流体包裹体RbSr等时线定年的可靠性

通过对Rb-Sr等时线原理应用的必要条件及流体包裹体样品的成因特点的分析，认为是否可以用流体包裹体Rb-Sr定年在理论上尚需解决以下问题：（1）因矿物中常有不同期次、不同成因的流体包裹体存在，必须保证所选择的各流体包裹体样品具有相同的初始Sr同位素比值；（2）流体包裹中Rb与Sr的分异机理以及分异程度问题，即流体中Rb与Sr之间是否存在分异和分异程度是否可以达到Sr同位素分析的精度分析。已有的流体包裹体的Rb-Sr等时线年龄研究资料和数据的分析检验结果普遍存在以下问题：等时线图上数据点分散；拟合年龄较老；等时线拟合品质参数的MSWD偏大，可靠性低。     

金属矿床的同位素直接定年方法

矿床的直接定年就是直接对成矿流体或矿石矿物进行同位素定年 ,这样确定的年龄就直接代表了成矿年龄。目前主要有石英和闪锌矿中流体包裹体的Rb Sr同位素定年、黄铁矿和石英中包裹体的Ar Ar同位素定年、金属硫化物的Rb Sr同位素定年、金属硫化物和氧化物的Sm Nd同位素定年、金属硫化物的Re Os同位素定年 ,以及单个矿石矿物的Pb逐步淋滤法定年     

微钻取样-TIMS/MC-ICPMS和LA-MC-ICPMS分析矿物岩石87Sr/86Sr比值的技术比较

微区Sr同位素体系相对于传统全岩Sr同位素研究,可以揭示样品自身存在的不均一性,更好地反映样品经历的地质过程,已被广泛应用于各种地质研究领域,如研究壳幔相互作用、岩浆起源和演化,岩浆体系开放性研究,沉积盆地物源示踪及气候环境研究。准确测定Rb-Sr同位素比值是应用该同位素体系的前提。微钻取样-热电离质谱/多接收电感耦合等离子体质谱(TIMS/MC-ICPMS)和激光剥蚀多接收电感耦合等离子体质谱(LA-MC-ICPMS)作为分析地质样品微区Sr同位素组成的有效手段,已经得到了较为广泛的应用。两种技术在样品制备、干扰校正和质谱测试等方面各具优势和不足。微钻取样-TIMS/MC-ICPMS的最大优势是可获得高精度的Sr同位素数据(外精度优于100×10-6,2SD);但由于需要进行化学处理,流程繁琐耗时(约10天),实验周期较长,同时需要严格控制化学流程空白,且取样直径(200~2000μm)和取样深度(100~2000μm)较大,空间分辨率较低,但是该方法可以对高Rb样品(如钾长石)进行有效分析。LA-MC-ICPMS的最大优势是样品制备简单,数小时即可完成,且分析效率高,根据样品Sr含量的大小激光束斑直径多在60~300μm之间变化,其空间分辨率较前一种方法高,可在短时间内对大量样品进行分析。但由于不能进行化学分离,分析过程中存在多种干扰(如Rb、Ca、Kr和REEs等),影响了测试的精度(约200×10-6,2SD)和准确度(约150×10-6)。该方法目前只能对高Sr低Rb的样品(如斜长石、磷灰石等)进行有效分析,而对于干扰元素含量较高的样品目前无法应用。本文认为,对于微钻取样法,应将改进化学流程作为重点研究方向,提高化学处理效率,同时改善微钻取样法的取样技术,减小取样直径和深度以提高空间分辨率;对于激光剥蚀法,重点突破Kr、Rb和二价REEs等干扰校正问题,提高干扰元素含量较高的样品的分析精度和准确度,同时需要提高仪器灵敏度以满足低Sr含量样品的分析要求。     

