论震旦系划分与对比问题

1922年葛利普根据我国早期地质工作者的资料和要求,把“震旦系”作为一个时间地层单位古生界的第一个系提出来,而其含义过于笼统而广泛,可以装进大量的、时间范围很长的地层。1924年李四光在长江峡东区确定了一个厚不过800米,时间范围较小的“震旦系”。1934年高振西等在河北蓟县又确定了一个厚达10000米,时间长达10多亿年的大“震旦系”。     

“西康系”的时代问题

1930年譚錫畴和李春昱在四川西部(原西康省)进行地貭調查吋,曾将康定以西的一套黑灰色板岩、頁岩和砂岩,以及綠灰色板岩和砂岩的地层命名为“西康系”,并在雅江以西地区采得植物化石。化石多为Podozamites,故将“西康系”与香溪煤系对比,并将它划归侏罗紀(見譚錫畴、李春昱,1959:四川西康地貭志)。黄汲清在1945年所著的“中国主要地貭构造单位”一书中,曾列举了五点証据,否定“西康系”为侏罗紀地层,并认为主要属古生代。在1955年所出的“康藏路线地貭图”中,将“西康系”地层另命名为“札科系”,将其时代定为二迭紀。1958年甘孜地貭队将它划为石炭二迭紀,另外亦有人将它定为石炭紀。总之,这套地层的时代,长期以來是爭論不休的。     

铸石结晶过程中球体的发育特征

在火成岩、变质岩、混合岩中,“球状”岩石是不乏见的。“球状”岩石最早为伯奇(Buch)所描述,以后一直为岩石学家所注意。对“球状”岩石中球体的成因,有各种各样的解释莱维森(Leveson)。凯斯勒(Kesler)用电子探针研究了球状安山岩中球体和基质的化学成分特点,并据基思(Keith)假说,推测了球体形成温度为900-1000℃,球体生长速度为10^-6厘米/秒。     

河北易县青白口群底部燧石角砾岩成因的探讨

引言 河北易县青白口群底部燧石角砾岩(下面简称“角砾岩”)系指震旦亚界蓟县群铁岭组之上、青白口群下马岭组下部之角砾岩。它在太行山北段、中段都有分布,厚度由二、三米至五、六十米不等,在易县南约十四公里的向阳、北考一带发育很好,厚达六十米,顶底接触关系清楚,是研究“角砾岩”成因的良好地段。     

江苏宁镇山脉仑山灰岩的新认识

“仑山灰岩”标准地点在江苏南部句容县的仑山。1933年,俞建章在研究“仑山灰岩”中的头足类动物群时,曾指出:“仑山灰岩”的时代应属于早、中奥陶世。1935年,李捷等在系统研究宁镇山脉地质时,对“仑山灰岩”重新进行划分,把上部含鞘角石(Vaginoceras)动物群的灰岩归入中奥陶统,称汤山灰岩。     

海南岛南部一地全新世生物屑灰岩的成岩作用

引言研究标本由我所碳酸岩组采自海南岛南部的一个地点。在那里,沿岸覆于原生礁之上有一套由生物骨屑(主要是珊瑚)砂、砾所组成的、已被碳酸盐胶结的岩层,其厚约3米左右(图1)。此岩层一般称为“次生礁”。它是由当时原生礁盘上的生物被海浪击碎并冲带到礁盘上沉积下来的,这里属连岛砂堤沉积,它现已完全暴露地表。次生礁在它抬升过程中,下部被海蚀形成海蚀龛。     

“四川运动”之否定

“四川运动"的由来“四川运动”一名,为谭锡畴、李春昱1929-1931年在四川及原西康进行地质调查时所拟,其调查报告《四川西康地质志》文字部分于1959年出版,在这之前,李春昱等(1943,1948)”、侯德封等(1945)已引用了这一名称,但正式命名和论述是在1950年。     

