郯庐断裂带新沂——泗洪段土壤气Rn体积活度和CO_2浓度特征研究

郯庐断裂带江苏段地区4个剖面进行了土壤气Rn体积活度和CO_2浓度测量结果显示,自北向南土壤气Rn体积活度均值分别为22.9kBq/m^3、35.5kBq/m^3、40.2kBq/m^3、26.6kBq/m^3;自北向南土壤气CO_2浓度均值分别为0.669%、0.400%、0.503%、1.109%。土壤气Rn体积活度和CO_2的浓度在空间分布上具有较好的一致性,这可能与CO_2是Rn的载气有关。综合分析土壤气Rn和CO_2测量结果以及水准资料可得,2017年土壤气Rn高值出现在晓店段可能与区域应力应变调整有关。本研究不仅为研究区以后的土壤气研究提供了参考,同时也可为研究区的构造活动研究提供地球化学资料参考。     

Alakit and Daldyn kimberlite fields,Siberia,Russia:Two types of mantle sub-terranes beneath central Yakutia?

Mineral data from Yakutian kimberlites allow reconstruction of the history of lithospheric mantle.Differences occur in compositions of mantle pyropes and clinopyroxenes from large kimberlite pipes in the Alakit and Daldyn fields.In the Alakit field.Cr-diopsides are alkaline,and Stykanskaya and some other pipes contain more sub-calcic pyropes and dunitic-type diamond inclusions,while in the Daldyn field harzburgitic pyropes are frequent.The eclogitic diamond inclusions in the Alakit field are sharply divided in types and conditions,while in the Daldyn field they show varying compositions and often continuous Pressure-Temperature(P-T) ranges with increasing Fe~# with decreasing pressures.In Alakit,Crpargasites to richterites were found in all pipes,while in Daldyn,pargasites are rare Dalnyaya and Zarnitsa pipes.Cr-diopsides from the Alakit region show higher levels of light Rare Earth Elements(LREE)and stronger REE-slopes,and enrichment in light Rare Earth Elements(LREE),sometimes Th-U,and small troughs in Nb-Ta-Zr.In the Daldyn field,the High Field Strength Elements HFSE troughs are more common in clinopyroxenes with low REE abundances,while those from sheared and refertilized peridotites have smooth patterns.Garnets from Alakit show HREE minima,but those from Daldyn often have a trough at Yand high U and Pb.PTX/O2 diagrams from both regions show similarities,suggesting similar layering and structures.The degree of metasomatism is often higher for pipes which show dispersion in P-Fe~# trends for garnets.In the mantle beneath Udachnaya and Aykhal,pipes show 6-7 linear arrays of P-Fe~# in the lower part of the mantle section at 7.5-3.0 GPa,probably reflecting primary subduction horizons.Beneath the Sytykanskaya pipe,there are several horizons with opposite inclinations which reflect metasomatic processes.The high dispersion of the P—Fe~# trend indicating widespread metasomatism is associated with decreased diamond grades.Possible explanation of the differences in mineralogy and geochemistry of the mantle sections may relate to their tectonic positions during growth of the lithospheric keel.Enrichment in volatiles and alkalis possibly corresponds to interaction with subduction-related fluids and melts in the craton margins.Incorporation of island arc peridotites from an eroded arc is a possible scenario.     

LA-ICP-MS heavy metal analyses of fish scales from sediments of the Oxbow Lake Certak of the Morava River (Czech Republic)

Heavy metal concentrations were studied in the scales of recent and subrecent (2–25 years old) fish buried in the oxbow lake sediments of the Morava River. The samples were taken from two cores up to 4-m deep and analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and an electron microprobe analysis (EMPA). The results were compared with heavy metal concentrations of bulk samples of the embedding sediment. The study has revealed substantial differences in heavy metal contents existing between the recent and subrecent fish scales documenting an extreme rapidity of the diagenesis/fossilization processes. The most apparent features of the early fossilization include the quick loss of the mucous envelope, collagen and magnesium and an enormous increase in the heavy metal concentrations in particular iron, which is connected with a colour change. The variations in heavy metal contents in fish scales within a sample are attributed to variations in heavy metal content in the environment and variable amounts of organic matter in the embedding sediment. In contrast to the contamination of the embedding sediment, no general increase in heavy metal concentrations in fish scales was observed down to the cores. It is inferred that the rapid sorption stabilizes the biologic hydroxyapatite of the fish scales, which thus rapidly attain a thermodynamic equilibrium with the embedding water-saturated sediment. The results show that the processes of sorption, fossilization and stabilization of hydroxyapatite can act very quickly over a time scale of several years and represent thus a great advantage in the preservation of the original signals of the ancient environments.     