闪锌矿分相Rb-Sr体系定年机理初探

为了探究Rb、Sr在闪锌矿中的赋存状态及其Rb-Sr定年机理,对挑纯闪锌矿开展了矿物、稀盐酸提取相和硫化物相(王水溶解相)的Rb、Sr、Pb、Zn、Fe、Ca、Mg和Al含量分析。结果表明,挑纯闪锌矿中,79.19%-97.61%(平均90.47%)的Rb与Pb、Zn、Fe主要分布在硫化物相中,而70.30%-98.12%(平均82.92%)的Sr与Ca、Mg主要分布在稀盐酸提取相中,且其中的Sr与Ca+Mg含量之和大致呈正相关,指示硫化物相较之全矿物的Rb/Sr比值变化范围增大和Rb-Sr定年成功率得以提高,是因为通过稀盐酸提取过程去除了方解石、白云石等包裹体中的普通Sr对硫化物相中少量(2.34%-9.79%)放射成因Sr的掩饰作用。上述结果表明,闪锌矿Rb-Sr同位素定年可能是基于硫化物相而非所含流体包裹体和碳酸盐包裹体中的Rb和Sr,从原理上初步证实该定年方法是有意义的。通过条件实验,检验了稀盐酸提取过程可将碳酸盐包裹体中的Sr完全提取出来,且提取酸浓度和浸泡时间对等时线年龄没有影响,验证了闪锌矿分相Rb-Sr体系定年分析流程稳定可靠。     

(LP)MCICPMS方法精确测定液体和固体样品的Sr同位素组成

MCICPMS是近年发展起来的高精度固体同位素分析仪器,利用MCICPMS可以精确测定Sr同位素组成,与TIMS相比,分析效率明显提高;对于含有Rb的实际样品,在Rb/Sr比值较小时(Rb/Sr<0.001),可以通过Rb扣除获得准确的87Sr/86Sr比值,而当Rb含量较高时,可以通过建立Rb/Sr与87Sr/86Sr偏差值的线性关系进行再一次校正,同样也可以获得准确的87Sr/86Sr比值.通过这种校正关系,可以直接分析固体微区的Sr同位素组成.     

利用激光气流分割技术同时测定斜长石的微量元素与Sr同位素

斜长石是火成岩中的主要造岩矿物之一。其微量元素和Sr同位素组成可以用来示踪多种地质过程。传统的斜长石研究需要进行2次独立的激光剥蚀电感耦合等离子体质谱分析,来分别测试微量元素和Sr同位素组成。然而对于具有复杂环带结构的斜长石, 2次激光剥蚀分析获得的微量元素和Sr同位素可能是解耦的。本研究采用近几年兴起的激光气流分割技术建立了通过1次激光剥蚀同时测试斜长石微量元素和Sr同位素的方法。该方法将1台激光剥蚀系统(LA)同时与1台高分辨率扇形磁场等离子体质谱(SF-ICP-MS)和1台多接收等离子体质谱(MC-ICP-MS)联机。在1次激光剥蚀过程中,通过Y形接头将激光剥蚀产生的气溶胶分为两路,一路气溶胶进入MC-ICP-MS进行同位素组成分析,另一路气溶胶进入SF-ICP-MS进行微量元素含量分析。使用本方法分析USGS玄武玻璃标样BHVO-2G和NKT-1G的Sr同位素组成和微量元素含量,分析结果在误差范围内均与推荐值或前人报道值一致。此外,本研究利用建立的方法对满洲里巴杨山塔木兰沟组火山岩中的斜长石斑晶进行了微量元素和Sr同位素的同时测试,并利用斜长石成分计算了平衡熔体的微量元素组成。...     

江西德兴铜厂斑岩铜矿床矿金属物质正岩浆来源

在讨论了目前对德兴铜厂斑岩铜矿床外围铜含量降低场的过分强调而忽略对引发成矿作用的斑岩体的研究之后,作者论述了Rb/Sr比值和Sr同位素组成自斑岩体中心至接触带的变化规律、铜品位空间分布分形结构以及流体包裹体研究等对Cu、Mo等金属成矿物质正岩浆模式来源的支持。     

内蒙古黄旗海全新世湖泊沉积物中Rb、Sr分布及其环境意义

内蒙古黄旗海H3剖面中发育黄旗海全新世高湖面时形成的湖相粉砂质沉积。对全样、77～20μm粒级、小于20,μm粒级沉积物的Rb、Sr含量,以及小于20,μm粒级样品中碳酸盐矿物种类及含量的测试结果表明,全新世早、中期形成的湖泊沉积物中,自生富锶文石是Sr在沉积物中含量较高的主要原因。各粒级沉积物中Rb、Sr含量与沉积物粒度组成的关系表明:Sr倾向富集于黏粒(4,μm)中,可能与湖泊自生碳酸盐以泥晶为主有关,而Rb倾向富集于4～28,μm颗粒粒级中,可能与其硅酸盐矿物碎化过程的特点有关;Sr与Rb存在粒度效应,且二者粒度效应明显不同。Rb/Sr与湖泊、流域的诸多过程及沉积物粒度效应有关,在不同湖泊演化阶段,其具体的环境含义不同,这是湖泊沉积与风化壳的不同之处。     

