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1.
班公湖蛇绿混杂岩带位于班公湖-怒江结合带西段,是中生代特提斯洋消亡的遗迹。根据西藏1∶25万日土县幅、喀纳幅地质填图成果,将班公湖蛇绿混杂岩带的时空结构划分为南、北两条亚带;综合分析研究认为,本区中特提斯洋的演化经历了三叠纪-早中侏罗世扩张,中晚侏罗世双向俯冲,晚侏罗世-早白垩世残余洋(海)盆和晚白垩世陆(弧)-陆碰撞等构造演化阶段。  相似文献   

2.
青藏高原中部狮泉河-拉果错-永珠-嘉黎蛇绿混杂岩带(简称SYMZ)位于班公湖-怒江缝合带与雅鲁藏布江缝合带之间,其构造属性存在很大争议,制约了对青藏高原多岛弧盆系构造演化的理解.根据新的地质调查资料、研究成果并结合分析数据,系统总结了该蛇绿混杂岩带的地质特征,讨论了其构造演化过程.一系列新资料及新认识表明SYMZ是分割北拉萨地块和中拉萨地块的一条独立的蛇绿混杂岩带,是特提斯构造域多岛弧盆系的组成部分.在狮泉河、拉果错、阿索、永珠、凯蒙等地发育比较典型的蛇绿岩组合,高精度年代学数据指示洋盆主体发育于178~160 Ma,比班公湖-怒江洋盆主体发育时限(188~162 Ma)要晚10 Ma左右,阿索一带蛇绿岩残片记录洋盆一直持续到113 Ma.SYMZ侏罗纪基性岩具有MORB型(洋中脊玄武岩)和IAT型(岛弧拉斑玄武岩)火山岩的地球化学性质,属于洋内弧型和洋中脊型蛇绿混杂岩;早白垩世基性岩具MORB和火山弧玄武岩的双重特性,指示其很可能形成于SSZ的构造环境,不同于同时期班公湖-怒江特提斯受地幔柱热点影响的洋盆性质.同时,在拉果错、永珠、凯蒙等地区识别出侏罗纪前弧玻安岩及玻玄岩系列,一致指示SYMZ洋壳发生过洋内俯冲.在此基础上,结合区域地质资料,构建了SYMZ特提斯洋的时空格架及构造演化历史,认为经历了晚三叠世-早侏罗世洋盆裂解-扩张、中-晚侏罗世洋内俯冲、早白垩世俯冲消减和早白垩世末期洋盆消亡四个阶段,为特提斯洋的构造演化及大地构造过程再造提供了重要的地质学证据.   相似文献   

3.
阿尔金红柳沟蛇绿岩研究进展   总被引:14,自引:0,他引:14  
实测了2条阿尔金地区红柳沟蛇绿混杂带的地质剖面.地球化学的研究发现混杂带中含有2种基性火山岩:MORB型和OIB型,其稀土配分型式分别为平坦型和轻稀土富集型,结合同位素εNd值,推断混杂带中变基性火山岩来自于不同的岩浆源.变质橄榄岩稀土总量低,具有亏损型和平坦型2种不同的稀土配分型式.这种MORB和OIB的组合代表了地幔柱物质与洋壳物质的混合作用.  相似文献   

