团簇同位素的基本原理与地质应用

团簇同位素指的是含有2个及2个以上的重同位素结合在一起形成的同位素体。团簇同位素的数值定义为同位素体的相对丰度偏离随机分布状态的程度。测量该相对丰度较低的同位素体需要高精度的质谱仪,难点在于利用同位素组成已知的参考气体和不同同位素组成的加热气体,以获得绝对参考体系下的数值。团簇同位素体的相对丰度非常低,但是具有非常独特的物理和化学性质。比如碳酸盐矿物中~(13)C~(18)O~(16)O的丰度对温度具有敏感性,而与矿物的全岩同位素以及矿物形成时期的流体性质无关,因此可以利用测量的碳酸盐团簇同位素来获得矿物的生长温度,再利用矿物的氧同位素(δ~(18)O),根据传统的氧同位素温度计原理,可以进一步获得矿物的生长流体(水)的氧同位素。目前,团簇同位素温度计已经在古气候(温度)重建、古高度恢复、碳酸盐岩的成岩作用以及甲烷的成因分析等方面得到了广泛应用。评估深埋高温过程引起的C-O化学键重置对碳酸盐团簇同位素的影响、测试仪器产生对团簇同位素的非线性误差校正、以及其他丰度更低的团簇同位素体或大分子的团簇同位素的测量,是下一步的研究方向。     

安徽宣城矿集区长山铅锌多金属矿床成矿流体特征及成因

长山铅锌多金属矿床位于长江中下游成矿带宣城矿集区东北部,文章在对该矿床开展详细的地质调查和岩相学研究基础上,对代表性矿化蚀变矿物(石英、方解石)开展了流体包裹体测温、激光拉曼光谱和氢、氧、碳稳定同位素分析。长山铅锌多金属矿床矿化蚀变组合从早到晚可以分为矽卡岩-氧化物阶段、早硫化物阶段和晚硫化物阶段。矿物流体包裹体温度和盐度测算显示,长山矿床的成矿流体温度和盐度从矽卡岩-氧化物阶段(315～382℃,w(NaCl)_eq为14.04%～16.24%)→早硫化物阶段(220～347℃,w(NaCl)_eq为4.49%～15.86%)→晚硫化物阶段(163～306℃,w(NaCl)_eq为1.40%～11.10%)逐渐降低。石英和闪锌矿中包裹体的δD和δ¹⁸O值分别为-89.5‰～-67.8‰和-3.2‰～7.62‰,方解石中δ¹³C和δ¹⁸O值分别是-6.8‰～-1‰和10.6‰～17.1‰,同位素特征指示长山矿床的成矿流体为岩浆水与海相碳酸盐中富含有机质流体混合,...     

亚洲树轮稳定氧同位素研究进展

树轮稳定氧同位素作为一种高精度的古气候代用指标,在亚洲地区的发展起步晚进步快。树轮稳定氧同位素比率（δ¹⁸O）对区域气候信息有较强的记录能力,且与水汽循环关系密切,对于理解复杂的亚洲气候起着重要作用。亚洲地区树轮δ¹⁸O对温度的响应主要出现在高纬度地区,中低纬度树轮δ¹⁸O主要记录与水分（降水、相对湿度、PDSI等）有关的信号。对亚洲地区已发表的树轮δ¹⁸O与气候要素（温度、降水、相对湿度）的相关分析显著性统计显示,生长季气候对树轮δ¹⁸O至关重要,树轮δ¹⁸O 与温度的显著相关关系呈正相关,与降水和相对湿度的呈负相关,温度和降水通过降水δ¹⁸O影响树轮δ¹⁸O,但各自的信号强度存在区域差异,而相对湿度信号则广泛记录在不同区域不同树种之中。亚洲树轮稳定氧同位素研究集中于中低纬度地区,因而对大气水文循环的响应主要侧重于对亚洲夏季风和ENSO的研究,对季风降水的记录反映了季风活动的变化特征以及与之有关的环流信息;季节分辨率的树轮稳定氧同位素研究限于低纬热带亚热带区域,但对于理解区域气候和季风活动的年内变化、挖掘年轮不清晰树种的树轮学研究潜力具有重要的意义。     

