西藏吉塘花岗岩地球化学特征及成因

沿澜沧江结合带发育一条长达1000余千米的印支期澜沧花岗岩带,吉塘岩体位于该带北段,产出在吉塘以西约3km,轴向NNW,侵位于古元古代吉塘群变质岩系中,长70km,宽2~10km、出露面积341km²。主要由花岗闪长岩和二长花岗岩组成,Rb-Sr等时线年龄值为220Ma。本文对吉塘岩体开展了系统的岩石地球化学特征分析。研究结果表明吉塘岩体为过铝质钙碱性S型花岗岩,吉塘岩体在岩石化学组成上,SiO₂含量63%~71%,平均66.5%,Na₂O含量2.8%~4.2%,K₂O含量1.7%~3.4%,铝饱和指数A/CNK=1.09~1.48,CIPW标准矿物中刚玉1.5%~5.6％,微量元素组成类似于片麻岩质的中地壳。(⁸⁷Sr/⁸⁶Sr)_i值为0.7280~0.7395,ε_Nd(i)为-14.1~-16.2,指示岩浆源区为地壳物质,成因上与俯冲作用无关,Nd同位素亏损地幔模式年龄(t_DM)在2.0Ga左右,与昌都陆块变质基底古元古代吉塘群的原始形成年代相当,岩体Sr、Nd同位素组成也与变质基底吉塘群片麻岩一致,综合分析认为,岩浆源岩为变质杂砂岩成分的古元古代吉塘群片麻岩,其原岩建造主要是火山弧成因的英安岩或英安质火山碎屑岩,微量元素组成指示为黑云母脱水熔融。分析认为岩浆形成于地壳加厚增温环境下的地壳深熔作用,构造上与板块碰撞后的环境相联系。支持澜沧江构造带为冈瓦纳与扬子大陆边缘多岛弧系统的边界即古特提斯主洋盆的观点。澜沧江洋的闭合时间早于澜沧花岗岩带的形成年龄220Ma,根据构造带上相关研究成果,倾向于认同碰撞时间在280Ma左右。     

恒山地区古元古代2.1Ga地壳重熔事件: 钾质花岗岩锆石U-Pb定年及Hf-Nd同位素研究

恒山高级片麻岩地体位于华北克拉通中部构造带,主体是形成于晚太古代~2.5Ga的TTG片麻岩和少量变质火山沉积岩,并且经历了古元古代末~1.85Ga的高级变质作用。近年来,在恒山片麻岩地体中识别出一套钾质花岗岩小侵入体群,主要岩性是角闪石二长花岗岩和黑云母二长花岗岩。本文针对这套花岗岩,采用LA-ICP-MS和Cameca 1280型离子探针进行锆石U-Pb定年,获得角闪石二长花岗岩岩浆锆石谐和年龄2052±17Ma和2084±4Ma,黑云母二长花岗岩岩浆锆石谐和年龄2060±18Ma和2083±15Ma。它们在误差范围内一致,代表花岗岩的形成时代。花岗岩锆石Hf同位素和全岩Nd同位素亏损地幔模式年龄分别为2.48~2.60Ga和2.43~2.68Ga,与围岩TTG片麻岩模式年龄范围基本一致。ε_Hf(t) 和ε_Nd(t)主要分布范围分别为-6.0~0.6和-3.3~-1.7,未显示同期幔源物质的添加。据此可以推断,这些钾质花岗岩是恒山晚太古代TTG岩石在~2.1Ga部分熔融的产物。该期岩浆活动在华北克拉通已识别出多处,恒山地区的这期岩浆活动显示了地壳重熔特征。结合五台、阜平等地对于同期事件的研究,我们推测这些区域上~2.1Ga的岩浆活动形成于拉张裂解环境中。     

