Chemical Weathering Rates, Erosion Rates and Mobility of Major and Trace Elements in a Boreal Granitic Till

Chemical weathering rates and erosionrates of granitic till in northern Sweden have beenestimated. The present-day chemical weathering rate iscompared with the long-term average weathering ratesince the last deglaciation approximately 8,700 yearsago. Also, the present-day release rates of major andtrace elements due to chemical weathering are comparedwith the mobility of these elements in a spodosolprofile as shown by soil water samples from the vadozezone. The estimation of the past weathering rate isbased on elemental depletion trends in a soil profile(typic haplocryod), whereas the present weatheringrate is based on elemental input/output budgets in asmall catchment (9.4 km²). The long-term averagechemical erosion rate, expressed as the sum of majorelement oxides (SiO₂, Al₂O₃, CaO,Fe₂O₃, K₂O, MgO, MnO, Na₂O,P₂O₅, TiO₂), was estimated to be4.9 gm^-2 yr^-1. The long-term base cation(Ca²⁺, Mg²⁺, Na⁺, K⁺) depletionwas 0.325 keq ha^-1 yr^-1. The currentchemical erosion rate was estimated to be2.43.0 g ^-2 yr^-1, which is at least an order ofmagnitude higher than the rate of physical erosion,and the base cation flux due to chemical weathering is0.356–0.553~keq ha^-1 yr^-1. However,0.074 keq ha^-1 yr^-1 of this flux may be related tocation exchange processes induced by atmospheric inputof acid rain. There is no evidence for any recentlyincreased weathering rate of silicates in this area.The inputs of Cd, Cu, Ni and Zn exceed the outputs,and hence, these elements are currently accumulatingin the soil.There is a distinct seasonal variation in thechemical composition of the soil water. Results fromthe soil water samples show that Na, followed by Siand S (Cl was not measured), are the most mobileelements in the spodosol profile between the E-horizonand the C-horizon, and that Al and Fe were the leastmobile elements. However, there is no simplerelationship between the mobility of an element in thespodosol profile and the current release rate due toweathering of that element. This fact may haveimplications for the validity of the comparisonbetween the past and present weathering rates asperformed in this study.     

Transport of BTEX Vapours Through Granular Soils with Different Moisture Contents in the Vadose Zone

The single-ring aromatic hydrocarbons benzene, toluene, ethylbenzene and m-xylene (BTEX) are common and dangerous pollutants in subsurface environments. The diffusive transport of BTEX vapours through the unsaturated zone of the ground is a potential health hazard to humans, living in the vicinity of petroleum fuel contaminated sites. Past studies have shown that gas transport through the vadose zone can be influenced by moisture content due to variations in gaseous permeability, phase partitioning and aerobic biodegradation. In this particular study laboratory soil column experiments were employed to compare the diffusive transport of BTEX vapours through a sand layer of high moisture content, where biodegradation of BTEX compounds occurred, with diffusion through air-dried sand. The presence of a thin soil layer of high moisture content reduced the gaseous concentrations of benzene and toluene and stopped the migration of ethylbenzene and m-xylene vapours, demonstrating its efficiency as a barrier on the diffusive transport of BTEX vapours in unsaturated soil.     

Modeling Uranium Transport in Koongarra, Australia: The Effect of a Moving Weathering Zone

Natural analogues are an important source of long-term data and may be viewed as naturally occurring experiments that often include processes, phenomena, and scenarios that are important to nuclear waste disposal safety assessment studies. The Koongarra uranium deposit in the Alligator Rivers region of Australia is one of the best-studied natural analogue sites. The deposit has been subjected to chemical weathering over several million years, during which many climatological, hydrological, and geological changes have taken place, resulting in the mobilization and spreading of uranium. Secondary uranium mineralization and dispersed uranium are present from the surface down to the base of the weathering zone, some 25 m deep. In this work, a simple uranium transport model is presented and sensitivity analyses are conducted for key model parameters. Analyses of field and laboratory data show that three layers can be distinguished in the Koongarra area: (1) a top layer that is fully weathered, (2) an intermediate layer that is partially weathered (the weathering zone), and (3) a lower layer that is unweathered. The weathering zone has been moving downward as the weathering process proceeds. Groundwater velocities are found to be largest in the weathering zone. Transport of uranium is believed to take place primarily in this zone. It appears that changes in the direction of groundwater flow have not had a significant effect on the uranium dispersion pattern. The solid-phase uranium data show that the uranium concentration does not significantly change with depth within the fully weathered zone. This implies that uranium transport has stopped in these layers. A two-dimensional vertically integrated model for transport of uranium in the weathering zone has been developed. Simulations with a velocity field constant in time and space have been carried out, taking into account the downward movement of this zone and the dissolution of uranium in the orebody. The latter has been modelled by a nonequilibrium relationship. In these simulations, pseudo-steady state uranium distributions are computed. The main conclusion drawn from this study is that the movement of the weathering zone and the nonequilibrium dissolution of uranium in the orebody play an important role in the transport of uranium. Despite the fact that the model is a gross simplification of what has actually happened in the past two million years, a reasonable fit of calculated and observed uranium distributions was obtained with acceptable values for the model parameters.     

