山东半岛基性高压麻粒岩的成因矿物学及变质演化

在山东半岛的平度-莱西-莱阳-烟台一带,广泛出露基性高压麻粒岩,它们呈大小不等的透镜体或不规则脉状体产于TTG片麻岩中,且与超镁铁质岩石密切"伴生"。根据岩相学、矿物相转变、变质反应以及温压条件的系统研究结果,确定山东半岛基性高压麻粒岩经历了四个阶段的变质演化。早期进变质阶段(M1)的标志性矿物组合以石榴石及其内部的细粒单斜辉石+斜长石±石英为特征,记录的温压条件为T=740～770℃、P=0.9～1.0GPa;峰期高压麻粒岩相变质阶段(M2)的矿物组合以基质中石榴石(富Ca核部)+单斜辉石(富Al核部)+斜长石(富Na核部)±石英为特征,记录的温压条件为T=850～880℃、P=1.45～1.65GPa;峰后近等温减压(中压)麻粒岩相退变质阶段(M3),以发生一系列典型减压反应和斜方辉石的大量出现为标志,典型的矿物组合为斜方辉石+单斜辉石+斜长石+磁铁矿±角闪石,记录的温压条件为T=780～830℃、P=0.65～0.85GPa;晚期角闪岩相退变质阶段(M4)以石榴石发生降温反应、形成角闪石+斜长石+磁铁矿±石英等退变矿物组合为特征,记录的温压条件为T=590～650℃、P=0.62～0.82GPa。高压基性麻粒岩的变质演化的P-T轨迹具有顺时针型式,先后经历了近等温减压过程(ITD)和近等压降温过程(IBC)变质演化过程,指示研究区基性高压麻粒岩是古老陆块之间在俯冲-碰撞造山过程中加厚下地壳折返地表的产物。该项成果对于重新认识华北克拉通在早前寒武纪古老陆块的碰撞-拼贴及其演化的动力学过程具有重要科学意义。     

蚌埠隆起区石榴辉石岩变质PT轨迹及年代学研究

蚌埠隆起位于华北克拉通东部陆块的胶-辽-吉造山带的最南缘,由于侧重点和关注度的差异,对于该地区的变质演化过程的探究一直较为缺乏,制约了人们对该隆起形成过程的理解。为此,本文通过对该隆起的石榴辉石岩及其退变的黑云斜长片麻岩详细的野外观测、岩相学分析、热力学评价和年代学的研究,较为充分地探讨了该隆起的形成机制。研究显示这两类岩石记录了5个变质阶段：阶段-Ⅰ的平均温压为：T=672±17 ℃和P=1.05±0.02 GPa;阶段-Ⅱ的平均温压为：T=805±30 ℃和 P=1.21±0.04 GPa;阶段-Ⅲ的平均温压为：T=615±13 ℃和 P=0.93±0.02 GPa; 阶段-Ⅳ的平均温压为：T=632±6 ℃和P=0.50±0.01 GPa;阶段-Ⅴ的温压为推测值：T=400 ℃～450 ℃和P=0.2～0.4 GPa。其中阶段-Ⅰ～阶段-Ⅲ表象为角闪岩相→麻粒岩相→角闪岩相的过程,显示了一个近等压的可能的快速升温和降温的过程。而阶段-Ⅲ～阶段-Ⅳ表现为一个近于等温降压的快速过程,直至阶段-Ⅴ表现为可能的缓慢降温降压过程。结合背景资料和前人年龄数据,以及本次对退变黑云斜长片麻岩的锆石U-Pb定年（1 885±16 Ma）研究,推测该全过程可能反映的是两期变质事件。其中,早期的变质以阶段-Ⅰ、阶段-Ⅱ和阶段-Ⅲ为代表,揭示了大约在2.5 Ga时期,蚌埠隆起经历了大规模岩浆上侵及紧密相伴的高温麻粒岩相变质事件;而晚期变质以阶-Ⅲ→阶段-Ⅳ等温降压为代表,可能反映的是大约1.9 Ga时期,胶-辽-吉造山带的形成过程。     