长江峡东区震旦系新见

为李四光教授所建立的长江峡东区的震旦系剖面,被看作南方各地同时期地层比较的标准。黄陵背斜东翼是所分各单位--“南沱砂岩”、“南沱冰碛层”、“陡山沱统”、“灯影灰岩”的典型地区,地层工作者来到峡区经常先察勘这里的剖面。考察过东翼剖面,可上溯一程去西翼或南翼探索其侧向变化。本文就笔者1961年冬,于西翼庙河-冀家湾区、东翼莲沱的沿江地带和南翼的秋千坪地区(见图1)所进行的一些观察及点滴认识,加以阐述。     

中国南方震旦纪地层问题

关于南方震旦系的下界,主要有两种意见:(1)以澄江组或莲沱群的底板为下界;(2)往下移到包括昆阳群、板溪群及其相当岩系。主张后一意见主要根据葛利普“寒武系之下的不变质或只轻变质的沉积岩系属震旦系”的概念,及“滹沱页岩群”和“东峪灰岩”等实例,认为昆阳群和板溪群等变质并不很深,而在岩性上有其相似之点,故可以归入震旦系。经过多年来的研讨,大多数趋向于将昆阳群及其相当岩系归属于前震旦系。但问题并不就此解决。     

“泥河湾层”的古地磁学初步研究

自本世纪二十年代以来,中外的地质和古生物学者曾对桑干河谷两岸出露的所谓“泥河湾层”进行过不少工作。1954年我国地质界正式提出把“泥河湾层”划归早更新世,从此“泥河湾层”就成为我国华北地区这一时期的标准地层。     

中国西藏南部珠穆朗玛峰地区构造特征

中华人民共和国成立以来,在中国共产党的领导下,曾几次派遣科学考察队到西藏地区进行考察。在无产阶级文化大革命期间,中国科学院组织了一支科学考察队,于1966-1968年在东起亚东西到吉隆我国喜马拉雅地区大约50,000平方公里的范围内进行了考察。在地质方面,根据地层发育、变质程度和构造变形的不同考察地区可以分成南、北两条东西向构造带。南带的地层层序非常完全,而北带则只有石炭-二迭纪和中生代地层出露。在南带发现了奥陶纪、志留纪和泥盆纪化石,对中生代和新生代沉积地层进行了较详细的划分,从而初步建立了珠穆朗玛峰(以下简称珠峰)地区比较完整的地层系统。     

新疆普鲁一带下古生界地层岩石组合及构造环境

西昆仑地块是西昆仑造山带的重要组成部分，南北边界分别为康西瓦—苏巴什华力西期缝合带和库地—其曼于特加里东期缝合带。新疆普鲁一带下古生界地层，分布于西昆仑地块东部，主要由一套海相火山岩和浅海陆棚相细碎屑岩组成，并遭受了绿片岩相的变质作用。通过1：25万《于田一伯力克幅)区调工作，将新疆普鲁一带下古生界地层厘定为下古生界奥陶—志留系，认为形成的大地构造环境为大陆活动边缘。     

Recognition of Paleo-Tethys Suture Zone in eastern Myanmar

The site of final closure of Paleo-Tethys Ocean during the Triassic-Jurassic was marked by the colli-sional event between the Shan Massif and Indochina plate, in eastern Myanmar. Previous site of consumption of Paleo-Tethys is now occupied by a complex zone of suturing and deformation along Than Lwin River and in the east of it, formed by drastic tectonic evolution. It is geographically located approximately between longitudes 98E and 100E, and it extends northwards to Yunnan and southwards into West Thailand. The sigmoidal wrench struc-tures of suture zone is situated in the east of step-like structures of Shan Massif, and the western boundary of the suture zone must be immediately on the west side of Than Lwin River and the eastern boundary is near the east border of Myanmar. The area is largely covered by younger rocks of Paleozoic and Mesozoic age. The Upper Pa-leozoic units of Carboniferous to Permian comprise limestone and dolomite of the Plateau Limestone overlying unconformably the Lower Paleozoic rocks. Metasedimentary rocks of the Carboniferous and their metamorphic equivalents and the flysch-like Triassic-Jurassic units are found as folded and thrusted beds in the area. Large complex of granitic rocks of Late Triassic are also found. Metavolcanics, gabbro and a large number of chromite occur along with these units. A preliminary delineation of a suture zone as the site of closure of Paleo-Tethys Ocean in Myanmar territory is made for the first time and this zone is believed to be a tectonic linkage between Changning-Menglian belt of West China and Inthanon Zone of West Thailand.     

