柴达木盆地那棱格勒河及其尾闾盐湖锂成矿物源：来自水化学和锶、硫同位素证据

柴达木盆地那棱格勒河尾闾盐湖（一里坪干盐滩、东台吉乃尔盐湖、西台吉乃尔盐湖和察尔汗盐湖别勒滩区段）赋存了我国目前最大的卤水锂矿床。那棱格勒河及其尾闾盐湖锂的物源仍存在一定争议,主要有围岩风化、古湖残留、含盐系地层淋滤、油田水、深部水等,目前缺乏有力的地球化学证据。本文系统采集了那棱格勒河流域及其尾闾盐湖不同水体样品16件,分析了其主、微量元素含量及锶、硫同位素组成。结合前人的研究成果,对区域水体中锂的来源进行了探讨,得出结论如下：那棱格勒河水锂含量（0. 45~0. 79 mg/L）比楚拉克阿拉干河支流（0. 00~0. 05 mg/L）高出一个数量级,其高锂含量主要受洪水河支流的补给;洪水河高锂含量与其上游热泉水的补给有关,该热泉水锂、锶含量高、 87 Sr/ 86 Sr比值偏高, δ 34 S值偏低,与青藏高原典型热泉水地球化学特征（锂含量0. 4~34. 8 mg/L,锶含量0. 07~4. 24 mg/L, 87 Sr/ 86 Sr比值0. 71224~0. 71259, δ 34 S值- 10. 6‰~7. 6‰）较一致。那棱格勒河水（0. 71170）和尾闾盐湖卤水（0. 71143~0. 71156）相似的 87 Sr/ 86 Sr比值,以及研究区河、湖水硫同位素组成符合主要蒸发浓缩过程 δ 34 S值逐渐下降的变化趋势,均证明研究区尾闾盐湖卤水锂资源主要受那棱格勒河的补给;而古湖残留水、盆地西部含盐系地层淋滤水或油田水具有明显不同的水化学特征和锶、硫同位素组成,这些水体对研究区尾闾盐湖锂补给的贡献较小,可忽略不计。     

滇西两个碱性岩体Rb、Sr同位素资料的再认识

滇西两个碱性岩体的Rb、Sr同位素研究结果：白云山正长岩同位素年龄为85MaBP，^76Sr／^86Sr的初始比值为0．7097；小桥头石英正长岩^87St／^86Sr的初始比值为0．7038。另据矿物组成和地球化学特征等，表明白云山正长岩类似钠质碱性系列的岩石。     

高喜马拉雅康布马曲和波曲河流放射成因^87Sr源岩追踪研究

虽然喜马拉雅河流Sr同位素对现代海洋Sr同位素产生了重要影响,但国际上目前对有关喜马拉雅河流Sr同位素异常源岩（如放射成因87Sr的来源）的认识仍存在着较大争议。为此,笔者等对高喜马拉雅河流波曲和康布马曲在中国境内河水主要离子化学和Sr同位素进行了分析研究,对河流放射性87Sr的来源进行了追踪研究。笔者等的研究数据表明,高喜马拉雅康布马曲和波曲河流主要离子水化学主要是受硅酸盐岩风化的影响。青藏高原河流河水TDS和HCO3-主要受岩性控制,片麻岩和花岗岩区河流TDS〈100（mg/L）、HCO3-〈60（mg/L）,沉积岩区河流TDS〉100（mg/L）、HCO3-〉60（mg/L）,除受蒸发盐岩和地下卤水影响的河流外,河水中HCO3-与TDS成正比,但河水中Si与TDS的关系并不明显。高喜马拉雅河流具有高n（87Sr）/n（86Sr）、低Sr的特征,河流Sr是主要来自于中央结晶岩系硅酸盐岩片麻岩和花岗岩的风化,而片麻岩和花岗岩中具有高n（87Sr）/n（86Sr）、低Sr特征的黑云母的风化应是河流放射成因87Sr的主要来源。     

