北京及邻区微震活动的初步分析

通过对北京遥测地震台网近年来记录到的北京及邻区地震的震中分布,地震活动频度及能量释放强度的分析,得到本区地震活动在时间分布上具有“聚堆性”。在年发震频度,地震强度和能释放方面均具有双峰值特征,并且具有较好的一致性和同步性,在空间分布上具有条带特征,且形成北东～南西和北西～南东的两条相互交汇的条带。又通过统计分析得到本区发震概率最大的时间段是每年的１０月前后,而地震主要发生在北西～南东带上。     

皖南变质岩中的疑源类、孢粉化石组合及其地质意义

皖南变质岩区地层原被认为属江南古陆的一部分,时代定为中、晚元古代。本文根据其中所含的Asperatopsophosphaera?sp.,Trachysphaeridium sp.,Nucellosphaeridium sp.,Lophosphaeridium sp.,Leiosphaeridia sp.,Baltisphaeridium spp.,Micrhystridium spp.和scolecodonts等疑源类和其它微体化石及笔者等以前发现的Lingulacea总面貌反映的时代,判断其中部分变质地层的时代应为晚元古代—早古生代和早古生代。同时还根据Crassispora sp.,Kraeuselisporites sp.和Lueckisporites ef.virkkiae Potonie ＆ Klaus,Triquitritessp.等孢粉化石组合面貌反映的时代,推断其中尚有一部分为晚古生代地层。因此认为本区是一个从晚元古代—早古生代开始到中生代结束的碰撞型造山带,而不是一个古陆。     

热液脉动与岩浆涌动控制机理浅论

热液脉动与岩浆涌动的控制机理,是基础地质理论所涉及的两个重要议题。本文首先对当今流行的构造控制机理提出了质疑,其后借助＂间歇喷泉＂原理和＂吹气球＂机制,分别对热浪的脉动和岩浆的涌动进行了必要的探讨。     

首都减灾圈的思考与建议

首都减灾圈,系首都减轻自然灾害预测防治圈。1991年12月20—21日在北京召开了《首都圈自然灾害及其减灾对策研讨会》。本文根据这次会议所提供的材料,在从整体上实现减灾的思想指导下,就首都减灾圈的“成灾背景”、“首都减灾圈的组成”、“首都减灾圈的灾害预测与防治状况”、“首都减灾圈的灾害关联性分析”、“首都减灾圈的减灾实效预估”和“首都减灾圈的减灾对策与实施”等六个带有共同性的问题,进行了讨论。供制定首都圈减灾方案时参考。     

福建石炭纪岩相古地理分析

笔者总结了福建省石炭纪生物地层与岩石地层的研究成果,提出了生物地层与岩石地层的划分对比。在详尽的相分析基础上对该纪地层进行了相系、相、亚相及微相的划分,并按“优势相”的原则分期编制了林地期、黄龙期及船山期的岩相古地理图。笔者采用“相、层、位”控矿观点对石炭纪的矿产成因及成矿规律作了探讨。     

四川木里耳泽岩溶型金矿床形成条件和成矿机制

四川本里耳泽金-菱铁矿建造矿床,赋存于上二叠统海相碳酸盐岩层中,矿化受古岩溶的严格控制,组成矿石的基本矿物为菱铁矿,金不均匀地分布于菱铁矿矿体内。成矿溶液来自加热的循环地下水。成矿过程分为早阶段和中-晚阶段。成矿温度为156-210℃,成矿深度小于1km.成矿物质主要来自地层。成矿热液呈碱性和弱还原性,贫硫,含中等盐度。矿床形成时的地质构造环境较稳定。这是我国仅见的一种特殊金矿类型。     

“地理学公理”质疑——与楚义芳同志商榷

本文运用地理学和物理学的规律进行论证,认为楚义芳同志在《地理学的逻辑方法与基本法则》一文中提出的“地理学公理”不能成立。并在此基础上进一步阐明一个公理体系不适合于地理学,而经验假设则是绝对必要的。     

Sulfur Isotope Fractionation in Magmatic Systems：Models of Rayleigh Distillation and Selective Flux

The effect of Rayleigh distillation by outgassing of SO2 and H2S on the isotopic composition of sulfur remaining in silicate melts is quantitatively modelled.A threshold mole fraction of sulfur in sulfide component of the melts is reckoned to be of critical importance in shifting the δ^34S of the melts mith respect to the original magmas.The partial equilibrium fractionation in a magmatic system is evaluated by assuming that a non-equilibrium flux of sulfur occurs between magmatic volatiles and the melts,while an equilibrium fractionation is approached between sulfate and sulfide within the melts.The results show that under high fo2 conditions,the sulfate/sulfide ratio in a melt entds to increase,and the δ^34S value of sulfur in a solidified rock might then be shifted in the positive direction.This may either be due to Rayleigh outgassing in case the mole fraction of sulfide is less than the threshold,or due to a unidirectional increase in δ^34S value of the sulfate with decreaing temperature,Conversely,at low fo2,the sulfate/sulfide ratio tends to decrease and the δ^34S value of total sulfur could be driven in the negative direction,either because of the Rayleigh outgassing in case the mole fraction of sulfide is greater than the threshold,or because of a unidirectional decrease inδ^34S value of the sulfide.To establish isotopic equilibrium between sulfate and sulfide,the HM,QFM or WM buffers in the magmatic system are suggested to provide the redox couple that could simultaneously reduce the sulfate and oxidize the sulfide.CaO present in the silicatte Melts is also called upon to participate in the chemical equilibrium between sulfate and sulfide,Consequently,the δ^34S value of an igneous rock could considerably deviate from that of its original magma due to the influence of oxygen fugacity and temperature at the time of magma solidification.     

Carbon-oxygen isotopic covariation in hydrothermal calcite during degassing of CO2

The effect of the outgassing of CO₂ from a hydrothermal fluid on the C- and O-isotopic compositions of calcite, which is precipitated from this fluid, is quantitatively modelled in terms of batch and Rayleigh distillation equations. Both CO₂ degassing and calcite precipitation are considered to be the removal mechanisms for dissolved carbon species from the fluid. Combined degassing-precipitation models are then developed by taking H₂CO₃ and HCO ₃ ^– , respectively, as the dominant dissolved carbon species. A positive correlation array between ¹³C and ¹³O values of calcite can be yielded by the precipitation of calcite from a H₂CO ₃ ^– -dominant fluid, accompanied by a progressive decrease in temperature during CO₂ degassing, whereas calcite precipitated from a HCO ₃ ^– -dominant fluid under the same conditions tends to display much smaller variation in ¹³C values than in ¹⁸O values. The combined processes of CO₂ degassing and calcite precipitation result in lowering the ¹³C value of calcites with respect to those precipitated in a closed system simply due to temperature effect. Carbon and oxygen isotopic data for calcite from the Kushikino gold-mining area in Japan illustrate the application of quantitative modelling, and degassing of CO₂ is suggested as a more likely cause for the precipitation of the calcite and quartz in this mining area.