Tectonics of the ophiolite belt from Naga Hills and Andaman Islands,India

The ophiolitic rocks of Naga Hills-Andaman belt occur as rootless slices, gently dipping over the Paleogene flyschoid sediments, the presence of blue-schists in ophiolite melange indicates an involvement of the subduction process. Subduction was initiated prior to mid-Eocene as proved by the contemporaneous lower age limit of ophiolite-derived cover sediment as against the accreted ophiolites and olistostromal trench sediment. During the late Oligocene terminal collision between the Indian and Sino-Burmese blocks, basement slivers from the Sino-Burmese block, accreted ophiolites and trench sediments from the subduction zone were thrust westward as nappe and emplaced over the down-going Indian plate. The geometry of the ophiolites and the presence of a narrow negative gravity anomaly flanking their map extent, run counter to the conventional view that the Naga-Andaman belt marks the location of the suture. The root-zone of the ophiolite nappe representing the suture is marked by a partially-exposed eastern ophiolite belt of the same age and gravity-high zone, passing through central Burma-Sumatra-Java. The ophiolites of the Andaman and Naga Hills are also conventionally linked with the subduction activity, west of Andaman islands. This activity began only in late Miocene, much later than onland emplacement of the ophiolites; it further developed west of the suture in its southern part. Post-collisional northward movement of the Indian plate subparallel to the suture, also developed leaky dextral transcurrent faults close to the suture and caused Neogene-Quatemary volcanism in central Burma and elsewhere.     

ZEDONG TERRANE, A MID CRETACEOUS INTRA-OCEANIC ARC, SOUTH TIBET

ZEDONG TERRANE, A MID CRETACEOUS INTRA-OCEANIC ARC, SOUTH TIBET     

雅鲁藏布江蛇绿岩的形成与日喀则弧前盆地沉积演化

雅鲁藏布江蛇绿岩被时代连续的日喀则群沉积覆盖及其形成时代(120-110Ma)与冈底斯弧开始发育的时代(115-100Ma)十分相近的事实使人们有理由提出:雅鲁藏布江蛇绿岩是否代表着印度板块与拉萨地块间的特提斯-喜玛拉雅洋残迹的疑问。根据近期的研究,笔者认为雅鲁藏布江蛇绿岩不是形成于三叠纪的特提斯-喜玛拉雅洋的残迹,而是特提斯-喜玛拉雅洋向拉萨地块俯冲的初期(阿普第-阿尔必期),由俯冲作用在冈底斯弧前地区引发的海底扩张作用形成的一种俯冲带上叠型蛇绿岩(supra-subduction zone ophiolites).至森诺曼期,弧前海底扩张作用停止,雅鲁藏布江蛇绿岩开始向南仰冲,在其南侧形成增生杂岩楔。仰起的蛇绿岩开始向日喀则弧前盆地提供蛇绿质碎屑,如冲堆组。森诺曼期-土仑期,盆地接受了一套深水复理石沉积,沉积物源部分来自南部边缘脊的蛇绿质碎屑,而大部分则来自北侧的弧火山岩和岩浆岩碎屑。森诺期-路坦丁期,盆地逐渐变浅,接受了浅海-滨海沉积,物源均来自北部的岩浆弧。至始新世末期,发育在盆地南侧的增生杂岩楔与印度板块发生碰撞,日喀则弧前盆地闭合。     

Two stages of granulite facies metamorphism in the eastern Himalayan syntaxis,south Tibet: petrology,zircon geochronology and implications for the subduction of Neo‐Tethys and the Indian continent beneath Asia