贵州喀斯特地区河流的研究--碳酸盐岩溶解控制的水文地球化学特征

测量了喀斯特地区乌江、沅江两大水系的河流枯水期的主元素、Sr2+离子浓度和Sr同位素比值。这些河流的化学组成代表了流经碳酸盐岩地层的河水的化学组成。这些河流及其支流有高的溶解盐,TZ+变化范围为：2.1～6.3 meq/L,高于全球河流的平均值(TZ+=0.725 meq/L)。河水含有较高的溶质浓度,河水水化学组成以Ca2+和HCO-3为主,其次为Mg2+和SO2-4,Na++K+和Cl-+Si分别只占阳离子和阴离子组成的5%～10%。 这些河流的化学和同位素组成主要受其自流盆地的地质特征控制。流经碳酸盐岩地层的乌江水系河流具有较高的Sr浓度（1.1～9.70 mol/L）和较低的87Sr/86Sr比值（0.7077～0.7110）,与流经碎屑岩地层的沅江水系的清水江河流中较高的87Sr/86Sr比值（0.7090～0.7145）及较低的Sr浓度（0.28～1.32 mol/L）形成鲜明的对比。 流域盆地的地理岩性控制了河水的化学组成和同位素组成。对河水的化学计量分析表明河水化学组成受碳酸盐岩溶解控制,而碳酸盐岩主要受碳酸和硫酸作用而溶解。乌江流域受硫酸作用特别明显,表明硫酸主要来源于燃煤或流域盆地硫化物矿物氧化而形成的大气输入。化学元素和同位素比值之间的相互关系表明3个主要来源为：石灰岩、白云岩和硅酸盐岩的风化。同时估计了碳酸盐岩和硅酸盐岩的化学风化速率,结果表明流域盆地的碳酸盐岩风化速率远远高于许多世界大河。岩石风化过程中硫酸的出现或土地的过度使用或土壤植被的退化等都可能是导致流域的碳酸盐岩风化速率如此高的原因。      

鄂尔多斯白垩系自流水盆地地下水锶同位素特征及其水文学意义

鄂尔多斯白垩系自流水盆地北部为沙漠高原区，南部为黄土高原区。区内经济以农业和畜牧业为主，地下水的污染较弱。地下水中Sr来源于含Sr矿物的溶解。因此，可以利用Sr及^87Sr／^86Sr比值来研究水岩作用和地下水的演化。采自盆地20个Sr及其同位素样品的分析结果表明：在区域上^87Sr／^86Sr比值是不均匀的，西南部^87Sr／^86Sr比值较大（0．711002-0．711570），其他地区。^87Sr／^86Sr比值较小（0．710378-0．710646）；在局域地下水系统中，埋深小于100m的浅层地下水，Sr含量较低，^87Sr／^86Sr比值较大，而埋深大于100m的深层地下水，Sr含量较高，^87Sr／^86Sr比值较小，并且沿地下水径流方向，sr的浓度越来越高。苏贝淖湖是自流水盆地北部局域地下水系统的一个排泻区，湖水Sr含量较低，而^87Sr／^86Sr比值较大，其Sr同位素组成特征与浅层地下水一致，表明湖水来源于浅层地下水。     

贵州河流河水的锶同位素与喀斯特地区化学风化作用

贵州省地处世界岩溶发育最复杂、类型最齐全、分布面积最大的东亚岩溶区域中心, 也是我国碳酸盐岩分布面积最大、岩溶最发育的省区, 同时也是我国水土流失严重的地区之一。由于河水的地球化学反映了流域盆地的化学风化、气候和上地壳的化学组成的重要信息, 本工作对贵州喀斯特地区两条主要水系(乌江水系、沅江水系)河流的主要阴、阳离子和Sr2＋离子及锶同位素组成变化进行了系统研究, 对河水地球化学组成变化特征及其控制因素进行了解释。 贵州喀斯特地区两条主要水系河流的水化学组成代表了典型碳酸盐岩地区河流的相应化学组成, 显示了与世界主要河流不同的水化学特征, 反映了喀斯特环境地表化学风化作用的特点。     

