长江三峡工程库首区滑坡与线性构造的关系

三峡工程库首区分布着许多大型滑坡 ,在空间上具有丛集性规律。为探明滑坡空间上丛集性与线性构造关系 ,并查明线性构造的发育特征 ,采用了SPOT卫星像片线性构造解译及线性构造密度统计和失真指数分析方法。结果显示 ,滑坡密集区与线性构造的高密度区有较好的吻合关系     

Magnetics in geoexploration

The magnetic method is the oldest and one of the most widely used geophysical techniques for exploring the earth’s subsurface. It is a relatively easy and inexpensive tool to employ, being applicable to a wide variety of subsurface exploration problems involving horizontal magnetic property variations occurring from near the base of the crust to within the uppermost meter of soil. Successful applications of the magnetic method require an in-depth understanding of its basic principles and careful field work, data reduction, and interpretation. Commonly, interpretations are limited to qualitative approaches which simply map the spatial location of anomalous subsurface conditions, but under favourable circumstances the technological status of the method will permit more quantitative interpretations involving specification of the nature of the anomalous sources. No other geophysical method provides critical input to such a wide variety of problems. However, seldom does the magnetic method provide the complete answer to an investigation problem. As a result, it is generally used in concert with other geophysical and geological data to limit its interpretational ambiguities.     

Transverse zones controlling the structural evolution of the Zipaquira Anticline (Eastern Cordillera,Colombia): Regional implications

We report paleomagnetic, magnetic fabric and structural results from 21 sites collected in Cretaceous marine mudstones and Paleogene continental sandstones from the limbs, hinge and transverse zones of the Zipaquira Anticline (ZA). The ZA is an asymmetrical fold with one limb completely overturned by processes like gravity and salt tectonics, and marked by several axis curvatures. The ZA is controlled by at least two (2) transverse zones known as the Neusa and Zipaquira Transverse Zones (NTZ and ZTZ, respectively). Magnetic mineralogy methods were applied at different sites and the main carriers of the magnetic properties are paramagnetic components with some sites being controlled by hematite and magnetite. Magnetic fabric analysis shows rigid-body rotation for the back-limb in the ZA, while the forelimb is subjected to internal deformation. Structural and paleomagnetic data shows the influence of the NTZ and ZTZ in the evolution of the different structures like the ZA and the Zipaquira, Carupa, Rio Guandoque, Las Margaritas and Neusa faults, controlling several factors as vergence, extension, fold axis curvature and stratigraphic detatchment. Clockwise rotations unraveled a block segmentation following a discontinuos model caused by transverse zones and one site reported a counter clockwise rotation associated with a left-lateral strike slip component for transverse faults (e.g. the Neusa Fault). We propose that diverse transverse zones have been active since Paleogene times, playing an important role in the tectonic evolution of the Cundinamarca sub-basin and controlling the structural evolution of folds and faults with block segmentation and rotations.     

柴达木盆地北部新生代构造运动及其对盐湖演化的影响

新生代以来,印度板块与青藏高原发生了强烈的碰撞,由此而产生的远程效应导致柴达木盆地北缘的阿尔金山脉晚古近纪以后发生了强烈的走滑,并导致盆内构造形式发生了一系列变化。在前人对盆地构造运动、古地磁、古地理及岩石地球化学研究结果的基础上,提出了上新世以来在NE和近NS向共同挤压作用的影响下,盆地内部棋盘格式不均匀隆升控制了柴达木盆地北部湖盆的形成,对后期盐湖沉积产生了重要影响。     

Structure of the Basin and Ridge System West of New Caledonia (Southwest Pacific): A Synthesis