湖南古台山金锑矿床成矿流体He-Ar、Sr同位素地球化学及深部找矿意义

古台山矿床是雪峰弧形构造带中段颇具代表性的石英脉型金锑矿床。矿床位于白马山复式岩体的外接触带,主要赋存于南华系长安组和板溪群五强溪组。本文对古台山矿床载金矿物毒砂流体包裹体氦、氩同位素和含矿石英流体包裹体铷、锶同位素进行了分析。He-Ar同位素分析显示,成矿流体的3He/4He为0.011~0.038 Ra,40Ar/36Ar值为414.4~732.6,表明成矿流体主要为地壳流体,同时有部分大气降水的加入。Sr同位素分析显示,含矿石英流体包裹体87Rb/86Sr变化于0.013~0.956,87Sr/86Sr变化于0.72529~0.73245;利用前人获得的成矿年龄(223.6 Ma)进行了初始锶同位素组成的返算,获得其ISr-223.6变化于0.72360~0.73167,平均0.72744。通过与印支期白马山岩体、板溪群等相关地质体锶同位素组成对比,认为古台山矿床成矿流体不可能单独来源于岩浆,而是岩浆流体运移过程中与来自基底具有高锶同位素比值的碎屑岩水岩相互作用的结果。He-Ar同位素揭示矿区深部及周缘地区板溪群具有更好的资源潜力。     

青藏高原中部2.8Ma以来的化学风化与环境演化的湖泊沉积记录

对采自青藏高原中部错鄂湖泊钻孔近200m以上深处、形成于2.8Ma以来的沉积岩岩芯中Sr,Rb,Zr含量变化及Rb/Sr,Zr/Rb比进行了研究,并结合其岩性、粒度、粘土矿物组成,分析了该地区2.8Ma来化学风化的相对强度和古环境演化过程。研究表明,2.8Ma来青藏高原中部的环境经历了3个演化阶段：在深约197－170m(2.8-2.5Ma)岩性段,低Sr含量,高Rb/Sr和Zr/Rb比揭示的是较弱的化学风化过程,反映了与当时强烈的高原隆升运动有关;在约170－38.5m（约2.5-0.8Ma)段,高Sr含量,低Rb/Sr和Zr/Rb比记录的是该流域较强的化学风化阶段,与高原在稳定期中部总体处于温湿或凉湿的环境下的结论吻合;在38.5-0m（约0.8-0Ma)段,总体Sr含量处于相对低值,Rb/Sr比相对较高,化学风化相对较弱,表明高原中部处于较寒冷的环境之中,高原整体已隆升到4000m以上。     

Quantitative trace element analysis of single fluid inclusions by proton-induced X-ray emission (PIXE): application to fluid inclusions in hydrothermal quartz

Single fluid inclusion analogues with known elemental composition and regular shape were analyzed for trace element contents by particle-induced X-ray emission (PIXE)—a nondestructive method for the analysis of single fluid inclusions—to evaluate the accuracy and detection limits of this type of analysis. Elements with concentrations of 10 to 1000 ppm were measured with average estimated relative error of ±7%. For natural fluid inclusions with 30 μm radius and 20 μm depth in quartz, the total analytical errors were estimated to be ±40% relative for Ca, ±16% for Fe, ±13% for Zn, ±12% for Sr, and ±11% for Br and Rb, by considering uncertainties in microscopic measurements of inclusion depths. Detection limits of 4 to 46 ppm for elements of mass numbers 25-50 were achieved for analyses of a spherical fluid inclusion with 30 μm radius and 20 μm depth in quartz, at an integrated charge of 1.0 μC. The trace element compositions of single fluid inclusions in a hydrothermal quartz crystal were also determined. The elemental concentrations in the inclusions varied widely: 0.2-9 wt.% for Ca and Fe, 300-8000 ppm for Mn and Zn, 40-3000 ppm for Cu, 100-4000 ppm for Br, Rb, Sr, and Pb, and less than 100 ppm for Ge. Elemental concentrations of secondary fluid inclusions on the same trail varied over an order of magnitude, even though all these inclusions were formed from the same fluid. Elemental concentrations in inclusions on the same trail are positively correlated with each other, except for Cu and Rb. Ratios of almost all elements in the inclusions on the trail were essentially unchanged; thus, the elemental ratios can provide original information on trace element compositions of a hydrothermal fluid.     