辽西北票早侏罗世兴隆沟组英安岩的地球化学特征

辽西北票早侏罗世兴隆沟组英安岩具有埃达克岩的地球化学特征。它们具有较高的SiO2（≥63．93％）、Al2O3（≥15．40％）、Na2O（≥3．65％）和MgO（≥2．32％，Mg^#=0．48～0．61）含量，较高的Sr（〉463μg／g）、Cr（〉119μg／g）、Ni（〉75μg／g）含量，较低的Yb（〈1．70μg／g）、Y（〈17μg/g）含量，高的La／Yb（〉18）、Sr／Y（〉34）值和低Rb／Sr（≤0．31）比值，稀土元素强烈分馏，弱的负铕异常（Eu／Eu^＋=0．80～0．87）．它们的Nd同位素（^143Nd/^144Nd=0．512414～0．512502．εND（t）=-2．10～-0．38，TDM：0．89～1．02Ga），Sr同位素（^87Sr／^86Sr=0．7073～0．7075，8Sr（t）=11．16～13．78）和Pb同位素（^206Pb／^204Pb=18．28～18．40，^207Pb／^204Pb=15．42～15．53，^208Ph／^204Pb=38．08～38．27）组成与华北陆块古老的岩石圈地幔及其中的中晚侏罗世和早白垩世火山岩不同。这表明兴隆沟组英安岩可能是古亚洲洋壳残片部分熔融形成的，熔体在上升过程中与地幔楔发生过强烈的混染作用。据此，推测古亚洲洋曾向华北陆块发生过俯冲作用。     

硫酸侵蚀碳酸盐岩对长江河水DIC循环的影响

对长江及其主要支流河水水化学和溶解无机碳（DIC）同位素组成（δ13GDIC）进行了研究。河水阳离子组成以Ca^2＋、Mg^2＋为主,阴离子以HCO3-、SO4^2-为主,水化学组成主要受流域碳酸盐岩矿物的化学侵蚀控制。DIC含量为0．3～2．5mmol／L,从上游到河口逐渐降低。δ13CDIC值为-12．0‰-3．4‰,与DIC含量具有相似的变化趋势。H2CO3溶解碳酸盐岩是控制河水DIC来源及其占δGDIC组成的主要机制。H2SO4溶解碳酸盐岩加剧了流域碳酸盐岩的化学侵蚀,一方面导致了河水的DIC含量增加,另一方面也使河水的δ13GDIC值升高。     

新疆三塘湖盆地古生代晚期火山岩地球化学特征及其构造-岩浆演化意义

三塘湖盆地早石炭世安山岩（ECA）、早二叠世粗面岩类（EPT）以及中二叠世玄武岩（MPB）样品都具有大离子亲石元素（LILE）相对于高场强元素（HFSE）富集，Nb和Ta强烈亏损，轻稀土元素（LREE）相对于重稀土元素（HREE）富集，类似于和俯冲带相关的岩浆特征。ECA具有高的Zr／Nb（4．67～12．39），低的Nb／La（0．27～0．30），Ce／Ce＊=0．63～0．89，Sr／Sr＊=1．32．2．49，并具有Ti的负异常，另外（^87Sr／^86Sr）i=0．70408～0．70451，εNd（t）=＋7．42-＋7．88。与ECA相比，EPT大离子亲石元素更为富集，Ti和P的负异常明显，特别是Ce／Ce＊=0．72—1．64，Sr／Sr＊=0．38～1．87，相对较低的Al2O3和CaO含量以及（^87Sr／^86Sr）；=0．70414～0.70481和εNd（t）=＋4．93～＋6．13而区别于ECA。MPB与ECA相比具有较低的大离子亲石元素含量和较高的Nb、Ta含量，Ce／Ce＊=0．69～0．84，Sr／Sr＊=1、44～2．13，未有明显的Ti负异常，（^87St／^86Sr）i=0．70388～0．70396，εNd（t）=＋7．10-＋7．99。所有的地球化学特征表明：早石炭世或更早，三塘湖盆地为与俯冲带相关的构造背景，ECA是典型的弧火山岩，其岩浆主要源于被流体或沉积物交待改造的亏损地幔楔。早石炭世以后，三塘湖地区逐渐进入碰撞后伸展拉张阶段，EPT和MPB都为后造山火山岩。EPT岩浆主要源于亏损软流圈底侵前二叠纪形成的造山组分的部分熔融；MPB的岩浆主要源于亏损地幔的部分熔融，并被前二叠纪形成的造山组分或是年轻地壳混染。三塘湖地区二叠纪伸展拉张的动力学机制主要是由于造山带增厚的岩石圈大范围拆沉而导致的大范围亏损地幔部分熔融岩浆和上部造山组分或是年轻地壳的相互作用，这种造山组分或是年轻地壳具有低的（^87Sr／^86Sr），比值和正的εNd（t）值。火山岩地球化学特征指示没有明显地幔柱的作用特征。     

