离子交换树脂法分离沉积物中锶和钕的影响因素研究   总被引：3，自引：3，他引：0  

尹鹏  何倩  何会军  赵志琦 《岩矿测试》2018,37(4):379-387

Sr和Nd同位素是地质学研究中经典的同位素定年和示踪体系。传统沉积物中Sr和Nd分离方法通常是利用AG50W-X8树脂分离Sr与稀土元素(REEs),再用Sr和Ln特效树脂分别对Sr和Nd纯化,但对于Fe元素含量较高的沉积物样品,该方法对REEs的洗脱率偏低,仅有50%。另外,AG50W-X8树脂高度、洗脱酸种类、Sr特效树脂淋洗酸体积以及Ln特效树脂过柱方式对Sr和Nd分离都有影响。为分析上述因素对Sr和Nd分离效果的影响,本文以水系沉积物标准物质GBW07309为例进行了研究,结果表明:(1)高含量的Fe会显著影响Sr和Nd的分离效果,而AG1-X8树脂可以有效去除Fe;(2)当AG50W-X8树脂高度为1 m L,硝酸作为洗脱酸时,Sr和REEs的分离效果较好;(3)Sr特效树脂淋洗酸中硝酸淋洗体积达到15 m L时可以有效分离Sr和Rb;(4)Ln特效树脂采用重力过柱方式时Sr和Nd分离效果较好,没有拖尾现象。本研究解决了Fe对分离Sr和Nd的干扰,K、Na、Ca、Mg、Fe、Rb、Sm去除率达到99%以上,完全满足Sr和Nd同位素分析的要求,为离子交换树脂法分离沉积物中Sr和Nd提供了较详细的前处理经验数据。  相似文献   

树脂柱串联法分离地质样品中Sr-Nd-U     

骆正骅  李超  赖正  王晨羽  郭玉龙  段知非  徐娟  杨守业 《岩矿测试》2023,(1):102-113

Sr、Nd、U等同位素体系被广泛应用于地球表生过程中年代测定及物源示踪等研究,高效地分离这些同位素体系,对于推广这些同位素方法的应用具有重要现实意义。若要同时分析地质样品中Sr、Nd、U三种元素的同位素,现有方法往往需要消解两份样品,一份用于Sr-Nd而另一份用于U的分离提纯。这种方法不但增加了样品用量,而且需要多次蒸干溶液转换介质,既延长了分离流程也增加了样品被污染的风险。为了提高样品利用率和分析效率,本文通过将树脂柱串联改进了分离流程,提出一种仅需消解一份样品,便可同时提取Sr、Nd、U三种元素的新方法。本方法中Sr的分离采用Sr特效树脂,包含Nd在内的稀土元素(REE)的分离采用AG50W-X8树脂,U的分离采用UTEVA特效树脂。实验中将三种树脂柱串联,采用3mol/L硝酸淋洗液淋洗,同步进行平衡树脂、上样、洗杂志,避免了蒸干操作。分离后的淋出液使用电感耦合等离子体质谱仪(ICP-MS)测试元素含量。结果表明：U的回收率接近99.9%,Sr的回收率超过90%,Nd的回收率超过80%;同时三种树脂柱串联的分离流程,主要基体元素(K、Ca、Na、Ba、Fe、Rb等)的去除率均超过9...  相似文献   

