新疆头屯河地区侏罗系砂岩成分变化及构造环境的探讨

对砂岩矿物成分的定量研究,发现砂岩矿物成熟度的变化与该区构造运动相吻合,源区构造环境为再旋回造山带和岩浆岛弧。     

Observation of recent tectonic movements by extensometers in the Pannonian Basin

In Hungary four extensometric observatories were established in the last two decades. The extensometers were installed primarily for observations of Earth tides. A 15-year continuous data series (1991–2005) was recorded at the Sopronbánfalva station and a 7-year record (1993–1999) was obtained at the Pécs station. The length of the measured continuous data series at the two other stations (Bakonya and Budapest) is only a few years. The long-term data records were also applied to the investigation of long-periodic deformations caused by recent tectonic movements. To get an insight into the present day tectonic processes on the margin of the Pannonian Basin, the measurement results of two additional stations (Vyhne in Slovakia and Beregovo in Ukraine) were also included into the investigations. The seasonal variations in the long data series due to temperature and air pressure effects were eliminated. The residual curve – after the correction of the seasonal effects and filtering the “high frequency” components (e.g. earthquakes, Earth tides, etc.) – contains the instrumental drift. It is impossible to determine this curve mathematically. It can be diminished by special instrumental solutions and by regular calibration of the instruments. This paper shows methods and possible solutions how the instrumental drift was investigated and eliminated in order to get the most reliable data for studying recent tectonic movements. The reliability of the extensometric measurements was tested by the tidal evaluation of the data series. The results of the observations show that the Pannonian Basin is under compressive stress. The strain rates measured by extensometers on the margin of the basin are about three orders of magnitude higher than the intra-plate strains obtained by GPS measurements. The reason for this large difference arises from the interaction between the plate boundary and intra-plate forces and from the different measurement techniques. Investigations showed that the rate of the tectonic movements varies, and depends on the local geographical and topographical conditions.     

Fracture development in Paleozoic shale of Chongqing area (South China). Part two: Numerical simulation of tectonic stress field and prediction of fractures distribution

A tectonics sedimentation evolution has been researched in Southeast Chongqing, and the reasonable Longmaxi shale highstand system tract (HST) and transgressive system tract (TST) geological model were built respectively based on the rock mechanical test and acoustic emission experiment which the samples are from field outcrop and the Yuye-1 well. The Longmaxi shale two-dimension tectonic stress field during the Cenozoic was simulated by the finite element method, and the distribution of fractures was predicted. The research results show that the tectonic stress field and the distribution of fractures were controlled by lithology and structure. As a result of Cretaceous movement, there are trough-like folds (wide spaced synclines), battlement-like folds (similar spaces between synclines and anticlines) and ejective folds (wide spaced anticlines), which are regularly distributed from southeast to northwest in the study area. Since the strain rate and other physical factors such as the viscosity are not taken into account, and the stress intensity is the main factor that determines the tectonic strength. Therefore, the stronger tectonic strength leads the higher stress intensity in the eastern and southeastern study area than in the northwest. The fracture zones are mainly concentrated in the fold axis, transition locations of faults and folds, the regions where are adjacent to faults. The fragile mineral contents (such as siliceous rock, carbonate rock and feldspar) in the shelf facies shale from south of the study area are higher than in the bathyal facies and abyssal facies shale from center of the study area. The shales characterized by low Poisson’s ratio and high elastic modulus from south of the study area are easily broken during Cenozoic orogenic movement.     