南阿尔金吐拉地区中压基性麻粒岩变质作用及地质意义

南阿尔金吐拉地区基性麻粒岩呈透镜体分布于泥质片麻岩中。基性麻粒岩主要矿物组成为石榴子石、斜方辉石、单斜辉石、角闪石、黑云母和斜长石,显示"巴罗式"变质作用(中压麻粒岩相变质作用)特征。目前南阿尔金吐拉地区发育的"巴罗式"变质岩研究相对薄弱,对岩石学特征、变质演化轨迹及"巴罗式"变质作用成因机制亦不明确。传统矿物温压计指示基性麻粒岩的峰期变质温压条件为T=820℃～870℃,P=8.0～8.5 kPa,退变质阶段温压T=700℃～750℃,P=6～7.5 k Pa,为一个降温降压顺时针型的P-T演化轨迹。锆石U-Pb定年加权平均年龄为～450Ma,结合岩相学研究和锆石特征,认为其代表了峰期麻粒岩相变质时代。基性麻粒岩与区域上深熔作用和花岗质岩浆作用变质年龄相似,较南阿尔金UHP榴辉岩和HP麻粒岩的峰期变质时代晚40～50 Ma,与榴辉岩折返过程中麻粒岩相叠加变质作用时代较相似。说明吐拉地区"巴罗式"变质作用及同时代花岗质岩浆作用和混合岩化作用可能是由于俯冲陆壳发生断离并开始折返上升,在伸展环境下由幔源岩浆上涌加热中地壳形成的。     

苏鲁造山带超高压变质作用及其P-T-t轨迹

基于超高压变质岩的岩石学,特别是超高压矿物生长成分环带、扩散环带和蚀变作用研究,综合前人的岩石学和年代学研究成果,提出苏鲁造山带超高压变质作用峰期发生在1000-1100℃和6-7GPa条件下,俯冲深度相当于200km,形成年代为240-250Ma。在此基础上,重塑了一个包括八期变质作用的P-T-t轨迹,揭示出超高压变质岩经历了三个不同的折返阶段,即从200km到100km深度的快速折返阶段,抬升速率为5km/Ma,冷却速率为10℃/Ma;从100km到30km的快速折返,抬升速率为4km/Ma,或为近等温降压,或为缓慢降温的快速降压过程;从下地壳到近地表的缓慢折返阶段,抬升速率为1km/Ma,但为快速降温过程,冷却速率可达20℃/Ma。     

鲁东南岚山头榴辉岩的变质作用演化PTt轨迹及地质意义

岚山头含柯石英榴辉岩呈透镜状块体产于晚元古代含霓石花岗质片麻岩中.榴辉岩的典型矿物平衡共生可划分为四个阶段:(1)前柯石英榴辉岩相阶段(M1);(2)柯石英榴辉岩相阶段(M2);(3)第一退变质阶段(M3);(4)第二退变质阶段(M4).M2阶段典型的矿物共生组合为石榴石+绿辉石+柯石英±蓝晶石.其石榴石中Pyr组分17.9%～31.7%, 绿辉石中Jd组分29.1%～52.8%.各阶段的变质温压条件是:M1阶段P≤1.56GPa,T=700℃;M2阶段P>2.74～2.95GPa,T=722℃～981℃;M3阶段P=1.34～1.54GPa,T=568℃～589℃;M4阶段P=0.61～1.04GPa,T=469℃.M2变质阶段单颗粒锆石207Pb-206Pb年龄为613.3Ma±30.4Ma,M4阶段的多硅白云母的 40Ar-39Ar坪年龄为313.49Ma.据上述资料可重塑一个较完整的顺时针PTt轨迹的变质作用演化.退变质作用的两个阶段反映榴辉岩折返可分为两个阶段.     

