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1.
碳酸盐胶结物中氧碳同位素组成研究是分析成岩过程中流体-岩石相互作用的重要技术方法.综合运用岩石学、矿物学和地球化学方法，对辽河盆地西部凹陷沙河街组砂岩中碳酸盐胶结物的化学组成和碳酸盐胶结物及成岩流体同位素组成特征进行系统分析.研究表明，研究区碳酸盐岩主要为方解石和白云石，胶结物主要类型为嵌晶式胶结、孔隙式胶结、斑块状胶结和星点状胶结.碳、氧稳定同位素组成能有效地反映成岩-成矿流体及其他物质的来源，碳酸盐胶结物与现今浅层地下水氧同位素组成差异巨大而与变质水同位素组成具有相似性，反映了盆地演化过程中活动热流体对成岩作用的影响.包裹体的氢、氧同位素组成可表征成矿溶液的演化特征，砂岩碳酸盐胶结物包裹体更富集氢的轻同位素和氧的重同位素，表明发生了明显的“氧-18漂移”.碳酸盐胶结的成矿溶液表现出“受热雨水”的同位素组成特征，反映了深源活动热流体对成岩作用的影响. 相似文献
2.
Zvi Sofer 《Geochimica et cosmochimica acta》1978,42(8):1141-1149
The isotopic composition of the hydration water of gypsum is a sensitive diagnostic tool for specifying the mechanisms of its formation, either from an evaporating brine, by hydration of anhydriate or in situ formation in surface or groundwaters through oxidation of sulfides. Primarily, gypsum is formed in isotopic equilibrium with the mother brine; later, exchange of water occurs rapidly under humid conditions by means of a mechanism of recrystallization of gypsum or through diffusion of water into the intact crystal. Under arid conditions, however, the primary isotopic record has been preserved, in some instances, since the Pleistocene. 相似文献
3.
成矿热液的氢、氧同位素组成与其水的类型、水/岩交换的岩石成分和同位素组成、水/岩交换时的温度及水/岩交换程度(W/R比值大小)等诸多因素有关,微生物和有机质也对其有一定的影响。因此,仅通过简单投影的方法将成矿热液的氢、氧同位素值与一些所谓的标准值进行类比,由此就推断出热液中水的来源,这种方法是不可取的;尤其当成矿热液的氢、氧同位素值介于大气降水和岩浆水的值之间时,切忌滥用两种水混合成矿模式,因为实际情况往往并不是这样。本文以胶东乳山金矿床为例,展开了这方面的讨论。 相似文献
4.
Oxygen isotope fractionation factors between calcium carbonates and water have been applied to ancient marine geochemistry
principally for the purpose of geothermometry. The problem was encountered, however, with respect to the direction and magnitude
of oxygen isotope fractionation between calcite and aragonite at thermodynamic equilibrium. This basically involves sound
understanding of both thermodynamics and kinetics of oxygen isotope fractionation between inorganically precipitated carbonate
and water at low temperatures. Thus the crucial issues are to acknowledge the processes of chemical reaction and isotopic
exchange during precipitation of CaCO3 minerals in solution, the kinetic mechanism of isotope equilibrium or disequilibrium, the effect of polymorphic transition
from metastable aragonite to stable calcite under hydrous or anhydrous conditions, and the presence or absence of isotope
salt effect on oxygen isotope exchange between carbonate and water in response to the hydrous or anhydrous conditions at thermodynamic
equilibrium. Because good agreements exist in carbonate–water oxygen isotope fractionation factors between theoretical calculations
and experimental determinations, it is encouraging to applying the thermodynamic and kinetic data to isotopic paleothermometry
and geochemical tracing. 相似文献
5.