东昆仑香日德地区晚三叠世花岗岩LA-ICP-MS锆石U-Pb定年、岩石成因和构造意义

东昆仑地区广泛分布了大量花岗岩.已有的研究工作表明,东昆仑地区的花岗岩主要形成于晚二叠世-中三叠世和晚三叠世两个时期.本文提供了香日德地区二长花岗岩和花岗闪长岩的锆石U-Pb定年数据和全岩化学,稀土微量元素及Sr、Nd同位素地球化学研究资料,结合前人对该区不同时期花岗岩的研究成果,对香日德晚三叠世花岗岩的成因及其形成的动力学背景进行了讨论.研究表明东昆仑东段香日德地区的二长花岗岩和花岗闪长岩分别形成于223.2±1.7Ma和220.6±1.5Ma,属晚三叠世花岗岩浆作用的产物.根据该花岗岩的主量元素(特别是A/CNK比值),岩石富集大离子亲石元素(LILE:Rb、Th和K)和轻稀土(LREE),明显亏损高场强元素(HFSE:Nb、Ta、Ti和P),以及岩石具有相对高的I_sr值(0.70820~0.71148)和相对低的ε_Nd(t)值为-6.4~-3.6和较古老的模式年龄t_2DM(1.5~1.7Ga)等地球化学特征,论证了该花岗岩的成因,指出香日德花岗闪长岩-二长花岗岩的起源和成因与碰撞后的背景下岩石圈的拆沉诱发的古老地壳物质的部分熔融作用有关,晚三叠世花岗岩岩浆作用是对自晚海西期以来幔源玄武质岩浆长期的底侵作用及地壳不断加厚的一种响应.它进一步证明在东昆仑地区,阿尼玛卿古特提斯洋的俯冲作用一直持续到早三叠纪,至晚三叠世才全面转入陆内碰撞造山阶段.晚三叠世花岗岩与晚二叠世-中三叠世花岗岩在暗色包体含量、岩浆混合作用的特征等方面的差异,可以用幔源物质贡献量的差异以及花岗质岩浆作用所经历的MASH过程的不同来解释.     

南阿尔金迪木那里克花岗岩地球化学、锆石U-Pb年代学与Hf同位素特征及其构造地质意义

迪木那里克花岗岩侵入到南阿尔金迪木那里克浅海相沉积地层中,岩性为钾长花岗岩。地球化学数据显示该花岗岩具有高SiO₂、高钾、高铝的特征,富集Rb、Th、K、La、Zr,亏损Ba、Ta、Nb、Sr、P、Ti,属于弱过铝质高钾钙碱性系列,具有S型花岗岩的特征;其源岩为杂砂岩,熔融温度和压力约为>800℃与~10kbar。锆石ε_Hf(t)介于-3.52~0.95,LA-ICP-MS 锆石 U-Pb 定年确定其形成时代为452.8±3.1Ma。迪木那里克花岗岩的形成时代明显晚于南阿尔金高压-超高压变质岩的峰期变质时代(486~504Ma),而与超高压岩石的退变质时代(455Ma)基本一致,又与形成时代为467Ma的长沙沟-清水泉一带裂谷型层状镁铁质-超镁铁质杂岩体伴生,其成因可能是阿尔金深俯冲陆壳板片发生断离后,深部地幔物质上涌导致地壳杂砂岩熔融的产物,具有同折返岩浆作用的特点。结合以往研究,南阿尔金俯冲碰撞杂岩带中早古生代花岗岩的演化期次可初步划分为:1)约500Ma,与高压-超高压变质岩的峰期变质时代一致,形成于陆-陆碰撞造山作用过程中的陆壳相互叠置加厚阶段;2)为466~451Ma,与超高压岩石的退变质时代大致相当,形成于深俯冲陆壳断离后的伸展构造背景;3)为426~385Ma,形成于碰撞造山作用结束后的伸展减薄阶段。     