Erratum to: Geochemical and environmental magnetic characteristics of high arsenic aquifer sediments from Datong Basin,northern China

Geochemical and environmental magnetic studies were carried out to identify the effect of iron oxyhydroxides on arsenic mobilization in high arsenic aquifer system. Using high arsenic sediment samples from two boreholes, specifically drilled for this study, chemical composition and magnetic properties including magnetic susceptibility, saturation remnant magnetization, and isothermal remnant magnetization were measured. Results of correlation analysis of element contents show that arsenic and iron are closely associated with each other (r ² = 0.40, α = 0.05, n = 21). In contrast, the correlation of phosphorus with iron (r = 0.11, α = 0.05, n = 21) and arsenic (r ² = 0.18, α = 0.05, n = 21) was poor, which might result from competitive adsorption of phosphorus and arsenic on the surface of Fe-oxyhydroxides. The high correlation coefficients between arsenic contents and magnetic parameters suggest that the ferrimagnetic minerals including maghemite and hematite are the dominant carrier of arsenic in aquifer sediments. The results of sequential extraction experiments also revealed the association of arsenic with reducible iron oxides, such as maghemite and hematite in aquifer sediments. Therefore, under reducing conditions, reductive dissolution and desorption of arsenic from Fe-oxyhydroxides into the aqueous phase should be the dominant geochemical processes for its enrichment in groundwater at Datong. An erratum to this article can be found at     

Geochemical characterization of karst groundwater in the cradle of humankind world heritage site,South Africa

The karst of the Cradle of Humankind World Heritage Site plays a major role in the assimilation or carrying of acid mine drainage, sewage effluent return flow and agricultural run-off. Infiltration of contaminated water has altered the chemical composition of the natural waters of the karst system. A multivariate statistical method in combination with conventional geochemical and spatial analysis was applied on groundwater and surface water quality samples to determine the spatial extent of hydrochemical impacts from different anthropogenic sources. The application of hierarchical cluster analysis of the major ions (148 samples) recognised three distinct hydrochemical regimes. Cluster 1 is moderately mineralized, especially with regard to chloride, nitrate and sulphate, cluster 2 has a low mineralization with all elements well within the recommended drinking water limits of South Africa and cluster 3 represents highly mineralized samples taken in the vicinity of decanting mineshafts. The cluster solution is confirmed by a simple mixing model, indicating varying contributions of three identified end members (acid mine drainage, treated sewage effluents and pristine dolomitic groundwater) to the groundwater quality in the catchment. The combination of statistical, geochemical and spatial methods in conjunction with end-member mixing analysis provides a reliable method to understand the processes responsible for the groundwater quality variations and to assist in the identification of anthropogenic impacts.     

Geochemistry and potential use of groundwater in the Rocca Busambra area (Sicily, Italy)

In the Rocca Busambra area (mid-west Sicily, Italy), from November 1999 to July 2002, 23 water points including wells and springs were sampled and studied for their chemical and isotopic compositions. Two rain gauges were also installed at different altitudes, and rainwater was collected monthly to determine the isotopic composition. The obtained results revealed the Rocca Busambra carbonate complex as being the main recharge area on account of its high permeability value. From a chemical view point, two main groups of water can be distinguished: calcium–magnesium–bicarbonate-type and calcium–magnesium–chloride–sulphate-type waters. The first group reflects the dissolution of the carbonate rocks; the second group probably originates from circulation within flyschoid sediments. Three water wells differ from the other samples due to their relatively high Na and K content, which probably is to be referred to a marked interaction with the “Calcareniti di Corleone” formation, which is rich in glauconite [(K, Na)(Fe³⁺, Al, Mg)₂(Si, Al)₄O₁₀(OH)₂]. In accordance with WHO guidelines for drinking water (2004), almost all the samples collected can be considered drinkable, with the exception of four of them, whose NO₃ ⁻, F⁻ and Na⁺ contents exceed the limits. On the contrary, the sampled groundwater studied is basically suitable for irrigation.     

山东岚山I型与A型复合片麻状变质花岗岩：年代学、地球化学及其构造指示意义

在山东日照岚山地区,出露有原岩为新元古代岩浆活动产物的I型与A型复合的片麻状变质花岗岩体,前者特征矿物组合为石英+钾长石+斜长石+黑云母,而后者则为石英+钾长石+斜长石+霓石+亚铁钠闪石+黑云母。锆石LA-ICP-MS U-Pb定年结果表明,I型片麻状变质花岗岩的原岩成岩年龄为795±32Ma,而A型片麻状变质花岗岩的原岩年龄则为772±26Ma,二者均经历了早中生代的超高压变质作用,并在220Ma左右遭受强烈的角闪岩相退变质作用的改造。地球化学上,I型和A型片麻状变质花岗岩均具有高硅、富铁和贫镁的特征,但A型片麻状变质花岗岩更富碱贫铝,其铝饱和指数仅为0.88~0.94,表现为准铝质,而I型片麻状变质花岗岩则具有准铝-弱过铝的特点（A/CNK=0.94~1.01）。在微量和稀土元素方面,A型片麻状变质花岗岩较I型稀土总量高,且具有高场强元素富集的特征,富Ga,10⁴×Ga/Al值为2.77~3.89。二类片麻状变质花岗岩具有不同的Nd同位素组成,ε_Nd (t)值分别为-6.26 ~ -8.00和-3.73 ~ -5.20,指示它们应具不同的岩浆源区,元素结晶分异模拟显示二者岩浆演化的历程也存在差异。岚山片麻状变质花岗岩叠加有"弧"和"裂谷"双重岩浆活动的地球化学印记,它们与由地幔柱上隆所引发的主动裂谷背景下岩浆作用产物的特征存在明显差别。I型与A型复合片麻状变质花岗岩的产出指示扬子板块北东缘在片麻状变质花岗岩原岩形成时（795~770Ma）应处于弧后伸展引发的被动裂谷环境的初始阶段。     

