作为运动学指示的碎斑体系

糜棱岩中相对坚硬矿物的碎斑通常具有由重结晶物质的尾部所决定的内部单斜对称性。碎斑及其尾部称为‘碎斑体系’。它可以作为有价值的旋涡方向指示物。根据尾部的几何特征可把碎斑体系分为σ-型和δ-型。σ-型有楔形重结晶的尾部,其中线分布在平行于尾部包含体系对称轴的参照面的两侧对边上。σ-型进一步分为σa-型,这种碎斑在相对均匀的基质中是孤零的;和σb-型,其碎斑是与基质中的剪切带叶理相伴出现。典型的σ-型有细长的重结晶的尾部,它的中线横穿邻近碎斑的参照面。接近碎斑的基质物质经常出现湾形,尾部还呈现了明显弯曲。糜棱岩中碎斑体系是与碎斑相邻其质中非共轴流动使碎斑外壳中相对弱功力重结晶颗粒集合体改变其形状而发育起来的。这一习性已在剪切箱的实验中被模拟。利用嵌入硅质油灰的刚性圆柱体周围的波动标志线进行简单剪切实验。这个实验是在不同变形速率条件下逐渐减小刚柱直径去模拟重结晶速率(R)相对变形速率(γ)的变化。R/γ比值决定发育何种碎斑体系的最重要因素之一。高R/γ值时,从碎斑流开的重结晶物质不断地被新生颗粒听补充,同时发育了楔形的σa-型尾部。低R/γ值时,相对地没有多少新生颗粒补充到变细的尾部。由于碎斑的旋转运动产生的牵引作用使尾部偏转。此外,大多数碎斑系统在低剪切应变时是σa-型或不显单斜对称,而σ-型仅在剪切应变中发育。复杂的碎斑体系以两个世代的尾部为特征。可在很多所研究的天然剪切带中见到,在模拟剪切带中由于不稳定的R/γ,也可以形成。用单个的σa-型和σ-型碎斑体系做为旋涡方向的指示物的使用条件是:体系应有一个单斜对称;基质颗粒粒度应小于碎斑的粒度;基质组构是均匀的;变形史简单以及在垂直于糜棱岩中推测的总旋涡向量的切面上进行。     

运用电子探针和质子探针分析确定Izok湖块状硫化物矿床中含银黄铜矿为银的主要来源

对于硫化物矿床中微量元素的深入研究已有100多年的历史了。Fleischer(1955)把已获得的关于方铅矿、闪锌矿、纤锌矿、黄铜矿、白铁矿、磁黄铁矿以及砷黄铁矿等硫化物的可资利用的大量资料进行了总结。他把8种测定结果(含量为10—2300ppm)的黄铜矿含银总量制成表。Hawly等(1961)测定了许多铜矿床样品中微量元素的含量及某金矿山的一个样品中微量元素的含量。他们获得铜矿床中银的平均品位为91—310ppm;金矿山黄铜矿中银的品位为165ppm。在对加拿大不列颠哥伦比亚Rossland地区的矿床研究中,Thorpe(1967)总结了黄铜矿中贵金属含量的资料,大部分是关于金的含量,少部分是银     

地震危险性分析中贝叶斯模型的意义及其应用

本文重点讨论贝叶斯模型的推理结构及其在地震危险性分析中的意义。当历史记录较少时,用定值参数的常用模型(如,用确定平均发生率的泊松模型)不能给出危险性的合理估计。贝叶斯模型考虑了参数本身的不确定性,且能灵活地结合来自地震地质的信息,给出逻辑上一致的危险性估计。本文还提供了把地震地质证据和统计资料结合起来的具体力法,并附有简单列子作为说明。     

南部非洲的花岗片麻岩—绿岩地盾

前言构成南部非洲地盾一部分的早前寒武纪(太古宙)花岗岩一绿岩层,是地球表面上已知最老的地层之一。在博次瓦纳东部、南非(阿扎尼亚)东北部以及津巴布韦,该地盾是由林波波活动带分割的两个克拉通、即卡普瓦尔和罗德西亚克拉通组成。在时间上从27—35亿年(或甚至更老)的地区,是作为30亿年前在大陆边缘条件下形成的一种独特的克拉通盆地基底。     