漓江水系汞的分布和污染研究

对漓江水系干流、支流、连体湖泊、较大的孤立湖塘和近岸水井设置40个采样点。水样采样周期为2个水文年,分枯水季和丰水季两次采样,现场测定水温、电导率、pH值等理化参数。系统采集水样112件、底泥样40件、水草样40件、近岸土壤样40件。底泥样用逐步浸提法进行不同形态汞分析。研究结果显示,干流河水、底泥和水草中汞的平均含量分别为0．12μg／L、0．20μg／g和0．032μg／g;主要支流河水、底泥和水草中汞的平均含量高于干流,分别为0．15—0．23μg／L、0．38～1．7μg／g和0．028—0．044μg／g。底泥中汞含量均高于近岸土壤汞含量。无论是干流还是支流,河水汞含量与底泥、水草汞含量有明显的相关关系。由上游至下游,漓江水系干流、主要支流河水样汞含量均不断增高,可高出源头河水汞含量的1．5—5倍。相应地指示重金属离子污染的参考指标——电导率值不断增高,河水的pH值亦逐渐增高。丰水期（5月至6月）河水中的汞含量（0．12—0．28μg／L）明显高于枯水期（9月至11月）河水中的汞含量（0．091—0．28μg／L）。不同断面河水汞含量均高于相应近岸井水汞含量。不同水体底泥中汞的形态分布一般顺序为：残渣态〉难氧化降解有机质结合态〉腐殖酸结合态〉碳酸盐和铁锰氧化物吸附态〉交换态〉易氧化降解有机质结合态〉水溶态。综合各项资料分析,认为漓江干流是桂林城市汞污染最大的汇。根据地表水环境质量标准（GB3838--2002）,仅汞而言,漓江水系均达到Ⅳ类水质标准（河水中汞含量≤1μg／L）。漓江支流汞污染高于干流,对干流存在较大的污染风险。     

Spatial and temporal variations of Rb/Sr ratios of the bulk surface sediments in Lake Qinghai

The Rb/Sr ratios of lake sediments have been suggested as indicators of weathering intensity by increasing work. However, the geochemistry of Rb/Sr ratios of lake sediments is variable between different lakes. In this study, we investigated the spatial and temporal patterns of Rb/Sr ratios, as well as those of other major elements in surface sediments of Lake Qinghai. We find that the spatial pattern of Rb/Sr ratios of the bulk sediments correlates well with that of the mass accumulation rate, and those of the terrigenous fractions, e.g., SiO₂, Ti, and Fe. The temporal variations of Rb/Sr ratios also synchronize with those of SiO₂, Ti, and Fe of each individual core. These suggest that Rb/Sr ratios of the surface sediments are closely related to terrigenous input from the catchment. Two out of eight cores show similar trends between Rb/Sr ratios and precipitation indices on decadal scales; however, the other cores do not show such relationship. The result of this study suggests that physical weathering and chemical weathering in Lake Qinghai catchment have opposite influence on Rb/Sr ratios of the bulk sediments, and they compete in dominating the Rb/Sr ratios of lake sediments on different spatial and temporal scales. Therefore, it is necessary to study the geochemistry of Rb/Sr ratio of lake sediments (especially that on short term timescales) particularly before it is used as an indicator of weathering intensity of the catchment.     