样品量差异对团簇同位素Δ47测定的影响

团簇同位素是地球化学领域的新兴技术,已成功应用于古温度重建研究。由于团簇同位素的自然丰度极低,目前碳酸盐中团簇同位素Δ₄₇测定所需要的样品量仍较大（约10 mg）,因此如何在保证Δ₄₇测定值可靠的前提下,使用更少量的样品进行测定一直是各实验室努力的目标。本研究在福建师范大学稳定同位素中心,以实验室高纯CO₂气体（Gas-lab）为测试对象,基于Mat 253 Plus同位素比质谱仪双路测定模式,通过不同气体量条件下的对比测定,探讨了双路模式下样品量的差异对测量结果的影响。研究结果显示：在可变体容积储样器体积为100%、 70%、 30%和15%的设定气体量条件下,每个测定过程中Gas-lab的Δ₄₇的测定值变化范围分别为-0.047‰～0.059‰、-0.054‰～0.039‰、-0.067‰～0.083‰和-0.065‰～0.058‰,当气体量较小时,测定的Gas-lab的Δ₄₇值更为分散。因气体同位素质谱仪在不同信号强度时测定的同位素值存在差异,在气体量较少条件下测量过程中...     

安徽省金寨县沙坪沟钼矿床稳定同位素地球化学特征

安徽省金寨县沙坪沟钼矿床是近年来秦岭—大别成矿带发现的超大型斑岩钼矿床,已探明钼资源储量246×10~4t。通过对沙坪沟钼矿床不同勘探线剖面和不同深度代表性样品的S、H、O稳定同位素地球化学的研究,揭示了沙坪沟钼矿床S、H、O同位素组成特征及其空间分布特征。矿床硫化物硫同位素组成变化范围较窄,δ³⁴S变化于+0.4‰～+6.2‰,平均值为+3.47‰,落在火成岩范围,分布具明显的塔式效应,硫的来源比较均一,主要为深源硫。成矿流体的δ¹⁸O_包裹体水为0.40‰～7.52‰。流体包裹体中δD变化范围为-90‰～-63‰。主成矿期成矿流体总体为岩浆水。在不同勘探线剖面上矿化中心具高的δ³⁴S、δ¹⁸O值,而且显示出从深部钠长石—钾长石—硅化带→黄铁绢英岩化带→浅部的绿泥石—碳酸盐化带δ³⁴S、δ¹⁸O值有降低的趋势。上述特征表明沙坪沟钼矿床主成矿期成矿环境由碱性向酸性过渡,且没有发生明显的低δ¹⁸O作用,成矿环境相对封闭,外部对流循环的雨水系统参与成矿作用程度相对较小,与东秦岭其他斑岩钼矿床不同。     

山东胶东地区某些金矿床的氩、氢、氧稳定同位素地球化学及矿床成因

通过矿床地质特征、流体包裹体及氧、氢稳定同位素的研究,认为马家窑金矿属再平衡岩浆热液矿床,金青顶和十里铺金矿属大气降水热液矿床。马家窑金矿石英的δD、δ¹⁸O值高,变化小,比较稳定;蚀变岩石的δ¹⁸O在磺向上由围岩向矿脉逐渐升高。金青顶和十里铺金矿石英的δD、δ¹⁸O值低、变化大;蚀变岩石的δ¹⁸O值由地表向深部逐渐降低。开展金矿的氮稳定同泣素研究,在国内尚数首次。马家窑金矿³⁶Ar在温度300℃以下相对含量不到10%,金青顶和十里铺金矿³⁶Ar则达90%以上,表明前者以岩浆成因⁴⁰Ar为代表,后者则以大气氩³⁶Ar为代表,进而表明马家窑金矿是再平衡岩浆热液成因,金青顶和十里辅金矿是大气降水热液成因。示踪结果与H、O同位素一致,表明氩同位素在示踪成矿热液、矿床成因研究方面是一种较为有效的手段。     

蓟县早寒武-新元古不整合界面处风化壳碳酸盐碳、氧同位素组成特征

由于土壤中有机质降解产生的CO₂ 和淡水成岩作用的影响,在蓟县早寒武世和晚元古代景儿峪组不整合界面处古风化壳中碳酸盐的δ¹³C值和δ¹⁸O 值明显偏负,从风化壳向下往原岩的方向,δ¹³C和δ¹⁸O 数值逐渐增加;此外,与风化壳上、下碳酸盐岩地层的δ¹³C和δ¹⁸O 数值具有明显的差别。上述同位素组成特征可以用于其它古风化壳剖面及地层不整合界面的判识。     