利用DCTA和HIBA快速有效分离Rb-Sr, Sm-Nd     

濮巍  高剑峰  赵葵东  凌洪飞  蒋少涌 《地球学报》2005,26(Z1):54-54

Rb-Sr和Sm-Nd的有效分离是精确测定这些同位素的关键。传统的分离方法以盐酸为介质，虽然能够有效地分离这些元素，但是需要耗用大量的酸，并且无法将Sr和Ca、Mg等元素分离，对于Sm、Nd含量低的样品，回收率较低。后来有一些实验室建立了用混合的有机酸（如甲酸、乙酸、DCTA、EDTA等）来分离Sr的方法，大大减少了分离时间，减少了试剂用量，从而降低了过程空白并能够将Ca和Mg与Sr分离。本实验室在此基础上建立了一种新的Rb-Sr,Sm-Nd化学分离方法，以用于地质样品的同位素测试。该方法选用AG50W×8阳离子交换树脂，并先后采用不同的淋洗剂进行分离提纯。首先用常规方法使用盐酸作为淋洗剂将Rb-Sr和REE分开并与其他大部分元素分离，然后使用DCTA和嗜咙的混合溶液(D. P. E.）作为淋洗剂分离Rb和Sr，使用HIBA作为淋洗剂在很小体积(0.6 mI.）的阳离子交换树脂中分离Sm和Nd。使用这样的分离方法可以有效地将一些干扰离子（如Mg、Ca、Ba）和Sr分离，同时使用该分离方法可以提高分离效率，缩短分离时间，减少试剂用量，降低实验过程空白。用该方法分离国际玄武岩标样BCR-2后的Sr同位素测试结果（87Sr/86Sr= 0.705018±3)与Brian等测定的0.705024±5基本一致，Nd同位素测试结果（143 Nd/144Nd = 0.512616±9 )与本实验室以前使用HCI介质分离测定的0.512624±3基本一致，与其他研究者最近报道的BCR-1的0.512644±11和0.512650也基本一致。说明本次研究采用的新分离方法效果良好。  相似文献   

微波消解-多接收电感耦合等离子体质谱高精度测定锶钕同位素组成   总被引：4，自引：4，他引：0  

袁永海  杨锋  余红霞  刘希军  许继峰 《岩矿测试》2018,37(4):356-363

应用多接收器电感耦合等离子体质谱仪(MC-ICP-MS)测定地质样品中锶、钕同位素组成时,化学前处理流程冗长、复杂,且容易出现样品未完全溶解的现象。本文采用微波消解法消解样品,在保证消解效果的前提下有效地缩短了溶样时间,在此基础上研究了锶、钕化学分离和质谱测试流程,重点考察了树脂柱的回收率和记忆效应。结果表明:树脂经10次使用后的锶、钕流程空白均低于1.0 ng,但回收率明显下降,分别由原来的98%和90%降到20%和50%,若待测样品中锶、钕含量较低,所接收的锶、钕则达不到质谱仪测试范围,因此建议锶特效树脂使用次数不超过5次,AG50W-X8稀土柱和Ln树脂使用次数不超过10次。整套流程应用于国际地质标准样品(BCR-2、W-2a、BHVO-2、AGV-2)的锶、钕分离,MC-ICP-MS所得的87Sr/86Sr、143Nd/144Nd测定值与文献报道值一致,仪器的内精度2SE(n=50)和方法的外精度2SD(n=6)均优于0.0015%,表明该流程可以满足地质样品中锶、钕同位素高精度测定的要求。  相似文献   

离子交换树脂在地质样品Sr-Nd同位素测定中的应用   总被引：2，自引：0，他引：2       下载免费PDF全文

刘文刚  刘卉  李国占  周红英  肖志斌  涂家润  李惠民 《地质学报》2017,91(11):2584-2592

Rb-Sr和Sm-Nd同位素测年及同位素示踪方法在同位素地质年代学和同位素地球化学中有非常广泛的应用。目前,Rb-Sr和Sm-Nd同位素质谱测试方法通常需要对Rb、Sr和Sm、Nd进行分离纯化,因此,如何对地质样品中的Rb、Sr、Sm和Nd进行分离富集对测试结果准确与否起到至关重要的作用。离子交换分离法是SrNd同位素化学前处理阶段应用最广泛的分离方法,本文结合笔者近几年的研究工作,系统介绍离子交换树脂在Sr-Nd同位素测试中应用的发展过程和现状,重点介绍几类使用率较高的离子交换树脂(Dowex50W树脂、AG50W树脂、锶特效树脂、LN树脂、P507树脂等)的优缺点,以及各自的萃取反应机理,探索和讨论未来离子交换树脂在Sr-Nd同位素测试中应用的发展趋势。  相似文献   