湖南塔山、阳明山花岗岩的岩石成因：来自锆石U-Pb年龄、地球化学及Sr-Nd同位素证据

湖南塔山、阳明山岩体位于扬子地块和华夏地块的结合部位,主要由不同粒度的斑状二长花岗岩构成,其中塔山岩体的粗中粒、中细粒、中粒斑状二长花岗岩的锆石La-ICP-MS定年结果分别为221.3±0.9Ma、221.5±1.9Ma、213.4±1.1Ma,阳明山中细粒斑状二长花岗岩的年龄为213.7±1.0Ma,均属印支晚期花岗岩。花岗岩富SiO_2(70.43%~74.06%)、Al_2O_3(13.25%~15.37%)、高A/CNK(1.03~1.24)、高分异指数DI(85.25~93.0)、富集Rb、Th、U、Ta,亏损Ba、Sr、Nb、Ti,具明显的负Eu异常(δEu=0.15~0.45),为高分异的过铝花岗岩。高(~(86)Sr/~(87)Sr)_i(0.72993~0.77391)、低ε_(Nd)(t)(-9.9~-12.11)、Nd的t_(DM2)(1801~1978Ma)较大等特征,表明塔山、阳明山花岗岩为壳源S型花岗岩。结合其形成年龄和区域构造背景,认为塔山、阳明山岩体是在印支运动晚期挤压作用向伸展作用转换形成的局部伸展-减薄的机制下,由加厚地壳中的中元古代变质砂屑岩、变质泥岩部分熔融形成,并经历了分离结晶作用。年龄为3523Ma的继承锆石核显示本区可能存在古太古代的古老基底。     

再生水干湿交替入渗过程中添加碳源对包气带脱氮的影响

干湿交替的回灌方法常被用于解决再生水地表回灌的堵塞问题,但干湿交替回灌可能造成硝态氮被淋洗进入地下水.通过室内土柱模拟入渗实验,对比研究了以葡萄糖作为碳源的低碳氮比再生水干湿交替回灌、干期前蒸馏水淋洗、干期前添加甲醇溶液和干期后添加甲醇溶液4种条件下对包气带氮素迁移转化和脱氮效果的影响.实验表明,对于碳氮比为2.5∶1...     

鄂尔多斯盆地北部风积沙覆基岩型包气带结构的生态意义

风积沙覆基岩型包气带结构在鄂尔多斯盆地北部分布面积最广.在其结构及其属性特征分析基础上,重点解析了结构内垂向上土壤水分的富集规律;以沙蒿为例,对喜沙耐旱植被的生长与风积沙厚度、地下水水位埋深间的关系进行了探讨.认识到风积沙覆基岩型包气带结构有利于土壤水富集,是鄂尔多斯盆地北部沙蒿、沙柳等耐旱喜沙植被分布与生长的决定性因素,对维系盆地北部生态系统有重要作用;而地下水位埋深与沙蒿等耐旱植被生长间的关系并不密切.在进行盆地北部地下水资源评价及开发方案制定过程中,应对风积沙覆基岩型包气带的生态意义给予重视.     

那邦地区花岗片麻岩的锆石U-Pb年代学及Hf同位素组成特征

滇西那邦地区三个花岗片麻岩样品的锆石U-Pb定年分别给出了55.0±0.5 Ma、50.4±1.3 Ma以及51.6±1.1 Ma的结晶年龄,其εHf(t)介于-6.7～ +7.8之间,具有壳幔双源特征,对应的二阶段模式年龄为0.63 ～1.55 Ga.上述年龄的获得表明滇西那邦地区原划为前寒武纪的混合岩和花岗片麻岩至少有相当一部分形成于新生代.经与邻近腾冲-梁河花岗岩带及西藏冈底斯岩浆带的年代学对比,认为沿冈底斯-那邦地区存在广泛的始新世岩浆事件,其成因可能与印度板块和欧亚板块的初始碰撞有关.     

