Diagenesis and Metamorphism of Triassic Flysch Along Profile Zoige-Lushan,Northwest Sichuan,China

We used illite and chlorite crystaHinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis （EMPA）, b0 geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan-Garze orogen along profile Zoige-Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in-between them are defined on the basis of the obtained data. lllite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2M1 white mica polytype are observed within the epizone whilst 2M1 and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370℃±21℃ at low-to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint： on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.

From Flysch to Molasse—Sedimentary and Tectonic Evolution of Late Caledonian -Early Hercynian Foreland Basin in North Qilian Mountains

The Late Caledonian to Early Hercynian North Qilian orogenic belt in no rthwestern China is an elongate tectonic unit situated between the North China p late in the north and the Qaidam plate in the south. North Qilian started in the latest Proterozoic to Cambrian as a rift basin on the southern margin of North China, and evolved later to an archipelagic ocean and active continental margin during the Ordovician and a foreland basin from Silurian to the Early and Middle Devonian. The Early Silurian flysch and submarine alluvial fan, the Middle to L ate Silurian shallow marine to tidal flat deposits and the Early and Middle Devo nian terrestrial molasse are developed along the corridor Nanshan. The shallowin g upward succession from subabyssal flysch, shallow marine, tidal flat to terre strial molasse and its gradually narrowed regional distribution demonstrate that the foreland basin experienced the transition from flysch stage to molasse stag e during the Silurian and Devonian time.

Flysch Trace Fossils from the Hercynian and IndosinianOrogenic Belts of North western China andTheir Palaeoenvironmental Significance

Twenty-three ichnotaxa have been found in the Silurian and Carboniferous turbidites of the Tianshan orogenic belt and the Triassic turbidites of the East Kunlun-West Qinling orogenic belt of northwestern China. They are Acanthorhaphe isp., ?Arthrophycus isp., Aulichnites parkerensis, Chondrites isp., C. intricatus, C. targionii, Cochlichnus anguineus, coprolite, Dendrotichnium haentzscheli, Helminthopsis isp., Helminthopsis abeli, H. hieroglyphica, H. cf. irregularis, Imbrichnus isp., Kunlunichnus qinghaiensis, Laevicyclus rotaeformis, Lophoctenium tianshanensis, Megagrapton isp., Micatuba verso?, Muensteria isp., Neonereites, Palaeophycus, and Zoophycos caudagalli, two of which, namely, Kunlunichnus qinghaiensis and Lophoctenium tianshanensis, are new ichnospecies. The described trace fossils can be grouped into five ichno-assemblages: the Aulichnites-Imbrichnus ichno-assemblage representing turbidity current deposits of a restricted anoxic deep-sea basin, the Lophoctenium ichno-assemblage showing the deep-sea or ocean environments relevant to a plate subduction, the Zoophycos-Helminthopsis ichnoassemblage representing the upper-middle turbidity fan deposits of a pelagic and hemipelagic environment, the Megagrapton-Chondrites ichno-assemblage representing the middle-lower turbidity fan deposits of an oceanic archipelago and the Kunlunichnus ichno-assemblage indicating bathyal turbidity current deposits.

Comparing the Upper Triassic Deep-sea Flysch of the Shannan Terrane with the Coeval Shallow Shelf Sediments of the Tethys Himalaya,Southern Tibet

The provenance and paleogeography of the Upper Triassic deep-sea flysch Langjiexue Group(LG)of the Shannan Terrane in the northeastern Himalaya orogen,south of Yarlung Zangbo,have been disputed in recent years since its affinity to the Tethys Himalaya was suspected during the early 2000 s.Based on the earlier discoveries of the Upper Permian–Triassic basalts and mafic dykes from the LG and of coeval detrital zircons from the Qulonggongba Formation(QF)in shallow shelf sediments of the Tethys Himalaya,the previous viewpoints on the basin and tectonics of the LG have been recently rejected.We compared the two units of the Upper Triassic,and our results reveal a number of differences,discrepancies,and inconsistencies in the debate,raising crucial questions on the postulation and provenance model of the remote Gondwanide Orogen for the LG.It is suggested that more observations and evidence are needed to further improve the paleogeographic understanding and relationship of the two units.