苏鲁超高压榴辉岩的石榴石生长成分环带及变质作用P—T轨迹

在南苏鲁东海地区，部分超高压榴辉岩中的变斑晶石榴石具有复杂的生长成分环带和多期矿物包体组合，它们记录了超高压变质岩的多阶段变质演化过程，即绿帘角闪岩相进变质、柯石英榴辉岩相峰期变质、石英榴辉岩相和角闪岩相退变质作用。运用相关的地质温、压计，使用代表最高变质温度的变斑晶石榴石慢部（具最低的Fe／Mg比值）和与其平衡的绿辉石包体成分，获得了〉900℃和4．1～4．5GPa的超高压变质务件。联合其他变质阶段的温、压条件，一个顺时针的变质作用P—T轨迹得以建立。它的特征是进变质与退变质路径近于平行，早期退变质作用为降温、降压过程．榴辉岩石榴石生长成分环带的保存说明超高压变质岩在峰期变质阶段有非常短暂的停留时间，并以很快的折返速率抬升到地壳浅部，超高压变质岩折返过程中的明显降温是石榴石生长环带得以保存的另一个有利条件，     

苏鲁-大别超高压岩石中锆石SHRIMP U-Pb定年研究——综述和最新进展

如何建立苏鲁-大别超高压岩石深俯冲-超高压-快速折返过程连续而完整的P-T-t轨迹及精细的年代谱系,是目前地学界研究的热点。而变质锆石是否记录深俯冲石英榴辉岩相进变质阶段的年代学信息和超高压峰期变质时代的准确归属,是目前苏鲁-大别超高压变质带需要深入研究的核心问题。本文在对前人同位素年代学方面所取得的成果进行系统总结的基础上。采用锆石中矿物包体激光拉曼和电子探针测试、锆石阴极发光图像成因分析以及SHRIMP U-Pb定年等综合研究手段,确定苏鲁-大别地体榴辉岩及其强退变质围岩在深俯冲-构造折返过程中主要经历了四个阶段的变质演化:深俯冲石英榴辉岩相进变质(Ⅰ)、超高压峰期变质(Ⅱ)、构造折返初期石英榴辉岩相退变质(Ⅲ)和构造折返晚期角闪岩相退变质(Ⅳ)。研究发现,扬子板块(中)新元古代巨量的陆壳物质在早三叠纪(246～244Ma)俯冲到华北板块之下约65km的深处。发生了石英榴辉岩相进变质,相应的变质温压条件为T=542～693℃,P=1.7～2.02GPa。这些高压石英榴辉岩相岩石在中-新三叠纪继续向下俯冲,在235～225Ma期间,俯冲的深度至少达到了170km的地幔深处,并发生了峰期柯石英榴辉岩相超高压变质,相应的变质温压条件为T=722～866℃,P>5.5GPa。苏鲁-大别超高压地体自石英榴辉岩相进变质阶段到超高压峰期变质阶段的俯冲速率为7.0km/Myr。这些超高压岩石在219～216Ma期间,发生了第一次构造抬升至75km的深处,并经历了石英榴辉岩相退变质作用的改造,退变质温压条件为T=730～780℃,P=1.7～2.6GPa。这些退变质岩石在212～205Ma期间,又经历了第二次抬升至25km中-下地壳深处,并叠加了角闪岩相退变质作用,该阶段变质温压条件为T=610～710℃,P=0.7～1.2GPa。苏鲁-大别超高压地体两次构造抬升的速率大致相同,为5.6km/Myr。该项成果不仅确定了苏鲁-大别榴辉岩及其强退变质岩石深俯冲过程石英榴辉岩相进变质-超高压峰期变质、构造折返过程石英榴辉岩相-角闪岩相退变质连续而完整的变质演化P-T-t轨迹及精细的年代谱系,而且对于重新建立苏鲁-大别巨量陆壳物质快速超深俯冲-快速折返的动力学模式有着重要的科学意义。     