吉林东部花岗岩区地下水化学成分及其对岩石风化作用的制约

在吉林东部花岗岩区地下水化学成分和化学类型研究的基础上,以Na作为参比元素,确定了花岗岩风化过程中22种主量元素和微量元素的相对活动顺序。花岗岩区地下水的地球化学类型属低矿化度(变化范围为69.51×10-6~386.49×10-6,平均值为199.48×10-6)的HCO3-Ca和HCO3-Na-Ca型。花岗岩风化过程中元素的活动性顺序(RM)从大到小依次为:B、Ca、Mo、Zn、Sr、Na、Mg、Cr、Cu、Ni、K、Co、Li、V、As、Ba、Si、Y、Fe、Ti、Al、Mn。风化产物中的粘土矿物主要为高岭土、蒙脱石,反映出本区花岗岩的风化淋滤程度较弱的特点。     

北方针叶林对气候变化响应的研究进展

北方针叶林地处北半球中高纬度地区,增温剧烈,是受气候变化影响最显著的地区之一.据预测,在未来气候变化情景下,北方针叶林将向北迁移,且可能完全移出我国,从而将对气候系统及全球碳收支产生重要的反馈作用.因此,北方针叶林在气候变化与全球碳收支中具有十分重要的作用.从气候变化的影响及碳循环研究方面综述了北方针叶林近年来的最新研究进展,探讨了未来北方针叶林拟重点加强的研究领域,为深入理解北方针叶林对气候变化的响应、制定适宜的气候变化对策提供参考依据.     

Origin,Occurrence, and Mobility of He and Ar Isotopes in Meliphanite

Doklady Earth Sciences - The U, Th, and 4He contents of meliphanite correspond to an age of metamorphism (1800 Ma) indicating good preservation of radiogenic 4He in mineral but contradicting the...     

Advances in Moisture Migration in Vadose Zone of Dryland and Recharge Effects on Groundwater Dynamics

The vadose zone is the zone in between the land surface and above the groundwater table at vertical profile with partial water saturation and under the unsaturation condition, which constitutes the connections among atmospheric water, surface water and groundwater. Soil moisture migration in the vadose zone is a rather complicate process, which controls the rates of groundwater depletion and recharge, and has close hydraulic connections with highly frequent water transfers on the interfaces among the irrigation farmland, sand dunes, wetlands, lakes, and other landscape types. Recent development on soil moisture migration simulations and the application of tracer techniques, geophysical techniques and other geological methods in the vadose zone research, the factors affecting soil moisture migration and groundwater recharge,and soil moisture migration effects on moisture exchange between different landscapes were reviewed in this paper. Several suggestions on the future research were presented here: ① An intense field observation and research database should be initiated and constructed to determine the soil hydraulic parameters, and quantify the influence of moisture migration in vadose zone on the groundwater recharge; ② The proposed observations and researches should learn from the “Critical Zone Observatory”, and focus on the coupling of the soil moisture migration, solute transport and groundwater recharge.     

氨氮污染源区包气带剖面微生物生态分布特征的研究

包气带土壤中氨氮污染迁移规律已成为近年来国内外学者研究的重点,目前在氨氮污染迁移规律研究中采用柱实验模拟以及软件模拟的方法较多,土壤生物技术则广泛应用于污染物降解领域,而在污染物迁移规律研究中应用较少。本文采用变性梯度凝胶电泳(DGGE)技术、16S rRNA序列分析技术以及典范对应分析相结合,对华北平原3个典型氨氮污染区土壤表层至包气带剖面微环境的细菌垂直分布特征及群落结构进行研究。结合污染区土壤理化性质分析,认为包气带土壤剖面的细菌群落中存在着与氮循环、硫酸盐代谢等过程偶联的优势细菌类群,说明土壤微环境中细菌群落分布明显受氨态氮、硝态氮、亚硝态氮和硫酸盐的分布影响,进一步表明污染土壤优势菌群的群落结构信息是描述包气带土壤环境氨氮污染物迁移规律的重要参数。     

