内蒙古黄土窑孔兹岩系的锆石与金红石年龄研究

内蒙古黄土窑及其毗邻地区孔兹岩系已有一些１８００￣１９００Ｍａ的锆石Ｕ－Ｐｂ年龄数据,但因孔兹岩是高级变质的沉积岩,其锆石Ｕ－Ｐｂ年龄往往代表峰期变质年龄而不是原岩沉积年龄,因此孔兹岩系属太古宙还是古元古代长期未决。内蒙古黄土窑是晋蒙孔兹岩系的经典产地之一,对其锆石和金红石研究和年龄测试,得到孔兹岩系的碎屑锆石年龄为２３１０Ｍａ,变质成因锆石年龄为１８７３Ｍａ,金红石代表的冷却年龄为１７９３Ｍａ。     

内蒙古孔兹岩带乌拉山-大青山地区古元古代孔兹岩系年代学研究

乌拉山-大青山孔兹岩系岩石出露于华北克拉通孔兹岩带中段,是洞悉华北克拉通前寒武纪基底构造演化历史的一个重要窗口。研究区孔兹岩系岩石包括堇青石榴黑云二长片麻岩、夕线堇青石榴黑云二长片麻岩、紫苏石榴黑云片麻岩和石榴长英质粒状岩石,系统的岩相学观察显示多种典型的减压反应结构。阴极发光图像特征显示乌拉山-大青山孔兹岩系岩石均存在大量继承性碎屑锆石和变质增生锆石,其中继承性碎屑锆石形态复杂,多显示典型岩浆结晶环带,标志着源区物质主要来源于岩浆岩。变质锆石为新生的单颗粒或围绕着继承性碎屑锆石核生长,内部结构均匀,整体的Th/U比值较低。锆石LA-ICP-MS U-Pb定年结果表明,该区孔兹岩系岩石的继承性碎屑锆石的207Pb/206Pb年龄主要集中在2400~2500Ma、~2300Ma和2000~2100Ma,进而可限定其最老沉积时代应为~2000Ma,表明乌拉山-大青山孔兹岩系的原岩形成时代为古元古代中期。乌拉山-大青山孔兹岩系中典型的变质锆石记录其变质时代为1850~1950Ma,并显示~1950Ma和~1860Ma两组年龄峰。结合前人对内蒙古孔兹岩带乌拉山-大青山地区高级变质地体的变质作用、构造演化和同位素年代学的研究结果,综合判断该期变质事件与古元古代华北克拉通西部陆块内北部的阴山陆块和南部的鄂尔多斯陆块之间的俯冲-碰撞并折返抬升至地表的动力学过程有关,其中~1950Ma代表了陆-陆碰撞形成孔兹岩带的初始阶段,而~1860Ma则代表了其折返抬升的时代。     

内蒙集宁地区孔兹岩系中大理岩的形成时代——长英质片麻岩中LA-ICP-MS锆石U-Pb测年的证据

研究区位于华北克拉通西部孔兹岩带东段的集宁一带,区内的孔兹岩系由下部的榴云片麻岩组合和上部的大理岩组合组成。在大理岩组合的底部发现了数层与薄层大理岩互层的长英质片麻岩,岩相学、锆石特征和原岩恢复指示该长英质片麻岩原岩为长石砂岩。对长英质片麻岩进行LA-ICP-MS锆石U-Pb测年分析,在70个锆石颗粒中获取了72组锆石数据。其中:碎屑锆石数据中年龄最小的为(2 091±20)Ma,可以代表长英质片麻岩原岩沉积时代的下限;19组集中在1.8～1.9Ga的变质锆石207Pb/206Pb表面年龄的加权平均值为(1 852±15)Ma(MSWD=0.7),该年龄值可以代表长英质片麻岩原岩沉积时代的上限。结合前人研究成果可以认为:集宁地区孔兹岩系中大理岩形成于(2 091±20)～(1 852±15)Ma的古元古代,并在(1 852±15)Ma遭受了区域变质作用,同时也进一步说明大理岩为孔兹岩系的重要组成部分;横贯西部陆块的孔兹岩带中,孔兹岩系原岩的源区曾存在大规模的花岗质岩浆活动,但是带内各个部位有着不尽相同的物源区;孔兹岩系不是由附近太古宙岩石提供碎屑物质的原地沉积,而是古元古代晚期构造作用叠置与附近太古宙岩石产在一起的外来构造岩片。     