Permeability in Flysch-Distribution Decrease with Depth and Grout Curtains Under Dams

A considerable number of in situ permeability tests in flysch are processed to a depth of 120m with a good spatial distribution. The distribution of permeability values for the different litho-types of this formation, their comparison and their decrease with depth is discussed. The depth where a permeability of 3 to 5×10-7m/sec can be retained (the limit of a reasonable grouting under a high dam) may be twofold if the geological history of the formation could not contain a compressional tectonic process. This depth may reach 100m in some cases. The differences in the mean values of permeability among the various litho-types are minor, while the presence of siltstones, always present although with varied participation, dramatically controls the global permeability.

Tunnel behaviour and support associated with the weak rock masses of flysch

Flysch formations are generally characterised by evident heterogeneity in the presence of low strength and tectonically disturbed structures. The complexity of these geological materials demands a more specialized geoengineering characterisation. In this regard, the paper tries to discuss the standardization of the engineering geological characteristics, the assessment of the behaviour in underground excava- tions, and the instructions-guidelines for the primary support measures for flysch layer qualitatively. In order to investigate the properties of flysch rock mass, 12 tunnels of Egnatia Highway, constructed in Northern Greece, were examined considering the data obtained from the design and construction records. Flysch formations are classified thereafter in 11 rock mass types （I-XI）, according to the siltstone -sandstone proportion and their tectonic disturbance. A special geological strength index （GSI） chart for heterogeneous rock masses is used and a range of geotechnical parameters for every flysch type is presented. Standardization tunnel behaviour for every rock mass type of flysch is also presented, based on its site-specific geotechnical characteristics such as structure, intact rock strength, persistence and complexity of discontinuities. Flysch, depending on its types, can be stable even under noticeable overburden depth, and exhibit wedge sliding and wider chimney type failures or cause serious deformation even under thin cover. Squeezing can be observed under high overburden depth. The magnitude of squeezing and tunnel support requirements are also discussed for various flysch rock mass types under different overburdens. Detailed principles and guidelines for selecting immediate support mea- sures are proposed based on the principal tunnel behaviour mode and the experiences obtained from these 12 tunnels. Finally, the cost for tunnel support from these experiences is also presented.

Influence of tributaries on downstream bed sediment grain sizes under flysch conditions

Tributaries are one of the most important factors contributing to variability in the downstream evolution of bed sediment grain size.The primary aim of this work is to evaluate the response of the bed sediment texture in the recipient channel induced by ten tributaries of the?ernáOstravice stream and find reach-scale and catchment-scale parameters that would be able to predict this response.The research was based on collecting information on the grain size distributions at sites adjacent to confluence zones.A significant change in sediment texture occurred in the vicinity of five confluences.Considering the other factors contributing to grain size variability(e.g.,local channel geometry,lithology,and lateral sediment sources),it was assumed that only four of them were associated with a sufficient bedload influx to alter the sediment calibre below the junction.Moreover,a significant morphological effect in the form of a large confluence bar was observed in one case.These tributaries had several common features:(i)they had a larger relative catchment area than that of nonsignificant tributaries;(ii)they were characterized by different bed grain sizes,with some exceptions;and(iii)they had a higher unit stream power close to the confluence in relation to that of the mainstream.These characteristics were represented by the proposed relative parameters,including the relative unit stream power and bed material texture,which allowed the best classification of significant and nonsignificant tributaries.In their simplified form,the parameters described the transport capacity and grain size distribution,which were generally considered to be primary factors responsible for a redefinition of the sediment texture in the recipient channel.However,it should be noted that these results are subject to some degree of uncertainty due to the relatively small sample size of only 10 tributaries.

