陕南硒中毒区地层时代的厘定

本文通过对南秦岭大巴山的紫阳县典型硒中毒区双安乡闹热村所在地及邻区分布的基岩的岩石类型、岩相和层序等进行研究和分析，发现紫阳县双安乡闹热村硒中毒区出露的地层主要为晚震旦世和早寒武世鲁家坪组下部厚约40余米的富硒高硫黄铁矿化黑色碳质硅质板岩和黄铁矿化火山凝灰岩，该层位可以和云南下寒武统筇竹寺组下部和贵州牛蹄塘组下部的地层对比。该层岩石含硒量为10～56mg／kg，平均为32mg／kg左右，是大巴山地区所有地层和岩石中含硒量最高的。该硒中毒区主要几块高硒田块(土壤含硒量为16～36mg／kg)下部分布的就是这套高硒的早寒武世黄铁矿化黑色碳质硅质板岩和黄铁矿化火山凝灰岩地层。     

东天山康古尔金矿成矿晚阶段地幔流体参与成矿作用的碳氢氧同位素证据

康古尔金矿位于塔里木板块北部被动大陆边缘阿奇山-雅满苏裂谷带之北侧,是一个典型的韧性剪切带型(造山型)金矿,成矿作用表现为含金石英脉和石英碳酸盐脉两个阶段。本文对矿石中的碳酸盐脉和矿床周围地层中的碳酸盐岩进行了C、H、O同位素测试。通过研究初步认为:矿床周围地层石炭纪干墩组和雅满苏组中大理岩的C、O同位素组成与世界上其他地区的海相碳酸盐基本相同,以富~(13)C和~(18)O为特征,明显有别于矿石中碳酸盐脉;后者的C、H、O同位素组成与地幔多相体系中的原始碳酸岩基本相似,暗示在康古尔金矿成矿晚阶段有地幔流体参与成矿作用。     

Free Radicals in Organic Matter for Thermal History Reconstruction of Carbonate Succession

Geothermometer is one of the most useful methods to reconstruct the thermal history of sedimentary basins. This paper introduces the application of free radicals concentration of organic matter as a thermal indicator in the thermal history reconstruction of carbonate succession, based on anhydrous thermal simulation results of type I and H1 kerogen. A series of free radicals data are obtained under thermal simulation of different heating temperatures and times, and quantitative modds between free radical concentration （Ng） of organic matter and time-temperature index （TTI） for types I and type H1 kerogen are also obtained. This Ng.TTI relation was used to model the Ordovician thermal gradients of Well TZ12 in the Tarim Basin. The modeling result is corresponding to the results obtained by apatite fission track data and published data. This new method of thermal history reconstruction will be benefit to the hydrocarbon generation and accumulation study and resource assessment of carbonate succession.     

Pb Isotope Study of Some Nonferrous Metallic Deposits in China

Based on Pb-Pb isochron data of more than 40 Precambrian polymetallic deposits, the authors consider that there are four mineralization periods for the Precambrian copper deposits in China, and the major copper deposits were formed at about 1800 Ma; there are three mineralization periods for gold deposits formed from Archaean to Proterozoic. By studying hundreds of lead isotope data from some Mesozoic continental subvolcanic Cu and Ag polymetallic deposits and fine-disseminated gold deposits, the authors found that the calculation based on the lead single-stage evolution model or two-stage evolution model cannot give the true ore-forming ages but can provide more information about mineralization and material sources of the deposits.     

金的矿源层讨论

岩层初始含矿丰度包括易释出和难释出两部分矿质,这与现今岩样所测得现存丰度截然有别;特殊的(火山)沉积建造是判别矿源层的综合标志,含矿丰度只是其中一个重要标志,其对比标准以区域背景值更为现实可行。     

MML-EM方法及其在化探数据混合分布中的应用

概率图法在筛分混合分布的问题上,只能对混合分布的各项参数作出粗略的估计.为了解决这一问题,引入了MML-EM法.模拟研究表明,在混合分布参数估计上,该方法比概率图法有更高的精度.以江西大吉山钨矿石英脉原生晕数据为例,经过该方法的筛分,得到钨、钽和铌的含量服从由2个子分布组成的混合对数正态分布,即双峰分布.结合前人的地质研究,可以初步得出结论:钨的高值总体代表了岩浆期后热液成矿期的热液充填石英脉型矿化,低值总体可能代表其他成矿期的事件,其中高值部分可能构成岩浆晚期浸染型的弱钨矿化.钽和铌的高值总体代表岩浆晚期的浸染型富矿化,低值总体代表其他成矿期的叠加矿化.该方法为化探数据中混合分布的筛分以及解释多地质成因总体提供了一种良好的定量化工具.      

