高反应温度对五氟化溴法氧同位素组成测定的影响

五氟化溴法在分析氧化物和硅酸盐矿物的氧同位素组成时,反应温度与反应时间是关键要素.在保证反应时间的前提下,研究较高反应温度条件(550～800℃)对五氟化溴法氧同位素组成分析的影响.在高反应温度条件下对国家标准物质GBW04409进行氧同位素样品制备与同位素组成分析表明:反应温度在550～675℃,获得了较足量的O2产...     

硅酸盐和金属氧化物矿物氧同位素组成的CO2激光氟化分析

我室采用MIR-10型CO2激光器,在一种富BrF5的氛围中使激光对硅酸盐和氧化物矿物样品加热形成O2,经多次纯化后用5A的分子筛吸收,再直接送至气体质谱仪进行氧同位素比值测定.这个实验流程与传统方法相比的改进不仅在使用激光加热技术及样品的放置上,而且在直接采用O2而不是CO2进行质谱测定.采用O2进行直接分析的优点不仅避免了向CO2转化过程中的潜在同位素分馏,而且能够得到样品的δ17O值,因此为宇宙样品分析提供了可能.CO2激光氟化技术的优点是所需样品量小(可低达1～2 mg),因此能够分析微小岩石区域或单矿物晶体内的氧同位素分布.同时,激光可以达到非常高的温度(＞4000K),因此能够对某些难熔矿物(如锆石、蓝晶石、橄榄石等)进行氧同位素分析.     

硅酸盐和金属氧化物矿物氧同位素组成的CO_2激光氟化分析

我室采用MIR 10型CO2 激光器 ,在一种富BrF5的氛围中使激光对硅酸盐和氧化物矿物样品加热形成O2 ,经多次纯化后用 5 的分子筛吸收 ,再直接送至气体质谱仪进行氧同位素比值测定。这个实验流程与传统方法相比的改进不仅在使用激光加热技术及样品的放置上 ,而且在直接采用O2 而不是CO2 进行质谱测定。采用O2 进行直接分析的优点不仅避免了向CO2 转化过程中的潜在同位素分馏 ,而且能够得到样品的δ1 7O值 ,因此为宇宙样品分析提供了可能。CO2 激光氟化技术的优点是所需样品量小 (可低达 1～ 2mg) ,因此能够分析微小岩石区域或单矿物晶体内的氧同位素分布。同时 ,激光可以达到非常高的温度 (>40 0 0K) ,因此能够对某些难熔矿物 (如锆石、蓝晶石、橄榄石等 )进行氧同位素分析。     

硅酸盐矿物氧同位素组成的激光分析

对于红外激光系统和紫外激光系统 ,由于它们加热样品的反应机理完全不同 ,决定了它们在稳定同位素地球化学分析中的不同使用范围。根据对CO2 激光系统分析地球化学样品的实践 ,发现对结果产生干扰的因素有 :(1)石英的粒径效应 ;(2 )微量样品接收电压过低 ;(3)分子筛的吸附能力 ;(4 )系统中的吸附水 ;(5 ) 14 N19F+ 对δ17O值的影响。由于石英的粒径效应而导致细粒石英 (粒径<2 5 0 μm)的δ18O值偏低 ,可以采用不聚焦激光的快速加热法来解决。由于样品量太少而决定了样品气体接收电压过低 ,导致δ18O值出现系统偏高或偏低 ,可以利用校正曲线对结果进行校正。分子筛吸附性能的下降会产生氧同位素的分馏 ,因此确定分子筛的使用寿命非常重要。系统中的吸附水利用氟化物试剂预氟化来去除 ,重要的是应避免在预氟化的过程中产生大量的HF腐蚀激光系统的BaF2 窗口玻璃并与部分矿物样品发生反应。     

氧同位素分析方法—BrF5法的实验研究

通过真空度、湿度、氧产额和反应温度等影响条件的研究，研制出氧化物、硅酸盐类矿物五氟化溴氧同位素分离方法，用该方法测定的氧同位素组成，精度和准确度均在国际允许分析误差范围内。     

