CRUSTAL STRUCTURE IN EASTERN REGION OF QINGHAI—TIBET PLATEAU

CRUSTAL STRUCTURE IN EASTERN REGION OF QINGHAI—TIBET PLATEAU     

THE CRUSTAL STRUCTURE OF NORTHEASTERN TIBET: A RESULT OF RECEIVER FUNCTION ANALYSIS FOR TELESEISMIC P WAVEFORM

THE CRUSTAL STRUCTURE OF NORTHEASTERN TIBET: A RESULT OF RECEIVER FUNCTION ANALYSIS FOR TELESEISMIC P WAVEFORM     

ICP－AES 法测定地质样品中微量锆、 铪的研究

摘 要　 在2％酒石酸介质中‚用阳离子交换树脂吸附干扰元素‚以 ICP-AES 法分别在 343∙823nm 和264∙141nm 直接测定地质样品中的微量锆和铪。锆的检出限为0∙5×10 －6 ‚铪 为0∙4×10 －6 。此方法简单、快速‚应用于地球化学标准样品中锆和铪的分析‚取得了满意 的结果。     

GEOCHEMISTRY OF THE PLIOCENE SHOSHONITIC ROCKS FROM OIYUG BASIN, CENTRAL TIBET

GEOCHEMISTRY OF THE PLIOCENE SHOSHONITIC ROCKS FROM OIYUG BASIN, CENTRAL TIBET     

SUBDUCTION AND ACCRETION TECTONICS OF HIMALAYAN AND KARAKORAM TERRANES AND THEIR PALAEOGEOLOGIC CONFIGURATION

he 2500km long Indus\|Tsangpo Suture has been recognized as one of the best examples of continent to continent collisional Suture Zone. It has come into existence as a result of subduction followed by continental collision (55～60Ma) between Indian (Sinha, 1989, 1997; Sinha et al., 1999) and Eurasian plates. While considering the recent palaeogeographic reconstruction of Pangea during late Palaeozoic it appears that a southern belt of Asian microcontinents stretching from Iran and Afghanistan through southern Tibet to western Thailand, Malaysia and Sumatra, comprise several continental blocks and numerous fragments that have coalesced since the Mid\|Palaeozoic along with the closure of Tethys. The origin, migration, assembly and timing of accretion of all these blocks to their present geotectonic position is not well known and there is no Permo—Triassic crust left in the present day Indian Ocean. The oldest ocean crust adjacent to the west African and Antarctic margin is of early or middle Cretaceous age (approximately 140～100Ma) (Searle, 1991). The Karakoram\|Hindukush microplate in the west and the Qiangtang\|Lhasa block in the central and eastern segment of South Asia margin are among those blocks already welded with Asian plates around 120～130Ma ago, before the collision of India (55～60Ma) with the collage of plates forming Peri\|Gondwanian microcontinents. But the reconstruction of palaeogeographic configuration remain incomplete due to paucity of authentic geologic information available from Karakoram, Pamir and Western Tibet. Prior to our discovery no early Permian plant remains and palynomorphs were ever reported from Karakoram terrane. Our discovery of Early Permian remains and late Asselian (about 280～275Ma) palynomorphs provides crucial clue regarding the palaeogeographic reconstruction of the Karakoram\|Himalayan block in the Permian time.     

青藏高原错那—沃卡裂谷中部电性结构及其动力学意义

藏南裂谷作为青藏高原最显著的伸展构造样式之一,是研究高原生长过程的重要窗口,但目前其深部成因机制仍存在较大争议。本文利用沿错那—沃卡裂谷中部的大地电磁数据,分析裂谷区域的大地电磁测深曲线特征和相位张量,并通过三维大地电磁反演获得邛多江地堑和沃卡地堑深部电性结构。三维大地电磁反演结果显示,沃卡地堑和邛多江地堑深部存在一条连续的显著高导异常,并呈现“俯冲”形态,且上覆高阻结构体,而在邛多江地堑两侧浅部则分布低阻异常。结合早期的研究结果,本文支持错那—沃卡裂谷深部的高导异常为地壳部分熔融,可能与南向地壳流相关,并研究认为在南北向持续挤压作用下,裂谷下方的弱地壳层,通过解耦上地壳和下部地壳,促进了藏南裂谷系的发育。     