雷琼地区晚新生代玄武岩地球化学：EM2成分来源及大陆岩石圈地幔的贡献   总被引：1，自引：1，他引：0  

韩江伟  熊小林  朱照宇 《岩石学报》2009,25(12):3208-3220

对雷琼地区21个晚新生代玄武岩样品的主量、微量元素和Sr、Nd、Pb同位素分别用湿化学法、ICP-MS和MC-ICPMS进行了测定.这些玄武岩主要为石英拉斑玄武岩,其次为橄榄拉斑玄武岩和碱性玄武岩.大多数样品的微量元素和同位素成分与洋岛玄武岩(OIBs)相似,而且随着SiO_2不饱和度增加,不相容元素含量也增加.除R4-1可能受到地壳混染外,其他样品相对均一的Nd同位素(ε_(Nd)=2.5-6.0)以及变化明显但范围有限的Sr同位素(0.703106～0.704481),可能继承了地幔源区的特征.~(87)Sr/~(86)Sr与~(206)Pb/~(204)Pb的正相关和~(143)Nd/~(144)Nd与~(206)Pb/~(204)Pb的负相关特征暗示DM(软流圈地幔)与EM2(岩石圈地幔)的混合.地幔捕虏体的同位素特征暗示EM2成分不可能存在于尖晶石橄榄岩地幔,而La/Yb和Sm/Yb系统表明岩浆由石榴石橄榄岩部分熔融产生,这意味着EM2成分可能存在于石榴石橄榄岩地幔.雷琼地区玄武岩的地球化学变化可以用软流圈地幔为主的熔体加入不同比例石榴石橄榄岩地幔不同程度熔融产生的熔体来解释:碱性玄武岩和橄榄拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较低程度(7%～9%)熔融体混合,而石英拉斑玄武岩是软流圈熔体与石榴石橄榄岩地幔较高程度(10%～20%)熔融体的混合.  相似文献   

高精度质谱计在同位素地球化学的应用前景   总被引：22，自引：0，他引：22  

陈福坤  李秋立  李潮峰  李向辉  王秀丽  王芳 《地球科学》2005,30(6):639-645

微量地质样品的高精度同位素比值测试已经成为地质和环境科学等领域极其重要的研究手段.新型固体热电离质谱计以其高精度和高灵敏度,将在同位素年代学和地球化学领域有广阔的应用前景.报道采用IsoProbeT质谱计测量标准物质溶液的结果.测量锶标准物质NBS987和钕标准物质Ames分别获得平均87Sr/86Sr比值0.7102418±0.0000051和平均143Nd/144Nd比值0.5121484±0.0000029,内部精度可达0.0003%.微量锶标准物质(0.3～1ng)的同位素比值测量内部精度可以优于0.003%.结合低本底化学流程,实现了微量地质样品的高精度同位素比值测试.这一结合将有效地促进单颗粒矿物年代学和同位素示踪在岩浆岩、变质岩、矿床、构造岩研究的应用.  相似文献   

地质样品中镥-铪同位素体系的化学分离与质谱测试新进展   总被引：2，自引：0，他引：2  

杨岳衡张宏福  谢烈文吴福元 《岩矿测试》2006,25(2):151-158

对自1980年以来地质样品中Lu—Hf同位素体系的化学分离方法与质谱测试技术的最新进展进行了综述。着重介绍热电离质谱、热二次离子质谱和多接收电感耦合等离子体质谱（MC—ICP—MS）在测定Lu—Hf同位素时，针对不同类型的仪器、不同的样品所采用的各种化学分离方法和质谱测试技术。主要参考文献46篇。通过文献综述表明，MC—ICP—MS技术是当前进行Lu—Hf同位素测试的主要技术，Eichrom Ln—Spec树脂是一次进行Lu—Hf同位素体系化学分离的有效手段，和其他成熟的同位素体系（Rb—Sr、Sm—Nd、U—Pb）结合，成为今后具有很大发展空间的研究方向之一。  相似文献   

长白山地区新生代火山岩的岩石化学及Sr、Nd、Pb同位素地球化学研究   总被引：12，自引：10，他引：12  

解广轰  王俊文  A.R.Basu  M.Tatsumoto 《岩石学报》1988,4(4)