关于“早些相对于晚些”发布地震预报的讨论

文章介绍了日本地震学会1982年秋季大会简况,会上共宣读241篇论文,包括八个方面;本文重点介绍了有关地震活动与地震预报研究两方面的内容。     

陆地卫星数字图象分析在区域地质凋查中的应用

矿产资源局(BMR)的地质学家们在最初获得陆地卫星影象之后即开始尝试在野外地质研究中将它作为航摄片的辅助手段使用。用传统航片解译方法来解译陆地卫星影象,其效果取决于影象质量和研究对象的特征。BMR野外研究中会遇到各种各样的地质问题,并表现为各种各样的地貌环境特征,诸如巴布亚新几内亚和伊里安查亚的森林,澳大利亚内陆的沙漠以及南极冰盖。     

昆士兰州艾萨山镇铜矿石形成物中先存硫化物的作用

昆士兰州西北部的艾萨山镇硫化物矿床,产在已变质成低级绿片岩相的,并在热液活动影响下发生不同程度蚀变的粉砂岩—页岩层序中。形成铅—锌—银矿体的方铅矿和闪锌矿以及细粒黄铁矿,与这些沉积物成互层;而黄铜矿矿化看来已迭加于其上。在最大的矿体-1100矿体中,有一个高品位的块状黄铜矿核,产在黄铁矿矿化强烈的同一层位上;这个核随着黄铁矿的富集而缩小。钴矿物与黄铜矿矿石密切伴生,并表现出与上述情况相同的关系。黄铜矿与黄铁矿的硫同位素值的变化范围相同,表明硫的来源是共同的。黄铁矿层中硫的丰度,并不随着铜品位的增长而增加。这些因素证实组成黄铜矿和富钴硫化物所必需的硫,来自先存地层层序的观点。硫的这种来源,控制了铜、二氧化硅和钴从矿化溶液中的沉积,并为解释铜与铅—锌—银矿石的空间关系提供了联系。     

Clostridium perfringens as a potential indicator for the presence of sewage solids in marine sediments

Marine sediment cores collected from several depths of water and distances from a California sewage outfall were tested to see if sediments influenced by sewage solids were a reservoir of enteric pathogens, and if concentrations of indicator bacteria were related to the presence of sewage solids. Vertical distributions of microorganisms in marine sediments were determined; there was a decrease of indicator bacteria with increasing sediment depth. Aeromonas was randomly isolated, but none of the enteric bacterial pathogens or viruses were detected. While classic indicator bacteria were of little value in predicting the presence of pathogens, or relative amounts of sewage solids, Clostridium perfringens may be a suitable indicator. Clostridium perfringens concentrations were not related to the presence of pathogens in sediments.     

The main issues affecting coasts of the Indian and western Pacific Oceans: a meta-analysis from Seas at the Millennium

A review of the world oceans in three volumes by 365 scientists, provides scope for several ‘meta-analyses' of the main problems affecting over 100 areas in the year 2000. This article summarises the main issues affecting a sub-set of the reviewed areas, covering Asian, African and Arabian countries dealt with in Volume 2, which included over 50 articles. From all issues raised, assessment is made of the nature of the major ones, including evaluation of reasons why so many of them remain important issues after so much attention to them. These include long standing problems, several problems more newly flagged as becoming particularly important, the issue of global warming and no less than three related issues connected with fishing and over exploitation. One or two issues such as industrial pollution and sewage, previously considered of almost universal concern, almost traditional pollution issues even, continue to feature strongly for some countries, but while these were almost always referred to in Seas chapters, by and large these categories appear not to be the most pressing of issues today, except in localized areas (albeit areas where huge numbers of people live). Perhaps other issues have simply taken over. They are excluded from this article.