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1.
冈底斯带西段那木如岩体始新世岩浆作用及构造意义 总被引：8，自引：4，他引：4
冈底斯带西段狮泉河南部那木如岩体岩性变化较大,其中产出大量基性岩透镜体及暗色微细粒包体,空间上与花岗岩类呈渐变过渡接触关系。本文在详细野外调研的基础上,对狮泉河-札达一带那木如花岗岩及其中基性岩石进行了系统的岩石学、地球化学和同位素年代学研究。结果表明,那木如岩体主体岩性为黑云母花岗岩,其SiO2为65%~76%,全碱含量较高,花岗岩中K2O+Na2O=5.50%~8.71%,基性岩石中则4.42%~6.7%。花岗岩类稀土元素最高含量为284.8×10-6,最低只有105.4×10-6;而基性岩类最高为120.4×10-6,最低72.48×10-6。两者稀土元素分配曲线均呈右倾平缓样式,花岗岩具有不明显Eu负异常,微量元素显示出花岗岩类和基性岩类具有相似的蛛网分布样式。两者均明显富K而亏损Nb、Ti等不活泼的HFS元素,显示出明显的岩浆混合作用趋势。4件花岗岩和基性岩样品所显示的LA-ICP-MS法锆石U-Pb年龄分别为46.11±0.78Ma、45.47±0.4Ma、46.7±2.9Ma和45.4±1.4Ma,变化在45.4~46.7Ma范围内,表明始新世早期(~46Ma)区域发生了岩浆混合作用。这一时限与冈底斯中、东部岩浆作用时代(40~52Ma)非常一致,表明始新世早期整个冈底斯发生了规模巨大的岩浆事件,暗示着印度-欧亚大陆碰撞作用在东西方向上所表现出的同时性。 相似文献
2.
具有特殊成因机制的埃达克质岩石是探究深部岩浆动力学过程与区域构造演化的重要岩石探针之一。本文对北祁连造山带东段宁夏南华山地区出露的石洼里花岗岩进行了系统的锆石U-Pb年龄、主量-微量元素及锆石原位Hf同位素分析,以探讨其岩石成因及地球动力学意义。LA-ICP-MS锆石U-Pb定年结果表明石洼里花岗岩侵位年龄为452±4 Ma, 为晚奥陶世岩浆活动的产物。岩石具有较高的SiO2(68.60%~71.42%)、Al2O3(14.95%~15.75%)和Na2O(5.06%~5.79%)含量,较低的K2O(2.23%~3.10%)、MgO(0.91%~1.73%)含量和较高的Mg# 值(55~59),属弱过铝质钙碱性系列岩石; 岩石具有高Ba(1 025×10-6~1 250×10-6)、Sr(324×10-6~577×10-6)和低Y(6.99×10-6~7.69×10-6)、Yb(0.65×10-6~0.71×10-6)含量,较高的Sr/Y(45~79)和(La/Yb)N(17~31)值,且无明显Eu负异常。锆石εHf(t)值相对较高,变化范围为+0.5~+15.5。主量-微量元素及同位素分析结果表明石洼里花岗岩具有高镁埃达克岩的典型特征, 可能是在30~40 km深度的岛弧基性下地壳部分熔融的产物,其源区中可能存在早古生代的新生地壳。结合区内蛇绿岩、高压变质岩、弧岩浆岩的研究成果, 笔者认为受北祁连原特提斯洋北向俯冲影响,石洼里高镁埃达克岩形成于老虎山弧后盆地洋壳在晚奥陶世的南向俯冲过程中。 相似文献
3.
为解释南冈底斯晚白垩世埃达克质岩石成因及其地球动力学机制,本文对西藏扎囊县札佐地区二长花岗岩开展了锆石U-Pb年代学、Hf同位素和全岩地球化学分析。札佐二长花岗岩锆石U-Pb定年为80.43±0.62 Ma,其SiO2为66.19%~66.84%,Al2O3为15.17%~15.48%,MgO为1.67%~1.91%,Mg#为47.4~51.5,K2O为3.86%~4.09%,A/CNK=0.91~1.01,属准铝质高钾钙碱性岩石。岩石轻稀土富集明显,高Sr（492×10-6~670.2×10-6）,低Y（8.27×10-6~14.99×10-6）,Yb（1.07×10-6~1.79×10-6）,高Sr/Y（35.0~81.0）,高La/Yb（17.4~21.4）,弱负Eu异常,具埃达克岩地球化学特征。相对富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）和重稀土。锆石εHf（t）值为10.5~14.1,单阶段Hf模式年龄（tDM1）为184.8~326.1 Ma,平均为203.4 Ma,二阶段Hf模式年龄（tDM2）为247.2~476.0 Ma,平均为287.1 Ma,略大于侵位年龄,指示岩浆物质来源于俯冲洋壳,并可能卷入俯冲沉积物。岩石中地幔组分印记Mg#值和相容元素Ni、Cr含量较高,表明熔体在上升过程中与上覆地幔楔发生反应。研究分析表明,在新特提斯洋洋脊俯冲作用下,高温热流透过板片窗导致洋壳（及俯冲沉积物）部分熔融形成札佐埃达克质二长花岗岩。同时表明,在80 Ma左右,新特提斯洋仍处于洋脊俯冲阶段。 相似文献
4.
