ⁴⁰Ar/³⁹Ar spectra of white mica give plateau ages of 44–40 Ma that are considered to represent dynamic recrystallization under peak or slightly post-peak high-pressure metamorphic conditions. Early stages in the prograde high-pressure evolution may be documented by older apparent ages in the high-temperature steps of some spectra. Eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation. Oxygen isotope thermometry of four quartz–magnetite pairs from greenschist samples gives temperatures of 440–470° C which cannot be distinguished from those deduced for the high-pressure event. The exhumation and overprint is documented by decreasing ages of 32–28 Ma in some greenschists and late-stage blueschist rocks, and ages of 30–20 Ma in the lower temperature steps of the Ar release patterns of blueschist micas. Almost flat parts of Ar–Ar release spectra of some greenschist micas gave ages of 23–21 Ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism. Oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a δ¹⁸O-enriched fluid. Rather, the compositions indicate that fluid to rock ratios were very low, the isotopic compositions being primarily controlled by those of the protolith rocks. We assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid. A quartz–magnetite sample from a contact metamorphic skarn, taken near the Miocene monzogranite of Tinos, gave an oxygen isotope temperature of 555° C and calculated water composition of 9.1%. The value of δ¹⁸O obtained from this water is consistent with a primary magmatic fluid, but is lower than that of fluids associated with the greenschist overprint, which indicates that the latter event cannot be directly related to the monozogranite intrusion.  相似文献   

数字宜昌建设初探     

魏明果 《地理信息世界》2002,(3)

数字地球、数字城市是近几年刚提出来的一个全新的概念 ,但数字城市的建设却以空前的速度向前发展着 ,国务院总理朱熔基在视察宜昌时提出要把宜昌建设成世界级的城市 ,未来的城市数字化程度将是衡量一个城市发达程度的重要指标 ,启动数字宜昌建设是跻身世界级城市 ,提高宜昌市综合竞争力的重要举措  相似文献   

测绘项目管理实施引论     

龚强 《地理信息世界》2002,(4)

根据我国测绘生产单位的实际情况 ,测绘项目管理的具体实施大致包括对项目的识别、选定、启动与筹集资金、计划、成本估算、执行计划、控制、收尾等主要步骤。当项目确定后 ,需要启动和筹集资金。而计划是项目管理的基本组成部分 ,包括明确项目目标和工作范围。项目成本估算有因素估算法和利用WBS方法的详细估算。项目质量管理规划的依据有质量目标、范围说明、标准和规范等。  相似文献   

Some thoughts on pulsation and binarity     

Christiaan Sterken 《Astrophysics and Space Science》2006,304(1-4):139-143

Intensive monitoring of main-sequence stars for pulsational studies continuously reveals new binaries and multiple systems. The resulting extensive data sets lead to exact orbital parameters, and to accurate masses of the components. This is also the case higher up the main sequence, though less frequently. We discuss a few examples where intensive observational efforts are necessary in order to improve our knowledge of the pulsational behaviour in the upper main-sequence instability domains, but we emphasize that observational efforts alone that turn out more and more of the same type of data, are by far insufficient, and that there is urgent need for theoretical developments. Determination of highly accurate stellar parameters is of paramount importance and is much more needed than time-series observations.  相似文献   

Methane‐related microbial gypsum calcitization in stromatolites of a marine evaporative setting (Münder Formation,Upper Jurassic,Hils Syncline,north Germany)     

GERNOT ARP  CHRISTIAN OSTERTAG‐HENNING  SELÇÜK YÜCEKENT  JOACHIM REITNER  VOLKER THIEL 《Sedimentology》2008,55(5):1227-1251