CHARACTERISTICS OF THE LATE CARBONIFEROUS FLYSCH FORMATION IN LIUSHUGOU-URHO, XINJIANG

In early Late Carboniferous only the South Junggaru-Bogeda area of the ancient North Xinjiang geosynclinal region was still in the geosynclinal stage,when it was the critical Period for closing of the geosynclinal region. The crust movement was in a special form with frequent rhythm,and there developed a typical flysch formation in Liushugou-Urho in Late Carboniferous. A thorough investigation and study on the flysch formation have been carried out,based on a great number of the firsthand field information and experiment analytical data.The Late Carboniferous flysch formation in Liushugou-Urho,Xinjiang,formed in the Bashkirian .consisting mainly of the Baogutu Formation. There are outcrops if the flysch at Liushugou ,Kesongertai, Kayinte, Hatu, Dongfeng Wudui, Urho, etc. The outcrops at Kesongertai and Urho, 422m and 1228m thick respectively,are more typical and complete flysch formation.The Late Carbonilerous flysch formation in Liushugou-Urho consists mainly of the rhythmic series of sandstone and shale. The shale (or mudstone) component increases southeastward to Urho and sandstone component increases southwestward to Liushugou-Kayinte. Body fossils are seldom in the formation but the Nereites ichnofacies are common. The distribution of trace elements is stable and belongs to the regular pattern. THe flysch formation at the Urho formed chiefly in a bathyal sedimentary environment,possessing a complete transgressive-and-regressive sequence. At Liushugou -Kayinte, the formation can obviously be divided into the upper and lower parts. The upper formed in a littoral-neritic oscillatory environment,while the lower deposited in a bathyal turbidite basin. The two parts constitute a transgressive sequence.

An integrated north–south paleo-Dadu-Anning River: New insights from bulk major and trace element analyses of the Xigeda Formation

The Xianshuihe-Anninghe fault extends SE–S and constitutes the southeastern margin of the Tibetan Plateau.However,the Dadu River which is associated with the fault does not flow following the path,but makes a 90ºturn within a distance of 1 km at Shimian,heading east,and joins the Yangtze River,finally flowing into the East China Sea.Adjacent to the abrupt turn,a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault.Therefore,many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River.However,evidences for the capture of the integrated N–S paleo-Dadu-Anning River,its timing,and causes are still insufficient.This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers.Similar with sands in the modern Dadu River,the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz(>50%),anorthite(about 10%),orthoclase(about 5%),muscovite(about 5%),and clinochlore(about 4%).Correspondingly,bulk major elements show high SiO_(2),with all samples>60%,and some of them>70%,low TiO_(2)(≤0.75%),P_(2)O_(5)(≤0.55%),FeO*(≤5%),and relatively high CaO(1.02%–8.51%),Na_(2)O(1.60%–2.52%),and K_(2)O(2.17%–2.71%),with a uniform REE patterns.Therefore,synthesizing all these results indicate that these lacustrine sediments have similar material sources,which are mainly derived from its course in the Songpan-Ganzi flysch block,implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake.The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the XianshuiheXiaojiang fault system.

四川小金复理石地质景观特征及保护利用建议

从成都出发,经都江堰到汶川映秀,进入中国熊猫大道,在小金县域段沿小金川两岸发育复杂褶皱图案的砂岩与板岩呈韵律互层的陡倾岩层,这就是小金复理石地质景观,为松潘-甘孜造山带复理石岩系的典型地区,极具视觉震憾力,也是申报四姑娘山世界地质公园核心地质遗迹群落之一。通过对小金复理石景观的地层结构、复理石沉积特征、赋存的古生物化石、叠加发育的西康式褶皱等综合分析,以及与世界典型西班牙复理石崖岸景观对比,确立了小金复理石景观的价值意义,从而奠定了小金复理石景观为世界级地质景观的地位。在此基础上对小金复理石地质景观提出可持续保护利用的措施建议。