河北省东坪碲化物金矿床流体包裹体研究：地幔流体与成矿关系

河北省东坪碲化物金矿床是我国迄今为止发现的一个比较典型的碲化物金矿床，矿化为含金石英大脉和含金钾长石脉，两者之间在空间上为过渡关系。为探讨成矿流体的来源，尤其是地幔流体参与成矿的程度，笔者从研究成矿流体入手，应用显微测温、激光拉曼光谱分析对矿区主矿脉进行了比较系统的流体包裹体均一温度、盐度、成分的测试，并测定了He-Ar同位素组成。结果显示，东坪碲化物金矿床中的流体包裹体主要为CO2－NaCl-H2O型和H2O－NaCl型，整体以CO2广泛发育为特征；矿区的成矿温度为250－400℃，集中于300－340℃，成矿压力为40－180MPa，主要为60－100MPa；流体成分主要为CO2和H2O，含少量H2S、N2、CH4、CO和C2H2；流体盐度w(NaCleq)为5％－7％；流体总密度为0．48－0．79g/cm^3；矿脉中石英的R／Ra比值高达0．3－5．2，明显高于地壳流体（0．001）。基于碲富集、高、R／Ra比值、成矿流体富CO2，笔者认为矿床成矿作用与地幔活动有着密切的关系。     

Strontium and oxygen isotope decoupling in the Hercynian Trois Seigneurs Massif,Pyrenees: evidence for fluid circulation in a brittle regime

Systematic shifts of oxygen isotopic compositions in the higher grade parts of the high temperature-low pressure Hercynian metamorphic sequence, exposed in the Trois Seigneurs Massif, have previously been explained as a result of an influx of surface-derived water during the prograde part of the metamorphic cycle. It has been suggested that this caused a regional lowering of ⁸⁷Sr/⁸⁶Sr in the metamorphic sequence. Mapping of strontium isotopic compositions across a 15 m meta-carbonate horizon in the higher grade pelite-psammite sequence shows that strontium isotopic compositions were homogenised over length scales of metres or less during the Hercynian metamorphism, which brought the carbonate and pelite-psammite to oxygen isotopic equilibrium with a common fluid. Comparison of model pre-Hercynian ⁸⁷Sr/⁸⁶Sr profiles across the carbonate (based on a depositional/diagenetic age of 450 Ma and initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7086 given by 10 m length scale averaging) with the post-Hercynian ⁸⁷Sr/⁸⁶Sr profile (calculated from analysed ⁸⁷Sr/⁸⁶Sr and Rb/Sr compositions) implies strontium isotopic diffusion distances of ca. 0.4 m in the carbonate and ca. 7 m in the pelite-psammite. The limited Sr-isotopic diffusion distance of 0.4–0.7 m within the carbonate is compatible with pervasive oxygen-isotopic exchange over distances restricted to 4–15 m if fluid strontium concentrations were between 4 and 50 ppm. The strontium isotopic transport distances are not compatible with pervasive oxygen isotopic alteration over the observed 5 km regional scale. Either the flow was perfectly layer-parallel or, more probably, the regional-scale alteration of oxygen took place by fluid circulation in the brittle regime early in, or prior to, the Hercynian metamorphic event. Flow along cracks with incomplete diffusive exchange between fluid and wall rock would allow greater decoupling of oxygen and strontium isotopic transport than pervasive advective transport with local fluid-solid equilibrium.     

