西藏措勤县敌布错地区“下拉组”中发现晚三叠世诺利期高舟牙形石

首次在措勤县江让乡敌布错地区“下拉组”中发现了晚三叠世诺利阶的高舟牙形石。这表明在该地区下拉组中至少有一部分是以前没有被识别出的晚三叠世诺利阶地层,这套地层暂时命名为江让组。更重要的是,剖面中江让组之上舍植物化石的碎屑岩地层可能是区域上广泛分布的敌布错组。江让组高舟牙形石的发现对敌布错组及其所含植物群的时代提出了质疑。     

An examination of the presence and topography of the D″ discontinuity under the Russia–Kazakhstan border region using seismic waveform data from a deep earthquake in Spain

The D″ layer, which is located atop the core–mantle boundary, has long been an area of focus for global seismology studies. A widely used approach to study the discontinuities in the D″ layer involves the use of the SdS phases between the S and ScS phases, which requires that certain stringent conditions be satisfied with respect to an epicentral distance and earthquake depth. Therefore, this approach is only practical for investigating the presence and topography of velocity interfaces in certain local regions around the world. The Russia–Kazakhstan border region has been a “blind spot” with respect to this detection method. The seismic network deployed in the northeastern margin of the Tibetan Plateau has recorded relatively clear SdS phases for the M _S 6.3 earthquake that occurred in Spain on April 11, 2010, allowing this blind spot to be studied. This paper compares the observed waveforms and synthetics and uses the travel times of the relevant phases to obtain a D″ discontinuity depth between 2,610 and 2,740 km in the examined area. This study provides the first results regarding the depth of the D″ layer discontinuity for this region and represents an important addition to the global studies of the D″ layer.     

Sedimentology and Chronology of Paleogene Coarse Clastic Rocks in East-Central Tibet and Their Relationship to Early Tectonic Uplift

A systematic sedimentological and chronological study of typical Paleogene basins in eastcentral Tibet suggests that the depositional characteristics of extensively developed huge-bedded, purplish-red coarse clastic rocks formed in a tectonic setting of regional thrusting and strike-slipping represent a typical dry and hot subaerial alluvial fan environment formed in a proximal and rapidaccumulating sediment body in debris flows and a fan-surface braided river. Combining results from basin-fill sequences, sequences of coarse clastic rocks, fauna and sporo-pollen associations and thermochronological data, it is conduded that the coarse clastic rocks formed in the period of 54.2- 24.1 Ma, nearly coeval with the formation of Paleogene basins in the northern （Nangqen-Yushu thrust belt）, middle （Batang-Lijiang fault belt）, and disintegration of large basins in the southern （LanpingSimao fold belt） segments of Tibet. The widespread massive-bedded coarse clastic rocks, fold thrusting and strike-slip, thrust shortening, and igneous activities in the Paleogene basins of eastcentral Tibet indicate that an early diachronous tectonic uplift might have occurred in the Tibetan Plateau from Middle Eocene to Oligocene, related to the initial stage of collision of the Indian and Asian plates.     

西藏自治区乃东县劣布铜矿区的矿床地质特征及找矿远景分析

在充分收集区内以往地质资料的基础上,对劣布铜矿区的地质特征、地球物理特征及矿体特征进行了初步的总结,并对其找矿远景进行简要分析,如果得以进一步证实,将对区内的地质矿产勘查具借鉴和指导意义.     

钾玄岩系列:藏东玉龙铜矿带含矿斑岩元素地球化学特征

西藏东部玉龙铜矿带,包括玉龙、扎拉尕、莽总、多霞松多和马拉松多等斑岩型Ｃｕ,Ｍｏ,Ｐｂ,Ｚｎ,Ａｕ,Ａｇ和Ｐｔ等多金属矿床．由于分析技术条件的限制,前人所获得的含矿斑岩微量元素数据精度较低．采用先进的ＰＥＥｌａｎ６０００型电感耦合等离子质谱仪（ＩＣＰ－ＭＳ）分析微量元素（包括稀土元素）,结果表明含矿斑岩和共生的钾质碱性深成岩、火山岩和煌斑岩在时空上具一致性,岩石化学成分均富碱（ｗ（Ｋ２Ｏ）＋ｗ（Ｎａ２Ｏ）＞８％）,高钾和ｗ（Ｋ２Ｏ）／ｗ（Ｎａ２Ｏ）比值远大于１,微量元素富集Ｓｒ,Ｂａ等大离子亲石元素和轻稀土元素等,均显示出钾玄岩系列岩石的特征,暗示西藏东部玉龙铜矿带的含矿斑岩属于典型的钾玄岩系列的斑岩     

