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1.
位于扬子板块西南缘的川滇黔接壤区,处于全球特提斯成矿域和环太平洋成矿域交汇部位、峨眉山大火成岩省内,成矿背景极其特殊,形成了独具特色的优势紧缺矿产(铅锌)、战略性关键矿产(稀散元素)为代表的大型-超大型矿床及相关的成矿系统。黔西北地区是川滇黔富稀散元素铅锌特色成矿系统的重要组成部分之一,近年来找矿不断取得重要突破。位于黔西北成矿区南部的丁头山铅锌矿床,是近期找矿突破的一个代表。通过对丁头山矿床闪锌矿LA-ICPMS原位微量元素分析,发现了该矿床Se显著超常富集现象,所测试的90个测点中w(Se)介于19.7×10-6～172×10-6,平均含量81.0×10-6,显著高于Se的地壳丰度(0.05×10-6)和整个扬子板块周缘同类型矿床硫化物的w(Se)(通常50×10-6),暗示其成矿环境极为特殊,很可能与研究区成矿背景有关。通过相关分析,发现丁头山矿床闪锌矿中Se并非直接替代Zn,而是很可能与Cd、In和Fe一起联合置换Zn,即Fe+Cd+Se+In?4Zn,是一种新的替代方式。丁头山矿床Se超常富集新发现,对理解稀散元素共生分异与超常富集成矿作用具有重要意义,同时表明丁头山矿区及外围具有良好的Se资源潜力,应加强系统勘查和深入研究工作。 相似文献
2.
分布于扬子地块东南缘的湘西铅锌成矿区是中国重要的铅锌生产基地,累计探明铅锌资源量超过2000万t.近年来,随着区内多个大型-超大型铅锌矿床相继被发现,其成矿特征和找矿工作也受到地质工作者的关注.唐家寨矿床是分布于湘西洛塔矿田中的一个大型铅锌矿床,文章通过电子探针(EPMA)和激光剥蚀等离子质谱(LA-ICPMS)发现唐家寨矿床闪锌矿中显著富集关键金属元素镓(Ga),2种方法获得平均w(Ga)分别为1320×10-6和928×10-6,其富集程度之高全球罕见.另外,结合LA-ICPMS Mapping分析发现,唐家寨矿床中的Ga元素主要与Cu元素一起耦合替代Zn元素进入闪锌矿晶格之中.上述这些发现表明,唐家寨铅锌矿床及其外围具有巨大的镓等战略性关键金属资源的找矿潜力. 相似文献
3.
正1研究目的(Objective)锗(Ge)是一种典型的稀散元素,其地壳丰度为1.5×10~(-6),主要富集在煤和铅锌矿床中。统计结果显示,闪锌矿是铅锌矿床中Ge的主要载体矿物,但不同类型铅锌矿床闪锌矿中Ge的含量存在差异。除热液脉型和浅成热液型铅锌矿床闪锌矿中Ge的含量较高(可达2500×10~(-6))外,其他主要类型(如喷流沉积型,SEDEX;火山块状硫化物型,VMS;密西西比河谷型,MVT,等)铅锌矿床闪锌矿中Ge的平均含量通常300×10~(-6)。本次发现贵州贵定竹林沟锌矿床闪锌矿中Ge的显著超常富集现象,现报道如下。 相似文献
4.
《矿物学报》2016,(2)
天桥铅锌矿床位于川-滇-黔铅锌成矿带中东部,为黔西北地区铅锌矿床的典型代表之一。长期以来,对该矿床的成因认识存在较多争议,前人的研究主要集中在分散元素的富集规律、稀土元素及同位素对成矿流体来源的指示意义等方面,对天桥矿床中闪锌矿的微量元素特征缺乏系统的研究。本文应用ICP-MS对天桥矿床中闪锌矿的微量元素进行测试分析,研究结果表明,该矿床中闪锌矿的微量元素具有富Ge、Ga贫Mn、In、Sn、Cd的特征,其微量元素富集规律明显与夕卡岩型、喷流沉积型及岩浆热液型铅锌矿床不同,而与典型MVT型矿床(如勐兴、牛角塘等矿床)非常类似,仅其中Cd含量较低(均值为1282×10-6),该特征与川滇黔地区MVT型铅锌矿床(会泽和杉树林)中闪锌矿微量元素组成一致。总体上,本矿床闪锌矿富集Ge和Ga等低温成矿元素,其In/Ga比值中等,Zn/Cd比值较高,暗示其形成于中温环境。综合前人研究成果及矿床产出地质特征,我们认为天桥铅锌矿床属于MVT型铅锌矿床。 相似文献
5.