威海地区超高压变质花岗片麻岩锆石U-Pb定年和氧同位素研究

在苏鲁超高压变质带东北端山东威海地区皂埠镇发现锆石δ18O值低至-7.8‰左右的花岗片麻岩, 与前人在苏鲁超高压变质带西南端江苏东海青龙山地区发现的锆石δ18O值为-7‰~-9‰左右的花岗片麻岩一致.对这些低δ18O值花岗片麻岩进行了锆石SHRIMP法UPb定年和系统的激光氟化法矿物氧同位素分析, 结果对低δ18O值锆石成因和花岗片麻岩的原岩性质提供了制约.研究得到: (1) 这些低δ18O值锆石以新元古代岩浆锆石为主, 但部分岩浆锆石在印支期超高压变质作用过程中发生了不同程度的重结晶作用.δ18O值为-7.08‰的岩浆核锆石UPb定年得到的花岗片麻岩原岩谐和年龄和不一致线上交点年龄分别为(760±49) Ma和(751±27) Ma, 变质谐和年龄和不一致线下交点年龄分别为(232±4) Ma和(241±33) Ma, 指示其原岩为新元古代花岗岩并经历了印支期变质作用; (2) 锆石δ18O值在局部范围内变化于-7.76‰~5.40‰之间, 低δ18O值岩浆锆石表明它们是从新元古代低δ18O值岩浆中直接结晶形成, 锆石δ18O值的局部变化表明其原岩岩浆的氧同位素组成具有不均一性, 指示低δ18O值岩浆源区物质曾经在地表与极度亏损18O的大气降水发生过不同程度的高温水岩反应; (3) 低δ18O值花岗片麻岩在印支期板块俯冲和折返过程中基本没有与外部发生显著的氧同位素交换, 在退变质作用过程中花岗片麻岩内部缓冲流体对原岩岩浆锆石的δ18O值影响不大.威海皂埠镇地区和东海青龙山地区的花岗片麻岩在原岩时代、变质时代和氧同位素组成等方面基本相同, 指示它们应具有相同的原岩性质, 并经历了相同的变质作用和水岩相互作用过程.因此, 极度亏损18O的新元古代双峰式基性-酸性岩浆岩可能分布于整个大别-苏鲁造山带.      

鄂尔多斯盆地风沙滩地区包气带水分运移特征研究

以鄂尔多斯盆地包气带水盐运移综合剖面试验资料为依据,运用土壤水分能量的观点分析鄂尔多斯盆地风沙滩包气带水分运移特征表明:(1)包气带水分运移大致可以分为三个带,0.8 m深度以内为土壤-大气水分积极交换带,0.8～2.8 m为水分入渗的过渡带与调节区,2.8 m以下至潜水面为水分传导带;(2)上细下粗层状包气带岩性结构不利于降雨入渗补给,上粗下细层状包气带岩性结构有利于降雨入渗补给。     

典型有机物在饱气带土和地下水中迁移的影响因素研究

研究区位于河北省保定市东部排污渠旁,是一处有近40年污水灌溉历史的农田,灌溉用污水主要为保定天鹅化纤有限公司和保定钞票纸厂排放的污水,主要种植农作物为小麦、玉米。饱气带厚度2.4~2.7 m,饱气带土以粉质粘土为主。通过分析距排污渠不同距离、不同深度的土样有机物的测试分析结果,选择苯、甲苯、二氯甲烷、三氯甲烷、苯并[a]芘为典型污染物,从饱气带土的物理与化学特征、5种有机物的物理化学特征、地下水的动力条件角度,分析了典型有机物在饱气带土与地下水中迁移的影响因素。     

冀东-辽西中-晚三叠世柏杖子花岗质侵入岩地球化学、Sr-Nd-Hf同位素特征及岩石成因

关于冀东-辽西中-晚三叠世具有埃达克质岩石特征的花岗质岩石的源区性质,存在较大争议,且以往对位于其北东向隆起区内的柏杖子岩体的成因研究程度低.对柏杖子花岗质侵入岩进行了系统的年代学、地球化学、Sr-Nd-Hf同位素研究,结果显示:柏杖子岩体结晶年龄为233±3 Ma,岩石具有低MgO、Mg#和Co、Ni、Cr含量;富集大离子亲石元素,亏损高场强元素,显示明显的Pb、Th正异常和Nb、Ta、Ti、P负异常;轻、重稀土元素分馏明显;87Sr/86Sr (t) 为0.704 45~0.705 24,ε_Nd(t) 值为-7.3~-1.7;锆石ε_Hf(t) 为-13.4~-5.9.综合分析认为,高Sr/Y比值和低Y含量的柏杖子岩体属于华北克拉通正常厚度镁铁质下地壳熔融的产物,岩石高Sr/Y比值、低Y含量和Nb-Ta负异常特征为继承的华北克拉通下地壳内在性质,并具有与太古宙-古元古代TTG岩石系列相一致的Nb-Ta解耦特征,表明柏杖子岩体源区物质有TTG岩石的贡献;岩石Sr-Nd-Hf同位素组成和低相容元素含量特征同样表明岩浆来源于受改造的下地壳熔融.早中生代玄武岩底侵过程中幔源组分的加入对华北克拉通下地壳形成改造,同时提供热源诱发下地壳物质熔融,形成的熔体向浅表侵位,经历一定程度的斜长石分离结晶,并最终形成柏杖子岩体.      