4.
目前对青藏高中部的蛇绿岩类型、形成环境及其深部地幔源区特征还缺乏很好的约束。在区域地质调查基础上,本文展示了青藏高原中部龙木错—双湖缝合带嘎错玄武岩、班公湖—怒江缝合带多玛、塔仁本玄武岩及那曲盆地西侧中生代玄武岩的单斜辉石Ar-Ar测年、锆石SHRIMP定年和地球化学及Sr,Nd,Pb同位素数据,以约束形成这些玄武岩的时代、构造环境和地幔源区特征。目前的数据表明:1羌塘双湖嘎错枕状玄武岩单斜辉石的中温坪年龄为232.5±2.4Ma,可能指示嘎错玄武岩浆活动发生于中三叠世晚期,班公湖—怒江缝合带多玛枕状玄武岩、塔仁本玄武岩浆活动时代大约在早白垩世中晚期(110Ma左右);2在这些蛇绿混杂岩带中的玄武岩显示OIB而不是MORB型地球化学特征,双湖嘎错玄武岩的地球化学特征介于峨眉山高Ti玄武岩与夏威夷碱性玄武岩之间;中晚三叠世那曲嘎加组玄武岩的地球化学特征非常类似于夏威夷碱性玄武岩;班公湖—怒江缝合带内的早白垩世多玛玄武岩和塔仁本玄武岩的地球化学特征在很大程度上可比于夏威夷碱性玄武岩;3双湖嘎错OIB型玄武岩可能形成于以增生楔为基底的裂谷环境而不是以洋壳为基底的大洋板内环境,那曲嘎加组OIB型玄武岩很可能形成于以弧内—弧前沉积物为基底的陆棚—陆坡环境下的裂谷背景,塔仁本和多玛OIB型玄武岩形成于以洋壳为基底的洋岛环境,这表明班公湖—怒江洋壳在大约110Ma时尚未彻底消亡,可能暗示班公湖—怒江洋盆的关闭时间明显晚于晚侏罗世—早白垩世早期闭合的早期认识;4地球化学指标显示青藏高原中部中生代玄武岩未受到地壳物质或很少受到陆下岩石圈物质改造,一些相对新鲜样品的Nd,Pb组成似乎可以用来代表其地幔源区的成分特点,其高206Pb/204Pb比值(>18.5)指示羌塘双湖中晚三叠世嘎错玄武岩、班公湖—怒江缝合带早白垩世洋岛玄武岩所代表的中生代特提斯地幔很可能不具“Dupal”异常。然而,由于研究程度的限制和缺乏更多的可靠数据,这种观察还需要进一步确认。  相似文献   

5.
班公湖-怒江结合带西段中特提斯多岛弧构造演化   总被引:13,自引:0,他引:13       下载免费PDF全文
本文根据1∶25万地质填图成果,将班公湖-怒江结合带西段弧-盆系时空结构自北向南划分为五峰尖-拉热拉新晚侏罗世—早白垩世陆缘火山-岩浆弧带、班公湖蛇绿混杂岩北、南亚带和昂龙岗日-班戈白垩纪—始新世岩浆弧带等,初步认为中特提斯洋经历了三叠纪—早侏罗世扩张,中—晚侏罗世往北、南双向俯冲,晚三叠世—早白垩世残余洋(海)盆和早—晚白垩世陆-弧(陆)碰撞等演化阶段。  相似文献   

6.
青海沱沱河地区乌石峰蛇绿混杂岩位于西金乌兰-风火山逆冲带中。通过对其岩石学和全岩地球化学研究,探讨了蛇绿混杂岩的构造类型及其形成环境。晚古生代乌石峰蛇绿构造混杂岩的岩石组合以及蛇绿混杂岩中玄武岩类岩石(主要为辉绿岩及辉长岩)的地球化学特征对构造环境的指示表明:其地球化学特征与MORB相似,超基性岩和基性岩形成于大洋板内环境与洋中脊环境的复合构造环境中。是古特提斯洋洋盆残片,体现了古特提斯洋壳的闭合位置,是古特提斯洋在早二叠世末闭合过程中形成的增生楔的一部分。  相似文献   

7.
阿尔金红柳沟蛇绿混杂岩中MORB与OIB组合的地球化学证据   总被引:23,自引:0,他引:23  
阿尔金红柳沟地区早古生代蛇绿混杂带中含有地幔橄榄岩、辉长辉绿岩、细碧化玄武岩、硅质岩、复理石等岩石组合。笔者研究证实,该地区蛇绿岩中变基性岩具有过渡型洋中脊玄武岩(T-MORB)的特征,并发现蛇绿岩在混杂带中与洋岛玄武岩(OIB)共生。在球粒陨石标准化的稀土元素配分图上,T-MORB型变基性岩配分型式为平坦型;OIB中TiO2含量高,近3%,富集高场强元素Nb、Ta等,稀土元素配分型式为轻稀土富集型。MORB和OIB组合的出现说明早古生代时,该地区存在过洋盆。这一组合可与北祁连进行对比。  相似文献   