作为华南大面积低温成矿域的重要组成部分,川滇黔铅锌矿集区是我国重要的铅锌银等资源基地之一,同时该矿集区也是Ge、Cd、Ga和In等稀散元素的超常富集区域。毛坪矿床是该矿集区内第二大铅锌矿床,累计探明铅锌金属储量超过3Mt(Pb+Zn平均品位≥18%),锗(Ge)保有储量182t。本文以新发现的Ⅵ矿带(铅锌金属已探明储量≥60万t,Pb+Zn平均品位≥20%)为研究对象,利用LA-ICPMS对主要矿石矿物闪锌矿和黄铁矿进行了微区原位微量元素组成和Mapping分析。研究结果显示Ⅵ矿带闪锌矿普遍富集Ge(最高580×10^(-6),均值81.1×10^(-6))、Cd(最高3486×10^(-6),均值1613×10^(-6))和Ga(最高190×10^(-6),均值44.4×10^(-6));黄铁矿普遍富集Mn、As、Pb、Cu、Ag和Sb。与Ⅰ和Ⅱ号矿带闪锌矿相比,Ⅵ号矿带闪锌矿更富集Ge和Ga。闪锌矿中Fe和Pb以类质同象为主,偶见黄铁矿和方铅矿显微包体;Cu、Ge、Ag和As赋存形式主要为类质同象,替代方式为Ge^(4+)+2(Cu+,Ag+,As+)↔3Zn^(2+);Cd以类质同象方式赋存为主,替代机制为Cd^(2+)↔Zn^(2+);Ga和In可能主要以类质同象方式存在。黄铁矿中Pb和Mn主要以方铅矿和碳酸盐矿物显微包体为主;Cu、As和Sb以类质同象形式存在于黄铁矿中;Ag和Zn可能以独立矿物形式赋存;Co和Ni以类质同象方式替代Fe进入黄铁矿晶格中,替代方式为Ni^(2+)+Co^(2+)↔2Fe^(2+)。毛坪矿床新发现Ⅵ矿带硫化物相比典型MVT矿床硫化物具有不同的In和Ge含量以及Cd/Fe比值,结合矿床地质特征和其他证据,表明毛坪矿床成因类型特殊,有别于经典MVT铅锌矿床,属于川滇黔型铅锌矿床。 相似文献
6.
云南省富乐铅锌矿床闪锌矿中微量元素地球化学特征——兼论深色闪锌矿富集Cd的原因 总被引：3，自引：0，他引：3
富乐铅锌矿床位于川滇黔铅锌多金属成矿域东南部,其闪锌矿中Cd含量居全国前列。单矿物常量分析表明闪锌矿内w(Fe)低,平均0.23%。微量分析和电子探针微区分析显示,微量元素w(B)主要为Cd 16 183×10-6,Cu 1 514×10-6;Ni 414×10-6;As215×10-6;Se 163×10-6;Ge 135×10-6;Ga 86×10-6;Sb 35×10-6;Ag 16×10-6,其次为Cr,Co,Mn,Ba,Ti,Sr,Mo等,其含量一般1×10-6～10×10-6。Cd与Cu,Ag,Sb,As,Ni等呈正相关。闪锌矿的颜色由这些微量元素共同引起,Ni使闪锌矿呈紫色,Cu使闪锌矿呈红色,Ga使闪锌矿呈黄色。Cd不影响闪锌矿颜色,Cd之所以在深色闪锌矿中相对富集,是因为Cd与引起闪锌矿颜色改变的这些微量元素含量正相关,它们同步进入闪锌矿的晶格。Fe因为含量过低,对闪锌矿颜色影响不明显。 相似文献
7.