湿度效应及其对降水中δ18O季节分布的影响

提出了湿度效应的概念,即降水中稳定同位素比率与大气的温度露点差ΔT_d存在显著的正相关关系.对两个气候特征完全不同的取样站乌鲁木齐和昆明降水中δ¹⁸O与温度露点差之间的关系进行了分析,尽管两站的δ¹⁸O与ΔT_d的季节变化存在差异,但它们的湿度效应是显著的.利用稳定同位素动力分馏模型并根据500hPa月平均温度的季节分布对昆明站云中凝结物中δ¹⁸O进行了模拟,模拟的月平均δ¹⁸O与月平均温度的变化具有非常好的一致性,说明昆明站云中凝结物中的氧稳定同位素具有温度效应.这个结果与地面降水中氧稳定同位素的降水量效应截然不同.昆明站降水中δ¹⁸O一定程度上指示大气的干湿状况,同时也间接地指示降水量的多寡或季风的强弱.湿度效应的存在,影响降落雨滴中稳定同位素蒸发富集的强度以及雨滴与大气之间稳定同位素物质迁移的方向.它不仅改变降水中稳定同位素比率的大小,也改变其季节分布的特点.     

南秦岭-大巴山地区下寒武统沉积层状钡矿床成因机制研究

为理清沉积层状重晶石、毒重石矿床成因机制及其差异成矿的控制因素，对南秦岭-大巴山地区下寒武统地层中不同成矿特征的钡矿床开展了矿物学和碳-硫-氧-锶同位素地球化学分析。结果显示，该区内沉积钡矿床有以重晶石为主或以毒重石为主的类型；矿石中碳酸盐矿物具有负的碳同位素组成(δ¹³C_Carb为-26.1‰～-6.3‰),重晶石具有非常大的硫、氧同位素分馏(δ³⁴S_Brt为25.1‰～62.2‰,δ¹⁸O_Brt为12.2‰～18.9‰和δ¹⁸O/δ³⁴S≈0.1),反映成矿时有强烈的甲烷驱动微生物硫酸盐还原作用；毒重石等碳酸盐矿物和重晶石的锶同位素组成较为一致，都具有宽的⁸⁷Sr/⁸⁶Sr变化范围(0.7070～0.7103)和低的⁸⁷Sr/⁸⁶Sr值(～0.7070),指示成矿流体可能是与基性-超基性岩有关的富金属热液，热液流体在运移过...     

硼同位素分馏的实验理论认识和矿床地球化学研究进展

硼是一种中等挥发性元素,具有¹¹B和¹⁰B两个稳定同位素。两个同位素间高达10%的相对质量差使其在地质过程中引起高达-70‰至+75‰的硼同位素变化。硼在自然界主要与氧键合形成三配位(BO₃)和四配位(BO₄)结构,因而¹¹B和¹⁰B间同位素分馏主要受控于三配体(BO₃)和四面体(BO₄)间配分。本文综述了低温和高温地质过程的硼同位素分馏的理论和实验研究进展。在溶液中B(OH)₃和${B(OH)^{-}_{4}}$间硼同位素分馏受pH和热力学p-T条件控制,实验和理论表征获得常温常压条件下的B(OH)₃和$B(OH)^{-}_{4}$间同位素分馏系数(α_3-4)变化范围为1.019 4至1.033 3。低温条件下矿物(如碳酸盐、黏土矿物(蒙脱石和伊利石)、针铁矿、水锰矿、硼酸盐)与溶液间硼同位素分馏行为除了受p-T-pH影响外,矿物表面吸附引起的分馏效应十分显著。在中高温过程(蒙脱石伊利石化、富硼电气石和白云母矿物与热液流体,以及硅酸盐熔体与流体)中硼同位素分馏行为受到硼配位构型、化学成分以及物理化学条件的控制。随着硼同位素分馏机理研究的深入以及越来越完善的地质储库硼同位素端员特征表征,硼同位素地球化学指标可以灵敏示踪成矿物质来源、探究成矿作用与成因模式和重建成矿过程物理化学条件。目前矿床硼同位素地球化学研究的难点在于实现不同赋存相(如流体、矿物和熔体)中硼配位键合结构和硼同位素组成的精细化表征。     

Clumped isotope thermometry of carbonatites as an indicator of diagenetic alteration

We measure the clumped isotopic signature of carbonatites to assess the integrity of the clumped isotope paleothermometer over long timescales (10⁷-10⁹ years) and the susceptibility of the proxy to closed system re-equilibration of isotopes during burial diagenesis. We find pristine carbonatites that have primary oxygen isotope signatures, along with a Carrara marble standard, do not record clumped isotope signatures lighter than 0.31‰ suggesting atoms of carbon and oxygen freely exchange within the carbonate lattice at temperatures above 250-300 °C. There is no systematic trend in the clumped isotope signature of pristine carbonatites with age, although partial re-equilibration to lower temperatures can occur if a carbonatite has been exposed to burial temperatures for long periods of time. We conclude that the solid-state re-ordering of carbon and oxygen atoms is sufficiently slow to enable the use of clumped isotope paleothermometry on timescales of 10⁸ years, but that diagenetic resetting can still occur, even without bulk recrystallization. In addition to the carbonatite data, an inorganic calibration of the clumped isotope paleothermometer for low temperature carbonates (7.5-77 °C) is presented and highlights the need for further inter-lab standardization.     