8.
西准噶尔蛇绿混杂岩中洋岛玄武岩研究新进展   总被引:2,自引:0,他引:2  
洋岛玄武岩(OIB)起源研究是当代固体地球岩石学及地球化学最基本问题之一,通常被认为源于地幔柱。西准噶尔位于中亚造山带的西南缘,该地区发育多条蛇绿混杂岩带,主要包括唐巴勒、玛依勒、达尔布特及克拉玛依蛇绿混杂岩带,它们组成相似,主要为蛇纹岩、蛇纹石化方辉橄榄岩、二辉橄榄岩、纯橄岩、铬铁矿、辉石岩、辉长岩、辉绿岩、玄武岩(拉斑质和碱性)、硅质岩及斜长花岗岩。随着研究的不断深入,在西准噶尔蛇绿混杂岩带中不断有不同时代OIB被识别。这些玄武岩属于碱性玄武岩系列,具有高TiO2和FeOt,低MgO,强烈富集轻稀土元素特征,没有明显Nb、Ta负异常,与日喀则及夏威夷洋岛玄武岩地球化学特征极为相似,可能形成于大洋板内的海山或洋底高原,认为其成因与地幔柱相关,表明在西准噶尔(洋)的演化过程中,不仅是洋内俯冲系统,还伴有地幔柱活动。结合前人研究,认为中亚造山带可能是洋内俯冲+地幔柱复合的演化模型。同时,对中亚造山带中的OIB及OIB型玄武岩形成时代进行系统总结发现,它们不仅时代宽度大,并且具有连续发育的特点。对正确认识地幔柱活动在显生宙中亚造山带地壳增生过程中的贡献提供新的资料和证据。  相似文献   

9.
布青山蛇绿混杂岩位于阿尼玛卿带西段,它是由早古生代和早石炭世一早二叠世两期蛇绿岩组成的复合蛇绿混杂岩带。蛇绿岩中的变质橄榄岩以方辉橄榄为主,高镁,∑PEE是球粒陨石的0.2-0.65倍,HREE是球粒陨石的0.28-0.32倍,属亏损的大洋岩石圈地幔。早古生代蛇绿岩中辉长岩、辉绿岩和玄武岩等镁铁质岩主要具N-MORB性质,少量具T-MORB性质。早石炭世一早二叠世蛇绿岩中玄武岩也主要具N-MORB性质、少量具T-MORB性质。它们均形成于洋中脊环境。本区曾存在成熟的早古生代洋盆和古特提斯洋盆,有更复杂的构造演化史。  相似文献   

10.
白云山蛇绿混杂岩是北山造山带中红柳河-牛圈子-洗肠井蛇绿岩带的一部分,由蛇纹石化二辉橄榄岩、蛇纹岩、辉长岩(堆晶辉长岩、块状辉长岩)、基性枕状熔岩(变玄武岩)及深海-次深海远洋、半远洋相沉积物(硅质岩、板岩)、白云岩等组成。其中辉长岩LA-ICP-MS锆石U-Pb测年结果为496.4±2.2 Ma,指示蛇绿岩形成于晚寒武世;混杂带中玄武岩地球化学特征为洋底玄武岩,兼有洋岛碱性玄武岩(OIB)和洋脊玄武岩(MORB)的地球化学性质,枕状熔岩与硅质岩交互产出,指示其形成环境为深水洋盆。结合区域地质资料,推测该蛇绿混杂岩带为寒武纪洋中脊存在的遗迹。  相似文献   