Fossil stromatolites may reveal information about their hydrochemical palaeoenvironment, provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made. Tithonian stromatolites of the Münder Formation at Thüste, north Germany, have traditionally been considered as formed by intertidal cyanobacterial communities. However, thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement, but no algal or cyanobacterial filament traces. Moreover, high Fe²⁺ and Mn²⁺ contents, oxygen‐isotope and sulphur‐isotope ratios of carbonate‐bound sulphates, and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that CaCO₃ precipitation occurred near the oxic–anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity. Furthermore, anaerobic oxidation of methane by Archaea may have driven CaCO₃ precipitation in deeper parts of the biofilm community, as reflected by high concentrations of squalane with a strongly negative δ¹³C in conjunction with evaporite pseudomorphs showing extremely low δ¹³C_Carb ratios. Consequently, the Thüste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms. Subsequently, early Mg‐calcitic calcitization within the biofilms occurred because of combined bacterial iron, manganese and sulphate reduction, with an increasing contribution of anaerobic oxidation of methane with depth. This model plausibly explains the prominent preservation of signals derived from oxygen‐independent metabolic pathways, whereas virtually no geochemical record exists for an aerobic community that may, nevertheless, have prevailed at the stromatolite surface. Photic‐zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in, and indicative of, oxygen‐depleted sulphate‐bearing environments with high rates of methane production, conditions that possibly were fulfilled at the Archaean to Proterozoic transition.  相似文献   

Source mechanism of mining induced seismic events — Resolution of double couple and non double couple models     

Jan &#x;ílený  Alexander Milev 《Tectonophysics》2008,456(1-2):3

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Relationship between footwall composition,crustal contamination,and fluid–rock interaction in the Platreef,Bushveld Complex,South Africa     

Julie Pronost  Chris Harris  Christian Pin 《Mineralium Deposita》2008,43(8):825-848

In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of 2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave. −7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef has generally higher plagioclase and pyroxene δ ¹⁸O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic evidence for sub-solidus interaction with fluids, and the Δ _{plagioclase–pyroxene} values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ _{plagioclase–pyroxene} in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO₂-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale. The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO₂ produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation.  相似文献   

A preliminary stable isotope study on Mogok Ruby, Myanmar     

Tzen-Fu Yui  Khin Zaw  Chao-Ming Wu 《Ore Geology Reviews》2008,34(1-2):192

The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ¹³C–δ¹⁸O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ¹⁸O depletion trend with relatively constant δ¹³C values. Ruby formation might have resulted from CO₂-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO₂-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data.  相似文献   

Biostratigraphic and isotopic record of the Cenomanian–Turonian deposits in the Ohaba-Ponor section (SW Haţeg, Romania)     

Mihaela Carmen Melinte-Dobrinescu  Ana-Voica Bojar 《Cretaceous Research》2008,29(5-6):1024

The middle Cenomanian–lower Turonian deposits of Ohaba-Ponor section (Southern Carpathians) were studied from biostratigraphic and isotopic points of view. Both the qualitative and semiquantitative nannofloral analyses, as well as the stable isotope (δ¹³C and δ¹⁸O) data support significant palaeoenvironmental changes in the investigated interval. Two δ¹³C positive excursions were recognized: (1) an excursion up to 1.8‰ (PDB) within the middle/late Cenomanian boundary; (2) an excursion up to 2.2‰ (PDB) in the Cenomanian/Turonian boundary interval. The oldest δ¹³C positive excursion recorded (placed within the Acanthoceras jukes-brownei/Eucalycoceras pentagonum Ammonite Zone boundary interval, and in the NC11 Calcareous Nannofossil Zone respectively) could be assigned to the middle Cenomanian Event II (MCEII). During the above-mentioned event, significant increase in abundance of Watznaueria barnesae, followed by successive blooms of Biscutum constans and Eprolithus floralis, were observed. The youngest δ¹³C positive excursion was identified in the Cenomanian/Turonian boundary interval (in the NC12 and lower part of the NC13 Calcareous Nannofossil Zones). Even the amplitude of this δ¹³C positive excursion is lower in the Ohaba-Ponor section, as generally reported, this may represent the regional record of the OAE2. The successive peaks of the nannofossils Biscutum constans, Zeugrhabdotus erectus and Eprolithus floralis indicate episodes of cooler surface water and high fertility, which preceded and lasted the Cenomanian/Turonian boundary event. Additionally, fluctuations of δ¹⁸O values between −2 and −6‰ suggest also cooler conditions within the Cenomanian/Turonian boundary interval.  相似文献