Seismic Features of the Crust-Upper Mantle Beneath Karamay-Kuqa, Xinjiang

1. IntoductionSponsored by the National 305 Program, China, a teleseismic experiment was performed jointly by the Chinese Academy of Geological Sciences and the French Scientific Research Center in Tian Shan area from June 1997 to February 1998. The array was mostly deployed along the main road, starting from Karamay in the north to Kuqa in the south. Geologically, the 700 km-long profile covers the Junggar basin, the Tian Shan Mts., the Bo-A Fault and the Korla Fault, ending in nort…     

Isotope geochronological study of Late Palaeozoic granitic rocks in the Nanling Region,South China

Fourty-four isotopic ages have been determined by K-Ar and U-Th-Pb methods for Late Palaeozoic granitic rocks in the Nanling Region, South China. All dating values vary within the range of 231–348 m.y. From the obtained dates, further evidence has been found that there do exist Late Palaeozoic granitic rocks, which can be subdivided into Late Devonian and Permian granitic rocks. Within a Late Devonian terrain, there is a granitic pluton, namely granodiorite with a zircon U-Th-Pb age of 348 m.y., while ten granitic plutons have been recognized within a Permian terrain where granites are predominant, yielding biotite K-Ar ages of 236–289 m.y. (λ _β =4.72×10^?10yr.^?1,λ _K=5.57×10^?11yr.^?1) and zircon U-Th-Pb ages ranging from 231 to 280 m.y., respectively. It is obvious from the dates that intrusive activity of granitic magma extensively took place in the Nanling Region during Late Palaeozoic, although no records of orogenie movements have been found, indicating that the faults are the main factor controlling the activity of granitic magma, whereas the orogenic movements are not the only prerequisite for the formation of granitic magma and the intrusive activity.     

辽北凡河群时代探讨兼论殷屯组的时代

辽宁北部地区凡河群源于斋藤林次的凡河系,其时代归属尚有争议。目前多数人将凡河群与蓟县地区的中、上元古界对比;殷屯组的时代则以暂置震且纪居主导地位。笔者稂据凡河群地史演化、所处大地构造位置、变质作用、含海相火山岩夹层、同位素年龄资料等综合因素分析;认为凡河群的时代以归属长城纪为宜,殷屯组时代归属蓟县纪较合适。     

新特提斯演化的热点与洋脊相互作用:西藏南部晚侏罗世-早白垩世岩浆作用推论

雅鲁藏布蛇绿混杂岩代表了新特提斯洋盆闭合的地表残余.本文在测试数据基础上,综合分析了目前雅鲁藏布江蛇绿混杂岩研究中取得的比较可信的晚侏罗世.早白垩世玄武岩的地球化学数据,并对其进行了较为详细的区域对比分析以讨论涉及新特提斯演化的地球动力学过程.结果表明:(1)雅鲁藏布蛇绿混杂岩带吉定洞拉村玄武岩、错拉山口北部玄武岩为大洋中脊玄武岩(MORB)型,错拉山口南部玄武岩为洋岛玄武岩(OIB)型,萨嘎桑单林玄武岩既包括OIB型,又包括MORB型;(2)在东西延伸约1500km的雅鲁藏布蛇绿混杂岩带中,至少可能存在OIB、MORB(包括N-MORB、E-MORB)和岛弧玄武岩LAB三种类型的晚侏罗世-早白垩世玄武岩.不活动的高场强元素比值(如Nb/Y,Zr/Y等)指示雅鲁藏布蛇绿混杂岩带中部仁布、杯玛让、吉定洞拉村和错拉山口北部地区以及中西部萨嘎地区的MORB型玄武岩中的亏损组分很可能来源于深部亏损的地幔柱源区.微量元素地球化学模拟表明,雅鲁藏布蛇绿混杂岩带OIB型玄武岩可能主要来源于石榴石二辉橄榄岩源区中等程度(10%～20%)的部分熔融,而MORB型玄武岩主要来源于尖晶石二辉橄榄岩源区中等程度(7%～25%)的部分熔融,IAB型玄武岩所代表的源区熔融深度以中部较浅而东西两端较深为特点,其中中部得几、杯玛让、吉定等地的lAB很可能与尖晶石二辉橄榄岩源区的部分熔融有关,而东部和西部达几翁IAB的熔融源区可能残留有石榴石.结合该带报道的He同位素数据和矿物学观察,以及在喜马拉雅带新获得的古地磁数据,可以认为热点与洋脊的相互作用是对晚侏罗世-早白垩世新特提斯演化的一种很可能的地球动力学解释.需要强调,虽然该模式可以较好地解释目前在藏南观察到的晚侏罗世-早白垩世岩浆作用特点和性质,但因资料有限,还需要做许多非常细致的工作来证实或否定.