用大地电磁勘探方法研究大陆动力学(英文)

大地电磁法通过测量地表的天然电场和磁场来提供地壳和上地幔的电阻率图像。在仪器和处理解释技术方面的进展使得大地电磁法现在能够快速采集大地电磁数据并进行二维或三维地质模型解释。由于电阻率对地下连通的流体 (如局部熔融和水 )反应灵敏 ,大地电磁资料能够给出地球介质结构成分和流变特性的信息 ,作为地震勘探所获得信息的补充。大地电磁法现在被应用于对构造运动活跃区域的大陆动力学研究。对美国圣安德烈斯断层的大地电磁研究已经揭示了地震比较活跃的断层区段和在脆性上地壳中的断裂带的电阻率之间的相关性。在青藏高原采集的大地电磁资料描绘了地壳中的主要局部熔融区域 ,其结果和大陆碰撞地球动力学模型的结果相一致。将大地电磁法应用于大陆动力学研究肯定能获得对形成大陆地壳的构造运动过程的新见解 ,尤其是在有“研究大陆动力学的天然实验室”之称的中国的构造运动活跃区域。     

隐伏在青藏高原中部的东西走向断裂的航磁异常场特征及其意义

1998～2000年完成的青藏高原中西部航磁数据的综合分析结果显示,在青藏高原中部存在一个重要的隐伏断裂带（大致沿革吉北-改则南-错勤北-申扎北）。结合藏东位场分析结果,革吉北-改则南-错勤北-申扎北隐伏断裂可与嘉黎走滑断裂相连。沿该隐伏断裂发生的地震震源机制解显示,该断裂性质与嘉黎走滑断裂相同。因此,该隐伏断裂与位于藏东的嘉黎走滑断裂一起构成了位于高原中部的东西走向的巨型走滑断裂。这种推测得到了相关地质、地球物理证据和数值模拟结果的证实。此外,该巨型走滑断裂可能调节着青藏高原内部的应力分布,从而控制着高原内部的变形特征。     

INDEPTH 与 INDEPTH-MT 项目简介

摘　 要　 介绍了 “国际喜马拉雅和西藏高原深剖面及综合研究” （简称 INDEPTH） 项目概况、 科学目标和已取得的主要科学成果。着重阐述了作为该项目组成部分的由中国地质大学 （北 京）、美国华盛顿大学 （西雅图）、加拿大地质调查局合作进行的 “国际喜马拉雅和西藏高原 深剖面探测的大地电磁研究” （简称 INDEPTH-MT） 的任务、科学目标和主要成果以及采用 的仪器设备、野外数据采集的方法和技术以及数据处理与反演方法所具有的特色和先进性。     

Application of the homogeneous function and modeling methods for reconstruction of a Tibetan geological section from a travel-time inversion

New structures were revealed in Central Tibet after reinterpretation of the first arrivals of refracted seismic waves along the INDEPTH III profile. The method that was used for travel-time inversion is the numerical generalization of the Herglotz-Wiechert formula for the case of a 2D inhomogeneous medium (the homogeneous-function method). The new section shows that the Bangong-Nujiang Suture (BNS) is a contact in the upper crust, while its continuation in the middle crust is a listric thrust; at the top of the lower crust, which has risen to a 32-km depth in the northern part of the section, this thrust become gentler. Below the middle crust top, a layer with a lower velocity of seismic waves is found. The middle crust is deformed and forms oblique southward listric thrusts. In the upper crust south of the BNS, higher-velocity zones (probable zones of magmatism) are distinguished. North of the BNS, undisturbed outlines of the structures are observed.     