Bio‐geomorphic effects on tidal channel evolution: impact of vegetation establishment and tidal prism change

The long‐term (10–100 years) evolution of tidal channels is generally considered to interact with the bio‐geomorphic evolution of the surrounding intertidal platform. Here we studied how the geometric properties of tidal channels (channel drainage density and channel width) change as (1) vegetation establishes on an initially bare intertidal platform and (2) sediment accretion on the intertidal platform leads to a reduction in the tidal prism (i.e. water volume that during a tidal cycle floods to and drains back from the intertidal platform). Based on a time series of aerial photographs and digital elevation models, we derived the channel geometric properties at different time steps during the evolution from an initially low‐elevated bare tidal flat towards a high‐elevated vegetated marsh. We found that vegetation establishment causes a marked increase in channel drainage density. This is explained as the friction exerted by patches of pioneer vegetation concentrates the flow in between the vegetation patches and promotes there the erosion of channels. Once vegetation has established, continued sediment accretion and tidal prism reduction do not result in significant further changes in channel drainage density and in channel widths. We hypothesize that this is explained by a partitioning of the tidal flow between concentrated channel flow, as long as the vegetation is not submerged, and more homogeneous sheet flow as the vegetation is deeply submerged. Hence, a reduction of the tidal prism due to sediment accretion on the intertidal platform, reduces especially the volume of sheet flow (which does not affect channel geometry), while the concentrated channel flow (i.e. the landscape forming volume of water) is not much affected by the tidal prism reduction. Copyright © 2012 John Wiley & Sons, Ltd.     

朝鲜半岛及华北上元古界-古生界沉积序列与碎屑锆石年代学记录及其构造属性分析

通过地层结构、沉积序列与碎屑锆石年代学记录等三方面的成因分析和区域对比,本文进一步探究了中-朝地块新元古代-古生代的构造属性及演化信息。研究指出,朝鲜半岛平南盆地、太白山盆地以及华北地块内部,其地层结构-沉积相序主要以寒武-奥陶系内陆架碳酸盐岩沉积、志留-泥盆系缺失、中上石炭统-二叠系海陆交互相含煤沉积为特征,并具有可对比的1.85Ga、2.5Ga以及1.15Ga、1.6Ga等碎屑锆石年龄峰值。而在临津江带、沃川带以及华北东南缘,则以泥盆-石炭系泥岩/片岩、中基性火山岩及火山碎屑岩、碳酸盐岩(透镜体)混杂发育为特征,总体显示外陆架沉积环境,且具有可对比的与地层时代接近的最小碎屑锆石年龄,这也是对沉积期较强构造-岩浆活动的反映。综合地层结构、相序、碎屑锆石年龄组成以及聚煤记录,提出朝鲜半岛与华北应属于统一的一级构造单元,即"中-朝板块";但朝鲜半岛西南部及华北东南缘毗邻板块边缘,因此其地层-沉积记录与板内存在差异,简单的一致性模式并不适用。     

The connection of geodynamics with seismicity patterns

When a study is to be made of seismic risks, the present-day geodynamic conditions are of fundamental importance: Earthquakes do not happen by themselves, they do have a cause. The cause of earthquakes is that the tectonic stresses exceed a critical limit. The build-up of these stresses is conditioned by the geodynamic processes occurring in the region in question. A knowledge of the geodynamics characteristic of a region is therefore fundamental for seismic risk studies. The general methodology for making such a geodynamic study is based on the entire set of manifestations of the plate-tectonic conditions of that region: these include the mechanism of earthquakes, the stresses observed in mines, the orientation of surface joints and even the direction of river valleys. Examples of geodynamic studies and their bearing on seismic risks are shown from various areas of the world, notably from China, India, and Colombia.     

Fractal analysis of the Oyo River, cave systems, and topography of the Gunungsewu karst area, central Java, Indonesia

Gunungsewu, the southernmost subzone of the Southern Mountains, central Java, is a classic karst terrain, bounded by the Oyo River on the north and the Indian Ocean on the south. In this study, the Oyo River, the main drainage in the area, is divided into 14 segments, and the fractal dimension of each segment is determined by the box-counting method. The 14 segments show various values of fractal dimensions, which are controlled by lithology and geologic structures of the area that is being dissected by the river. Easily eroded lithologies have larger fractal dimensions, and the value changes abruptly when the river crosses faults. Fractal dimensions of six underground rivers in the Bribin, Sodong, Semuluh, Jomblang, Soga, and Sumurup caves, and the surface topography above the caves were also determined. The caves have fractal dimensions that range from 1.043 ±0.01 to 1.08±0.01; the surface topography has fractal dimensions that range from 1.49±0.01 to 1.732±0.01. The fractal dimension of an underground river is proportional to the fractal dimension of the surface topography over the passage. Larger fractal dimensions of underground rivers are associated with smaller flow rates of the rivers. Received, June 1998Revised, March 1999, August 1999, February 2000Accepted, February 2000     