新桥矿床是长江中下游成矿带铜陵矿集区内典型的大型层控矽卡岩型铜金硫多金属矿床。矿床成矿过程中除了铜、金、铁、硫等主要成矿元素富集成矿以外,钴、硒、碲等关键金属元素也以伴生形式产生了不同程度的富集。前人对新桥矿床开展了大量研究工作,但对矿床中关键金属钴、硒、碲的分布规律、赋存状态和富集机制等方面系统研究尚未开展。本次研究在新桥矿床系统采集距离成矿岩体不同位置的两条代表性剖面(3804、E601)的岩矿石样品,通过光学显微镜观察、扫描电子显微镜、全岩主微量元素化学分析和矿物原位LA-ICP-MS微量成分测试等分析技术方法,查明了矿床中钴、硒、碲等关键金属的空间分布规律和赋存状态,初步探讨了钴、硒、碲的富集机制。新桥矿床中估算伴生Co、Se、Te资源量分别为:2326t、2590t、1463t,达到大-中型规模。近成矿(热)中心3804剖面Co、Se含量自矿体底板→顶板呈逐渐降低的趋势,Te含量变化没有明显规律,Co、Se、Te均主要在黄铁矿矿石中产生富集;远成矿(热)中心E601剖面上Co、Se、Te含量自矿体底板→顶板均呈逐渐降低的趋势,且主要富集高品位黄铁矿矿石中。矿体走向上自成矿(热)中心→远端,Co含量明显降低,Se、Te含量相对增高。矿床中Co、Se主要以类质同象置换的形式赋存于黄铁矿中,Te的赋存状态以独立碲矿物为主,包括辉碲铋矿和碲银矿。Co主要在石英-硫化物阶段产生富集,成矿流体温度较高,流体中Co大部分随黄铁矿沉淀富集于近成矿(热)中心的黄铁矿矿石中,至碳酸盐-硫化物阶段,成矿流体温度降低,流体中Se、Te大部分沉淀富集于远成矿(热)中心的高品位黄铁矿矿石中,其中Se主要随黄铁矿大量沉淀富集,Te较少进入黄铁矿等硫化物中,主要以独立矿物的形式产出。 相似文献
8.
扬子板块周缘MVT型铅锌矿床闪锌矿微量元素组成特征与指示意义:LA-ICPMS研究 总被引：3，自引：1，他引：2
扬子板块周缘铅锌多金属成矿带内分布着数以百计的沉积岩容矿型铅锌矿床,它们不仅是我国主要的铅锌矿产地,同时也是重要的稀散元素(Ge、Ga等)生产基地。本次研究采用LA-ICPMS技术分别测定了扬子板块西南缘的会泽铅锌矿床、金沙厂铅锌矿床、大梁子铅锌矿床,扬子板块北缘的马元铅锌矿床以及扬子板块东南缘的凤凰茶田锌(铅)汞矿床中闪锌矿的微量元素组成,以揭示闪锌矿中微量元素(稀散元素)的富集规律和赋存状态,并为矿床成因类型的厘定及稀散元素矿产资源综合利用提供更多依据。LA-ICPMS微量元素测定结果显示闪锌矿中不同微量元素(稀散元素)分布不均匀,但这些矿床中闪锌矿总体以富集稀散元素Ge、Ga、Cd,贫In、Se、Tl、Te为特征,其Fe、Mn含量要明显低于与岩浆热液有关的高温闪锌矿,指示了扬子板块周缘铅锌矿床可能形成于中-低温成矿流体,而与岩浆热液无直接的成因联系,此外这些矿床中闪锌矿富Ge贫In的特征与其他的密西西比河谷型铅锌矿床(MVT)一致。