西藏驱龙矿区早侏罗世斑岩的Sr-Nd-Pb及锆石Hf同位素研究

近年的研究基本揭示,在冈底斯南缘存在一条晚三叠世-侏罗纪的花岗岩带,其成因认识有助于恢复青藏高原中生代演化历史,但却存在争议。为此,本文选择拉萨东部驱龙早侏罗世花岗斑岩开展Sr-Nd-Pb及锆石Hf同位素研究,调查岩浆源区特征,以期查明岩浆成因。分析结果显示,驱龙早侏罗世斑岩具有相对较低的⁸⁷Sr/⁸⁶Sr初始比值(0.7029~0.7050)、正的ε_Nd(t)(平均0.7)和锆石ε_Hf(t)值(2.6~8.2),表明岩浆来自新生地壳物质的部分熔融。综合对比发现,冈底斯南部晚三叠世-早侏罗世花岗岩的锆石Hf同位素在500km宽的范围内显示出由西向东亏损程度逐渐减弱、甚至变得富集的规律,表明在此类花岗岩的形成过程中,成熟地壳组分的贡献自西向东逐渐增多。这既可因南部拉萨地体基底Hf同位素组成的东西向不均一所引起,也可能因东段驱龙、米林等地花岗岩更靠近古老的拉萨微陆块所致。     

东昆仑野马泉铁矿相关花岗质岩体年代学、地球化学及Hf同位素特征

野马泉大型铁多金属矿床位于东昆仑造山带祁漫塔格地区,矿区发育大量与铁多金属成矿关系密切的花岗质岩体。LA-ICP-MS锆石U-Pb定年表明北矿带隐伏二长花岗岩、花岗闪长岩年龄分别为393±2Ma、386±1Ma;南矿带斑状石英二长闪长岩、正长花岗岩年龄为219±1Ma、213±1Ma,分别为早-中泥盆世和晚三叠世岩浆活动的产物。早-中泥盆世花岗闪长岩与二长花岗岩均为高钾钙碱性,A/CNK值（0.92~1.01）<1.1,具中等强度的负Eu异常（δEu为0.60~0.81）,明显亏损P、Nb、Ta、Ti、Sr、Ba等,富集LREE、Rb、Th、U、K等,显示了I型花岗岩的特征。晚三叠世斑状石英二长闪长岩含有少量角闪石,A/CNK值（0.88~0.95）<1,轻稀土富集,具中等负Eu异常（δEu为0.49~0.67）,富集Rb、U、Th、K等大离子亲石元素,亏损P、Nb、Ta、Ti、Sr、Ba等,具有I型花岗岩的特征;正长花岗岩高硅（SiO₂=77.20%~78.13%）、富碱（K₂O+Na₂O=7.91%~8.27%）、贫铝（Al₂O₃=11.71%~12.18%）、贫钙（CaO=0.90%~1.01%）,富集LREE、Y、Zr、Hf、Th、U、Ga等,强烈亏损Ba、Sr、P、Ti、Eu,具强烈的负Eu异常（δEu为0.08~0.13）,显示弱过铝质A型花岗岩的特征。锆石Hf同位素组成表明,早-中二叠世岩体的ε_Hf（t）为-3.3~6.2,晚三叠世岩体的ε_Hf（t）为-6.3~5.5,显示在成岩过程中有地幔组分的参与。综合研究认为,野马泉矿区早-中泥盆世、晚三叠世岩体分别形成于早古生代构造-岩浆旋回的碰撞-后碰撞阶段和晚古生代-早中生代构造-岩浆旋回的碰撞-后碰撞阶段,可能是由地幔底侵古老陆壳,幔源基性岩浆与壳源花岗质岩浆发生不同程度混合作用而生成,壳幔物质交换为区内大规模铁铜铅锌多金属矿化提供大量成矿物质。     

福建漳州角美花岗岩与闪长质包体的岩石成因及意义

本文选择福建沿海漳州地区的角美花岗岩和包体进行了锆石U-Pb年代学和Hf同位素地球化学研究。结果表明,黑云母花岗闪长岩(106.4±1.8Ma)和岩体中的闪长质包体(105.6±1.0Ma 和106.5±1.0Ma)具有相同的锆石U-Pb年龄,为同期岩浆作用的产物,它们都是高钾钙碱性系列偏铝质岩石。花岗闪长岩具有相对较为均一的锆石Hf同位素组成(ε_Hf(t)=2.2~3.7),表明其为新生地壳部分熔融的产物。闪长质包体具有更亏损的锆石Hf组成(ε_Hf(t)=0.9~5.5)。地球化学数据结合野外证据表明岩体形成过程中经历了岩浆混合作用。福建沿海地区96~106Ma岩浆作用的发育处于古太平洋板片俯冲造成的伸展背景。     

