On Palaeozoic Tectonics in the Alxa Region, Inner Mongolia, China

Two ophiolitic melange belts in the Late Carboniferous formations have been discovered recently in the Alxa region. One is in the Engger Us fault and possesses properties of oceanic crust. The other is in the Badain Jaran fault and shows properties of a back-arc basin. These two faults, together with the Yagan fault, constitute the important boundaries of tectonic units in the Alax region. The four tectonic units delimited by these faults are different in rock assemblages, metamorphism and geochemistry. They reflect the nature of tectonic environments in which they are found. The tectonic units may be traced and correlated to the eastern and western neighbouring areas. The formation and evolution process of the units and their interaction in the Alxa region may be described in terms of the evolution of the Palaeo-Mongolian Ocean and its continental margins.     

Five-Stage Model of the Palaeozoic Crustal Evolution in Xinjiang

The great majority of the Palaeozoic orogenjc belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.     

Reform of Carbonate Rock Subsurface by Crustose Lichens and Its Environmental Significance

Crustose lichens are distributed extensively in karst areas in Southern China. They can be found on the surface of carbonate rocks. Through biophysical and biochemical processes, crustose lichens reform the subsurface of carbonate rocks and in the meanwhile change their physical and chemical properties: (1) the mechanical strength decreases by 17.04° on average (up to 33.2° ); (2) the chemical solution surface area increases from 28.26% to 75.36% (lichen microholes considered only); and (3) the water-holding capacity is greatly improved. Comparative field experiments between biokarst samples underneath crustose lichens and fresh rock samples with the same composition and texture show that the corrosional rate of carbonate rocks of the former is 1.264-1.643 times higher than that of the latter. Crustose lichens are considered as an activator of the surface corrosion of carbonate rocks.     

北淮阳盆岭带的构造演化与铀成矿

北淮阳盆岭构造带是大别造山带的重要组成部分。佛子岭岩群代表了早古生代扬子地块北缘大别古岛弧弧前海盆的火山沉积建造,在加里东运动陆块对接过程中变形变质。石炭系梅山群具磨拉石建造特征。在华力西印支期陆内俯冲褶皱带的基础上,燕山期沿桐柏桐城断裂伸展北移,近东西向断陷盆地发育,形成盆岭构造景观。南侧大别山强烈隆升,铸就了现今大别山变质核杂岩构造格局。中生代岩浆活动是区内重要铀源,具有成矿潜力的地质体是响洪甸正长岩体和北带粗面质火山碎屑岩     

从地方病和环境污染性疾病看微量元素与钙的关系

从地方病和环境污染性疾病看微量元素与钙的关系李广生井玲（白求恩医科大学,长春１３００２１）关键词微量元素钙地方病环境污染性疾病我国几种主要地方病都与一定的微量元素有关,这已为大家所熟知。而值得重视的是,除了微量元素之外,它们又都在某些环节上与宏量元素...     

蔓箐沟一带石榴基性麻粒岩变质反应与矿物演化

蔓箐沟地区石榴基性麻粒岩发育多期变质反应结构。矿物组合演化可划分三个阶段：①峰期阶段（Ｍ１）,以包裹于石榴石中的Ｏｐｘ＋Ｃｐｘ±Ｈｂ＋Ｐｌ±Ｑｚ和由Ｇｔ＋Ｏｐｘ＋Ｃｐｘ±Ｈｂ＋Ｐｌ±Ｑｚ组成基质矿物组合为代表;②退变早期近等温减压阶段（Ｍ２）,形成蠕虫状后成合晶Ｏｐｘ＋Ｈｂ＋Ｐｌ±Ｍｔ;③退变晚期阶段（Ｍ３）,则形成细粒、黄绿色Ｈｂ＋中酸性Ｐｌ的较低温组合。并揭示该区石榴基性麻粒岩从中下部地壳的麻粒岩相变质,到快速抬升至中浅部地壳发生的近等温减压及晚期降温退变的复杂ｐＴ演化历史。     

十万大山地区构造演化和含油气评价

十万大山盆地地构造演化过程为：在华夏被动大陆边缘发育的弧间洋盆基础上,经东吴、印支和燕山期碰撞造山运动,形成晚古生代－中生代前陆盆地,又经过短暂的弧后陆内裂谷阶段,形成了喜马拉雅期右列张扭性盆地。共原型盆地经历了镀嵌、交错、披盖、再镶、交错、披盖、再镶嵌等四个叠置过程。其构造发展由正反转向负反转变化,以多次构造运动叠加后保留的基底部分卷入的冲断－推覆构造形成占主导,并发育典型的楔状前陆盆地、斜坡带     

实验变形煤结构演化的电子顺磁共振研究

通过１４件高温高压实验样品及其原样的电子顺磁共振研究,论述了温度、压力、应力、应变速率和应变强度等是影响变形煤化学结构演化的重要因素,但在不同的煤级中和不同的实验条件下,各因素所起的作用是不同的。变形煤ＥＰＲ参数的演化与镜质组反射率的变化密切相关,并且具有较好的规律性。说明镜质组反射率是煤化学结构演化的外在反映,是煤田构造研究中极为重要的标志物之一。     

鲁西茌平背斜构造带的演化及其古生界原生油气勘探前景

鲁西茌平背斜构造带被夹持在东侧寿张凹降和西侧监清坳陷的莘县凹陷之间,处于“凹中之隆”的有利勘探位置。该构造带的演化受西侧兰聊断裂活动的严格控制,晚三叠世,该断裂的产生接开背斜带演化的序幕。兰聊断裂的燕山期具右旋平移性质,使区内北北东向次级正断层发育,构造带基本定型。该带是相邻两凹限油气运移的主要指向地区,两凹陷内含下古生界开阔（局限）海相烃源岩和上古生界煤系源岩;带内下古生介顶部风化壳为良好储层;     

A new population of brown dwarfs

In this paper we report the first results from a survey for low-mass stars and brown dwarfs, based on a photographic stack of around 100 Schmidt plates. This survey extends photographic searches by about 2 mag, and covers an area of 25 deg². Some 30 faint objects with large R − I colours were selected for further study, and were found to have very strong molecular absorption in their spectra, but only moderately red infrared colours. Five of these stars were selected for a parallax programme; three of these were found to be at a distance of around 45 pc, implying a very low luminosity. On the basis of their luminosity alone it is clear that these stars are field brown dwarfs, and we discuss their likely evolutionary status in the context of current models of low-mass stellar evolution.