洞穴次生碳酸盐沉积的Mg/Ca与Sr/Ca比值研究进展——兼论洞穴次生沉积物Mg/Ca与Sr/Ca的影响机制

微量元素是岩溶洞穴沉积中非常重要的一类古气候环境替代指标,为近20年来国内外的一个研究热点。总结前人的研究,主要取得了以下一些重要认识:（1）洞穴上覆土壤 和围岩是洞穴次生碳酸盐沉积Mg、Sr的主要来源;（2）Mg/Ca与Sr/Ca能够指示气候环境变化,但需结合其它指标综合考虑。（3）洞穴次生碳酸盐沉积Mg/Ca与Sr/Ca受多种气候环境因素（包括土壤和围岩的组成和性质、水-岩相互作用、先期碳酸盐沉积、分配系数等）影响,其古气候环境指示意义具有多解性;（4）矿物结晶作用对Mg/Ca与Sr/Ca有一定的影响,特别是文石在向方解石转变的过程中容易丢失Mg、Sr,此外,杂质的混入也将抑制Mg、Sr进入方解石,从而引起洞穴次生碳酸盐沉积Mg/Ca与Sr/Ca比值的变化。今后应进一步加强对石笋中这些微量元素的影响机制研究,尤其是对一些影响因素与微量元素含量变化之间的定量关系进行探讨。      

Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment,Vosges mountains,France)

Strontium and particularly ⁸⁷Sr/⁸⁶Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and ⁸⁷Sr/⁸⁶Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and ⁸⁷Sr/⁸⁶Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, ⁸⁷Sr/⁸⁶Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, ⁸⁷Sr/⁸⁶Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members.     

黔东松桃南华系大塘坡组锰矿层物源:来自Sr同位素的证据

锰矿床的物质来源是锰矿床研究的难点问题之一.辨别黔东松桃地区南华系大塘坡组锰矿沉积的物质来源有助于加深对锰矿成矿过程的理解.对黔东松桃地区南华系大塘坡组锰矿沉积的Sr同位素研究显示,15个锰矿石、锰质页岩及炭质页岩样品87Sr/86Sr同位素比值变化范围为0.705 727~0.732 536,其中炭质页岩样品具有最高的Sr同位素比值0.732 536,含锰岩系样品87Sr/86Sr同位素比值平均值为0.711 128.样品中87Sr/86Sr比值随着Al含量的上升,分别出现87Sr/86Sr比值上升与下降的两个分异趋势.87Sr/86Sr比值随Mn含量的上升总体呈现下降的趋势,但该趋势无显著相关性,残差分析显示这主要是由于样品中87Sr/86Sr比值随着Mn含量上升出现收敛性波动造成.上述现象是由于陆源碎屑成分和海底热液成分混合输入造成.通过与大塘坡组同时代(约660 Ma)古海水Sr同位素组成,世界范围内不同时代锰矿沉积以及现代红海沉积物的Sr同位素结果对比,发现黔东松桃地区南华系锰矿层中Sr同位素比值分布范围较宽,部分锰矿样品87Sr/86Sr比值低于古海水87Sr/86Sr比值,与典型大洋成因的锰矿层或铁锰结核具有不同的Sr同位素特征.联系黔东南华系大塘坡组锰矿层形成时期的特殊地质背景,认为锰质积累过程与沉淀过程为不同阶段产物——锰质的积累过程在Sturtian冰期盆地缺氧水体中完成,可能主要以海底热液喷溢系统完成;而锰矿的沉淀过程则是在间冰期伊始古海洋化学条件动荡的水体中完成.      

Isotopic Composition of Strontium in Rocks of the Fen Alkaline Complex, South Norway