大别造山带宿松杂岩中石榴斜长角闪岩变质演化过程、原岩时限及其构造涵义

大别造山带是由扬子板块向华北板块俯冲碰撞而形成的,出露了世界上规模最大的、种类最齐全的各类超高压岩石,全面深刻地记录了大陆深俯冲过程。然而,对于该造山带“浅层”(地壳层次)俯冲折返过程的研究则较少涉及,这制约了对大别造山带形成全过程的整体理解。为此,本次研究以大别造山带最南缘经历绿帘-角闪岩变质的宿松杂岩为研究靶区,针对该杂岩别河地区的石榴斜长角闪岩展开了精细的岩相学、矿物化学、温压评价和年代学研究。研究表明,该岩石记录了三个变质阶段,其中第二阶段可进一步分为a和b两个亚阶段,具体的变质温压条件分别为：(1)阶段Ⅰ:T=562±12℃、P=1.03±0.05GPa;(2)阶段Ⅱ-a:T=663±8℃、P=1.09±0.04GPa;(3)阶段Ⅱ-b:T=508～584℃、P_-设定=0.5～0.7GPa;(4)阶段Ⅲ:T=396～472℃、P_-设定=0.1～0.3GPa。其中,(1)→(2)表现为近等压增温型式,反映了一个俯冲迟滞过程,暗示了“浅层”俯冲止于莫霍面附近,并受下伏岩石地幔热源供给导致其持续增温,而(2)→(3)→(4)则显示降温降压...     

浙西南八都杂岩早中生代泥质麻粒岩变质作用及构造意义

遂昌-大柘泥质麻粒岩出露于华夏地块东北部的浙西南八都杂岩中,该岩石保留了典型的减压反应结构.但其变质演化特点、变质作用时代及构造意义目前尚不明确.通过系统的岩相学、矿物化学和同位素年代学分析,结果表明遂昌-大柘泥质麻粒岩记录了4个阶段的变质矿物组合,其中早期进变质阶段M₁的矿物组合为石榴石+黑云母+石英;压力峰期变质阶段M₂的矿物组合为石榴石+铝绿泥石+金红石+蓝晶石+刚玉+黑云母+石英±十字石,该矿物组合可能预示着岩石曾经历了超高压变质作用过程;峰期变质阶段M₃的矿物组合为石榴石+黑云母+夕线石+石英±钾长石±斜长石±钛铁矿;峰后近等温降压M_4-1阶段的矿物组合为石榴石+黑云母+夕线石+堇青石+石英+钛铁矿±尖晶石±斜长石±钾长石;M_4-2阶段的矿物组合为石榴石+堇青石+夕线石+斜长石+黑云母+石英±钾长石.相平衡模拟结合传统地质温压计限定其峰期变质阶段的温压条件为T=780~810 ℃、P=8.0~9.2 kbar;峰期后近等温降压的M_4-1阶段的温压条件为T=780~860 ℃和P=5.7~6.0 kbar,M_4-2阶段的温压条件为T=~700 ℃和P=~4.4 kbar,具有典型的顺时针近等温减压型P-T轨迹特征.LA-ICP-MS U-Pb定年结果表明其麻粒岩相变质作用时代为233.5~238.9 Ma.变质作用历史说明浙西南地体可能卷入了古特提斯洋域内印支-华南-华北板块之间的俯冲-碰撞过程,并经历了早中生代的麻粒岩相变质作用后快速折返至地表.      

柴北缘鱼卡榴辉岩的pT演化历史

鱼卡榴辉岩位于柴北缘HP/UHP变质带的西段,榴辉岩呈透镜状或似层状分布在变质泥质岩、花岗质片麻岩及少量大理岩中,主要由石榴石和绿辉石组成,具有含量不等的多硅白云母、角闪石、黝帘石(斜黝帘石或绿帘石)、金红石和石英等。岩相学和矿物化学研究显示榴辉岩经历了3期与俯冲和折返作用有关的变质演化阶段:(1)前榴辉岩相进变质阶段,榴辉岩矿物组合为石榴石(核) 绿帘石 斜长石 角闪石,以包体的形式保存于具有生长环带的石榴石核部,形成的温压条件为p=1.06～1.11GPa,t=560～577℃;(2)榴辉岩相变质阶段,以绿辉石、多硅白云母等矿物围绕石榴石定向分布为特征,其矿物组合为石榴石(边) 绿辉石 多硅白云母±黝帘石,温压估算获得榴辉岩相的变质条件为p=2.35～2.52GPa,t=610～680℃;(3)后榴辉岩相变质阶段,矿物组合为石榴石 角闪石 斜长石,主要存在于围绕榴辉岩透镜体分布的退变榴辉岩(角闪石化榴辉岩)中,形成的温压条件为p=1.09±0.12GPa,t=635±44℃。研究结果显示榴辉岩的pT轨迹具有“发卡”型特点,表明鱼卡榴辉岩经历了快速俯冲和折返的演化历史。     

Wavelength-dispersive X-ray fluorescence spectrometric determination of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites

Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.     