Leonel da Silveira Lobo O&#x;Reilly Sternberg Michael Joseph DiGiacomo DeNiro 《Geochimica et cosmochimica acta》1983,47(12):2271-2274
Carbonyl oxygens of organic molecules undergo isotopic exchange with water during reversible hydration reactions. The equilibrium isotopic fractionation factors between the carbonyl oxygen of acetone and water at 15°, 25°, and 35°C are 1.028, 1.028, and 1.026 respectively. The differences between the δ18O values of the carbonyl oxygen of acetone and of the water with which it is in equilibrium are similar to the differences that have been observed between the δ18O values of cellulose and the water used in its synthesis by a variety of aquatic plants and animals. Additionally, the identity of the acetone-water fractionation factors at 15° and 25°C parallels the observation that the difference between the δ18O values of cellulose and water shows no temperature dependence for individual species of plants grown over the same temperature range. These results are discussed in relation to the proposal that the oxygen isotopic relationship between cellulose and water is established by isotopic exchange occurring during the hydration of carbonyl groups of the intermediates of cellulose synthesis. 相似文献
6.
Shizishan ore-field is a nonferrous and noble metal ore-field which is most rich in copper and gold.There are many types of fluid inclusions in minerals of the deposits.The homogeneous temperatures and the salinities of the fluid inclusions in main mineralization stages have wide ranges,while the different types of the fluid inclusions existed together and their homogeneous temperatures are almost identical in the same mineralization stage,which indicates that the ore-forming process has great relation with the fluid boiling.The gas and liquid chemical compositions and the carbon,hydrogen and oxygen isotopic compositions of the fluid inclusions show that the ore-forming fluids of copper-gold deposits have the same characteristics and evolution tendency,which reflects that the ore-forming material mainly came from the magmatism.The stratigraphic component and the meteoric water may mix in ore- forming fluids in the later mineralization stages.Furthermore,with the fall of the ore-forming temperature the ratios of water and rock decreased.The characteristics of chemical composition and carbon isotopic composition of fluid inclusions indicate that CH4 may play an important role for separating copper and gold in the ore-forming process. 相似文献
7.
氢氧同位素在地热水研究中得到了广泛应用,但由于影响因素较多,对地热水氢氧同位素组成的控制过程通常缺少全面认识。本文以贵德盆地周边两条断裂带上五处温泉为例,通过对比不同地热水之间的水化学差异和热储温度差异,建立了不同地热水的水岩反应程度与氢氧同位素是否偏离大气降水线的关系。在前人识别并定量出扎仓寺地热水存在冷水混合作用的基础上,借助冷水混合比例估算了冷水混合和水汽分离引起的氢氧同位素的变化幅度,在此基础上通过“氧漂移”规律恢复了扎仓寺地热水在发生水岩反应前的氢氧同位素组成。本文关于三个过程对氢氧同位素影响程度的计算方法可以用于分析其他地区地热水的氢氧同位素成因,从而加深对地热水循环过程的认识。 相似文献
8.
得尔布干成矿区(北片)成矿条件初步研究 总被引：17，自引：3，他引：14
该区有色、贵金属矿床的主成矿期为晚侏罗世-早白垩世.不同成因类型矿床成矿温度亦有差异,"斑岩型"属中高温矿床,"火山热液型"属中低温矿床,"新类型"金矿床和"浅成低温热液型"金矿应属低温热液矿床.有色、贵金属矿床中S的来源主要与深源岩浆关系密切,成因类型应属广义的"岩浆热液型矿床",但有少量S来源于容矿岩或为外生S.成矿热液的主体或组成的总趋势,是以岩浆水和大气降水的混合水为特征,热源来自中生代火山侵入岩浆,而莫尔道嘎金矿点是浅成低温热液型,其成矿热液的主体是大气降水.西吉诺山方铅矿包裹体除了显示出岩浆热液的性质外,更多地反映了地下热卤水的介质特征. 相似文献
9.
The hydrogen isotopic composition of structural water in MnO(OH) minerals from manganese oxide and massive sulfide deposits
(Kuroko) in Tertiary formations fall within a narrow range from -261 to -275 permil relative to standard mean ocean water
(SMOW). The δD of two manganites from manganese deposits in Paleozoic formations were -236 and -298 permil, indicating a wider
range than in those of Tertiary manganese deposits. The MnO(OH) minerals are more deuterium-depleted. than any other hydrothermal
minerals reported to date.