通过主元素、稀土元素、Sr、Nd、Pb同位素地球化学特征并结合板块俯冲模式来讨论长白山地区新生代火山岩系的形成和演化。大部分样品都进入上地幔Sr演化范围,具低Sr高~(87)Sr/~(86)Sr特点;∑Nd介于-2.3—+2.9之间;不同岩性熔岩的Pb同位素组成变化不大。主元素、REE模式和同位素的资料都证实区内火山岩是源自上地幔的同源岩浆分异演化而成,并有地壳物质的混染。  相似文献   

AG MP-1M阴离子分离Cu、Fe、Zn及其在Fe同位素测定上的应用   总被引：1，自引：0，他引：1  

马信江  梁细荣  涂相林  曾文  李杰 《地球化学》2009,38(5)

采用新型阴离子交换树脂AG MP-1M,分别以8.2 mol/L HCl+0.01%HF、4 mol/L HCl、2 mol/L HCI和0.5 mol/L HNO,可以有效分离地质样品中Cu、Co、Fe和Zn,克服了AG MP-1阴离子交换树脂分离Cu时Co随Cu同时淋洗下来,以及在分离Co含量较高的地质样品时Co和Cu需过二次柱分离的弊端.对花岗闪长岩等地质标样的研究结果表明,AG MP-1M阴离子交换树脂能有效分离Cu、Fe和Zn,并且它们的回收率均大于99%.标准样品经过离子交换分离后Fe同位素未发生分馏,可满足多接收器电感耦合等离子体质谱(MC-ICPMS)的同位素测定要求.  相似文献   

高Rb/Sr岩石样品中Sr同位素多接收等离子体质谱分析校正方法研究   总被引：1，自引：1，他引：0  

戴梦宁  宗春蕾  袁洪林 《岩矿测试》2012,31(1):95-102

在利用多接收电感耦合等离子体质谱(MC-ICPMS)进行Sr同位素研究中,⁸⁷Rb对于⁸⁷Sr干扰严重。岩石样品经化学分离后,若Rb/Sr≤0.0005,可以采用传统的Rb干扰扣除方法对⁸⁷Sr/⁸⁶Sr测定值进行准确校正;但如果样品经化学分离后仍含有较高的Rb/Sr比,同量异位素的干扰不能完全消除,则无法准确校正⁸⁷Sr/⁸⁶Sr测定值,直接影响测试结果的准确度。本文针对Rb含量较高的地质样品设计两组实验,确定了⁸⁷Sr/⁸⁶Sr同位素比值与Rb/Sr元素含量比值的关系曲线,并在理论分析的基础上,提出包含同位素分馏校正在内的重叠干扰校正方法。通过实际地质样品验证,该校正方法在较高含量Rb元素共存(Rb/Sr<0.2)的Sr纯化液中,能够较为准确地测量⁸⁷Sr/⁸⁶Sr同位素比值,降低了MC-ICPMS分析地质样品中Sr同位素时对化学分离步骤的要求。而对于Rb/Sr>0.2的地质样品,因仪器分馏效应和记忆效应影响,测试精确度大大降低,无论采用何种校正方法均无法得到准确的Sr同位素组成。  相似文献   

High‐Precision Sr‐Nd‐Hf‐Pb Isotopic Composition of Chinese Geological Standard Glass Reference Materials CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5 by MC‐ICP‐MS and TIMS     

Yue‐Heng Yang  Ming Yang  Klaus Peter Jochum  Shi‐Tou Wu  Han Zhao  Lie‐Wen Xie  Chao Huang  Xiu‐Chun Zhan  Jin‐Hui Yang  Fu‐Yuan Wu 《Geostandards and Geoanalytical Research》2020,44(3):567-579

To assess the homogeneity of and provide the first Sr‐Nd‐Hf‐Pb isotopic reference values for the Chinese Geological Standard Glasses CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5, we measured these isotopes in several measurement sessions over the course of nearly 3 years. The results were obtained by high‐precision MC‐ICP‐MS and TIMS. Our investigation indicates that these CGSG glass reference materials are homogenous with regard to Sr‐Nd‐Hf‐Pb isotopic distribution and are therefore suitable geochemical materials for Sr‐Nd‐Hf‐Pb isotope measurements. Clear differences in Sr‐Nd‐Hf‐Pb isotopic composition were observed between the glasses and the original powdered rock reference materials (CGSG‐2 and GSR‐7, and especially CGSG‐5 and GSR‐2) because of flux addition during preparation of the glasses. The new Sr‐Nd‐Hf‐Pb isotope data provided here might be useful to the geochemical community for in situ and bulk analysis.  相似文献   