CCSD中HP-UHP岩石稀有气体同位素地球化学及其对板块折返过程的示踪意义

利用高真空气相质谱系统测定了CCSD中HP-UHP变质岩中主要造岩矿物流体包裹体的稀有气体同位素组成,得出其3He/4He为(0.004~0.775)×10-6,相应R/Ra为0.003~0.553,40Ar/36Ar变化较大,为316.2~11358.8,高于大气40Ar/36Ar(295.5);20Ne/22Ne和21Ne/22Ne分别为9.47~12.4和0.026~0.051,而134Xe/132Xe和136Xe/132Xe分别为0.376~0.484和0.324~0.416,均高于其相应大气值。CCSD中HP-UHP岩石主要造岩矿物的He-Ar、Xe和Ne等同位素组成清楚显示其中流体包裹体主要由地壳变质流体和少量大气饱和水组成,而深源地幔流体组分很低,其中He主要来自地壳,Ar主要由壳源放射性成因40Ar*和少量(平均32.6%)大气Ar混合组成,少量Ne和Xe可能来自地幔。CCSD中HP-UHP岩石具有F40Ar相似文献   

Isotopic evolution of common lead

The isotopic composition of lead from galenas and feldspars of granitic rocks covering a time span of 3600 m.y. is reviewed. Hew data are combined with data from the literature, all ratios being normalized to a fixed value for the isotopic composition of lead in an inter-laboratory reference sample. Comparison of feldspar and galena results show that the isotopic composition of initial lead in granitic rocks may be identical to, or more radiogenic than, that in coeval stratiform (or ‘single stage’) ore deposits. The isotopic evolution of terrestrial lead over the past 3600 m.y. deduced from the stratiform ore data does not fit the closed system source. The data are best fitted to evolution models in which the value of μ (U²³⁸/Pb²⁰⁴ normalized to the present day) in the source has increased either over approximately the past 3.6 billion years or since the time of formation of the Earth. A limited number of high precision data for strontium likewise indicate open system isotopic evolution. In this system the Rb/Sr ratio appears to have decreased as a function of time. Physical models that explain the data are presented. Either mantle differentiation or crustal contamination processes could account for the change in μ in the source for the lead. The strontium data and some detailed studies of the isotopic composition of lead in oceanic volcanic rocks support mantle differentiation rather than crustal contamination. The exact nature of the mantle differentiation process cannot be specified, although empirical data favoring the existence of such a process are given. The best estimate of the age of the Earth, calculated with the data from 2750 and 3290 m.y.-old lead ores, is 4660 m.y.     

湘西头坡脑汞锌矿成矿流体特征及地质意义

湘西头坡脑汞锌矿床位于扬子陆块东南缘,矿床受北西向构造带控制,赋矿围岩为寒武系中统敖溪组第三段细晶白云岩,矿石矿物主要为辰砂及闪锌矿,脉石矿物主要为石英、白云石及方解石。头坡脑汞锌矿床矿石中的流体包裹体主要为纯液相包裹体,部分气液两相包裹体及少量纯气相包裹体。成矿流体具有中低温(84.3℃~183.9℃)、中高盐度(6.16 wt%~22.24 wt% NaCl)及中高密度(0.97~1.10 g/cm~3)等特征。气相成分测定显示包裹体中气相成分主要为CH_4,少量N_2及CO_2,液相成分为H_2O,成矿流体富烃。氢氧同位素组成分别为δD(-105×10~(-3)~-46×10~(-3))和δ~(18)O_(H_2O)(-7.1×10~(-3)~11.4×10~(-3)),指示成矿流体主要为建造水,也有大气降水的加入。根据头坡脑汞锌矿床成矿地质背景、流体特征、流体来源及区域成矿特点,认为本区汞成矿事件应当为上扬子台褶带构造运动长期性和持续性的产物。     

Ion microprobe measurement of strontium isotopes in calcium carbonate with application to salmon otoliths

The ion microprobe has the capability to generate high resolution, high precision isotopic measurements, but analysis of the isotopic composition of strontium, as measured by the ⁸⁷Sr/⁸⁶Sr ratio, has been hindered by isobaric interferences. Here we report the first high precision measurements of ⁸⁷Sr/⁸⁶Sr by ion microprobe in calcium carbonate samples with moderate Sr concentrations. We use the high mass resolving power (7000 to 9000 M.R.P.) of the SHRIMP-RG ion microprobe in combination with its high transmission to reduce the number of interfering species while maintaining sufficiently high count rates for precise isotopic measurements. The isobaric interferences are characterized by peak modeling and repeated analyses of standards. We demonstrate that by sample-standard bracketing, ⁸⁷Sr/⁸⁶Sr ratios can be measured in inorganic and biogenic carbonates with Sr concentrations between 400 and 1500 ppm with ∼2‰ external precision (2σ) for a single analysis, and subpermil external precision with repeated analyses. Explicit correction for isobaric interferences (peak-stripping) is found to be less accurate and precise than sample-standard bracketing. Spatial resolution is ∼25 μm laterally and 2 μm deep for a single analysis, consuming on the order of 2 ng of material. The method is tested on otoliths from salmon to demonstrate its accuracy and utility. In these growth-banded aragonitic structures, one-week temporal resolution can be achieved. The analytical method should be applicable to other calcium carbonate samples with similar Sr concentrations.     