青藏高原拉萨地体北部的前寒武纪变质作用及构造意义

青藏高原南部拉萨地体中分布的角闪岩相至麻粒岩相变质岩一直被认为是前寒武纪变质基底,但并没有获得可靠的年代学证据。本文运用原位锆石U-Pb定年方法,在拉萨地体北部那果地区的变质岩中获得了约720Ma的变质年龄,从而证明拉萨地体北部在新古元代经历了角闪岩相变质作用和近同期的岩浆作用。基于这一成果和在拉萨地体中、南部高级变质岩中陆续获得的中、新生代变质年龄,对拉萨地体变质作用的时、空变化及其成因进行了初步探讨。     

藏东地区新生代构造体系与成矿的关系

区域构造和微构造分析表明,新生代藏东地区构造应力场自印支燕山期的NE-SW向挤压向喜马拉雅山期的NNE-SSW向压扭性转变,表现在：（1）沿昌都地块两侧及古生代一中生代形成的深大断裂带发生了大规模的右旋走滑活动,伴重型较强的碎裂岩化、拉伸线埂和剑鞘褶皱等,沿主断裂两侧叠加一系列NW、NNW及NE向雁行式排列的褶皱和张扭性断裂;（2）在区域上,沿大规模右旋走滑断裂两侧形成一系列雁行式排列的第三系走滑拉分盆地;（3）新生代岩浆活动沿走滑断裂两侧的张扭性次级断裂有规律分布,新生代构造体制的转变造成大规模成矿流体与富集,使新生代成为本区最重要的成矿时期,而北澜沧江,妥坝、温泉断裂带及车所乡断裂带北段是该期矿产最有利的富集部位。     

藏东南泥石流沟纵剖面演化的最小功模式

西藏东南地区的泥石流可分为雨水、冰雪融水和冰湖溃决等3种成因类型,其沟谷纵剖面演化均遵循最小功原理,即通过调整坡降使流速增大,表现为单位流体的全程流速平均值ū与纵剖面形态指数N正相关:ū∝f(N),对雨水型泥石流沟,流速函数f(N)={1/3-2/[(N+1)(N+2)(N+3)]}^1/2;对融水型泥石流沟,f(N)={2/3-2/[(N+1)(N+3)]}^1/2;对溃决型泥石流沟,f(N)=[NP(N+1)]^2/3。在泥石流沟谷演化进程中,与ū值由小变大相应,N值由小变大,沟谷纵剖面从上凸抛物线形变为下凹抛物线形,泥石流沟谷地貌演化阶段按泥石流孕育阶段、发展阶段、旺盛阶段、衰减阶段的顺序演替。以藏东南典型泥石流沟作为实例,检验了上述沟谷地貌演化的模式与规律。     

藏北地区自然灾害及其防治--以巴青县-索县地区为例

巴青县-索县地处西藏那曲地区NE部，唐古拉山山脉两翼，是青藏高原上的高原。区内高寒缺氧，交通不便，自然条件恶劣，灾害活动频繁、生态环境脆弱。文章以1／25万《仓来拉幅》区域地质调查过程中实地获得的灾害调查资料为依据，将研究区15635km^2范围内的自然灾害划分为11类。其中，鼠兔灾、草场退化、风灾及雷雨冰雹是全区普遍的灾害类型；土壤盐渍化、荒漠化、水质成化在唐古拉山以北尤为严重；雪灾、雪崩集中于唐古拉山及其南侧终年积雪区，洪涝灾害、泥石流主要发育于唐古拉山南部的藏北高山深谷区。文章综合分析了各类自然灾害形成因素，指出灾害的演化趋势不容乐观。当务之急应采取有效措施和政策，变被动为主动，开展多种形式防灾减灾知识宣传活动，及早成立专业机构对区内灾害进行全面深入的调查研究，探索其发生发展规律，针对不同的灾害类型采取切实的防灾治灾措施，将灾害造成的损失降低到最低程度。     

青藏高原沙尘天气的遥感研究

由于分布在青藏高原上的气象观测站点稀少,难以对沙尘天气进行充分的地面观测。通过对近年来的5次沙尘天气进行遥感识别,分析了青藏高原沙尘天气过程、影响范围和沙尘来源。结果表明,青藏高原在冬春季存在明显沙尘天气,主要分布在藏北高原、藏南谷地和青海高原地区,这与高原大风对地面的风蚀有密切关系。卫星遥感作为一种重要的观测手段,提供了对高原沙尘天气的有效观测。