马厂箐复式岩体w(SiO2)变化于61.56%～71.63%,平均67.30%（≥56%）;w(Al2O3)变化于13.38%~17.18%,平均15.44%（≥15%）;w(K2O)变化于3.36%~8.92%,平均5.35%,w(K2O)+ w(Na2O)变化于7.75%~11.55%,平均9.08%,w(K2O)/ w(Na2O)变化于0.65~4.00,平均1.49,明显地具高钾钙碱性或钾玄岩系列的特征;w(MgO)变化于0.40%~4.59%,平均1.11%。在R1-R2图解中处在造山晚期和同碰撞期岩浆岩的范围内。地球化学特征显示高场强元素HFSE（Nb、Ta、Ti）相对亏损,wSr高（337×10-6~1 046×10-6）,wY主要集中在6.2×10-6~15.8×10-6之间（≤18×10-6）,wYb变化于0.20×10-6~1.63×10-6之间（≤1.9×10-6）,轻重稀土元素强烈分异,且具有明显的轻稀土富集的特点,LREE/HREE变化于8.02~24.01,wSr/wY变化于40.5~57.4之间,平均48.2（＞40）,wLa/wYb变化于17.5~75.1之间,平均43.4（＞20）,wSc变化于2.5×10-6~7.9×10-6之间(＜10×10-6);δEu 变化于0.81~1.38之间,显示出弧火山与埃达克岩的过渡特征,可称为似埃达克岩或总体上属于C型埃达克岩。 相似文献
5.
内蒙古查干敖包三叠纪碱性石英闪长岩的地球化学特征及成因 总被引：6，自引：3，他引：3
近年来在西伯利亚板块南缘发现多处三叠纪碱性花岗岩, 构成了一个碱性花岗岩带。产出在该碱性花岗岩带上的查干敖包石英闪长岩岩体,SHRIMP 年龄为237Ma。本文通过元素地球化学和同位素地球化学分析,结果显示SiO2含量60.70%~62.67%,平均值61.76%;K2O+Na2O为9.18%~10.48%,平均值9.74%,且Na2O＞K2O。这些岩石具有REE总量为(236.3~260.0)×10-6,平均246.5×10-6,右斜式稀土配分模式,LREE/HREE为18.91~20.11,平均19.48,显示微弱的Eu负异常的特征。它们也表现高的Sr和Ba含量、低的Y含量,其中Sr为1216×10-6~2028×10-6,平均为1707×10-6,Ba为1597×10-6~1947×10-6,平均为1717×10-6。Y为12.9×10-6~16.5×10-6,平均为15.3×10-6。206Pb/204Pb比值为18.172~18.529,平均值为18.314,207Pb/204Pb值为15.465~15.529,平均值为15.503,208Pb/204Pb值为37.831~38.120,平均值为38.016;初始锶比较集中,变化于0.70405~0.70411,平均0.70408;147Sm/144Nd的比值为0.0671~0.0679,平均0.06747;143Nd/144Nd的比值变化范围为0.512605~0.512631,平均值为0.512619。εNd(t)均为正值,变化范围为3.3~3.8,平均3.5。Pb、Sr、Nd同位素特征均显示地幔来源的特征。这些地球化学和同位素特征值指示查干敖包石英闪长岩属于碱性岩类,源于西伯利亚板块与中朝板块碰撞后,由残留的古老俯冲洋壳部分熔融并经过富钾的基性幔源物质污染而成,与中朝板块北缘的三叠纪碱性岩带属同一期次岩浆活动的产物。该成果为西伯利亚板块与中朝板块碰撞闭合的时限提供了新证据。 相似文献
6.