辽宁省清原县南口前岩体锆石U-Pb年代学、地球化学及Hf同位素

华北板块周边地区板块的俯冲与碰撞对华北后来的岩石圈破坏可能产生了重要影响.对南口前岩体进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学研究,确定其时代及形成的构造背景.测年结果表明,岩石为晚三叠世(224±1 Ma)岩浆侵入的产物.地球化学研究表明岩石为高钾钙碱性系列,A/CNK值为0.98~1.07,属准铝质-过铝质花岗岩类.高Sr(394×10-6~545×10-6),低Yb(0.61×10-6~0.93×10-6),判断岩石属于埃达克岩类.岩石的ε_Hf(t)值为-13.2~-6.9,二阶段模式年龄(T_DM2)变化于1 669~1 825 Ma之间,判断岩石源于元古代地壳岩石的部分熔融.综合前人研究成果,认为岩石形成于古亚洲洋闭合后的造山后拉张环境.      

包气带黏性土层对氮素污染地下水的防污性能试验研究

包气带土层是保护地下水的天然屏障,在阻控、拦截氮素污染源的过程中起到了重要作用。通过对北京市典型地区包气带土体进行定水位入渗的土柱淋溶试验,研究土体对于氮素的去除能力和包气带的截污容量。试验中采用了蒸馏水、再生水和河水3种不同的水源。试验结果显示,张家湾包气带土层对氮素污染地下水具有较强的截留和防护能力。对氮素的去除过程具有分段性特征,经历了较稳定和波动下降两个不同的阶段,其中稳定阶段是计算柱体去除能力的关键,提出了考虑滞后区间的时段去除率计算公式。水源对柱体的渗流速度及初期的吸附解析效应有明显影响。土体对氮素的去除作用受环境温度变化的影响,温度15 ℃左右时所达到的稳定阶段对氮素有极强的去除能力。     

试验模拟包气带CO2变化及对水化学的影响

包气带作为参与碳循环的重要场所,CO2起到重要作用。利用土柱模拟不同条件下包气带CO2含量变化及水化学成分变化。研究发现:不同条件下土柱内CO2存在明显差异,均随着深度增加CO2含量增加;CO2含量植被组大于无植被组。随着降水不断入渗包气带,CO2含量不断增加。植被存在时,增加幅度略大于无植被组,且降水后期杀菌组包气带CO2增加幅度达一百倍。降水后pH值降低,Ca^2+、Mg^2+离子浓度增大,NO3^-、Cl^-、SO42-离子含量也出现一定程度的增加。植被、微生物和降水均可影响包气带中CO2含量,且包气带CO2在降水与地下水转化过程中起到重要作用。     

花岗质基岩风化壳结构特征及油气地质意义:以柴达木盆地东坪地区基岩风化壳为例

近年来,不少学者开始关注基岩油藏,但有关基岩风化壳的研究尚未有报道.以柴达木盆地东坪地区基岩风化壳为研究对象,结合东坪地区的地质资料、测井资料及地球化学资料,对花岗质基岩风化壳的结构特征及其与油气储集的关系进行了系统的研究.结果表明:(1) 建立了以Al₂O₃、CaO、Na₂O、K₂O为主要判别依据的花岗质基岩风化指数,准确的识别出古土壤层、残积层、半风化层、未风化层;(2) 根据成像测井响应特征及常规测井曲线可以很好地识别古风化壳特征;(3) 东坪地区基岩风化壳的主要储集空间有基岩溶蚀孔洞、基质矿物溶孔和基岩裂缝,共3种,为致密储层,风化壳由风化基面向上,孔隙逐渐发育,至半风化岩石中部的孔隙度较大,且以大孔隙为主,由半风化岩石到风化粘土层,孔隙的规模变小,逐渐以微孔隙为主,纵向上,孔隙度与风化程度、构造缝发育情况、埋藏深度及其和应力释放中心的距离具有相关性.风化壳的存在大大的改善了储层物性,扩展了含气面积,增加了含气层系,对花岗质基岩地层油气藏和深层油气勘探具有重要的理论价值和科学意义.