Hydrogen isotopic fractionation factors between manganite and water were experimentally determined to be 0.7894, 0.7958, and
0.8078 at 150°, 200°, and 250° C, respectively, under hydrothermal conditions at 500 bars. The present experimental results
indicate that if manganites were formed at temperatures below 250° C under isotopic equilibrium conditions, then most manganite
mineralization in the ore deposits must have precipitated from meteoric hydrothermal solutions. 相似文献
10.
HANS PIRLET LAURA M. WEHRMANN BENJAMIN BRUNNER NORBERT FRANK JAN DEWANCKELE DAVID VAN ROOIJ ANNELEEN FOUBERT RUDY SWENNEN LIEVEN NAUDTS MATTHIEU BOONE VEERLE CNUDDE JEAN‐PIERRE HENRIET 《Sedimentology》2010,57(3):786-805
Authigenic gypsum was found in a gravity core, retrieved from the top of Mound Perseverance, a giant cold‐water coral mound in the Porcupine Basin, off Ireland. The occurrence of gypsum in such an environment is intriguing, because gypsum, a classic evaporitic mineral, is undersaturated with respect to sea water. Sedimentological, petrographic and isotopic evidence point to diagenetic formation of the gypsum, tied to oxidation of sedimentary sulphide minerals (i.e. pyrite). This oxidation is attributed to a phase of increased bottom currents which caused erosion and enhanced inflow of oxidizing fluids into the mound sediments. The oxidation of pyrite produced acidity, causing carbonate dissolution and subsequently leading to pore‐water oversaturation with respect to gypsum and dolomite. Calculations based on the isotopic compositions of gypsum and pyrite reveal that between 21·6% and 28·6% of the sulphate incorporated into the gypsum derived from pyrite oxidation. The dissolution of carbonate increased the porosity in the affected sediment layer but promoted lithification of the sediments at the sediment‐water interface. Thus, authigenic gypsum can serve as a signature for diagenetic oxidation events in carbonate‐rich sediments. These observations demonstrate that fluid flow, steered by environmental factors, has an important effect on the diagenesis of coral mounds. 相似文献
11.
ABSTRACT
The carbon and oxygen isotopic composition of the Austin Chalk was examined in cores representing a range of depths from surface to 3000 m in order to document the effects of burial diagenesis on carbon and oxygen isotopic composition. Low magnesium calcite oysters were separated (from 500 um wide areas) and analysed to estimate the starting composition of Cretaceous marine sediment. These gave an average value of -2·5%δ18 O; + 2·0%δ13 C (PDB). The compositions of micrite, intergranular cement, and fracture cement were analysed, and their deviation from this original marine composition was evaluated to document the progression of chalk diagenesis. Interestingly, micrite exhibits only minor variation in composition from marine values despite present burial depth ranges in excess of 3000 m. The average deviation from δ18O marine is less than 1·5. Furthermore, intergranular cement and particularly fracture cements, which occur only in the deepest cores and which clearly post-date micrite lithification, are generally indistinguishable from micrite in composition. Isotopic compositions exhibit no correlation with depth of burial despite abundant petrographic evidence of deep burial diagenesis. This uniformity in composition is interpreted as reflecting a closed, rock-dominated diagenetic system in which the compositions of precipitated carbonate cements were controlled by the composition of dissolving carbonates during lithification. As such, the composition of burial cement is not representative of the rock-water temperatures during precipitation.
Thus, in the context of isotopic analyses from other carbonate systems, unless the degree of openness of the diagenetic system is known, oxygen isotopic signatures of cements cannot directly be converted to the rock-water temperatures at which they were precipitated unless the composition of the ambient porefluid is also known. 相似文献
The carbon and oxygen isotopic composition of the Austin Chalk was examined in cores representing a range of depths from surface to 3000 m in order to document the effects of burial diagenesis on carbon and oxygen isotopic composition. Low magnesium calcite oysters were separated (from 500 um wide areas) and analysed to estimate the starting composition of Cretaceous marine sediment. These gave an average value of -2·5%δ
Thus, in the context of isotopic analyses from other carbonate systems, unless the degree of openness of the diagenetic system is known, oxygen isotopic signatures of cements cannot directly be converted to the rock-water temperatures at which they were precipitated unless the composition of the ambient porefluid is also known. 相似文献
12.