内蒙古道郎呼都格地区A型花岗岩年代学、地球化学及地质意义 总被引：5，自引：3，他引：2
道郎呼都格钾长花岗岩体位于华北克拉通北缘白乃庙构造带。SHRIMP锆石U-Pb定年获得139.6±1.7Ma岩体侵位年龄。岩体富硅(SiO2=75.79%~78.07%)、富碱(K2O+Na2O=7.39%~8.29%)、贫钙(CaO=0.22%~0.59%);稀土配分曲线呈现"海鸥式"分布特征,显示强烈的Eu负异常(δEu =0.03~0.12);微量元素特征显示具有较高Ga(21.2×10-6~26.6×10-6)、Zr(173×10-6~417×10-6)、Nb(32.3×10-6~42.4×10-6)和Y(24.6×10-6~53.9×10-6)含量,较低的Sr(14×10-6~44×10-6)、Ba(18×10-6~211×10-6)含量,在微量元素原始地幔标准化蛛网图上显示明显的Ba、Sr、P、Eu和Ti的负异常。以上特征表明道郎呼都格钾长花岗岩为A型花岗岩,为高温低压下长英质地壳的部分熔融及其后长石、榍石等的分离结晶作用的产物。结合区域构造演化,本文认为该区钾长花岗岩形成于板内伸展背景。在晚中生代期间,华北板块北缘的构造体制经历了重要的转变,由挤压体制转变为岩石圈减薄和地壳伸展,在伸展体制下,软流圈地幔上涌对上覆长英质地壳的直接加热作用促使其部分熔融形成该区A型花岗岩。 相似文献
7.
安徽牯牛降A型花岗岩的年代学、地球化学和构造意义 总被引：9，自引：6，他引：3
皖南地区牯牛降岩体位于扬子板块东南缘,江南隆起带内。本文报道了牯牛降花岗岩体新的锆石U-Pb年龄和地球化学数据,并对岩体成因及其构造意义进行了探讨。锆石原位LA-ICP-MS U-Pb定年表明牯牛降岩体的形成年龄为130.1±1.3Ma (95% confidence, MSWD=0.55)。结合己发表的其他高质量锆石U-Pb同位素年龄数据表明皖南地区花岗岩的形成年龄主要集中在125~130Ma。牯牛降花岗岩为高钾钙碱性、准铝质岩石,SiO2 含量为72.21%~74.85%,具有高K2O含量(>5.11%)、高铁值(FeOT/(FeOT+MgO)>0.91)和K2O/Na2O比值(>1.61),低MgO和CaO含量的特征。微量元素地球化学性质上表现为强烈亏损Ba、Sr、Eu(Eu*/Eu=0.29~0.30),富集REE(>419×10-6)、Rb、Th 和U,较高的高场强元素Zr、Nb、Y和Ga含量。主量和微量元素均表现为A型花岗岩的特征。非常低的Mg#值(0.14~0.16)和较低Cr含量(Cr=10×10-6),高Yb(7.08×10-6~9.02×10-6)、Y(78.7×10-6~90.8×10-6)含量和较高的Th/U比值(5.17~7.79)说明古老地壳物质的部分熔融可能是牯牛降岩体主要形成机制。牯牛降A2型花岗岩特征代表了拉张的碰撞后构造环境。 相似文献
8.
江达-维西火山岩浆弧中段德钦岩体年代学、地球化学及岩石成因 总被引：6，自引：5，他引：1
本文对江达-维西火山岩浆弧德钦岩体的寄主岩石——花岗闪长岩及其镁铁质微粒包体(MME)——闪长岩进行了详细研究。二者LA-ICPMS锆石U-Pb年龄分别为254.6±1.8Ma和253.5±1.6Ma,二者形成时代一致。地球化学研究结果表明,花岗闪长岩富K2O和Na2O,且K2O>Na2O,富Al2O3,A/CNK平均为0.96;闪长岩富K2O和Na2O,但K2O2O,富Al2O3和MgO,A/CNK平均为0.72;花岗闪长岩的稀土总量低于闪长岩,二者轻重稀土分馏明显,配分曲线为右倾的轻稀土富集型;二者均富集大离子亲石元素而亏损高场强元素Nb、Ta等;二者均具有相对较高的Mg#(58.8~65.8),并具有相对较高的相容元素Cr、Ni含量(花岗闪长岩平均值分别为115×10-6和31.6×10-6,闪长岩平均值分别为398×10-6和98.2×10-6;花岗闪长岩和闪长岩176Hf/177Hf的平均值分别为0.282383和0.282287,二者εHf(t)平均值分别为-8.3和-11.8,反映了二者属于I型花岗岩,可能为岩浆混合作用的产物。地球化学特征及Hf同位素组成一致显示岩浆来源于地壳的部分熔融,伴有不同比例的地幔物质加入,形成于弧陆碰撞-后碰撞的构造背景,暗示金沙江结合带在~255Ma已经进入了弧陆碰撞-后碰撞的地质时期。 相似文献
9.
