湘中锡矿山超大型锑矿床的碳、氧同位素体系

本文系统地研究了锡矿山锑矿床的围岩、蚀变围岩和热液成因方解石的碳、氧同位素组成。研究表明，相对于区域地层，矿区灰岩明显亏损^18O；围岩蚀变过程中，围岩的δ^18O值趋于减小并有明显的空间变化趋势。不同期次方解石的碳、氧同位素特征明显不同：成矿早期显示出深特征；成矿晚期方解石的碳、氧同位素组成呈正相关，为水－岩反应和温度降低耦合作用所致；成矿期后方解石的碳、氧同位素组成呈明显的负相关，这种方解石的沉淀介质成成矿流体明显不同。水－岩反应的理论模拟显示，成矿流体不可能为未经深部循环的大气降水；成矿流体中的可溶性碳以H2CO3为主；早期成矿流体的δ^13C、δ^18O分别为－6‰、＋10‰，晚期成矿流体的δ^13C、δ^18O分别为0‰、4‰。     

锂同位素及其地质应用研究进展

锂同位素示踪是近几年发展起来的一门新兴的稳定同位素地球化学方法,锂有两个稳定同位素：^6Li和^7Li。自在界锂同位素的组成变化很大,其δ^6Li值变化幅度超过60‰,现代大洋水的δ^6Li值为－31．0‰,洋中脊玄武岩（BORB）的δ^6Li值为－4．7‰--3.7‰,由于锂同位素存在大的分馏和不同地质体中在截然不同的δ^6Li值,因此锂同位素地质应用前景十分广泛。目前,锂同位素在研究星云形成过程和宇宙事件,洋壳蚀变和海底热液活动,壳－幔物质循环和板块俯冲作用过程,判断卤水起源和演化等方面的研究中成效显著。     

碾子山晶洞碱性花岗岩矿物-水氧同位素交换反应动力学

对黑龙江碾子山碱性花岗岩的全岩及其主要单矿物进行了氧同位素分析，结果表明，全岩和单矿物不仅δ^18O 值变化范围较大（全岩－2．4－2．0‰，石英0．0－5．8‰，碱性长石－3．8－0．1‰，磁铁矿－8．5－1．0‰），而且强烈亏损^18O。共生矿物之间表现出明显不平衡的氧同位素分馏特征，指示在花岗岩侵位之后与水之间发生了同位素交换，根据锆石和现代大气降水的氧同位素组成，对岩石与外来流体的δ^18O值进行了估计，多维矿水－岩反应时限约为0．3－3Ma，水／岩比（氧摩尔比）介于0．11－1．02之间。水－岩反应温度较高（约400度）和反应时间较长是导致石英δ^18O值降低的主要原因。     

西南大别榴辉岩和麻粒岩的氧同位素地球化学

报道了大别造山带西南部湖北红安榴辉岩和罗田麻粒岩的氧同位素组成，并讨论了氧扩散作用对矿物氧同位素平衡的影响，结果得到，红安榴辉岩的全岩δ^18O值为6．4－7．3‰，罗田黄土岭麻粒岩的全岩δ^18O值为6．6－7．8‰，罗田惠兰山麻粒岩的全岩δ^18O值为3．9‰，这些榴辉岩和麻粒岩全岩的氧同位素组成保持了峰期变质条件下的平衡分馏特征，得到的氧同位素温度对于红安榴辉岩425－620度，对于罗田麻粒岩为740－945度。根据快速颗粒边界扩散模型计算的矿物对氧同位素温度不仅与大多数实测氧同位素温度一致，而且与岩石学测温结果相吻合，因此，这些岩石与东大别榴辉岩一样在形成后经历了快速冷却过程，退变质反应过程中没有外来流体加入。     