硅酸盐类样品中硅、铁、铝、钛、锰、钙、镁、钾、钠和磷的x射线荧光光谱测定

本文拟定了一种以熔融法制备样片,用X射线荧光光谱测定硅酸盐类样品中Si、Fe、Al、Tj、Mn、Ca、Mg、K、Na、P等元素的分析方法。在对不同靶材X光管和分光晶体实验对比的基础上,选择了最佳的测量条件。该法具有快速、准确,测量范围广,检测限低,价格便宜等优点。经过近百个各种类型标样或管理样品的分析对比表明,本法不仅适用于硅酸盐类岩石样品的分析,还适用于铁矿、铝土矿、碳酸盐类岩矿样品以及水泥、耐火材料等样品的分析。     

高压微波消解法测定醋酸纤维过滤器采集的微尘粒子中的砷镉钴铬铜铁锰镍铅钒锌

最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提     

Isotopic systematics of He,Ar, S,Cu, Ni,Re, Os,Pb, U,Sm, Nd,Rb, Sr,Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (³He/⁴He, ⁴⁰Ar/³⁶Ar, ³⁴S/³²S, ⁶⁵Cu/⁶³Cu, ⁶²Ni/⁶⁰Ni, ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ^206–208Pb/²⁰⁴Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.     

Viscous, cohesive, non-Newtonian, depositing, radial slurry flow

Mining induced subsidence can significantly affect mining costs where major surface facilities and natural environment need to be protected. Overburden grout injection is a technology used to control coal mine subsidence by injecting the mine waste material extracted from the coal back into the inter-burden rock during longwall mining. The flowing slurry is here categorised as a nonlinear viscous cohesive (Bingham plastic) fluid. During longwall mining the grout slurry is pumped into the separated beds of the rock mass through a central vertical borehole, which is drilled deep into the inter-burden rock strata above the coal seam. However, a blockage can occur in the injection system when the slurry velocity falls below a certain critical threshold velocity, indicating a material phase change from cohesive-viscous to cohesive-frictional. In situ field injection tests through boreholes have been simulated at a smaller scale at the CSIRO laboratory in Brisbane by pumping the slurry through a radial disk (gap = 4 mm) from its centre. Laboratory experiments indicate a general, nonlinear, cohesive, viscous, frictional model for shear behaviour of the slurry, in which the material shear parameters are functions of the disk radial distance. Complete dimensional and dimensionless analytical solutions have been developed based on an approach related to Bingham–Herschel–Bulkley fluid mechanics. The derived formulae include relations for minimum pump pressure, local pressure and pressure gradient, wall shear stress, volume rate, velocity and velocity gradient. The theoretical results match the experimental measurements. The experiments covered slurries with maximum particle sizes of 0.5 to 2 mm with about 50% being larger than 100 µm. The viscosities at the various solids concentrations were measured with a standard torsion viscometer. This study differs from the previous research in several distinct aspects, namely, consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behaviour, and implementation of a friction function to mimic behaviour of the deposited and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance.     

硅酸盐中铁、锰、钛、钙、钾、磷、硅、铝、镁、钠、锶、铷、钡的X-射线荧光光谱定量测定

本文介绍样品经四硼酸锂熔融制成玻璃小饼。采用Lachance模式和理论a系数来校正元素间的效应,由3080E型X-射线荧光谱仪和DF-350B数据处理系统完成硅酸盐中十三个项目的测定。     