Complementary to previous work mainly based on seismic interpretation, our compilation of geophysical data (multibeam bathymetry, gravity, magnetic and seismic) acquired within the framework of the ZoNéCo (ongoing since 1993) and FAUST (1998–2001) programs enables us to improve the knowledge of the New Caledonia Basin, Fairway Basin and Fairway Ridge, located within the Southwest Pacific region. The structural synthesis map obtained from geophysical data interpretation allows definition of the deep structure, nature and formation of the Fairway and New Caledonia Basins. Development of the Fairway Basin took place during the Late Cretaceous (95–65 Ma) by continental stretching. This perched basin forms the western margin of the New Caledonia Basin. A newly identified major SW–NE boundary fault zone separates northern NW–SE trending segments of the two basins from southern N–S trending segments. This crustal-scale fault lineament, that we interpret to be related to Cretaceous-early Cainozoic Tasman Sea spreading, separates the NW–SE thinned-continental and N–S oceanic segments of the New Caledonia Basin. We can thus propose the following pattern for the formation of the study area. The end of continental stretching within the Fairway and West Caledonia Basins ( 65–62 Ma) is interpreted as contemporaneous with the onset of emplacement of oceanic crust within the New Caledonia Basin’s central segment. Spreading occurred during the Paleocene (62–56 Ma), and isolated the Gondwanaland block to the west from the Norfolk block to the east. Finally, our geophysical synthesis enables us to extend the structural Fairway Basin down to the structural Taranaki Basin, with the structural New Caledonia Basin lying east of the Fairway Basin and ending further north than previously thought, within the Reinga Basin northwest of New Zealand.     

The Phanerozoic Reconstitution of Indian Shield as the Aftermath of Break-up of the Gondwanaland

The Indian crust, generally regarded as a stable continental lithosphere, experienced significant tectono-thermal reconstitution during the Phanerozoic. The earliest Phanerozoic tectonic process, which grossly changed the geological and geophysical character of the Precambrian crust, was during the Jurassic when this crustal block broke up from the Gondwana Supercontinent. There were two earlier abortive attempts to fragment the supercontinent in the Palaeozoic. Different types of geological processes were associated with these aborted events. The first was the intrusion of anorogenic alkali granites during the Early Palaeozoic (at 500±50 Ma), while the second was linked with formation of the Gondwana rift basins during Late Palaeozoic. The tectonic history of the Indian Shield subsequent to its separation from the Gondwanaland at around 165 Ma is a complex account of its northward journey, which was culminated with its collision with the northern continental blocks producing the mighty Himalayas in the process. Considerable reconstitution of the Indian Shield took place due to magma underplating when this lithospheric block passed over the four mantle plumes. While the underplating events grossly changed the geophysical character of the Indian Shield in isolated patches, the propagation of the underplated materials was assisted by the deep crustal fractures (geomorphologically expressed as lineaments), which formed during the break-up of the Gondwanaland. Several of these deep fractures evolved through the reactivation of the pre-existing (Precambrian) tectonic grains, while some others developed as new fractures in response to either the extensional stresses generated during the supercontinental break-up or the plume-lithosphere reactions. Significant geomorphological changes occurred in peninsular India subsequent to the continental collision. Most of these changes were brought about by the movements along the lineaments, which fragmented the Indian Shield into a number of rigid crustal blocks. The present day seismic behaviour of the Indian Shield is a reflection of movements of the rigid crustal blocks relative to each other. An interesting feature of the Phanerozoic geological history of the Indian Shield is the evolution of a number of sedimentary basins under different tectono-thermal regimes.     

Identification of groundwater prospective zones by using remote sensing and geoelectrical methods in Jharia and Raniganj coalfields, Dhanbad district, Jharkhand state