滇西昌宁-孟连带三叠纪花岗岩地球化学、年代学及其意义

癞痢头山、云岭和耿马岩体位于昌宁-孟连带的中北段,主要岩性为二长花岗岩,锆石LA-ICP-MS U-Pb定年结果表明,这三个岩体几乎同期侵位于约231Ma。这三个岩体的SiO₂含量为65.65%～67.68%,富钾(K₂O/Na₂O=2.71%～1.42%)和较低钙CaO(1.35%～2.98%),铝饱和指数(A/CNK)为1.10～1.22,富集Rb、Ba、Th、U、K、La和LREE等元素,相对亏损Nb、Ta、Ti、Zr及Hf等高场强元素。这些特征表明3个岩体属于强过铝质高钾钙碱性S型花岗岩。这三个岩体负且变化范围大的锆石ε_Hf(t)值(-26.8～-8.2)和古老的Hf同位素地壳模式年龄(1.2～2.7Ga),表明它们主要来源于古老地壳物质(如含长石和黑云母且贫粘土的杂砂屑岩)的重熔,并有不同程度的幔源物质加入。它们可能侵位于后碰撞背景,可能指示缅泰马微陆块与思茅地块的主体碰撞在232Ma之前(即晚三叠世之前)已经发生。     

浙江绍兴地区广山花岗杂岩体的锆石U-Pb年代学、锆石Hf同位素、岩石地球化学特征及其地质意义

广山花岗杂岩体主体部分由中粒碱长花岗岩和侵入其内部的细粒碱长花岗岩组成,LA-MC-ICP-MS锆石U-Pb定年显示其形成年龄分别为162.4±0.9Ma和156.3±0.7Ma,表明岩体为燕山期多期次岩浆活动产物。两期岩体为高钾钙碱性系列,A/CNK值为0.95~1.05,属准铝质-弱过铝质花岗岩类;稀土含量中等,强Eu亏损,呈略右倾的海鸥型稀土配分模式,均为A₂型花岗岩。锆石Hf同位素研究表明,ε_Hf（t）变化范围主要集中在-4.35~0之间,均为负值,二阶段模式年龄t_Hf2（Ma）变化范围主要集中于1219~1478Ma,反映其源区物质来源于中元古代地壳物质。结合前人研究成果,本文认为华南燕山早期晚阶段A型花岗岩形成于由碰撞造山向板内（非造山）环境转换的后造山拉张阶段。     

西藏聂荣微陆块早侏罗世中期花岗岩及其包体的岩浆混合成因:锆石LA-ICP-MS U-Pb定年和Hf同位素证据

西藏早侏罗世聂荣岩体中偏基性包体与酸性寄主岩的岩浆源区性质和岩石成因以及相互关系尚未得到很好约束,直接限制了对聂荣微陆块在早侏罗世特提斯构造岩浆演化中的作用的认识。为探讨这一问题,本文对采自聂荣地区的一对花岗岩及其闪长岩包体样品进行了锆石U-Pb定年和原位Hf同位素分析。寄主花岗岩的结晶年龄为185.1±1.5Ma,闪长岩包体的结晶年龄为183.6±1.1Ma,指示酸性岩浆和基性岩浆同时侵位。寄主花岗岩的锆石ε_Hf(t)值介于-17.8~-0.9,其Hf同位素地壳模式年龄变化于1.3~2.4Ga,闪长岩包体的锆石ε_Hf(t)值和Hf同位素地壳模式年龄值分别分布于-11.9~-2.9和1.4~2.0Ga,均表现出很大的变化范围。同时于~185Ma结晶的两种岩浆锆石Hf同位素的不均一性和继承锆石的出现,指示了聂荣微陆块早侏罗世中期发生了古老基底深熔或重熔的熔体和富集岩石圈地幔来源的岩浆间的混合,之后再与围岩混染的岩浆作用过程。     

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.     

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.     

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     

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。     

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.     

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.     

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。     

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.