Isotopic composition of silicon in meteorites

Samples of bulk meteorites show only mass-dependent fractionation of silicon isotopes. No isotopic anomalies were found. The variation of the ratios ²⁹Si/²⁸Si and ³⁰Si/²⁸Si over the meteorite classes is small; 1%. per mass unit difference. The average Si isotopic composition for each class of meteorites is identical, within analytical uncertainties. This is quite unlike O, whose anomalous isotopic abundances in bulk samples differentiate among the classes of meteorites. The overlapping abundance ranges of Si isotopes among many classes of meteorites suggest closed-system behavior for this element prior to meteorite accretion and allow calculation of an average solar system Si isotope composition.     

大庄子金矿成矿作用地质地球化学特征及成因

胶东平度大庄子金矿床产于胶莱盆地西北缘荆山群变质岩中,主矿体的展布受一低角度层间滑动断层控制,该断层发育于黑云二长片麻岩和斜长角闪岩所夹持的透镜状大理岩中.成矿作用地球化学研究表明：大庄子金矿δ³⁴S组成比胶西北其他金矿高,且高于老地层和中生代花岗岩的δ³⁴S值,反映大气降水循环淋滤作用使硫同位素发生了一定程度的分馏;矿石铅为异常铅,铅同位素组成与同胶东群及玲珑、焦家等中生代花岗岩有关的金矿相比,范围变化大.碳氧同位素组成介于岩浆碳酸岩与荆山群大理岩之间.同位素地球化学研究表明成矿物质具多源性,这与该类金矿所处的构造边缘（转换）环境有关.石英流体包裹体均一温度为280~160℃,包裹体成分和氢氧同位素组成反映成矿流体来自变质水、大气降水和岩浆水的混合.     

黔西南灰家堡金矿田热液方解石稀土元素与C-O-Sr同位素地球化学特征

为探讨灰家堡金矿田矿化剂和成矿物质来源,系统开展了热液方解石的稀土元素和C-O-Sr同位素研究。结果表明,热液方解石的稀土元素具有"上凸型"配分模式,低的(La/Sm)N值(0.003~0.580),较高的(Gd/Yb)_N值(1.21~15.73),Eu正异常,显示成矿流体的壳源特征;产于龙潭组(P3l)的矿体中的方解石δ13CPDB为-9.3‰~1.7‰(均值为-3.93‰);产于构造蚀变体(SBT)的矿体中的方解石δ¹³CPDB为-7.8‰~3.3‰(均值为1.04‰),C-O同位素组成介于地幔碳酸岩与海相碳酸盐岩之间,在δ¹³CPDB-δ¹⁸OSMOW图解上呈近水平分布,与矿体全岩及围岩碳同位素组成相似,表明成矿流体的C可能具有多来源特征。成矿流体与围岩之间的水-岩反应并未改变矿石的碳、氧同位素组成,流体-岩石相互作用不是导致热液方解石沉淀的主要机制,而更可能与CO₂的脱气作用有关;方解石的⁸⁷Sr/⁸⁶Sr值接近碳酸盐岩围岩、明显高于幔源物质的平均值,表明成矿热液中的Sr可能主要来自碳酸盐岩围岩。     

灰岩碳氧同位素特征与隐伏花岗岩的关系——以栗木水溪庙矿区为例

对栗木水溪庙矿区泥盆系上统融县组灰岩的碳氧同位素进行了研究,该地区灰岩的碳氧同位素组成可提供隐伏花岗岩隆起及其相关流体的重要信息。受隐伏花岗岩侵入驱动的流体与上覆融县组灰岩发生反应的温度在110℃左右,流体的初始同位素组成为δ18OSMOW=-3‰,δ13CPDB≤-7‰,反应的水岩比值（w/r）可能小于5。这种岩浆水与大气降水的混合流体与围岩之间的水岩反应使得地表灰岩的δ18O和δ13C值降低,产生负异常。研究表明,围岩的δ18O值降低受反应的水岩比值和温度控制;δ13C值降低主要与反应的水岩比值有关。反应的温度越高,w/r值越大,灰岩的碳氧同位素负异常越明显。因此,水溪庙矿区地表出露的碳酸盐地层中的碳氧同位素变化可在地球化学勘查中用于指示下伏花岗岩岩脊的隐伏位置。     

辽河盆地西部凹陷沙河街组砂岩碳酸盐胶结物特征

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.      