华东南相山铀矿田的氢氧同位素地球化学研究

矿物及包裹体水的氢氧同位素组成的研究结果表明，相山铀矿田成矿热液的δ^18O与δD值分别变化于－67‰－－7．2‰（SMOW）和－44．1‰－－5．2‰，属大气降水成因流体，蚀变体系δ^18O的变化情况显示，与岩石作用的流体具低δ^18O的降水特征，不同水／岩比值条件下的水－岩同位素平衡交换反应的理论计算和综合分析揭示，本矿田的铀成矿热液起源于大气降水与相山主要岩石的相互作用，岩浆水对成矿热液的贡献不大。     

济阳拗陷第三纪玄武岩的Nd—Sr同位素研究

本文报道了济阳拗陷29个第三纪玄武岩的Nd，Sr同位素组成。结果表明，该区早、晚第三纪玄武岩的Nd-Sr同位素组成变化且具有一定的区别：早经三纪玄武岩的εNd值为0．70481－0．70830；晚第三纪玄武央的εNd值为0．1－2．3，^87Sr/^86Sr比值为0．70421－0．70530。鉴于εNd与1/Nd有^87Sr/^86Sr与1／Sr之间不存在相关特征，Nb正异常以及SiO2与MgO，Fe2O3 FeO,P2O5呈负相关，与Al2O3呈正相关，但与K2I为不存在相关特征，因此，地壳混染作用并不是第三纪玄武岩同位素组成变化的主要原因。玄武岩^87Sr/^86Sr比值的升高是由热液蚀变造成的，而εNd值的变化而归因于源区混合。如果热液蚀变作用没有发生，这些玄武岩的所有数据点在Nd-Sr相关图上将可能位于地幔系列内部。这表明第三纪玄武岩主要是由DMM和EMI两个端员组分不同程度混合形成，EMII的贡献是次要的。     

北祁连山石居里铜矿硅、铅、硫同位素组成特征

石居里铜矿是北祁连山典型的塞浦路斯型铜矿。通过对矿石和围岩的硅、铅和硫同位素研究,作者认为,硅同位素组成δ^30Si(-0．9‰～-0．2‰)与火山岩的δ^30Si范围一致(落在火山岩范围内),由此可知是火山成因的产物。矿石中黄铁矿、黄铜矿的铅同位素组成同各矿区范围玄武岩的铅同位素组成相近,以此为线索结合Rona(1983)的试验规律,推断本区成矿金属主要来源于蚀变玄武岩。硫同位素δ^34S值变化于1．5‰～8．88‰。矿化剂硫来源于火山岩源与海水源的不同比例混合。     

湖南柏坊铜矿床稳定同位素地球化学初步研究

对湖南柏坊铜矿床矿石和脉石矿物进行矿物包裹体、碳、氧、氢和硫同位素测定,获得成矿均一温度约为182℃～192℃,盐度为1．2～4．7wt％。方解石的δ^13C为-2．0‰～3．1‰,δ^18Osmow为12．6‰～20．9‰,δD为-67．3‰～-131．6‰,氢、氧和碳同位素数值随矿体浅部到深部由小到大的变化,显示出热液可能是多来源的。硫化物中辉铜矿的δ^34S为-31．8‰～2．9‰,黄铁矿的δ^34S为-2．1‰～＋2．9‰。黄铁矿的硫同位素组成大于辉铜矿的硫同位素组成,表明硫同位素达到平衡,并估算出δ^34S∑s为0‰,δ^34S∑s值小,指示出硫可能是岩浆来源。     

四川牦牛坪稀土矿床地幔流体成矿的碳、氢、氧、硫同位素证据

选取2种主要矿石类型——碳酸岩伟晶岩型矿石和重晶石伟晶岩型矿石进行了成矿流体的C、H、O、S同位素测试，获得δ^13CV-PDB值为-3．0‰～-5．6‰，δDV-SMOW值为-57‰～-88‰，δ^18OH2O-VSMOW值为8．0‰～13．3‰，δ^34SV-CDT值为3．3‰～5．9‰，以及方解石的δ^13CV-PDB值为-6．9‰和δ^18OV-SMOW值为7．3‰～7．4‰。所有这些数据表明，四川牦牛坪稀土矿床在成矿过程中有大量地幔物质参与。     