大别山麻粒岩和TTG片麻岩的Sr,Nd,Pb同位素地球化学   总被引：4，自引：1，他引：4  

葛宁洁  柏林等 《地质学报》2001,75(3):379-384

北大别4个麻粒岩和4个TTG片麻岩样品的Sr,Nd同位素分析结果表明，样品普遍具有较高的锶同位素比值（^87Sr/^86Sr=0.7066-0.7461)，较低的Nd同位素比值（^143Nd/^144Nd=0.5108-0.5124)，表现出明显的壳源特征，结合铅同位素的组成来看，北大别麻粒岩及TTG片麻岩的同位素成分相当于－下地壳。岩石的特源为古老的地壳，大约在2－3Ga之间，少数样品的同位素特征可能暗示源区有年轻地壳物质的加入。  相似文献   

Compilation of radiogenic isotope data in Mexico and their petrogenetic implications     

Ignacio S. Torres-Alvarado  Surendra P. Verma  Gerardo Carrasco-Núñez 《Journal of Earth System Science》2000,109(1):67-78

Seven hundred and twenty-five Sr, two hundred and forty-three Nd and one hundred and fifty-one Pb isotopic ratios from seven different Mexican magmatic provinces were compiled in an extensive geochemical database. Data were arranged according to the Mexican geological provinces, indicating for each province total number of analyses, range and mean of values and two times standard deviation (2σ). Data from seven provinces were included in the database: Mexican Volcanic Belt (MVB), Sierra Madre Occidental (SMO), Baja California (BC), Pacific Ocean (PacOc), Altiplano (AP), Sierra Madre del Sur (SMS), and Sierra Madre Oriental (SMOr). Isotopic values from upper mantle and lower crustal xenoliths, basement outcrops and sediments from the Cocos Plate were also compiled. In the MVB the isotopic ratios range as follows:⁸⁷Sr/⁸⁶Sr 0.703003-0.70841;¹⁴³Nd/¹⁴⁴Nd 0.512496-0.513098;²⁰⁶Pb/²⁰⁴Pb 18.567-19.580;²⁰⁷Pb/²⁰⁴Pb 15.466-15.647;²⁰⁸Pb/²⁰⁴Pb 38.065-38.632. The SMO shows a large variation in⁸⁷Sr/⁸⁶Sr ranging from ∼0.7033 to 0.71387.¹⁴³Nd/¹⁴⁴Nd ratios are relatively less variable with values from 0.51191 to 0.51286. Pb isotope ratios in the SMO are as follows:²⁰⁶Pb/²⁰⁴Pb 18.060-18.860;²⁰⁷Pb/²⁰⁴Pb 15.558-15.636;²⁰⁸Pb/²⁰⁴Pb 37.945-38.625. PacOc rocks show the most depleted Sr and Nd isotopic ratios (0.70232-0.70567 for Sr and 0.512631-0.513261 for Nd). Pb isotopes for PacOc show the following range:²⁰⁶Pb/²⁰⁴Pb 18.049-19.910;²⁰⁷Pb/²⁰⁴⁷Pb 15.425-15.734;²⁰⁸Pb/²⁰⁴Pb 37.449-39.404. The isotopic ratios of the AP rocks seem to be within the range of those from the PacOc. Most samples with reported Sr and Nd isotopic data are spread within and around the “mantle array”. The SMO seems to have been formed by a mixing process between mantle derived magmas and continental crust. The MVB appears to have a larger mantle component, with AFC as the dominant petrogenetic process for the evolved rocks. There is still a need for Pb isotopic data in all Mexican magmatic provinces and of Nd isotopes in BC, AP, SMS, and SMOr.  相似文献   

The Pb-Sr-Nd isotope geochemistry of some recent circum-Mediterranean granites     

Martine Juteau  Annie Michard  Francis Albarede 《Contributions to Mineralogy and Petrology》1986,92(3):331-340