矿物氧同位素模式温度计算

根据对现遥氧扩散模型的解析分析,通过模拟矿物之间的氧同位素交换轨迹进行模式温度计算,改进了常规矿物对氧同位素地质温度计方法。将模式温度计算与矿物氧－扩散封闭次上结合,建立了一个系统独立的同位素温度计算方法,因此所得到的同位素温度能够更好地反映矿物在高温岩石冷却过程中,的氧同位素交换行为;模式温度计算有如下优点：（１）考虑到了矿物之间扩散引起的同位素交换;（２）遵循质量守恒原理,更严格地适用于有限封     

内蒙古白云鄂博稀土、铁矿床的硅同位素组成

主矿、东矿矿石及其中的钠辉石、钠闪石、黑云母的δ30Si值相近，大多在-1.0‰--0.3‰之间，低于H1-H2石英砂岩、石英岩的δ30Si值（0-0.1‰）。北铁矿石为0-0.1‰，北矿区塞乌素金矿的δ30Si值为-0.5%--0.2‰；它们之间无成因联系。     

鄂东地区岩石,矿物的氧同位素组成及其地质应用

本文通过对鄂东地区部分氧、碳同位素资料的分析整理,建立了金云母-水氧同位素平衡分馏方程和磁铁矿-金云母氧同位素平衡分馏方程;探讨了岩浆成矿系列及沉积-改造型矿床的氧同位素组成特征;初步探讨了氧同位素在本区找矿上的应用及前景.     

镀镍碳为还原剂在线高温裂解法测定硫酸钡中氧同位素组成

测定矿物或水中硫酸根的氧同位素组成(δ18O)能够识别物质来源及转化过程,常用的方法是将硫酸根转化为硫酸钡再用离线或在线法测试其δ18O值。目前普遍采用1420℃在线测试硫酸钡的氧同位素组成,该方法极易缩短反应炉的寿命,通过添加还原剂碳可以降低反应温度,但是已有报道对于添加还原剂后的反应温度讨论较少。本文选择镀镍碳(Ni-C)作为还原剂,将样品经Ni-C高温处理后进行一系列条件实验,确认了采用元素分析仪-稳定同位素质谱仪(EA-IRMS)测定硫酸钡中氧同位素组成的分析方法的关键技术参数:硫酸钡在线反应温度为1350℃; Ni-C与硫酸钡样品量的质量比范围选择0. 73～2. 15;为了获得更加精确的数据,硫酸钡与Ni-C用量都控制在700±100μg。在以上实验条件下,EA/HT-IRMS测定硫酸钡δ18O值的精密度为±0. 12‰～±0. 26‰,优于在线法已报道的精密度±0. 20‰～±0. 50‰。本方法在满足测试精密度的前提下,通过添加Ni-C降低了硫酸钡在线反应温度,延长了反应炉使用寿命。     

Oxygen isotope study of quartz-Al2SiO5 pairs from the Mica Creek area, British Columbia: implications for the recovery of peak metamorphic temperatures