南盘江盆地中三叠统复理石中的同沉积挤压构造——一类新的沉积构造的归类、命名和构造意义探讨

南盘江盆地在中三叠世时接受了厚达5000m的复理石沉积,而该复理石中保存有丰富的原生沉积构造。笔者等在这些沉积构造中识别并命名了一类新的构造——同沉积挤压构造,并用简单的实验定性地模拟了该类构造的形成机理。这些同沉积挤压构造包括:挤压皱纹、挤压岩枕、挤压裂隙和挤压皱脊,发育于复理石砂岩层的底面或泥岩层的顶面,是相关砂层或泥层沉积后到成岩前复理石盆地遭受挤压收缩的动态记录。根据这些同沉积挤压构造的方向初步判断,南盘江盆地在中三叠世接受复理石沉积的同时受到了SSW—NNE方向的挤压作用,盆地处于挤压收缩阶段。这些构造为复理石盆地的动态演化研究提供了新的证据。

藏北查桑上三叠统复理石沉积大地构造背景的初步探讨

藏北羌塘地块的构造性质和构造格局是中国地学界长期争论的重要问题。这里人迹罕至 ,研究程度很低 ,基础地质资料缺乏。这是有关地质问题得不到解决的根本原因之一。本项研究的首要目的也就是为该地区的地质研究提供一份基础资料。羌塘地块腹地查桑地区的上三叠统肖茶卡组 ,下部为细碧岩、中基性火山岩、玄武质角砾岩夹灰岩和大理岩 ,上部主要为碎屑岩 (复理石 )和灰岩。我们在肖茶卡组上部的复理石中采集砂岩、粉砂岩样品 ,进行主量元素地球化学分析 ,并利用分析结果对其沉积大地构造背景物源区性质进行判别。研究结果表明 ,当时本区属于活动大陆边缘大洋岛弧环境 。

龙门山断裂带印支期左旋走滑运动及其大地构造成因

位于青藏高原东缘的龙门山构造呈北东—南西向将松潘—甘孜褶皱带和华南地块分割开。前者主要是由一套巨厚的三叠纪复理石沉积组成 ,分布在古特提斯海的东缘。后者由前寒武纪基底和上覆的古生代和中生代沉积盖层组成。位于汶川—茂汶断裂以东的前龙门山存在一系列倾向北西的逆掩断层 ,它们将许多由元古宙和古生代岩层组成的断片向南东置于四川盆地的中生代红层之上 ,构成典型的薄皮构造。许多研究由此断定松潘—甘孜褶皱带和四川盆地之间在中生代发生过大规模的北西—南东向挤压。然而 ,汶川—茂汶断裂西侧的松潘—甘孜褶皱带内部的挤压构造线大多是垂直于而不是平形于龙门山断裂带 ,这表明当时的挤压应力不是北西—南东向而是北东—南西向。近年来在龙门山构造带内发现 ,在三叠纪时龙门山断裂带在发生推覆的同时还经历过大规模的北东—南西向的左旋走滑运动 ,协调走滑运动的主要构造为汶川—茂汶断裂。走滑运动的成因与松潘—甘孜褶皱带北东—南西向缩短有关。汶川—茂汶断裂的左旋走滑在龙门山的北东端被古特提斯海沿勉略俯冲带的消减和发生在大巴山的古生代 /中生代岩层的褶皱和冲断作用所吸收 ,在龙门山的南西端被古特提斯海沿甘孜—理塘俯冲带的消减和松潘—甘孜三叠纪复理石的褶皱和冲断作用所吸?