The isotopic composition of Sr and the abundances of Rb andSr have been determined in the alkaline rocks of the Fen Complex,South Norway. The ⁸⁷Sr/⁸⁸Sr ratios range from as low as 0.703in carbonatite (s?vite) to as high as 0.710 in rauhaugite. Thewhole rock analyses do not plot on a Nicolaysen diagram as anisochron. Calculation of the initial isotopic composition ofSr in the rocks at the time of intrusion of the complex, approximately550 m.y. ago, shows that the rocks are not simply related asthe differentiation products of a single magma, since they donot possess similar initial ⁸⁷Sr/⁸⁶Sr ratios. The lowest initialratio is seen in the s?vites and it is concluded that this rockrepresents the magma from which the other rocks of the complexwere derived. Production of hybrid rocks by bulk assimilationof granite gneiss in carbonatite is inadequate to account forthe observed Rb/Sr ratios. It is envisaged that selective concentrationof granitic Sr of high ⁸⁷Sr/⁸⁶Sr ratio together with loss orgain of variable amounts of Rb has taken place. The processis closely connected with the fenitization observed at the marginsof the complex and is of a metasomatic nature. Thus, the genesisof rocks of the melteigite-ijolite-urtite series may be consideredto be a rheomorphic process. The ⁸⁷Sr/⁸⁶Sr ratios observed inr?dberg and rauhaugite can be explained in terms of the metasomaticalteration of damtjernite.     

Relative contributions of silicate and carbonate rocks to riverine Sr fluxes in the headwaters of the Ganges

Exhumation of the Himalayan-Tibetan orogen is implicated in the marked rise in seawater ⁸⁷Sr/⁸⁶Sr ratios since 40 Ma. However both silicate and carbonate rocks in the Himalaya have elevated ⁸⁷Sr/⁸⁶Sr ratios and there is disagreement as to how much of the ⁸⁷Sr flux is derived from silicate weathering. Most previous studies have used element ratios from bedrock to constrain the proportions of silicate- and carbonate-derived Sr in river waters. Here we use arrays of water compositions sampled from the head waters of the Ganges in the Indian and Nepalese Himalaya to constrain the end-member element ratios. The compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two-component mixing of silicate and carbonate-derived components and lie on a plane in multicomponent composition space. Key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes Na = 0 for carbonate and constant Ca/Na for silicate. The fractions of Sr derived from silicate and carbonate sources are then calculated by mass-balance in Sr-Ca-Mg-Na composition space. Comparison of end-member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low-Mg trace calcite in silicate rocks may explain discrepancies in Sr-Ca-Na-Mg covariation. Alternatively, composition-dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation-ratio diagrams. However the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained. Silicates are calculated to provide ∼50% of the dissolved Sr flux from the head waters of the Ganges assuming that discrepancies between Ca-Mg-Na covariation and the silicate rock compositions arise from addition of trace calcite. If the Ca-Mg-Na mixing plane is rotated by composition-dependent secondary calcite deposition, this estimate would be increased. Moreover, when ⁸⁷Sr/⁸⁶Sr ratios of the Sr inputs are considered, silicate Sr is responsible for 70 ± 16% (1σ) of the ⁸⁷Sr flux forcing changes in seawater Sr-isotopic composition. Since earlier studies predict that silicate weathering generates as little as 20% of the total Sr flux in Himalayan river systems, this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated.     

Strontium isotope geochemistry of groundwater affected by human activities in Nandong underground river system, China

The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural ⁸⁷Sr/⁸⁶Sr ratios signature of groundwater that was otherwise dominated by water-rock interaction. Three major sources of Sr could be distinguished by ⁸⁷Sr/⁸⁶Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1-0.2 mg/L) and low ⁸⁷Sr/⁸⁶Sr ratios (0.7075-0.7080 and 0.7080-0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.7080-0.8352 for agricultural fertilizers and 0.7080-0.7200 for sewage effluents, respectively), with higher Sr concentrations (0.24-0.51 mg/L). Due to the overlapping ⁸⁷Sr/⁸⁶Sr ratios, it is difficult to distinguish the sources of Sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their ⁸⁷Sr/⁸⁶Sr ratios. However, ⁸⁷Sr/⁸⁶Sr ratios do provide key information for natural and anthropogenic sources in karst groundwater.     

湖光岩玛珥湖非残渣态Rb/Sr比值研究及其古气候意义

湖泊沉积物Rb/Sr比值变化主要受控于Sr含量的变化,而真正反映流域化学风化强度的主要是迁移至集水盆地(湖泊)的溶解态Sr2+,在沉积物中主要以碳酸盐结合态和铁锰氧化物结合态等形式存在.通过对不同赋存状态的Rb/Sr比值与相应的Sr含量之间相关关系的对比分析发现,沉积物非残渣态Rb/Sr比值更好地反映了流域化学风化.根...     