11.
International unity is becoming ever stronger in this country owing to an increasing similarity in the development of the cultural environment. This comprises the provision of all the country's republics with a sufficient number of schools, theatres, and other institutions and cultural information media in accordance with the needs of the population. An important part is played by the rise in ‘the general educational level, as well as the level of professional qualifications and skills. Among all the Soviet nations and nationalities, this rise being more rapid among formerly backward peoples. Prominent among the factors of internationalization is the progressive development of the nationalities’ cultural resources, while professional culture is being increasingly brought within the reach of the masses.The implementation of the nationalities policy promotes the all-round development of all Soviet nations and nationalities, their drawing together, the upsurge of the individual capabilities of every Soviet citizen.  相似文献   

12.
13.
Chronological analyses of correlations between certain global repeating events (mass extinctions of marine organisms, meteorite impacts, and flashes in the frequency of geomagnetic reversals) during the Phanerozoic Eon and the motion of the solar system in the Galaxy are presented for five rotationally symmetrical models for the regular Galactic gravitational field. Thirteen of sixteen mass-extinction events can be described by a repetition interval of 183±3 million years. This is in agreement with the anomalistic period (interval between two subsequent passages of the Sun through the apocenter of its Galactic orbit) in the model of Allen and Martos. The positions of the minima and maxima in Gaussian functions approximating the frequency distribution for geomagnetic reversals also agree with the times of passage of the Sun through the apocenter and pericenter, respectively, of its Galactic orbit in this model. The maximum in the distribution of the deviations of the dates of mass extinctions from the nearest dates of impacts of large, crater-forming bodies is close to zero, providing evidence that many such events are correlated. As a rule, extinctions follow impact events. The impacts of large bodies have occurred most often when the solar system passes through the Galactic plane, while mass extinctions occur more often at some distance from the Galactic plane (about 40 pc). As a rule, intervals of increases in the frequency of geomagnetic reversals coincide with dates of impacts of large bodies. At the same time, these intervals do not show a clear correlation with the dates of mass extinctions. The intensity of mass extinctions, like the energy released by impacts, is consistently higher in periods when the Sun is moving from the apocenter toward the pericenter of its orbit, than when it is moving from the pericenter toward the apocenter. Thus, there is evidence for a variety of relationships between repeating global events in the Phanerozoic and the motion of the Sun in the Galaxy. Long-period variations in the frequency of geomagnetic reversals are correlated with the orbital motion of the Sun, and increases in the frequency of geomagnetic reversals are correlated with impacts. Mass extinctions are correlated with the impacts of large bodies, whose motions may have been perturbed by clouds of interstellar material concentrated toward the Galactic plane and by the shock front associated with the Perseus spiral arm, through which the solar system passes. The velocity of the Sun relative to the spiral pattern is estimated.  相似文献   

14.
It is known from observations that the center of mass of the Moon does not coincide with the geometric center of its figure, and the line connecting these two centers is not aligned with the direction toward the center of the Earth, instead deviating toward the Southeast. This stationary deviation of the axis of the inertia ellipsoid of the Moon to the South of the direction toward the Earth is analyzed. A system of five linear differential equations describing the physical libration of the Moon in latitude is considered, and these equations are derived using a new vector method taking into account perturbations from the Earth and partly from the Sun. The characteristic equation of this system is obtained, and all five oscillation frequencies are found. Special attention is paid to the fifth (zero) frequency, for which the solution of the latitude libration equations are stationary and represents a previously unknown additional motion of the rotational axis of theMoon in a cone with a small opening angle. In contrast to the astronomical precession of the Earth, the rotation of the angular-velocity vector is in the positive direction (counter-clockwise), with the period T 3 = 27.32 days. On this basis, this phenomenon has been named “quasi-precession.” This quasi-precession leads to a stationary inclination of the major axis of the inertia ellipsoid of theMoon to the South (for an observer on Earth), making it possible to explain one component of the observed deviation of the center of mass of the Moon from the direction toward the Earth. The opening angle of the quasiprecession cone is approximately 0.834″.  相似文献   