Oxygen isotope analyses of quartz-Al₂SiO₅ pairs have been made for samples from the Mica Creek area, British Columbia. We have analysed quartz–kyanite nodules and quartz–kyanite and quartz–sillimanite in multiphase pelitic rocks from the staurolite–kyanite, kyanite, and sillimanite zones. Apparent temperatures calculated from oxygen isotopic fractionation range from 555 °C (staurolite–kyanite zone) to 695 °C (sillimanite zone). Temperatures from the quartz–kyanite nodules range from 630 to 675 °C. Some of the nodules show isotopic disequilibrium. Most of the results confirm predictions that bimineralic rocks will yield an estimate of peak metamorphic temperatures, when the less abundant mineral (an aluminium silicate) is the slower oxygen diffuser. Using cooling rates of 10–100 °C Ma^?1 for the multiphase rocks, measured crystal sizes and modes, the Fast Grain Boundary diffusion model with ‘wet’ diffusion data (P_H2O?1.0 kbar) yields predicted apparent temperatures which are generally lower than the measured apparent temperatures. The agreement is improved if slower diffusion coefficients are used. This suggests that f (H₂O) during cooling was lower than that of the hydrothermal experiments and thus that there was little interaction with aqueous fluids of internal or external origin to modify the isotopic compositions. The measured apparent isotopic temperatures and apparent garnet–biotite Fe–Mg exchange temperatures show very poor agreement for the sillimanite zone samples, with the garnet–biotite Fe–Mg exchange temperatures generally higher than the oxygen isotope temperatures. Compared with the other calibrations that we tested the measured apparent temperatures using the Sharp calibration show the best agreeement with recently published P–T grids, although some variability in agreement is expected due to variable f (H₂O) during cooling.     

Primary cracking of kerogens. Experimenting and modelling C1, C2–C5, C6–C15 and C15+ classes of hydrocarbons formed

Mathematical models of hydrocarbon formation can be used to simulate the natural evolution of different types of organic matter and to make an overall calculation of the amounts of oil and/or gas produced during this evolution. However, such models do not provide any information on the composition of the hydrocarbons formed or on how they evolve during catagenesis.From the kinetic standpoint, the composition of the hydrocarbons formed can be considered to result from the effect of “primary cracking” reactions having a direct effect on kerogen during its evolution as well as from the effect of “secondary cracking” acting on the hydrocarbons formed.This report gives experimental results concerning the “primary cracking” of Types II and III kerogens and their modelling. For this, the hydrocarbons produced have been grouped into four classes (C₁, C₂–C₅, C₆–C₁₅ and C₁₅₊). Experimental data corresponding to these different classes were obtained by the pyrolysis of kerogens with temperature programming of 4°C/min with continuous analysis, during heating, of the amount of hydrocarbons corresponding to each of these classes.The kinetic parameters of the model were optimized on the basis of the results obtained. This model represents the first step in the creation of a more sophisticated mathematical model to be capable of simulating the formation of different hydrocarbon classes during the thermal history of sediments. The second step being the adjustment of the kinetic parameters of “secondary cracking”.     

矿物中4He同位素提取和含量测定研究

(U-Th)/He定年是一种有效的低温热年代学定年技术,现已被广泛应用于地质研究的各个领域,而矿物中4He同位素的有效提取和含量准确测定是该技术的关键。磷灰石和锆石是(U-Th)/He定年最常用的矿物,其4He提取条件及铀钍含量测定方法都较为成熟;而其他矿物(如磁铁矿、橄榄石、针铁矿、石榴子石等)的研究则相对较少。文章介绍了当前国内外(U-Th)/He研究中采用的4He同位素提取方法———真空炉加热法和激光加热法,激光加热法因具有低4He背景值和耗时短的优点而成为主要的提取方法。以磷灰石样品测试为例,介绍了成都地质矿产研究所建立的采用激光加热法和四极杆质谱提取4He同位素及其含量测量过程、含量计算和校正方法。指出未来(U-Th)/He测试技术除继续改进现有分析方法外,应加强对更多不同矿物的测试研究。     

Selection of coals of different maturities for CO2 Storage by modelling of CH4 and CO2 adsorption isotherms

CO₂ injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO₂ and CH₄) for well-characterised coals of different maturities to determine the most suitable coal for CO₂ storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO₂ and CH₄ pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO₂ adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO₂ storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO₂ adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO₂ storage capacities. Our study provides high quality affinity parameters and values of CO₂ and CH₄ adsorption capacities on various coals for the future modelling of CO₂ injection in coal seams.     