Pb, Sr and Nd isotopic compositions have been analyzed in recent granites from Northern Africa, Northern Italy and Greece. Lead isotope compositions of K-feldspars are rather homogeneous, and cluster close to the modern lead of Stacey and Kramers (1975) but with slightly higher²⁰⁷Pb/²⁰⁴Pb and²⁰⁸Pb/²⁰⁴Pb ratios. The Cyclades samples, however, have higher²⁰⁶Pb/²⁰⁴Pb ratios. Addition of mantle-derived lead was probably very limited, which supports a quasi-closed system evolution of this element in the continental crust. The Sr, Nd data fall in the enriched part of the¹⁴³Nd/¹⁴⁴Nd vs.⁸⁷Sr/⁸⁶Sr diagram and define a smooth hyperbolic mixing curve. Over a wide area, straddling different orogens, most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle-like component. No correlation is observed between either Pb and Sr or Nd isotopic ratios, or any isotopic ratio and major element contents. Quantitative modelling suggests that two cases fit the Sr and Nd characteristics of these granites: they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes. In the first case, the mantle-derived component may be represented by differentiated Island Arc-type magmas, and the granites result from mixing these magmas with anatectic melts. In the second case, mantle-derived igneous rocks, such as obducted ophiolites, are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations.CRPG Contribution n 630.  相似文献   

Comprehensive Chemical and Isotopic Analyses of Basalt and Sediment Reference Materials   总被引：2，自引：0，他引：2  

Catherine Chauvel  Sarah Bureau  Christèle Poggi 《Geostandards and Geoanalytical Research》2011,35(1):125-143

Geochemical studies of geological samples require the precise determination of their major and trace element contents and, when measured, of their isotopic compositions. It is now commonly accepted that the accuracy and precision of geochemical analyses are best estimated by the concomitant analysis of international reference materials run as unknown samples. Although the composition of a wide selection of basalts is relatively well constrained, this is far from being the case for sedimentary materials. We present here a comprehensive set of major and trace element data as well as Nd, Hf, Sr and Pb isotopic compositions for thirteen commonly used international reference materials – eight magmatic rocks (BHVO‐2, BR, BE‐N, BR 24, AGV‐1, BIR‐1, UB‐N, RGM‐1) and five sediments (JLk‐1, JSd‐1, JSd‐2, JSd‐3, LKSD‐1). We determined the concentrations of over forty elements in the magmatic rocks together with Sr, Nd, Hf and Pb isotopic compositions. Our trace element results were both accurate (difference ≤ 3%) and precise (reproducibility at 1s ≤ 3%) and the isotopic results were very similar to other published values. In contrast, we observed a significant chemical and isotopic variability in the sedimentary materials, which we attribute to mineral heterogeneities in the powders. Despite the limitation imposed by this heterogeneity, our work presents a complete set of data determined with a precision not yet achieved in the literature for sedimentary material. We also provide the first Nd, Hf and Pb isotopic measurements for the five sediments, which are commonly used by the geochemical community. Our study of both basalt and sediment reference materials represents a comprehensive and self‐consistent set of geochemical data and can therefore be considered as a reference database for the community.  相似文献   

Pb-Sr-Nd isotopic compositions and trace element geochemistry of megacrysts and melilitites from the Tertiary Urach volcanic field: source composition of small volume melts under SW Germany     