西昆仑康西瓦韧性走滑剪切带的两类剪切指向、形成时限及其构造意义

详细的野外观察和显微构造研究表明，西昆仑南缘康西瓦韧性走滑剪切带主要由宽7km的孔兹岩质糜棱岩组成．具有早期自西向东的右行走滑剪切、后期自东向西的左行走滑剪切的剪切应变特征。韧性剪切带孔兹岩质糜棱岩中典型造岩矿物的晶格优选方位的电子背散射（EBSD）测量结果表明，钠长石具（010）[001]或（100）[001]滑移系，矽线石具{hk0}[001]滑移系，均反映了高温（〉650℃）和中-高温（650-550℃）的应变特征。差应力作用下的变质生长与剪切所致的刚性旋转进一步增加了矽线石的组构强度。然而。石英却具形成于中温→中低温→低温环境（〈550℃）的{10T0}〈a〉→{10il}〈a〉→{0001}〈a〉3组滑移系，均指示自东向西的左行剪切指向，EBSD组构的结果与野外剪切应变的判断一致。Ar／Ar同位素年代学及锆石SHRIMPU-Pb同位素定年结果表明，右行韧性走滑作用形成于加里东期（445～428Ma），继后的左行走滑作用主要经历了3次明显的构造热事件（250Ma、203Ma和101-125Ma）。在白垩纪时期。阿尔金左行走滑断裂和康西瓦左行走滑断裂连接成一条连续的巨型（长度2200km）走滑构造带．同时康西瓦走滑断裂和铁克里克逆冲断裂之间的挤压转换域的形成制约了青藏高原西北缘塔里木南部前陆盆地的发育。     

贺兰山孔兹岩系的变质时代及其对华北克拉通西部陆块演化的制约

贺兰山孔兹岩系作为华北克拉通西部孔兹岩带的重要组成部分,其变质时代问题一直悬而未决.利用SHRIMP锆石U-Pb定年技术,对贺兰山孔兹岩系中3个代表性富铝片麻岩(石榴堇青钾长片麻岩、石榴堇青二长片麻岩与石榴黑云斜长片麻岩)样品进行了精确定年.发现这3种岩石虽处不同层位,但其碎屑锆石年龄却非常集中,各测点207Pb/206Pb年龄总体变化在2.0～2.1Ga之间,加权平均年龄则在2017～2040Ma之间.这些碎屑锆石都具有岩浆结构特征,反映当时曾存在大规模花岗质岩浆活动,所成岩体为孔兹岩系沉积提供了充足物源.另有少量大于2.5Ga的碎屑锆石(2520～2949Ma),表明本区存在太古代岩浆活动记录.本区石榴堇青二长片麻岩中发育典型的变质增生锆石,其成因很可能与黑云母的脱水熔融反应有关.利用该锆石确定贺兰山孔兹岩系的变质时代为1950±8Ma.该时代与东部大青山、乌拉山孔兹岩系变质时代相同,表明华北克拉通西部的阴山地块与鄂尔多斯地块大体是以平行的方式正面拼贴到一起的,形成了目前的孔兹岩带.     

西藏长青温池波弄贡变质带片麻岩锆石 ELA-ICP-MS U-Pb年龄及地质意义

西藏林芝至通麦一带出露大面积变质岩,变质岩中含长柱状锆石。长柱状锆石晶体形态特征、矿物包裹体、CL图像及Th/U比值在0.1～0.4之间,表明锆石主要来自火山岩,受后期变质流体改造。长柱状锆石ELA-ICP-MSU-Th-Pb年龄为(40.7±0.3)Ma,MSWD=2.35。变质流体改造边缘部分年龄和核部年龄基本一致。长柱状锆石特征及年龄表明长青温池至通麦一带片麻岩原岩为新生代含火山物质的沉积岩而不是元古宙变质基底。     

辽北地区早-中二叠世变质火山-碎屑岩年代学和地球化学特征:对华北板块北缘东段构造演化的启示SCIEI北大核心CSCD

新识别的“下二台”构造杂岩作为华北板块北缘东段分布的构造混杂岩带重要组成部分,其物质组成、形成时代和构造属性仍需进一步研究,这将为探讨华北板块北缘东段晚古生代构造演化提供重要依据。作者在“下二台”构造杂岩中识别出一套早-中二叠世变质火山-碎屑岩,其以变质碎屑岩为主,并夹变质火山岩,二者在野外产出上混杂在一起。变质火山岩原岩类型包括流纹岩、英安岩、安山岩、玄武安山岩,为一套钙碱性火山岩,属于准铝质-弱过铝质岩石。根据岩相学和地球化学特征,将其分为变质酸性火山岩和变质中-基性火山岩;二者均相对富集轻稀土元素,亏损重稀土元素,轻重稀土元素分馏明显,Eu负异常不明显,但变质酸性火山岩明显亏损P、Ti元素,结合高场强元素相关性特征,认为二者不是同一基性岩浆分异的产物。变质火山岩锆石LA-ICP-MS U-Pb同位素年龄为272~288Ma,代表其原岩结晶年龄,时代为早二叠世;变质酸性火山岩原始岩浆来源于地壳物质的部分熔融,变质中-基性火山岩原始岩浆来源于岩石圈地幔(俯冲带附近),并遭受了地壳物质的混染,二者均形成于活动大陆边缘火山弧环境。变质碎屑岩原岩恢复为泥砂质沉积岩和砂泥质沉积岩,相对亏损轻稀土元素,富集重稀土元素,轻重稀土元素分馏较明显,Eu异常不明显。两件碎屑岩样品锆石LA-ICP-MS U-Pb同位素年龄主要介于267~347Ma,推断其沉积下限为267Ma和269Ma,均为中二叠世;泥砂质沉积岩可能来源于再旋回的以长英质岩石为母岩的沉积岩,砂泥质沉积岩可能来源于再旋回的以长英质和镁铁质岩石为母岩的沉积岩,二者分别形成于活动大陆边缘大陆岛弧和大洋岛弧环境。下二台地区早-中二叠世变质火山-碎屑岩为“下二台”构造杂岩重要组成部分,它表明二叠纪时期华北板块北缘东段经历了三个构造演化阶段:早二叠世古亚洲洋加速俯冲,形成新的大陆弧阶段;中二叠世古亚洲洋持续俯冲,大陆弧和大洋弧碰撞阶段;晚二叠世陆-陆碰撞前阶段。     