Reconstructing the response of C3 and C4 plants to decadal-scale climate change during the late Pleistocene in southern Illinois using isotopic analyses of calcified rootlets

The δ¹³C and δ¹⁸O values of well-preserved carbonate rhizoliths (CRs) provide detailed insights into changes in the abundance of C₃ and C₄ plants in response to approximately decadal-scale changes in growing-season climate. We performed stable isotope analyses on 35-40 CRs sampled at 1-cm intervals from an 18-cm-thick paleosol formed in southern Illinois during Wisconsin interstadial 2. Minimum δ¹³C values show little variation with depth, whereas maximum values vary dramatically, and average values show noticeable variability; maximum δ¹⁸O values vary less than the minimum δ¹⁸O values. These findings indicate that a diverse and stable C₃ flora with a limited number of C₄ grass species prevailed during this interval, and suggest that the maximum growing-season temperatures were relatively stable, but minimum growing-season temperatures varied considerably. Two general patterns characterize the relationships between the δ¹³C and δ¹⁸O values obtained from the 1-cm samples. In some cases, low δ¹³C values correspond to low δ¹⁸O values and high δ¹³C values correspond to high δ¹⁸O values, suggesting that cooler growing-season temperatures favored C₃ and warmer growing-season temperatures favored C₄ plants. In other cases, low δ¹³C values correspond to high δ¹⁸O values, likely suggesting that wetter growing-season conditions were favorable to C₃ plants. The high density of well-preserved CRs in this paleosol provides a unique opportunity to study detailed ecological responses to high-resolution variability in growing-season climate.     

广州市大气颗粒物PM2.5显微形貌特征和来源解析

PM_2.5是近年来影响我国城市大气环境的首要污染物,其成因机制复杂。本文采用扫描电镜和ICP-MS研究了广州市大气颗粒物PM_2.5的显微形貌及其化学组成特征,并应用富集因子法进行源解析。结果表明,PM_2.5的颗粒形态以无定形态为主;主要物质表现为含Fe、Mg、Al、K、Na的硅酸盐组合,具有道路扬尘、建筑施工排放等一次粒子特征;单个无定形颗粒物能谱表现出硫酸盐+硝酸盐的组合特征,为汽车尾气所排放的前体污染气体NO_x和SO₂进入大气环境中,在特定的物理化学条件下通过成核作用发生相态改变所形成的二次粒子。PM_2.5中高度富集Cd、Se、Zn、Cu、Pb、As等重金属,异常富集的Br主要为当地普遍使用的阻燃剂十溴联苯醚和拆解电子垃圾所致,稀土元素的浓度在0.022~0.582 ng/m³之间,具有重稀土元素富集的特征。这些特征反映出广州市PM_2.5颗粒物的组成既有一次粒子,也有二次粒子,物质来源具有多重性。     

用于单体氢同位素分析的混合溶剂洗脱5分子筛吸附正构烷烃的方法

混合溶剂萃取洗脱5分子筛吸附正构烷烃的方法在单体碳同位素分析研究中已得到了应用。由于5分子筛在长时间加热条件下可能对有机分子的氢交换反应具有一定的催化作用,因此对于该方法能否用于正构烷烃的单体氢同位素分析需要做进一步研究。本文以两种不同类型原油的饱和烃和正构烷烃混合标准样品为对象,采用环己烷-正戊烷溶剂和氢氟酸溶解-正戊烷溶剂洗脱5分子筛吸附的正构烷烃,对比分析两种萃取方式的分离效果,并分别测定了正构烷烃的单体氢同位素比值。结果表明:两种萃取方式都得到了纯化效果良好的正构烷烃组分,氢同位素测定结果的差值总体上小于4‰,在仪器分析误差范围内。经过三次环己烷-正戊烷洗脱方式获得正构烷烃回收率平均值为58%,氢氟酸溶解-正戊烷洗脱方式经过多次萃取操作获得正构烷烃回收率平均值为68%。尽管环己烷-正戊烷洗脱方式提取正构烷烃的效率较低,并且涉及在分子筛条件下多次较长时间的加热过程,但这两个因素没有导致氢同位素发生明显的分馏或交换过程,适合用于正构烷烃分离、纯化以及单体氢同位素测定。