新疆西昆仑库地复理石源区性质及构造背景分析

出露于库地北一些克沟中的复理石作为西昆仑库地蛇绿岩的基本组成单元之一,其本身具有重要的大地构造位置。但长期以来,有关其形成的构造环境分析却尚属空白。笔者等在对该套复理石沉积序列详细分析的基础上,本文从沉积大地构造学的角度,利用岩石矿物、主量元素、微量元素及稀土元素等地球化学数据对其母源区性质及构造背景进行了一系列分析判别,确定其形成的构造环境为大洋岛弧的弧前盆地。

试论西藏南部上三叠统复理石郎杰学群与涅如组

根据新资料结合前人的研究成果对西藏南部仁布以东上三叠统复理石两套地层郎杰学群和涅如组的岩层特征、化石面貌、碎屑组成、沉积特性、地球化学等方面进行了总结及分析。对比研究结果显示,除亚相、岩层厚度分布、砂岩与板岩比例、重矿物ZTR指数变化趋势有一定的差异外,郎杰学群和涅如组的其他十余项特性(颜色、岩性、碎屑组分、重矿物组成、ZTR指数、沉积构造、微量元素、稀土元素、Hf同位素、碎屑锆石同位素年谱、变质变形)相似度极高。分析认为,少数特性差异是地层体地质记录的正常现象,不应成为郎杰学群和涅如组各自独立的主要依据;另一方面,大量相似度极高的各项特性指示它们具有相同或极其相似的沉积盆地和物源构造背景,既不属于喜马拉雅地体也不属于增生楔,而可能同源于拉萨地体或者其他未知地体,属于与造山带有关的沉积盆地建造。进而建议,将涅如组归并为郎杰学群的一个组,仁布-张达-隆子断裂可能是雅鲁藏布江缝合带俯冲消减的东部主断裂或者早期俯冲的南部边界断裂。

昆仑山深部结构与造山机制

本文根据INDEPTH-Ⅳ剖面所做的地质、地球物理探测所取得的资料,进行综合研究,提出了一个新的昆仑山造山模式,论述了：（1）在早二叠世松潘—甘孜洋向昆仑—柴达木地块下俯冲使地块南缘形成陆缘弧和弧后拉张区,使昆仑—柴达木地块在持续碰撞挤压过程中,分别形成了造山带与古近—新近纪盆地的不同构造演化特征;（2）昆仑地段老结晶基底在地块对挤中不断向上抬升成山,同时又受到强烈剥蚀,使老结晶基底及深成岩呈现在地表;南昆仑地块则沿昆仑地块中央断裂向北逆冲到北昆仑地块之上,断裂深10km;昆仑地块没有发生向北逆冲推覆到柴达木地块上;（3）昆仑地块地壳增厚主要发生在中地壳（6.2～6.6 km/s）,是中基性岩石层的增厚;（4）柴达木盆地作为昆仑弧弧后拉张地带,随昆仑造山隆升而下沉,新生界陆相沉积达12～14km厚,由“沉积”与“挤入”两个作用造成了地壳增厚;结晶基底发生断陷形成新裂谷,裂谷宽度约12km,深度约4km,导电带显示裂谷通过断裂与深部发生热流体联系;（5）再次确定了,柴达木盆地莫霍界面深52 km,昆仑山的莫霍界面深65～70 km,莫霍界面台阶位于格尔木附近（185km距离处）;（6）松潘—甘孜地体复理石层厚度为10～14 km,其下面的6.2～6.3 km/s均匀速度层（同时有高导电性显示）是本地块所特有,推测为残留洋壳的堆积,约15km厚;浅层通过古近—新近系风火山推覆系增厚,另在中地壳部位挤入了15km厚岩层;（7）否定了亚洲岩石圈地幔向柴达木地块地幔岩石圈之下俯冲的模式,提出印度大陆地幔岩石圈从高喜马拉雅下拆离成两层,并沿高原地壳底部向北伸展,直到中祁连山之下,成为高原南北对挤过程中岩石圈地幔长度调节的新方式.