TWO TYPES OF CENOZOIC HIGH-K MAGMATINSM IN EASTERN TIBET:IMPLICATIONS FOR THE NATURE OF MANTLE SOURCES

TWO TYPES OF CENOZOIC HIGH-K MAGMATINSM IN EASTERN TIBET:IMPLICATIONS FOR THE NATURE OF MANTLE SOURCES1　ArnaudNO ,VidalP ,TapponnierP ,etal.ThehighK2 OvolcanismofnorthwesternTibet:geochemistryandtectonicim plications[J] :EarthPlanetSciLett,1991,11:351～ 36 7. 2　DengW .CenozoicvolcanicrocksinthenorthernNgaridistrictoftheTibet Discussionontheconcurrentsubduction[J] .Ac taPetrolSinica ,1989( 3) :1～ 11. 3　HarrisonTM ,LeloupPH ,RyersonFJ,…     

天津静海-津南剖面地壳上地幔电性结构特征

在天津市区南部的静海-津南一线布置了32个大地电磁测深点,剖面方位角92°,对采集的资料采用远参考与Robust技术进行了处理和解释.对该区的构造维数及构造方向做了分析,揭示了该剖面地壳上地幔电性结构特征,并进行了划分.成果显示:中下地壳存在双层低阻构造层,上地幔表现为中、高阻互层.在断裂带附近受构造活动影响,低阻高导构造层会发生上下错断与缺失.沧东、白塘口、天津断裂均是多组断层构成的断裂带,控制了双窑凸起、白塘口凹陷、板桥凹陷及静海斜坡带次级构造单元.     

THE BALANCED CROSS-SECTION AND SHORTENING IN QIANGTANG TERRAIN QINGHAI—TIBET PLATEAU

THE BALANCED CROSS-SECTION AND SHORTENING IN QIANGTANG TERRAIN QINGHAI—TIBET PLATEAU     

MT在天津地热勘查中的应用及主要成果

利用大地电磁测深法(MT)反映地质体的电性差异,可以确定具有不同电性特征的地质体的空间展布。近十年来,天津在多个地热资源勘查项目中,利用MT方法确定断裂、地层并尝试圈定地热远景区,取得了一定效果。本文通过不同构造单元的MT成果,分析了这一方法在地热勘查中的适用性,从而得出:对于深大断裂、尤其是坳陷与隆起区的分界断裂在MT上有较明晰的显示;对上、下层电阻率相差较大、且分布较为稳定的地层,MT确定的地层界面较为准确;以剩余电阻率等值线圈定的地热异常区与盖层平均地热梯度等值线圈定的地热异常区相吻合的区域,通常具有比周边地区更好的地热资源条件。     

从INDEPTH-MT结果探讨雅鲁藏布江缝合带的电性结构

ＩＮＤＥＰＴＨ ＭＴ研究结果表明，在雅鲁藏布江未发现反映深断裂的电性显示，而在江孜和仁布之间见有规模宏大、底界深达５５ｋｍ、向北倾斜的低阻高导体。这表明该区可能为雅鲁藏布江缝合带在地表出露的实际位置。高导体范围内存在３组反映断裂构造的电性梯度带和畸变带。３条断裂带向北倾斜，沿纵深向主断裂带Ｆ３汇聚。其北侧，发育多条南倾断裂，它们共同构成雅鲁藏布江缝合带发散状断裂构造特征。大规模高导体的存在与地下热状态是密切相关的。     

关于印度板块俯冲的探讨———据 INDEPTH-MT 研究结果

摘 要　 西藏高原的隆升与印度板块俯冲有着密切联系‚因而关于板块俯冲的研究一直成为 国际地学界十分关注的焦点问题。本文回顾了这一地学前缘课题的研究现状;阐述了 IN- DEPTH-MT 所提供的西藏中、南部全新的地壳电性结构特点;结合地质及深地震探测结果提 出了对印度地壳俯冲过程的推测。认为‚由于熔融及底熔现象可能使俯冲的地壳逐渐消减‚ 并向北迅速减薄‚所以估计印度板块俯冲的前沿不会超过当雄。     