The eastern Himalayan syntaxis in southeastern Tibet consists of the Lhasa terrane, High Himalayan rocks and Indus‐Tsangpo suture zone. The Lhasa terrane constitutes the hangingwall of a subduction zone, whereas the High Himalayan rocks represent the subducted Indian continent. Our petrological and geochronological data reveal that the Lhasa terrane has undergone two stages of medium‐P metamorphism: an early granulite facies event at c. 90 Ma and a late amphibolite facies event at 36–33 Ma. However, the High Himalayan rocks experienced only a single high‐P granulite facies metamorphic event at 37–32 Ma. It is inferred that the Late Cretaceous (c. 90 Ma) medium‐P metamorphism of the southern Lhasa terrane resulted from a northward subduction of the Neo‐Tethyan ocean, and that the Oligocene (37–32 Ma) high‐P (1.8–1.4 GPa) rocks of the High Himalayan and coeval medium‐P (0.8–1.1 GPa) rocks of the Lhasa terrane represent paired metamorphic belts that resulted from the northward subduction of the Indian continent beneath Asia. Our results provide robust constraints on the Mesozoic and Cenozoic tectonic evolution of south Tibet.     

Kinematics and dynamics of the Namche Barwa Syntaxis, eastern Himalaya: Constraints from deformation, fabrics and geochronology

Field observations, deformation and fabric analyses, and precise age data acquired by zircon SHRIMP, LA-ICP-MS U-Pb and ⁴⁰Ar-³⁹Ar dating methods have yielded new constraints on the kinematics and dynamics of the Namche Barwa Syntaxis (NBS) which is the eastern corner of the Himalaya. A two-stage model has been established to explain the formation and evolution of the NBS. The northward indentation of the Indian plate beneath the Lhasa terrane began at 55-40 Ma, and crustal materials at this corner were subducted to depths > 70 km where they experienced HP (UHP?) metamorphism. Since 40 Ma, large-scale, right-lateral strike-slip along the Sagaing fault has accommodated the rapid northward movement of the eastern Indian plate corner with respect to the Indochina block. This caused significant and progressive bending of the Indus-Yarlung suture zone (IYSZ) such that it became the Dongjiu-Milin left-lateral, strike-slip, shear zone (DMSZ) in the west and the Aniqiao-Motuo right-lateral, strike-slip, shear zone (AMSZ) in the east. Both zones underwent strong mylonitization. Meanwhile, the HP (UHP?) metamorphic rocks were rapidly exhumed, first into the deep crust at 22-18 Ma and then to the shallow crust to form an antiformal dome at 6-2 Ma. Our model provides new insight into the processes of post-collisional crustal thickening related to the formation of the Himalayan orogenic belt.     

北京西山——一个早中生代拗拉谷的一部分

华北地台北部的燕辽带在晚元古代时为一拗陷带,蓟县地区的整个层系厚度在10,000m以上。中生代时发生强烈的岩浆活动和形变。其构造性质与地台的含义并不相符,前人对该区有沉降带、台褶带等提法。     

青藏高原北部可可西里狮头山含硬玉岩类的基本特征及地质意义

描述了可可西里山南狮头山含硬玉岩类的岩石学、矿物学特征。含硬玉岩类的原岩为辉长岩，围岩为石炭—二叠系。由于变质作用不彻底，保留有原岩的矿物组合。典型的高压变质矿物组合为：钠长石 硬玉 霓石 蓝闪石 绿帘石 绿泥石。硬玉SiO2、FeO偏低，Al2O3、Na2O明显偏高，变质矿物组合中以富钠矿物为主，缺少石英，与国内外含硬玉岩类的原岩成分、变质矿物组合均不相同，是一种新的高压低温硬玉岩类。狮头山高压变质带向西延至若拉岗日、大横山一带，与北侧的西金乌兰—金沙江板块缝合带(西段)平行产出，以此推测缝合带南侧的羌北—昌都板块向北消减于巴颜喀拉板块之下。