E. Hegner  H. J. Walter  M. Satir 《Contributions to Mineralogy and Petrology》1995,122(3):322-335

 The Urach volcanic field is unique within the Tertiary–Quaternary European volcanic province (EVP) due to more than 350 tuffaceous diatremes and only sixteen localities with extremely undersaturated olivine melilitite. We report representative Pb-Sr-Nd isotopic compositions and incompatible trace element data for twenty-two pristine augite, Cr-diopside, hornblende, and phlogopite megacryst samples from the diatremes, and seven melilitite whole rocks. The Pb isotopic compositions for melilitites and comagmatic megacrysts have very radiogenic ²⁰⁶Pb/²⁰⁴Pb ratios of 19.4 to 19.9 and plot on the northern hemisphere mantle reference line (NHRL). The data indicate absence of an old crustal component as reflected in the high ²⁰⁷Pb/²⁰⁴Pb ratios of many basalts from the EVP. This inference is supported by ²⁰⁶Pb/²⁰⁴Pb ratios of ∼17.6 to 18.3 and ɛ_Nd of ∼−7.8 to +1.6 for five phlogopite xenocryst samples reflecting a distinct and variably rejuvenated lower Hercynian basement. The ⁸⁷Sr/⁸⁶Sr ratios of 0.7033 to 0.7035 in the comagmatic megacrysts are low relative to their moderately radiogenic Nd isotopic compositions (ɛ_Nd +2.2 to +5.1) and consistent with a long-term source evolution with a low Rb/Sr ratio and depletion in light rare-earth elements (LREE). The melilitite whole-rock data show a similar range in Nd isotopic ratios as determined for the megacrysts but their Sr isotopic compositions are often much more radiogenic due to surface alteration. The REE patterns and incompatible trace element ratios of the melilitites (e.g. Nb/Th, Nb/U, Sr/Nd, P/Nd, Ba/Th, Zr/Hf) are similar to those in ocean island basalts (OIB); negative anomalies for normalized K and Rb concentrations support a concept of melt evolution in the lithospheric mantle. Highly variable Ce/Pb ratios of 29 to 66 are positively correlated with La/Lu, La/K₂O, and Ba/Nd and interpreted to reflect melting in the presence of residual amphibole and phlogopite. The data suggest an origin of the melilitites from a chemical boundary layer very recently enriched by melts from old OIB sources. We suggest that the OIB-like mantle domains represent low-temperature melting heterogeneities in an upwelling asthenosphere under western Europe. Received: 9 March 1995/Accepted: 24 July 1995  相似文献   

Baseline determination of the atmospheric Pb,Sr and Nd isotopic compositions in the Rhine valley,Vosges mountains (France) and the Central Swiss Alps     

M. Lahd Geagea  P. Stille  F. Gauthier-Lafaye  Th. Perrone  D. Aubert 《Applied Geochemistry》2008

The Pb, Sr and Nd isotopic compositions of biomonitors (lichen, moss, bark) and soil litter from different regions in the Rhine valley, as well as of <0.45 μm particles separated out of ice of the Rhône and Oberaar glaciers and lichens from the Swiss Central Alps, have been determined in order to deduce the natural baseline of the atmospheric isotopic compositions of these regions, which are suggested to be close to the isotopic compositions of the corresponding basement rocks or soils at the same sites. ²⁰⁶Pb/²⁰⁷Pb and ⁸⁷Sr/⁸⁶Sr isotope ratios are positively correlated. Most polluted samples from traffic-rich urban environments have the least radiogenic Pb and Sr isotopic compositions with ²⁰⁶Pb/²⁰⁷Pb and ⁸⁷Sr/⁸⁶Sr ratios of 1.11 and 0.7094, respectively. These ratios are very different from those of the atmospheric baseline for the Vosges mountains and the Rhine valley (²⁰⁶Pb/²⁰⁷Pb: 1.158–1.167; ⁸⁷Sr/⁸⁶Sr: 0.719–0.725; ε_Nd: −7.5 to −10.1). However, this study indicates that the baseline of the atmospheric natural Pb and Sr isotopic compositions is affected by anthropogenic (traffic, industrial and urban) emissions even in remote areas. Lichen samples from below the Rhône and Oberaar glaciers reflect the baseline composition close to the Grimsel pass in the Central Swiss Alps (⁸⁷Sr/⁸⁶Sr: 0.714 − 0.716; ε_Nd: −3.6 to −8.1). The ¹⁴³Nd/¹⁴⁴Nd isotope ratios are highly variable (8ε units) and it is suggested that the variation of the ¹⁴³Nd/¹⁴⁴Nd is controlled by wet deposition and aerosols originating from the regional natural and industrial urban environments and from more distant regions like the Sahara in North Africa. The least anthropogenetically affected samples collected in remote areas have isotopic compositions closest to those of the corresponding granitoid basement rocks.  相似文献