东天山哈尔里克山区二叠纪高钾钙碱性花岗岩成因及地质意义 总被引：10，自引：5，他引：5
本文从岩石学、地球化学和同位素等方面讨论东天山克拉麦里-哈尔里克岛弧东段八大石和小铺东两个岩体的特征和成因。八大石岩体和小铺东岩体主要为二长花岗岩,SiO2含量分别为61.92%~74.40%和69.17%~74.92%,K2O+Na2O的含量分别为6.50%~8.32%和7.74%~8.14%,绝大部分岩石具有高钾钙碱性花岗岩特征;∑REE分别为105×10-6~210×10-6和100×10-6~172×10-6,(La/Yb)CN分别为4.1~8.9和9.1~15.3,配分模式右倾,δEu分别为0.40~0.93和0.59~0.80,为中-低负异常;两个岩体均富Rb、Ba等大离子亲石元素和Th、U、Hf、Zr等高场强元素,而贫Ta、Nb、Sr、Ti等。通过LA-ICP-MS分析得到八大石岩体中锆石206Pb/238U加权平均年龄为298±2Ma,表明岩体形成于早二叠纪,计算得到八大石和小铺东岩体的模式年龄tDM分别为944Ma和648Ma;八大石和小铺东岩体的εNd(t)u分别为+3.06和+4.47,(87Sr/86Sr) i分别为0.70475和0.70384,表现出高εNd(t)u 低(87Sr/86Sr) i。综上所述,认为哈尔里克高钾钙碱性花岗岩可能为碰撞后挤压-伸展转折阶段的产物,主要由来自新生地壳的中钾钙碱性岩浆经过结晶分异作用而成。 相似文献
10.
甜水海地块寒武纪安山岩的地球化学和年代学研究:对西昆仑-喀喇昆仑造山带原特提斯洋演化的启示 总被引：1，自引：1，他引：0
甜水海地块作为西昆仑-喀喇昆仑造山带重要的组成部分,夹持于麻扎-康西瓦板块缝合带和洪山湖-乔尔天山板块缝合带之间,其构造属性的探讨对认知西昆仑地区早古生代地质演化具有重要的科学意义。笔者在甜水海地块中部麻扎地区通过野外填图新发现并厘定出一套火山岩-沉积岩组合,主要由安山岩、英安岩、流纹岩及其火山碎屑岩和少量沉积岩组成;与安山岩互层产出的英安岩和流纹岩锆石U-Pb年龄为519~513Ma,表明这套火山-沉积地层形成于中寒武世。该火山岩套的地球化学特征为：安山岩SiO2含量为57.0%~67.2%,具有高MgO（1.91%~7.17%）含量和Mg#值（39.1~65.3,平均值为55.0）,较高Cr（31.0×10-6~190×10-6）和Ni（12.2×10-6~121×10-6）含量,低FeOT/MgO比值（1.12~3.26）,低Al2O3（13.7%~17.3%）和K2O（1.12%~5.52%）含量的特征,属于低铁钙碱系列高镁安山岩-镁安山岩;英安岩较安山岩SiO2含量高（63.8%~71.8%）,具有相似的Al2O3（13.4%~15.4%）含量,低MgO（0.28%~1.19%）含量和Mg#值（9.98~36.5,平均值为25.3）,低Cr（11.5×10-6~25.2×10-6）和Ni（4.33×10-6~11.8×10-6）含量,高FeOT/MgO比值（3.64~18.9）和K2O（4.84%~9.27%）含量的特征,属于高钾钙碱性系列。安山岩和英安岩总体表现出右倾轻稀土富集分配模式,富集Rb、Ba、K、Th等大离子亲石元素,亏损Nb、Ta、Ti高场强元素,具有典型的岛弧岩浆岩特征。野外调查表明,安山岩与英安岩在空间上相邻,呈互层产出,且它们都出露于中寒武系地层中,暗示了二者在成因上紧密相联。岩石地球化学特征指示了安山岩和英安岩可能源于富集地幔楔不同比例的部分熔融作用,所产生的岩浆在上升过程中又遭受了不同比例的地壳混染。推测麻扎地区寒武纪火山岩形成于原特提斯洋向南俯冲消减机制下的岛弧构造环境,同时结合区域资料,认为在寒武纪甜水海地块存在两期岩浆作用,在早寒武系末期（~520Ma）原特提斯洋发生双向俯冲,甜水海地块北缘转化为活动大陆边缘。 相似文献
11.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
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. 相似文献
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13.
奥地利安东帕有限公司 《岩矿测试》2009,28(3):306-306
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 相似文献
14.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
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. 相似文献
15.
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. 相似文献
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17.
Alexander E. C. Broberg J. S. Kehren A. R. Graziani M. M. Turri W. L. 《Environmental Geology》1993,22(4):353-361
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. 相似文献
18.
Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA 总被引：1，自引：0，他引：1
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. 相似文献
19.
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. 相似文献
20.
岩石密度和超高压岩石折返速率 总被引：1，自引：3，他引：1
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。 相似文献