东昆仑南缘布青山得力斯坦地区马尔争组物源分析及其构造背景研究

布青山地区马尔争组复理石岩系位于东昆仑南缘,其主体是一套沉积于深海一半深海环境的浊积岩,本文研究了复理石岩系中砂岩的沉积岩石学、碎屑骨架模型及岩石地球化学特征.碎屑组分统计结果表明其砂岩类型主要为长石岩屑砂岩,石英、岩屑、长石的平均含量分别为42％、37％、21％,物源类型为切割型岛弧及再旋回造山带.马尔争组砂岩SiO2含量介于50.18％～74.05％,平均值为66.69％,CIA=43～69;∑REE为59.99×106～171.07×10-6,∑LREE/∑HREE=6.6～8.8;（La/Yb）N=6.6～10.7,（La/Sm）N=3.2～4.6,δEu=0.59～1.04.砂岩地球化学特征指示马尔争组复理石岩系形成于沟弧系活动大陆边缘构造环境,砂岩属大陆岛弧型,物源区为北侧东昆仑地块火山-深成岩浆岛弧造山带及变质基底,源岩为长英质火山岩、同源深成侵入岩及基底变质岩,沉积盆地为俯冲杂岩外侧的古海沟环境.它间接地记录了阿尼玛卿-布青山古特提斯洋的持续扩张 向北俯冲消减—洋盆闭合的过程.

西藏金沙江缝合带西段晚三叠世碰撞作用与沉积响应

青藏高原是由若干条缝合带和其间所夹的沉积盆地构成 ,其中晚三叠世北羌塘盆地位于金沙江缝合带南缘 ,盆地的充填实体显示为南薄北厚 ,为楔形沉积体 ;在垂向上 ,以不整合面为界可将该套充填地层划分为两个构造层序 ,下部构造层序以复理石建造为特征 ,上部构造层序以磨拉石建造为特征 ,具有典型的前陆盆地充填序列 ;盆地具双物源和双古流向体制 ,沉降中心和沉积中心具有不一致 ,显示其为金沙江缝合带南侧的周缘前陆盆地 ,从而确定了晚三叠世北羌塘前陆盆地与金沙江缝合带的成因关系。在此基础上 ,结合在金沙江缝合带西段新发现和确定的蛇绿岩的最小年龄和碰撞型花岗岩的年龄 ,本文根据下部构造层序复理石的年龄、前缘隆起的形成年龄、冲断带隆升成为地貌高地的年龄、下部不整合面的时代和前缘隆起型碳酸岩缓坡的形成时间标定了金沙江缝合带碰撞事件的时代下限 ,根据上部构造层序磨拉石的年龄、上部不整合面的年龄、花岗岩和构造碎裂岩成为物源的年龄标定了金沙江缝合带碰撞事件的时代上限 ,表明金沙江缝合带初始碰撞事件为卡尼克期与诺利克期之间 。

塔里木盆地西北缘克孜布拉克剖面下二叠统砂岩沉积构造背景的初步研究

塔里木盆地西北缘的下二叠统由下部的凝灰岩和上部的碎屑浊积岩组成 ,后者的地球化学特征明显不同于被动大陆边缘沉积 ,是前渊复理石建造。南天山洋盆经早二叠世的大规模消减后在晚二叠世大部分闭合 ,相应地 ,塔北的二叠 三叠系组成了从前渊复理石深海沉积经海陆交互相沉积发育为前陆磨拉石粗碎屑岩的完整序列。

内蒙古西乌旗下二叠统寿山沟组海底扇的发现及意义

西乌珠穆沁旗地区下二叠统寿山沟组沉积环境的认识尚缺乏确凿证据.对塔宾庙林场剖面寿山沟组的研究认为是一套海相碎屑岩沉积,岩石类型以长石岩屑砂岩为主,发育粒序层理和平行层理,属于鲍马序列中的A和B段,并伴有Zoophycos相遗迹化石组合,属于海底扇沉积.根据岩石类型、砂岩的单层厚度、砂岩和泥岩的比值,划分出内扇、中扇、外扇3个亚相,内扇亚相发育水道砾岩,外扇亚相发育复理石相遗迹化石.该区寿山沟组厚层暗色泥岩,是良好的烃源岩,而扇体可以作为有效的储层,具有很好的油气勘探前景.