新疆西天山高硫化型京希-伊尔曼德金矿床的识别标志及其找矿意义

经过详细的野外地质勘查、热液蚀变及蚀变矿物学研究，流体包裹体和同位素研究，首次将西天山京希－伊尔曼德金矿床确定为高硫化型浅成低温热液金矿床。该矿床的主要识别标志为：发育以多孔状石英为特征的硅化蚀变带和高级泥化蚀变带；成矿流体性质为低盐度[W(NaCl)为0.3-4.2%]、低pH值（3－4）和高氧化态；氧同位素δ（^18O)为1.7 ‰-4.3‰,δ(D)为－60‰--80‰。金主要富集在高级泥化带和中心硅化蚀变带内。系统研究和总结了成矿地质－地球化学制约因素以及区域、靶区和勘探区尺度的找矿标志。     

德兴斑岩铜矿成矿热液来源及其演化——花岗闪长斑岩的氧同位素制约

作者研究了德兴铜厂花岗闪长斑岩的氧同位素组成特征在垂直方向上的变化规律,及蚀变作用对花岗闪长斑岩全岩和单矿物氧同位素组成的影响。结果表明,从地表到深部,花岗闪长斑岩全岩和长石单矿物的δ＾１８Ｏ值总体上有逐渐降低的趋势,反映花岗闪长斑岩受到已演化的大气降水水－岩氧同位素交换作用的影响。水－岩交换作用对花岗闪长斑岩氧同位素组成的影响在浅部和深部是不同的,这主要受控于水－岩交换温度和交换水的初始氧同位素组成等因素。石英的氧同位素组成及变化特征不同于全岩和长石,其值与岩石的蚀变作用有关从花岗闪长斑岩的氧同位煮组成及其变化规律可以推论,由大气降水演化为德兴斑岩铜矿成矿热液是可能的。     

甘肃阳山金矿带构造岩浆演化与金矿成矿

甘肃阳山金矿带位于西秦岭南部,结合同位素测年资料发现阳山金矿区在侏罗纪早期、白垩纪早期及第三纪早期曾发生3期岩浆活动;稳定同位素分析结果显示,矿石中石英的流体包裹体δD值为-75‰～-56‰,δ¹⁸O_H2O为3.7‰～12.2‰,矿脉中黄铁矿及辉锑矿的δ³⁴S为-2.2‰～-0.7‰,表明阳山金矿成矿热液及成矿物质主要来自于岩浆作用;构造变形分析显示该区在三叠纪曾发生韧性变形,在侏罗纪早期产生韧-脆性变形;侏罗纪晚期以后区内构造转为脆性,早期以逆冲推覆构造为主,晚期主要为脆性伸展活动。结合该区地质构造演化史认为本区的3期岩浆活动与区域伸展作用有关,而与岩浆侵入有关的多期岩浆热液活动是促成阳山金矿床形成的主要因素。     

Carbon and oxygen-isotope stratigraphy of the Early Cretaceous carbonate platform of Pădurea Craiului (Apuseni Mountains,Romania): A chemostratigraphic correlation and paleoenvironmental tool