中国东北地区西部~500Ma泛非期孔兹岩系地球化学特征及其地质意义

最近在兴安、额尔古纳地块均发现原岩为中基性-中酸性火山岩、陆源碎屑沉积岩及碳酸盐岩组合组成的孔兹岩系,岩石组合主要分为富铝片岩-片麻岩类和斜长角闪岩两类。岩石地球化学特征表明,富铝片岩-片麻岩类的原岩为泥岩和砂岩,主量和微量元素的分配形式接近澳大利亚后太古宙页岩(PAAS)和北美页岩(NASC),稀土元素的分布特征与NASC相似,显示轻稀土元素富集及Eu负异常,(La/Yb)N=4～17,δEu=0.32～0.79。其Cr/Ti(0.01～0.03)、Zr/Y(1.2～13.3)、Cr/Th(0.1～8.63)、Cr/Zr(0.02～0.47)、Th/U(1.5～7.7)、CIW(68～99)表明物源区以花岗岩类为主,并可能含有碎屑沉积岩。其Ceanom(-0.04～-0.01)、Ce/Ce#(0.90～1.30)表明富铝片岩-片麻岩类原岩沉积环境为亚稳定的大陆边缘沉积。斜长角闪岩原岩为玄武岩或安山质玄武岩,其富Fe2O3(1.83%～12.37%)、MgO(4.28%～7.29%)、贫SiO2(47.06%～56.13%),呈低碱性。轻稀土元素相对富集,MORB标准化的微量元素配分型式为大隆起型,Zr/Nb、Hf/Th值均类似于板内拉斑玄武岩的特征。因此,研究区孔兹岩系应形成于裂谷沉积背景。这与佳木斯地块麻山群孔兹岩系形成环境一致,表明东北地区各地块的变质基底均为孔兹岩系,其原岩均形成于裂谷沉积环境,并统一经历～500Ma泛非期变质事件,这为研究我国前寒武纪的大陆演化、再造我国东北地区的构造格局及其在Gondwana大陆重建中的位置都将具有重大的理论意义。     

西昆仑柳什塔格峰西侧火山岩的特征、时代及地质意义

在西昆仑麻扎-康西瓦-苏巴什结合带的柳什塔格一带发现了一套火山岩建造,主要由强蚀变玄武岩、绿帘阳起石岩、阳起石岩(原岩为玄武岩)组成,上覆少量深水沉积岩。火山岩的岩石地球化学特征表明其主要来源于富集地幔玄武岩浆,形成于洋岛环境,因此它是一个古结合带大洋洋壳的残留。采样作Rb-Sr等时线年龄分析,时代为震旦纪(563±48Ma),说明麻扎-康西瓦-苏巴什结合带所代表的洋盆在震旦纪就已经存在。这个发现对重新认识麻扎-康西瓦-苏巴什结合带的演化时限具有重要意义。     

中国东北地区西部约500Ma泛非期孔兹岩系中斜长角闪岩原岩恢复及其构造背景

孔兹岩系普遍发育在华北克拉通,中国东北孔兹岩系最早发现是在佳木斯地块麻山群.近期对兴安、额尔古纳地块孔兹岩系中斜长角闪岩的主量、微量、稀土元素进行了研究.斜长角闪岩的主量元素以Fe2O3(1.83%~12.37%)、MgO(4.28%~7.29%)、CaO(6.27%~10.29%)含量较高,K2O(0.56%~2.09%)、SiO2(47.06%~56.13%)含量较低为特征.微量元素Sr、Cr、Ni、Co等元素的含量较高,轻、重稀土元素分异不明显,(La/Yb)N=2~6,具有弱的负Eu异常,δEu=0.76~1.05.斜长角闪岩的原岩为玄武岩或安山质玄武岩,具有板内拉斑玄武岩的特征,因此研究区孔兹岩系形成于裂谷沉积环境.这与佳木斯地块麻山群孔兹岩系形成环境一致,表明东北地区各地块的变质基底均为孔兹岩系,其原岩均形成于裂谷沉积环境,并统一经历约500Ma泛非期变质事件.西伯利亚克拉通南缘Sayang-Baikal造山带和蒙古地体晚泛非期变质岩也经历约500Ma变质作用,因此,中亚造山带内各地块均经历约500Ma变质作用,中国东北各地块可能起源于西伯利亚克拉通南缘晚泛非期造山带的一部分.     

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.     

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。     

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。     

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.     

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。