同时,本次研究综合分析了闪锌矿中不同微量元素(稀散元素)之间的相关关系,并与闪锌矿微量元素LA-ICPMS时间分辨率特征相结合,研究表明:这些铅锌矿床中稀散元素Ge可能主要通过3Zn2+?Ge4++2(Cu+,Ag+)和2Zn2+?Ge4++□(晶体空位)的替代方式进入闪锌矿,Ga在闪锌矿中富集机理主要为2Zn2+?(Cu,Ag)++(Ga,As,Sb)3+。此外,为进一步揭示不同成因类型铅锌矿床中稀散元素的富集规律,本文还系统对比了全球范围内不同类型铅锌矿床闪锌矿的稀散元素(均为LA-ICPMS数据)组成特征,并初步探讨了造成不同成因闪锌矿中稀散元素(Ge、Ga和In)差异性富集的主要控制因素,研究表明:(1) Ge在中低温盆地卤水成矿系统(MVT和SEDEX矿床)和岩浆-火山热液成矿系统(浅成脉状铅锌矿床和VMS矿床)形成的闪锌矿中均可能富集成矿,但中低温浅成脉状矿床中Ge的富集程度要明显高于高温脉状矿床,指示了成矿温度是控制闪锌矿中Ge富集的一个重要因素。(2)铅锌矿床闪锌矿中In主要为岩浆来源,In倾向于在成矿温度较高的岩浆及火山热液成因铅锌矿床中富集成矿,而壳源的MVT和SEDEX型铅锌矿床中闪锌矿均贫In。可见除形成温度外,成矿物质来源是决定闪锌矿是否富In的关键因素。(3)除矽卡岩型铅锌矿床外,其他不同成因类型、不同形成温度的铅锌矿床中闪锌矿均可能富Ga。矽卡岩型铅锌矿床闪锌矿具有明显的贫Ga、Ge的特征,这可能是由于矽卡岩化过程中稀散元素Ga、Ge大量进入早期矽卡岩矿物,进而导致了成矿流体以及随后形成的闪锌矿中Ga、Ge的贫化。综上所述,闪锌矿中稀散元素富集与否和富集程度受成矿物质来源、成矿流体性质以及流体演化过程等多因素的综合控制。(4)扬子板块周缘铅锌矿床闪锌矿的微量元素(稀散元素)组成特征指示了它们形成于中低温成矿环境,稀散元素的富集规律与其它MVT型铅锌矿床类似。 相似文献
9.
《西北地质》2021,(3)
笔者在安康西部县域土壤地球化学调查评价基础上,研究了紫阳、汉阴两县农田土壤Se含量及赋存形态、主要农作物富Se能力特征。研究区农作物根系土Se平均含量为1.24×10~(-6)～2.27×10~(-6),高于天然富硒土地划定标准(DD-2019-10)2.1～4.7倍。土壤中Se各形态含量占全量的比例由高到低排序为:残渣态(0.891×10~(-6))腐殖酸结合态(0.255×10~(-6))强有机结合态(0.217×10~(-6))水溶态(0.015×10~(-6))≥碳酸盐结合态(0.015×10~(-6))离子交换态(0.012×10~(-6))铁锰氧化态(0.008×10~(-6))。8种农作物可食部位Se含量均达到或超过富硒农产品标准,农作物Se富集系数由大到小排序为:油菜(1.03)水稻(0.47)大蒜(0.36)茶叶(0.20)玉米(0.13)红薯(0.11)、魔芋(0.10)土豆(0.08)。建议当地农业生产充分利用土壤的Se资源,按照作物富Se能力大小合理规划种植结构。 相似文献
10.