安徽铜陵老鸦岭层状铜矿床的成矿地球化学研究

安徽铜陵老鸦岭铜矿床是长江中下游地区的一个典型的层状矿床，以远离侵入岩体和赋存于二叠系钙质－硅质岩中为特征，其矿石矿物组合简单，近矿围岩蚀变较弱，为绢云母化、高岭石化、碳酸盐化和绿泥石化等，且分带性不明显。按照矿物形成的时间序列，矿床矿物可分为四个共生组合：（1）磁黄铁矿＋黄铁矿组合；（2）黄铜矿＋黄铁矿＋闪锌矿＋磁黄铁矿组合；（3）石英＋黄铜矿组合；（4）方解石＋黄铜矿组合。矿物包裹体以气液两相为主，气液比从早到晚逐渐减小直至成为单一的液相。均一法测温表明，组合1的均一温度为290～320℃，组合2为240～265℃，组合3为180～220℃，和组合4为110～116℃。矿物包裹体液相成分属于NaCl－H_2O体系，并含有F~－和，盐度小于10wt％。根据热力学计算，圈定了矿物共生组合的物理化学场，从组合1到4，成矿热液的fo_2、fs_2及∑S浓度依次降低，pH值变化不大，但还原性降低，氧化性增强。矿床硫同位素组成δ~34S_∑S为：组合1是＋0．5％。，组合2为1‰～3‰，组合3大于＋5‰和组合4大于＋6‰。这证实成矿热液中硫来源于岩浆，并随着时间的演化有地层硫的加入。氧和氢同位素研究说明参与成矿作用的热液除岩浆源之外，还有相当多的大气水或地下水的加入。矿石普通铅同位素为异常     

Trace Element Determination of Single Fluid Inclusions in Quartz by Laser Ablation ICP-MS

Single fluid inclusions in quartz from a Pb-Zn-Ag carbonate replacement deposit were selected for trace element determination by laser ablation ICP-MS. Spikes in element intensities were noted between first breached fluids versus subsequent analyses, suggesting that accurate element concentrations may not be determined in smaller fluid inclusions when only one analysis is obtained before the fluid is exhausted. Elemental concentrations in the fluid inclusions were determined by external standardisation using solutions sealed in microcapillary tubes. Standards and single natural inclusion analyses give repeatabilities (%RSD) of ˜ 20% for Rb and Sr. Rubidium and strontium concentrations range from 0.56-5.07 μg ml^-1 and 1.12-27.4 μg ml^-1, respectively, whereas Zn and Ag are below detection limits (< 10 ng ml^-1). The results suggest that nearly all Zn and Ag are removed by the time hydrothermal fluids precipitate gangue minerals.     

察尔汗盐湖石盐的流质包裹体氢氧稳定同位素分析及其地球化学意义

本文是在建立了盐酸胍法制备样品用于氧同位素分析方法研究的基础上,测定了察尔汗湖区各类天然水及ZK88-01占孔岩心的原生石盐流质包裹体氢氧稳定同位素组成。该方法适用于高盐度卤水微量δ18O分析,具有成本低、操作简便和定量转化的优点,值得在国内推广。 根据原生石盐包体水δD、δ18O的分布特征,论述了察尔汗盐湖距今5万年来湖水的演化历程。划分出三种不同成盐环境下的演化期,各期中古湖水体具有波动的继承性,各期间可能存在成盐环境的突变.根据天然水δD、δ18O关系初步获得该区蒸发线为:δD=2.5δ18O-45.3;证实了剖面上部淤泥水与达布逊湖水下渗有关;下部明显地有侧向水补给.