锶同位素在古岩溶研究中的应用——以塔河油田奥陶系为例

为探讨锶同位素在古岩溶研究中的应用,系统分析了塔里木盆地塔河油田奥陶系岩溶缝洞方解石的87Sr/86Sr值。研究结果表明,加里东中期岩溶形成的方解石以低87Sr/86Sr值为特征,其锶同位素组成主要由围岩的重溶锶控制。而海西早期岩溶形成的方解石则以高87Sr/86Sr值为特征,锶同位素组成主要由壳源锶和重溶锶控制;同时,不同产状的方解石锶同位素比值也不相同,渗流岩溶带的方解石比潜流岩溶带富集87Sr,主要受控于岩溶系统的渗流机制和水岩反应。在平面上,桑塔木组覆盖区比北部地区富集87Sr,其主要原因是来源于围岩的重溶锶比重加大。87Sr/86Sr值在区域上的变化,结合区域地质背景,表明海西早期岩溶对北部地区和桑塔木组覆盖区均有重要的影响,是奥陶系岩溶缝洞型储层的主要形成时期。另外,极低的锶同位素比值可能与幔源锶有关,早二叠纪末的火山活动是提供幔源锶的主要时期。通过塔河油田奥陶系古岩溶作用的实例研究,锶同位素具有良好的流体示踪能力,在划分古岩溶期次方面具有明显的优势。     

Evolution of Calc-alkaline Magmas in Continental Arc Volcanoes: Evidence from Alicudi, Aeolian Arc (Southern Tyrrhenian Sea, Italy)

Major, trace element, and Sr isotopic data are reported forvolcanic rocks from the island of Alicudi, Aeolian Arc, SouthernTyrrhenian Sea. The island is constructed of basalt, basalticandesite to high-K andesite lavas, and pyroclastites, whichshow a continuum in the variation of many major and trace elements.Total iron, MgO, CaO, Ni, Co, Sc, and Cr decrease with increasingsilica, whereas incompatible elements Rb, Ba, Th, and LREE displaythe opposite tendency. Very significant positive correlationsare defined by incompatible elements on interelemental variationdiagrams. Sr isotopic ratios vary from 0–70352 to 0–70410.Overall, basalts (0–70352–O-70410) and basalticandesltes (0–70356–0–70409) are enriched in⁸⁷Sr compared with high-K andesites (O–70352–O–70367),which display the lowest Sr isotopic ratios within the entireAeolian archipelago. Overall negative relationships exist between⁸⁷Sr/⁸⁶Sr and several incompatible trace element abundancesand ratios, such as Th, U, LREE, Zr, La/Yb, and Th/Hf. Otherelemental ratios such as La/Rb, Ba/Rb, and Sr/Rb show more complexbehaviour, even though negative correlations with Sr isotopicratios are observed in the basalts. The observed compositional variations are best explained interms of a model in which primitive calc-alkaline magmas evolvedby crystal-liquid fractionation to give a series of variouslydifferentiated liquids, which underwent different degrees ofinteraction with crustal material. The more mafic and hotterbasaltic liquids appear to have assimilated higher amounts ofmetamorphic wall rocks than did the cooler late erupted andesiticmagmas. This process produced significant variations of Sr isotopicratios, Rb, Cs, Rb/Sr ratios, and LILE/Rb ratios in mafic magmas,but had only minor effects on the abundances and ratios of otherincompatible elements such as Th, LREE, La/Yb, and Th/Hf. When compared with mafic rocks from other Aeolian islands, theAlicudi basalts are more primitive geochemically and isotopically.Going eastward, there is a decrease in Ni and Cr abundances,mg-number and Nd isotopic ratios which parallels an increaseof Sr isotopic ratios in basaltic rocks along the arc. Thesecompositional variations are typical of volcanic series whichhave undergone interaction with upper-crustal material, andsuggest that this process may have contributed significantlyto the regional geochemical and isotopic trends observed inthe Aeolian arc.