15.
从榴辉岩与围岩的关系论苏鲁榴辉岩的形成与折返   总被引:4,自引:1,他引:4       下载免费PDF全文
位于华北和扬子两板块碰撞带中的苏鲁榴辉岩形成的温压条件不但是超高压,而且是高温。榴辉岩的PTt轨迹表明其为陆-陆磁撞俯冲带的产物。榴辉岩的区域性围岩花岗质片麻岩为新元古代同碰撞期花岗岩,榴辉岩及其他直接围岩皆呈包体存在于其中,并见新元古代花岗岩呈脉状侵入榴辉岩包体中。区域性围岩新元古代花岗岩的锆石中发现有柯石英、绿辉石等包裹体,表明新元古代花岗岩的组成物质也经受过超高压变质作用,且榴辉岩与围岩新元古代花岗岩的锆石U-Pb体系同位素年龄基本相同。但新元古代花岗岩所记录的变质作用和变形作用期次(或阶段)却少于榴辉岩。椐上述可得如下推断:超高压榴辉岩与新元古代花岗岩岩浆是同时在碰撞带底部(俯冲板块前部)形成的;榴辉岩的第一折返阶段是由新元古代花岗岩岩浆携带上升的,其第二折返阶段是和新元古代花岗岩一起由逆冲及区域性隆起而上升,遭受剥蚀。  相似文献   

16.
某高速公路下伏煤矿采空区稳定性分析   总被引:10,自引:0,他引:10  
在论述某高速公路下伏砦脖煤矿采空区地质、采矿和工程地质特征的基础上,进行了稳定性数值模拟分析,定性与定量地分析与评价了该煤矿采空区的地表变形特征及稳定性。研究结果表明:该煤矿采空区的变形尚未完成,对拟建的高速公路将产生很大的危害,必须采取相应的工程治理措施。  相似文献   

17.
摩擦桩基桩土间极限摩阻力取值问题探讨   总被引:1,自引:0,他引:1  
陈银生 《世界地质》1999,18(1):54-59
通过对广珠东线高速公路横沥大桥的试桩及土体的工程地质条件分析,总结出影响摩擦桩基桩土间极限摩阻力取值的一般问题以及解决问题的方法和措施。  相似文献   

18.
19.
The structure of the eastern Pyrenees consists mainly of south-directed thrusts involving basement and cover rocks. An antiformal stack developed by the piling up of basement thrust sheets which outcrop in the Axial zone. These structures account for a thin-skinned thrust model rather than a vertical fault model in which the Axial zone would be essentially autochthonous, and the North-Pyrenean fault the axial plane of a fan thrust system. New data from the Eastern Pyrenees and the thin-skinned model suggest that(1) the structure east of the Pedraforca nappe is similar to that of the Central Pyrenees; (2) the cover rocks of the South-Pyrenean units and of the Axial zone-after restoration—built up a northwards-thickening prism consistent with the existence of a unique Pyrenean sedimentary basin during Mesozoic time; (3) the Axial zone is only a complex antiformal stack developed as a part of South-Pyrenean system related to the Paleogene thrusting-tectonics. The Axial zone palaeogeographic area had no special meaning during Mesozoic time.  相似文献   

20.
We first re-examined the apparent polar wander curves for stable Eurasia and Africa since the Triassic. These curves were then combined together with curves of North and South America according to the kinematics of the Atlantic ocean and a synthetic polar wander curve was given. Then, most of the paleomagnetic results from the Tethys mobile belt, from the Atlantic to the Pamirs, were analysed.Several groups of plates, microplates and blocks can be seen. First, relatively stable regions like Maghreb and Sicily, which have not moved much. Then we have a group formed by Iberia, Sardinia, Italy and, to a lesser extent, Corsica and the Western and Central Alps. For these blocks, movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of Africa, but they are sometimes stronger.To the east, a major change takes place. The north of the Aegean Sea and the Ionian zone are clockwise rotated and these rotations are recent: Oligocene-Miocene for the first part, Pliocene to the present for the second part.A major problem arises in Turkey, Caucasus and Iran. Paleomagnetic results indicate a position far to the south of Eurasia, and, at the same time, geological evidence is in favour of a position close to Eurasia. We discuss these discrepancies.  相似文献   

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