THE ORIGIN OF DOUBLE HIGH CONDUCTIVITY LAYERS IN THE CRUST OF SOUTHERN TIBET AND ITS GEODYNAMIC CONSEQUENCE

THE ORIGIN OF DOUBLE HIGH CONDUCTIVITY LAYERS IN THE CRUST OF SOUTHERN TIBET AND ITS GEODYNAMIC CONSEQUENCE     

The lithospheric transition between the Delamerian and Lachlan orogens in western Victoria: new insights from 3D magnetotelluric imaging

The magnetotelluric (MT) method was used to image the crust and upper mantle beneath the Delamerian and Lachlan orogens in western Victoria, Australia. During the Cambrian time period, this region changed from being the extended passive margin of Proterozoic Australia into an Andean-style convergent margin that progressively began to accrete younger oceanic terranes. Several broadband MT transects, which were collected in stages along coincident deep (full crust imaging) seismic reflection lines, have now been combined to create a continuous 500 km east–west transect over the Delamerian–Lachlan transition region in the Stawell Zone. We present the electrical resistivity structure of the lithosphere using both 3D and 2D inversion methods. Additionally, 1D inversions of long-period AusLAMP (Australian Lithospheric Architecture Magnetotelluric Project) MT data on a 55 km regionally spaced grid were used to provide starting constraints for the 3D inversion of the 2D profile. The Delamerian to Lachlan Orogen transition region coincides with the Mortlake Discontinuity, which marks an isotopic discontinuity in Cenozoic basalts, with higher strontium isotope enrichment ratios in the Lachlan Orogen relative to the Delamerian Orogen. Phase tensor ellipses of the MT data reveal a distinct change in electrical resistivity structure near the location of the Mortlake Discontinuity, and results of 3D and 2D inversions along the MT profile image a more conductive lower crust and upper mantle beneath the Lachlan Orogen than the Delamerian Orogen. Increased conductivity is commonly ascribed to mantle enrichment and thus supports the notion that the isotope enrichment of the Cenozoic basalts at least partially reflects an enriched mantle source rather than crustal contamination. Fault slivers of the lower crust from the more conductive Lachlan region expose Cambrian boninites and island arc andesites indicative of subduction, a process that can enrich the mantle isotopically, and also electrically, by introducing carbon (graphite) and water (hydrogen).     

TECTONIC EVOLUTION OF THE EOCENE DROSH-VOLCANO-SEDIMENTARY BASIN IN NW-KOHISTAN ISLAND ARC TERRANE, HINDUKUSH, N. PAKISTAN

In NW Himalayas, the suture zone between the collided Indian and the Karakoram plates is occupied by crust of the Cretaceous Kohistan Island\|Arc Terrane [1] . Late Cretaceous (about 90Ma) accretion with the southern margin of the Karakoram Plate at the site of the Shyok Suture Zone turned Kohistan to become an Andean\|type margin. The Neotethys was completely subducted at the southern margin of Kohistan by Early Tertiary, leading to collision between Kohistan and continental crust of the Indian plate at the site of the Main mantle thrust.More than 80% of the Kohistan terrane comprises plutonic rocks of (1) ultramafic to gabbroic composition forming the basal crust of the intra\|oceanic stage of the island arc, and (2) tonalite\|granodiorite\|granite composition belong to the Kohistan Batholith occupying much of the intermediate to shallow crust of the terrane mostly intruded in the Andean\|type margin stage [2] . Both these stages of subduction\|related magmatism were associated with volcanic and sedimentary rocks formed in Late Cretaceous and Early Tertiary basins. This study addresses tectonic configuration of Early Tertiary Drosh basin exposed in NW parts of the Kohistan terrane, immediately to the south of the Shyok Suture Zone.     

雅鲁藏布江缝合带中段构造特征及成因模式新见解

雅鲁藏布江缝合带中的蛇绿岩在西藏南部不同地段,表现形式并不相同.通过对缝合带中段的构造特征及蛇绿岩组合特征的深入研究,认为印度板块的大陆地壳北缘具有特殊的波状弯曲的几何边界--东西两端为向北突出的犄角,构造结之间为向南突出的弧形边界.这种特殊的边界条件,在新特提斯洋俯冲碰撞过程中,新特提斯洋首先在突出结点处完成关闭,而...