A Review of Magnesium Isotope System in Rivers

In recent years, a series of important progresses have been made in the aspect of magnesium isotopes behavior in weathering processes. These progresses are not only favorable to understand the change of the magnesium isotopic compositions in rivers, but also establish the foundation to further reveal the magnesium isotope geochemical cycle. The magnesium in rivers is both magnesium sink for weathering and magnesium source for the ocean. The Mg isotopic compositions in rivers are dominated by the magnesium sources and Mg isotope fractionations processes. The sources of magnesium in rivers originate mainly from draining rocks, as well as less contribution from the eolian deposition, groundwater, plant debris, and precipitation. The Mg isotope fractionations in rivers are mainly related to precipitation and dissolution of carbonate minerals, silicate mineral hydrolysis, adsorption on mineral or colloidal matter surface, and plant uptake. Generally, the contribution of carbonate minerals dissolution or precipitation is equal to add or reduce magnesium from carbonate endmember, which has a remarkably negative δ²⁶Mg value. Based on the fact that most clay minerals are rich in ²⁶Mg during nature silicate mineral hydrolysis, then it is possible to infer that residual weathering products enrich in ²⁶Mg. However, there is no significant Mg isotope fractionation causing by the adsorption on mineral or colloidal matter surface during river water migration. For the plant uptake, the root prefers to have ²⁶Mg, leading the plant itself rich in heavier Mg isotopic composition. In addition, formation of secondary minerals in rivers could also reflect the changes of chemical parameters in rivers (such as major elements, CO₂ solubility, pH, etc.). Hence, Mg isotopic composition in rivers and associated isotope fractionations are not only the basis for the application of magnesium isotope to trace surface material cycle, but also have important significance for the further understanding the geochemical cycle of magnesium isotopes.     

Paleo-environmental implication of clumped isotopes in land snail shells

Clumped isotopes analyses in modern land snail shells are reported and used to interpret shell oxygen isotopes within the context of terrestrial paleo-climatology. Carbonate clumped isotopes thermometry is a new technique for estimating the temperature of formation of carbonate minerals. It is most powerful as an indicator of environmental parameters in combination with δ¹⁸O, allowing the partitioning of the δ¹⁸O signal into its temperature and water components. Results indicate that snail shell calcification temperatures are typically higher than either the mean annual or the snail activity season ambient temperatures. Small inter- and intra-snail variability suggests that shell aragonite forms at isotopic equilibrium so that the derived temperatures are an eco-physiological parameter reflecting snail body temperature at the time of calcification. We attribute these higher body temperatures to snail eco-physiological adaptations through shell color, morphology, and behavior. In combination with shell oxygen isotope composition, these temperatures allow us to calculate snail body water composition, which is in turn interpreted as a paleo-hydrological indicator, reflecting isotopic composition of local precipitation modified by local evaporation.     

Temperatures and Oxygen Isotopic Compositions of Hydrothermal Fluids for the Takatori Tungsten-copper Deposit, Japan

Abstract. Fluid inclusion and oxygen isotope studies are performed to obtain temperatures and oxygen isotopic compositions of hydrothermal fluids for the vein-type tungsten-copper deposit at Takatori in Ibaraki Prefecture, Japan. Temperatures of the hydrothermal fluids are calculated from fluid inclusion data. The calculation incorporates the effects of the salinity, gas concentration, and fluid pressure. The fluid temperatures range from 370 to 460C. For these calculations, this study obtains a density equation for H₂O-NaCl-CO₂ solution at the vapor-liquid two-phase boundary. Then the present study combines the obtained equation with the equation of state by Bowers and Helgeson (1983).
The fluid temperatures determined in this study are applied to the calculation of oxygen isotopic compositions of the hydrothermal fluids. The calculation of the oxygen isotopic compositions is based on the oxygen isotope analyses of vein quartz. The oxygen isotopic compositions of vein quartz range from +13.5 to +14.4 % relative to SMOW. Then, the oxygen isotopic compositions of the hydrothermal fluids in equilibrium with the vein quartz are calculated to be from +9.7 to +10.5 %. These δ¹⁸O_fluid values agree with those of magmatic fluids derived from the ilmenite-series granitic rock, which is related to the mineralization. Keywords: Takatori tungsten-copper deposit, fluid inclusion, oxygen isotope, vein quartz, H₂O-NaCl-CO₂ solution, density