Stable C and O isotope records were obtained from carbonate rocks spanning the Hauterivian to Cenomanian interval collected in several sections from the carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania). In the absence of some key biostratigraphic marker species, stable isotopes were applied as a tool for stratigraphic correlation and dating. The composite δ¹³C and δ¹⁸O curves for the Early Cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes. The Hauterivian and the Barremian limestones (Blid Formation) display lower δ¹³C values (−2.8‰ to +2.9‰) relative to the Aptian–Albian deposits (−2.6‰ to +5.4‰) (Ecleja, Valea Măgurii and Vârciorog Formations). The red detrital formation (Albian–Cenomanian) is characterized by a highly variable distribution of the δ¹³C values (−3.5‰ to +3.9‰). Based on the similarities between the C-isotope curve established in Pădurea Craiului and from other sections in the Tethyan and the Pacific regions, two major oceanic anoxic events characterized by δ¹³C positive excursions were clearly recognized. The first is the OAE1a event (Early Aptian) in the upper part of the Ecleja Formation and the Valea Măgurii Formation. The second is the OAE1b event (Late Aptian–Albian) in the upper part of the Vârciorog Formation and in the Subpiatră Member. The position of the Aptian/Albian boundary is estimated to be at the upper part of the Vârciorog Formation, immediately after the beginning of the δ¹³C positive excursion. The δ¹³C data show major negative excursions during the Barremian (Blid Formation), Early Aptian (Ecleja Formation), and Late Aptian (Vârciorog Formation). The O isotope variation pattern (−10.2‰ to −2.1‰) is consistent with progressively warming temperatures during the Early Barremian followed by a cooling period. A subsequent warming period culminated in the Early Aptian. A significant cooling phase corresponds to the Late Aptian and Early Albian and the climate cooled again during the Late Albian and into the Early Cenomanian stage. The data provide a better understanding of the Early Cretaceous sedimentation cycles in Pădurea Craiului and create a more reliable framework for regional correlations.     

Oxygen isotope composition of xenoliths from the oceanic crust and volcanic edifice beneath Gran Canaria (Canary Islands): consequences for crustal contamination of ascending magmas

Xenolith samples of marine terrigenous sediments and altered Jurassic MORB from Gran Canaria (Canary Islands) represent samples of sub-island oceanic crust. These samples are postulated to define end-members for crustal contamination of basaltic and felsic ocean island magmas. The meta-igneous rocks show great heterogeneity in oxygen isotope compositions (δ¹⁸O 3.3–8.6‰), broadly correlating with their stratigraphic position in the oceanic crust. Gabbros interpreted as fragments of oceanic crust layer 3 have δ¹⁸O values of 3.3–5.1‰, which is lower than MORB (5.7–6.0‰). Layer 2 lavas and dykes show a broader range of δ¹⁸O of 4.1–8.6‰. Therefore, high-temperature metamorphism seems to have been the dominant process in layer 3, while both high- and low-temperature alteration have variably affected layer 2 rocks. Siliciclastic sediments have high δ¹⁸O values (14.1–16.4‰), indicating diagenesis and low-temperature interaction with seawater. The oxygen isotope stratigraphy of the crust beneath Gran Canaria is typical for old oceanic crust and resembles that in ophiolites. The lithologic boundary between older oceanic crust and the igneous core complex at 8–10 km depth—as postulated from geophysical data—probably coincides with a main magma stagnation level. There, the Miocene shield phase magmas interacted with preexisting oceanic crust. We suggest that the range in δ¹⁸O values (5.2–6.8‰) [Chem. Geol. 135 (1997) 233] found for shield basalts on Gran Canaria, and those in some Miocene felsic units (6.0–8.5‰), are best explained by assimilation of various amounts and combinations of oceanic and island crustal rocks and do not necessarily reflect mantle source characteristics.     

Zoned calcites in Jurassic ammonite chambers: trace elements, isotopes and neomorphic origin

Zoned calcites were found in the phragmacone chambers of three Sonniniid ammonites from marine Middle Jurassic sandstones (Isle of Skye, U.K.). Each ammonite has a unique sequence of up to nine zones of calcite which fill or partially fill the chambers. Zones are defined by changes in the density of minute opaque inclusions and variation in trace-element composition. Proximal (early) calcites have undulose extinction and some exhibit the specific fabrics of fascicular-optic and radiaxial fibrous calcites. Microdolomite inclusions are found in one specimen. Early calcites, interpreted as replacements after a single isopachous fringe of acicular carbonate (probably high magnesium calcite), are succeeded by blocky ferroan calcite cement. In one specimen there are two distinct generations of calcite, in the others there is a continuous mosaic incorporating both early calcites and late cement. Isotopic composition of the early calcite zones demonstrates the initial importance of organic derived carbon (δ¹³C =— 26‰, δ¹⁸O ‰ O). Further cementation and mineralogical stabilization took place at increased temperatures and probably after modification of the pore water isotopic composition (calcites with δ¹³C =— O‰, δ¹⁸O～— 10‰). The distinctive fabrics and zonal patterns probably developed during the replacement of the precursor cement and are not primary growth features. Reversals in isotopic and trace element trends are believed to be related to the rate of neomorphic crystal growth and hence to the degree of exchange with external pore waters. Further increase in temperature, probably during Tertiary igneous activity, gave rise to the extremely light δ¹⁸O values of the late cements in the ammonite which had previously had least contact with external waters (cements with δ¹³C ～ O, δ¹⁸O ～— 20‰).     