武山铜矿床是长江中下游成矿带九瑞矿集区内典型的层控-接触带矽卡岩型铜多金属矿床,铜资源量达到大型,此外还共生硒、碲、钴、镓、铊等关键金属矿产,具备良好的矿产资源综合利用前景,但矿床中关键金属的分布规律、赋存状态和富集机制等研究尚未开展。本文以武山铜矿床为研究对象,系统采集了矿床南矿带接触带矽卡岩型矿体3条勘探线(W3-2、S4-2、N6-1)、北矿带层控硫化物型矿体3条勘探线(E9-2、E2-1、W4-1)和层控矽卡岩型矿体1条勘探线(E7-3)代表性岩矿石样品。通过光学显微镜和扫描电镜的观察,结合全岩地球化学和矿物原位LA-ICP-MS分析,查明了矿床中硒、碲、钴等关键金属的空间分布规律与赋存状态,初步探讨了硒、碲、钴的迁移沉淀机制。研究结果表明矿床中伴生硒、碲、钴的估算资源量分别为5513t、611t和9597t,均达到大-中型规模;武山矿床是成矿带内硒含量最高、潜在资源量最大的矿床。北矿带矿体中Se、Te、Co含量明显高于南矿带,北矿带中部成矿中心向东西远端,矿体中Se、Te、Co含量规律性增高。矿石中Se、Te、Co含量与S含量具有较强的正相关性,矿石中硫化物的含量是关键金属含量主要控制指标;Se和Co富集于含铜黄铁矿矿石、含铜白云岩矿石、含铜矽卡岩矿石(高硫)中;Te富集于含铜黄铁矿矿石和含铜白云岩矿石中。矿床中硒、碲主要以独立矿物和硫化物中类质同象替换两种赋存形式,钴则主要以Co^(2+)类质同象形式进入黄铁矿矿物晶格。矿床中硒、碲随着成矿流体温度降低、硫逸度升高、氧逸度降低、pH值升高逐渐沉淀富集;钴主要随着硫化物的沉淀富集在黄铁矿中。 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
12.
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
13.
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
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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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Between 1985 and 1991, two new mountain protected areas (MTNPA) covering more than 35,000 km2 and based on participatory management models — the Makalu-Barun National Park and Conservation Area, Nepal, and Qomolangma Nature Preserve, Tibet Autonomous Region — were successfully established through the collaborative efforts of Woodlands Mountain Institute and conservationists in China and Nepal. Characteristics common to both projects include the importance of establishing (1) effective rationales, (2) local support constituencies, (3) a senior advisory group, (4) a task force, (5) linkages between conservation and development, and (6) fund raising mechanisms. The lessons derived from the experiences of Woodlands Mountain Institute are of significant value to others in preserving MTNPA. Increased collaboration and communication between all interested in conservation, however, will remain a critical component for expanding mountain protected area coverage to throughout the world. 相似文献
19.
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
20.
《Applied Geochemistry》2001,16(2):137-159
Five hundred and ninety-eight samples of terrestrial moss (Hylocomium splendens and Pleurozium schreberi) collected from a 188,000 km2 area of the central Barents region (NE Norway, N Finland, NW Russia) were analysed by ICP-AES and ICP-MS. Analytical results for Al, B, Ba, Ca, K, La, Mg, Mn, Na, P, Rb, Si, Sr, Th, U and Y concentrations are reported here. Graphical methods of data analysis, such as geochemical maps, cumulative frequency diagrams, boxplots and scatterplots, are used to interpret the origin of the patterns for these elements. None of the elements reported here are emitted in significant amounts from the smelting industry on the Kola Peninsula. Despite the conventional view that moss chemistry reflects atmospheric element input, the nature of the underlying mineral substrate (regolith or bedrock) is found to have a considerable influence on moss composition for several elements. This influence of the chemistry of the mineral substrate can take place in a variety of ways. (1) It can be completely natural, reflecting the ability of higher plants to take up elements from deep soil horizons and shed them with litterfall onto the surface. (2) It can result from naturally increased soil dust input where vegetation is scarce due to harsh climatic conditions for instance. Alternatively, substrate influence can be enhanced by human activity, such as open-cast mining, creation of ‘technogenic deserts’, or handling, transport and storage of ore and ore products, all of which magnify the natural elemental flux from bedrock to ground vegetation. Seaspray is another natural process affecting moss composition in the area (Mg, Na), and this is most visible in the Norwegian part of the study area. Presence or absence of some plant species, e.g., lichens, seems to influence moss chemistry. This is shown by the low concentrations of B or K in moss on the Finnish and Norwegian side of the (fenced) border with Russia, contrasting with high concentrations on the other side (intensive reindeer husbandry west of the border has selectively depleted the lichen population). 相似文献