岩石密度和超高压岩石折返速率

在常温常压条件下对中国大陆科学钻CCSD主孔100-3000米岩心样品进行了密度测量,建立了密度连续剖面,并界定了不同超高压岩石的密度值。通过对比高温高压物性实验资料,岩石密度随着退变程度增强而降低,榴辉岩密度变化序列为3.52g/cm3→3.49g/cm3→3.07g/cm3→2.93g/cm3。超高压长英质岩石密度变化序列为3.00g/cm→2.80g/cm3→2.65g/cm3。上述实验资料是讨论不同折返阶段岩石所受浮力的基础,为研究折返速率大小提供了基本参数。本文通过折返板块运动平衡时,上浮力与粘滞力平衡这一关系式,定量研究了大陆俯冲板块的折返速率,认为密度差产生上浮力从而引起折返,温度对板块折返速率的影响最为显著;密度差大小、折返角度、折返板块大小对折返速率也有直接的影响。定量模拟分析表明,在温度高于850℃时,板块的折返速率可以超过100mm/a;当温度降至700℃时,折返速率则低于1.5mm/a。作者认为在折返早期,温度较高,板块快速折返至60-70km榴辉岩相深度;随着传导散热,温度降低,板块以较慢的速率折返至中下地壳。折返速率的估算表明,浮力是板块折返第一阶段(从>100km深部折返至<40km的中下地壳)的主要驱动力。     

Bellechester,Minnesota, USA,lagoon collapses

Bellechester, Minnesota, is a small community of approximately 155 residents located on the county line between Goodhue and Wabasha counties in southeast Minnesota's karst region. Bellechester is served by a 21-year-old wastewater treatment facility (WWTF) consisting of three waste-stabilization ponds. On 28 April 1992 six sinkholes were discovered to have drained cell 2 of the WWTF resulting in the loss of approximately 8.7×10⁶ 1 of partially treated effluent and about 600 m³ of soil into previously undetected subsurface voids of unknown dimensions. In the week following the collapse, approximately 200 water wells located within a 5-km radius of the WWTF were sampled in an after-the-fact, emergency sampling program. Twelve samples with elevated fecal coliform levels, 18 samples with nitrate-nitrogen greater than the 10 mg/1 standard, and no samples with elevated chlorides were found. However, the elevated levels could not be unambiguously attributed to the WWTF collapse. This is the third WWTF to fail by sinkhole collapse in southeast Minnesota since 1974. All three collapsed lagoons have been located in similar geomorphic and stratigraphic settings. However, at least two lagoons have collapsed in the adjacent area in northeast Iowa, and these lagoons are located at different stratigraphic positions. Twenty-two WWTFs constructed in southeast Minnesota's karst region in the last 25 years have been identified as subject to potential sinkhole collapse. An unknown but significant number of manure storage lagoons, flood control structures, etc., have also been constructed in the karst region and are at risk. Public agencies are beginning to develop plans to deal with the risk associated with existing and future waste lagoons in this environment. The critical hydrogeologic parameters that can be used to prioritize the risk of collapse at existing facilities include: (1) the lithology of the first bedrock beneath each lagoon, (2) the thickness of surficial materials between the lagoon and the bedrock surface, (3) the presence and construction of liners (seepage rate), and (4) the proximity to existing sinkholes.     

Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA

The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.     

滇东南花岗岩与锡、银、铜、铅、锌多金属矿床的成因关系

滇东南锡、银、铅、锌多金属矿床主要分布在个旧、白牛厂、都龙3个矿区,而滇东南较大的3个花岗岩体又分别出露在3个矿区或附近.花岗岩体均形成于燕山晚期,岩石化学、矿物成分相似,富含锡、银、铅、锌、钨、铜等成矿元素.矿床主金属元素组合与岩体之间的距离由远而近出现由锡、钨、(铍、铌、钽)→锡、钨、(铁)、铜、铟→锡、铅、锌、银、铟、(锑)有规律的变化.花岗岩浆是成矿物质来源和成矿热源.岩浆侵入初期使上覆地层隆起产生背斜(凹陷部位成向斜);同时使地层产生一系列裂隙、压性断层或层间断裂;岩浆侵入晚期,这些断层再次活动,表现为张性,岩浆产生的含矿热液沿由其活动所造成的断裂迁移、充填、交代、沉淀而形成矿床.