Merlin Méheut Michele Lazzeri Francesco Mauri 《Geochimica et cosmochimica acta》2007,71(13):3170-3181
Isotopic fractionation factors for oxygen, hydrogen and silicon have been calculated using first-principles methods for the kaolinite, quartz, water (ice and gas water) system. Good agreement between theory and experiment is obtained for mineral-water oxygen isotope fractionation. This approach gives reliable results on isotopic fractionation factors as a function of temperature, within a relative precision of typically 5%. These calculations provide independent quantitative constraints on the internal fractionation of oxygen in kaolinite, the fractionation of silicon isotopes at equilibrium, or hydrogen fractionation between kaolinite and water. Calculated fractionation factors at 300 K are 12.5‰ for the kaolinite internal-fractionation of oxygen, and 1.6‰ for silicon fractionation between quartz and kaolinite. 相似文献
13.
Isotopic analyses (18O and 34S) of the Eocene gypsum from the Paris basin show a range beyond the normal Tertiary marine values. The possibility of a reduction process during diagenesis is discussed.A hypothesis of continental origin by leaching of Permotriassic deposits is proposed for this formation on the basis of a comparison of the isotopic contents recorded from Germany and eastern France. 相似文献
14.
V. N. Kuleshov 《Lithology and Mineral Resources》2001,36(5):429-444
Isotope-geochemical features of the formation of carbon and oxygen isotopic compositions in sedimentary and diagenetic carbonates are considered. Isotopic criteria for the identification of early diagenesis zone are proposed. The transition from sedimentogenesis to diagenesis (upper boundary of the early diagenesis zone) is accompanied by the alteration of carbon isotopic composition in the HCO–
3(hydrosphere)–HCO–
3(pore water of sediment)system. The lower boundary of early diagenesis zone is registered by the alteration of oxygen isotopic composition in the pore water of sediments and authigenic carbonates. 相似文献
15.
The sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules (10 FeO-poor and 5 FeO-rich chondrules) in the least metamorphosed ordinary chondrites, Bishunpur and Semarkona, have been measured by ion microprobe. Some troilite grains are located inside metal spherules within chondrules. Since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies, those troilites are most likely primary, having survived chondrule-forming high-temperature events. If they are primary, they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass-dependent isotopic fractionations. However, the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations (<1 ‰/amu) relative to large troilite grains in matrix. Among other chondrule troilites that we measured, only one (BI-CH22) apparently has a small excess of heavy isotopes (2.7 ± 1.4 ‰/amu) consistent with isotopic fractionation during evaporation. All other grains have isotopic fractionations of <1 ‰/amu. Because sulfur is so volatile that evaporation during chondrule formation is probably inevitable, non-Rayleigh evaporation most likely explains the lack of isotopic fractionation in putative primary troilite inside chondrules. Evaporation through the surrounding silicate melt would have suppressed the isotopic fractionation after silicate dust grains melted. At lower temperatures below extensive melting of silicates, a heating rate of >104-106 K/h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors. This heating rate may provide a new constraint on the chondrule formation processes. 相似文献
16.
矿物稳定同位素地球化学研究 总被引：36，自引：2，他引：34
通过测定矿物中元素H ,C ,O和S的同位素比值 ,认识矿物体系中的同位素效应 ,不仅能够确定矿物之间和矿物与流体之间的同位素平衡关系 ,而且能够了解影响矿物平衡和动力学同位素性质的因素。文中评述了稳定同位素分馏系数校准的理论计算、实验测定和经验估计方法 ,讨论温度、压力、化学成分和晶体结构等对矿物同位素性质的影响。由于同位素效应取决于矿物的物理和化学性质 ,因此应用稳定同位素来作为示踪剂不仅能够追索各种矿物学反应的路径 ,而且能够提供证据来阐明矿物晶体结构的某些细节。 相似文献
17.