The Dhanbad district in Jharkhand faces acute water scarcity and is chronically drought-prone. The groundwater resources in the area have not been fully exploited. The present study was undertaken to evaluate the groundwater prospective zones. Landsat-5 Multi Spectral Scanner (MSS) data of band 2 and band 4 and false colour composite (FCC) of band 2, 3, 4 were interpreted visually to differentiate different hydromorphogeological units and to delineate the major trends of lineaments. The different geomorphic features identified are linear ridges, residual hills, and pediplain, buried pediment and dissected pediplain, besides lineaments. The study shows that the pediplain and buried pediments are promising zones for groundwater prospecting. The occurrence and movement of groundwater is restricted to the unconsolidated material, weathered and fractured rocks. For the selection of tube well sites, geoelectrical resistivity investigations have been carried out at the sites, which were found suitable based on hydrogeomorphological and hydrogeological studies. Twenty-six Vertical Electrical Soundings (VES) have been carried out by using Schlumberger electrode configuration, which have brought out 3 to 7 layered sub-surface layers. The resistivity of water-bearing weathered/fractured rocks varies from 120–150 ohm m. The integrated studies have revealed that the blue colour zones are most promising for groundwater exploration and dug wells may be dug up to depths of 30±5m.     

The Alpine evolution of the Southern Alps around the Giudicarie faults: A Late Cretaceous to Early Eocene transfer zone

Data supporting relevant Late Cretaceous–Early Eocene sinistral displacement along the Giudicarie fault zone and a minor Neogene dextral displacement along the Periadriatic lineament are discussed. The pre-Adamello structural belt is present only in the internal Lombardy zone, located W of the Adamello massif. This belt is unknown in the Dolomites and surrounding areas located to the E of the Giudicarie lineament. Upper Cretaceous–Early Eocene thick syntectonic Flysch deposits of Lombardy and Giudicarie are well preserved along the southern and eastern border of the pre-Adamello belt (S-vergent Alpine orogen). Towards the E, in the Dolomites and in the Carnic Alps and external Dinarides, only incomplete remnants of Flysch deposits, Aptian–Albian and Turonian–Maastrichtian in age, are present. They can be considered as equivalent to those of Lombardy and Giudicarie formerly in connection to each other along the N-Giudicarie corridor. To the S, the syntectonic Flysch deposits are laterally replaced by the calcareous red pelagites of the Scaglia Rossa and by the carbonate shelf deposits of the Friuli (to the E) and Bagnolo (to the S) carbonate platforms. The different location in the southern structural accretion of the eastern and western opposite blocks (the Dolomites versus the pre-Adamello belt) can be related to the Cretaceous–Eocene convergence. In this frame, the N-Giudicarie fault has been considered as part of a former transfer zone, which produced the sinistral lateral displacement of the Southern Alps front for an amount of some 50 km. During the Late Eocene to Early Oligocene the transfer zone was mostly sealed by the Paleogene Adamello batholith. Oligocene to Neogene compressional evolution inverted the N-Giudicarie fault into a backthrust of the Austroalpine units over the South-Alpine chain.     

河北阳原新生代玄武岩中两类辉石岩包体的矿物学和地球化学特征

位于大兴安岭-太行山重力梯度带西侧的阳原新生代玄武岩中含有大量橄榄岩和辉石岩包体。辉石岩包体含有绿色的Cr辉石岩和黑色的Al辉石岩包体两种类型,均为二辉岩,且多数样品中单斜辉石含量高于斜方辉石。岩石结构和主微量元素组成说明阳原辉石岩是高压堆晶体。其EMI型Sr-Nd同位素特征,明显不同于寄主玄武岩,暗示两者没有成因联系,而可能代表古老岩浆事件的产物。综合文献资料发现重力梯度带西侧的辉石岩包体大多具有富集同位素特征,而东侧的样品以亏损同位素组成为主。这种空间上的成分差异暗示重力梯度带分隔两个不同的地幔域,也可能与重力梯度带两侧岩石圈地幔形成时代不同有关。     

遥感图像构造线性体模式及结构分析

在江西省上饶地区的构造填图中，根据陆地卫星ＴＭ图像构造体的几何学特征，对赣东北造山带的主要构造单元进行了基于空间推理的地质结构分析。论述了影像线性体的信息提取和解译方法，通过对斜列式、“Ｓ”形、弧形、菱形网络等构造线性体模式的构造几何学研究，揭示了赣东北造山带构造演化过程中的运动学机制。