A stable isotope study of serpentinization and metamorphism in the Highland Border Suite,Scotland, U.K.

$\text{D}\text{H}$ and ${}^{18}\text{O}{}^{16}\text{O}$ ratios have been measured for whole-rock samples and mineral separates from the mafic and ultramatic rocks of the Cambro-Ordovician Highland Border Suite. The H- and O- isotopic compositions of these rocks record individual stages in a relatively complex 500 Myr old hydrothermal/metamorphic history. Lizardite serpentinites (δD ～ ? 105‰; δ¹⁸O ～ + 6.2‰) record a premetamorphic history and indicate that parent harzburgites, dunites, and pyroxenites were serpentinized through low-temperature interaction with meteoric waters during cooling. The other rocks of the Highland Border Suite record subsequent interaction with metamorphic fluids. Amphibolite facies hornblende schists were produced through thrust-related (dynamothermal) metamorphism of spilitic pillow lavas. During dehydration, D-enriched fluids were driven off from the spilites thus leaving the hornblende schists to equilibrate with a relatively D-depleted internal fluid reservoir (δD ～ ? 45‰). The expelled D-enriched fluids may have mixed with more typical Dalradian metamorphic waters which then exchanged with the remaining mafic rocks and lizardite serpentinites during greenschist facies regional metamorphism to produce antigorite serpentinites (δD ～ ? 62‰; δ¹⁸O ～ + 8‰) and greenschist metaspilites (δD ～ ? 57‰; δ¹⁸O ～ + 7.3‰) with similar H- and O-isotopic compositions. Serpentinites which have been only partially metamorphosed show intermediate H-isotopic compositions between that of metamorphic antigorite (δD ～ ? 62‰) and non-metamorphic lizardite δD ～ ? 105‰) end members.     

川西甘孜－理塘结合带碳酸盐岩碳氧同位素特征

本文对甘孜-理塘结合带中段出露的碳酸盐岩进行了详细的野外地质调查,按其产状可分为两类:覆于玄武岩之上的碳酸盐岩构造岩片和包裹于玄武岩内的厘米-米级不规则棱角状碳酸盐岩砾岩块。经碳酸盐岩碳、氧同位素测试分析,前者δ¹³C值主体位于0.113‰~1.625‰之间,δ¹⁸O数值为-10.263‰~-5.745‰,总体变化较小,有小幅震荡;而后者δ¹³C值明显较前者大,为4.254‰~3.786‰,δ¹⁸O数值则明显偏小,为-13.471‰~-13.592‰,总体变化量较前者更小,具明显的后期成岩作用改造特征。所有样品Z值均大于123,表明研究区内碳酸盐岩为正常海相碳酸盐岩;结合玄武岩地球化学分析数据认为,碳酸盐岩总体沉积于海山环境,且包裹于其中的碳酸盐岩角砾岩块要早于上覆大套碳酸盐岩形成。     

新疆博格达山西南麓石炭—二叠纪碳酸盐岩的碳氧同位素与古环境研究

<正> 新疆乌鲁木齐西南自柳树沟—祁家沟—塔什库拉沟—井井子沟—郭家沟出露厚达80000m的石炭—二叠纪沉积,早二叠世以前大都为海相,其后为陆相,很多学者进行详细的工作,在沉积方面存在以下争议。一种是中石炭世—早二叠世该地区为一套海退相序的沉积,即由浅海—潮坪相或海陆过渡相—三角洲相。另一种是中石炭世至石炭纪末