微细浸染型金矿床的稳定同位素特征与成因探讨 总被引：22，自引：1，他引：21
对我国众多沉积岩系中的微细当染型金矿床开展了较为系统的稳定同位素地球化学研究,非常分散复杂的氢氧同位素组成被认为是沉积盆地流体的一个典型特征,这是因为盆地流体中水的两个主要来源－海水和大气降水,经不同程度的水－岩反应同位素交换后又以不同比例相互混合,再加上有机物和粘土矿物的相变水在不同阶段以不同比例加入。 相似文献
18.
胶东金矿床碳酸盐矿物的碳-氧和锶-钕同位素地球化学研究 总被引：16，自引：8，他引：16
对胶东四类金矿床(盆地边缘砾岩型、斑岩型-浅成热液型、石英脉型和破碎带蚀变岩型)矿石中的碳酸盐矿物开展了系统的碳-氧同位素和锶-钕同位素地球化学研究。研究结果表明，与宏观的成矿地质条件和矿床地质特征相对应，山东金矿床可能有亲岩浆岩和亲沉积盆地两个不同的成矿系统。前者包括斑岩型-浅成热液型、石英脉型和破碎带蚀变岩型三类金矿床，后者指盆地边缘砾岩型金矿床，二者具有不同的碳-氧和锶-钕同位素地球化学特征。山东亲岩浆岩系列的金矿床，其锶-钕同位素与同时代的幔源岩浆岩一致，碳同位素显示幔源碳和岩浆碳的特征，氧同位素则显示初生水与大气降水不同比例混合的可能性，因此有可能是以CO2为主、富合成矿金属的地幔流体与浅部下渗大气降水相互作用的结果。而与岩浆岩关系不密切、主要受盆地边缘断裂控制的盆地边缘砾岩型金矿床，其碳-氧和锶-钕同位素组成均较分散，可能主要与地壳浅部下渗大气降水对上地壳各种岩石淋滤萃取演化而成的成矿流体有关。 相似文献
19.
Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5%. and in O18 by 0.8%. relative to the residual solution. No additional isotopic fractionation due to a salt filtering mechanism was observed at NaCl concentrations up to 0.01 N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role.The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. 相似文献
20.
The Cangyuan Pb-Zn-Ag polymetallic deposit is located in the Baoshan Block, southern Sanjiang Orogen. The orebodies are hosted in low-grade metamorphic rocks and skarn in contact with Cenozoic granitic rocks. Studies on fluid inclusions (FIs) of the deposit indicate that the ore-forming fluids are CO2-bearing, NaCl-H2O. The initial fluids evolved from high temperatures (462–498 °C) and high salinities (54.5–58.4 wt% NaCl equiv) during the skarn stage into mesothermal (260–397 °C) and low salinities (1.2–9.5 wt% NaCl equiv) during the sulfide stage. The oxygen and hydrogen isotopic compositions (δ18OH2O: 2.7–8.8‰; δD: −82 to −120‰) suggest that the ore-forming fluids are mixture of magmatic fluids and meteoric water. Sulfur isotopic compositions of the sulfides yield δ34S values of −2.3 to 3.2‰; lead isotopic compositions of ore sulfides are similar to those of granitic rocks, indicating that the sulfur and ore-metals are derived from the granitic magma. We propose that the Cangyuan Pb-Zn-Ag deposit formed from magmatic hydrothermal fluids. These Cenozoic deposits situated in the west of Lanping-Changdu Basin share many similarities with the Cangyuan in isotopic compositions, including the Laochang, Lanuoma and Jinman deposits. This reveals that the Cenozoic granites could have contributed to Pb-Zn-Cu mineralization in the Sanjiang region despite the abundance of Cenozoic Pb-Zn deposits in the region, such as the Jingding Pb-Zn deposit, that is thought to be of basin brine origin. 相似文献