北京白查A型花岗岩的地球化学特征及其成因与构造指示意义

位于北京昌平区的年龄为127Ma的白查岩体是一个晶洞过碱性花岗岩岩株,其侵位于燕山造山带西段的八达岭岩基中。白查岩体具有高硅、Zr、Ga、Pb、HFSE和REE含量,高Fe/Mg和Ga/Al比值,强烈亏损Ca、Sr、Eu,具有亏损放射性成因Pb同位素的特征。白查岩体属于Dall’Agnol和Oliveira (2007)定义的典型的还原型A型花岗岩,其地球化学特征与燕山带中生代晚期的后石湖山(山海关)和窟窿山A型花岗岩非常相似。白查花岗岩起源于华北克拉通下地壳镁铁质源岩在相对贫水、高温、低氧逸度条件下的低程度部分熔融。综合区域地质背景和该岩体的成岩机制判断,白查花岗岩的形成标志燕山西段造山崩塌阶段的到来。除浙江东南瑶坑过碱性花岗岩外,白查岩体是具有A1型花岗岩元素地球化学特征但并非形成于非造山大地构造背景的过碱性花岗岩的又一个实例。     

滁州火山岩地球化学及其对郯庐断裂带内岩石圈减薄的指示

位于郯庐断裂带张八岭隆起北段上的滁州早白垩世火山岩,属于准铝质、硅过饱和岩石,为一套中酸性的高钾钙碱性系列火山岩,部分样品（129~125Ma）具有类似于埃达克岩的地球化学特征。该套火山岩富集大离子亲石元素和轻稀土元素、亏损重稀土元素及高场强元素,并具有类似于EMⅠ型的Sr-Nd-Pb同位素组成。地球化学特征显示该火山岩的岩浆源区属于华北克拉通,早期火山岩（约132Ma）是富集地幔来源岩浆和古老的华北下地壳源区混合的结果;中期和晚期火山岩（129~117Ma）是幔源底侵组分和古老的华北下地壳来源岩浆不同比例混合的产物。由早到晚,滁州火山岩中古老壳源物质比例逐渐增加,源区逐渐变浅,指示软流圈顶面不断抬升、岩石圈内等温面逐渐升高的过程。研究表明,热异常背景下强烈的壳-幔相互作用是该处断裂带内岩浆形成的主要方式,其具体过程是在岩石圈底部持续减薄、软流圈上涌背景下,幔源岩浆底侵而诱发了古老下地壳的部分熔融,从而形成了壳-幔过渡带内混源的岩浆。郯庐断裂带内较浅的岩浆源区、较高的源区熔融程度、强烈而持久的伸展及岩浆活动、强烈的壳-幔相互作用以及现今较薄的岩石圈厚度,都指示郯庐断裂带是华北克拉通东部岩石圈减薄中的强减薄带,在华北克拉通破坏中起着重要的作用。     

西天山达巴特斑岩型铜矿床流体地球化学特征和成矿作用

本文对西天山地区达巴特斑岩铜钼矿床矿石中石英的流体包裹体进行了均一法和冷冻法测温,对相应的石英单矿物进行了氢氧同位素测定,据此判断了成矿流体的来源和成矿物理化学条件。结果表明含铜钼矿石中的流体包裹体主要为气液两相包裹体和含子矿物三相包裹体,不同样品中同类包裹体具有基本一致的均一温度、子矿物溶化温度、冰点、盐度和密度值, 数据显示成矿流体均呈中温低盐度的特点。矿石氢氧同位素组成表明矿床的成矿流体属于岩浆水范畴,而且具有深部来源甚至幔源的可能性。根据矿体主要分布在火山机构南北两侧与地层的接触带及其内发育的断裂构造中这一空间关系,结合流体包裹体测温结果,推测尽管该矿床成矿流体具有深源特征,但成矿作用发生在中浅部环境,成矿与火山机构最晚期的花岗斑岩具有密切的成因关系。