印度与欧亚板块碰撞以来东喜马拉雅构造结的演化

在野外填图,构造观察及前人研究的基础上,本文识别并描述了东喜马拉雅构造结中的推覆断裂、正断裂及走滑断裂、背斜(形)和向斜(形)等构造类型,讨论了这些构造位置及与印度板块挤入,印支地块旋转的关系,还探讨了东喜马拉雅构造结对印度板块持续向北推挤下的特殊应变调节方式。在印度大陆部分,东喜马拉雅构造结由3个向外逐渐变新的构造结组成,即北东向的南迦巴瓦峰复式背斜、北西向的桑复式向斜及北东向的阿萨母复式向斜。上述3个构造结是协调印度板块的挤入、喜马拉雅弧的扩展及印支地块的旋转的构造。在欧亚大陆内部的冈底斯岛弧,在派区及阿尼桥走滑断裂协调下,高喜马拉雅结晶岩的基底挤入冈底斯岛弧内部,在大拐弯顶端形成向上的挤出构造。在南迦巴瓦峰构造结的北西侧,由于掀斜式抬升及重力滑动,使得冈底斯盖层与结晶基底脱耦,上盘盖层沿东久向北西方向滑动。在南迦巴瓦峰构造结北东侧,由于印支地块的挤出和旋转,形成一系列的北西向走滑断裂,如实皆断裂、嘉黎—高黎贡断裂、澜沧江断裂及红河断裂等。     

Central Himalayan crystallines as the primary source for the sandstone–mudstone suites of the Siwalik Group: New geochemical evidence

Geochemistry of the Sub-Himalayan foreland basin Siwalik sediments has been used for interpreting the nature of the source rocks. This study has shown that the compositional changes are a function of stratigraphic height, demonstrated by the upward increase of P₂O₅, Na₂O, CaO, MgO and SiO₂ content from Lower to the Upper Siwalik rocks. On the other hand, K₂O, Fe₂O₃, TiO₂ and Al₂O₃ show decrease with the increasing stratigraphic height. These trends are a clear reflection of time-controlled changes in the source lithology. Ratios such as Eu/Eu*, (La/Lu)_cn, La/Sc, Th/Sc, La/Co, and Cr/Th suggest a prominent felsic source area for the Siwalik sediments. Chondrite-normalized REE pattern with LREE enrichment and moderately flat HREE pattern with sharp negative Eu anomaly are attributed to a felsic source. Contrary to the existing belief, this study has ruled out any contribution from the mafic sources and highlighted the compositional similarities of Siwalik sediments with the crustal proxies like PAAS, NASC and UCC. The geochemical data point to a significant role played by the Precambrian and early Paleozoic granitic rocks of the Himalayan tectogene in shaping the composition of the foreland sediments. The variable CIA values and marked depletion in Na, Mg and Ca exhibited by the Lower, Middle and Upper Siwalik sediments reflect variable climatic zones and variations in the rate of tectonic uplift of the source area. Our results demonstrate that in the Lower Siwalik and part of the Middle Siwalik, Higher Himalayan Crystalline sequence (HHCS) was the primary source area with minor contributions by the meta-sedimentary succession of the Lesser Himalaya. Later, during the deposition of the upper part of the Middle Siwalik and Upper Siwalik, the source terrain switched positions. These two prominent source terrains supplied sediments in steadily changing proportion through time.     

Strain analysis in Jurassic argillites of the Monte Sirino area (Lagonegro Zone,southern Apennines,Italy) and implications for deformation paths in pelitic rocks

Analysis of strain in Jurassic argillites forming part of the folded and thrusted sedimentary succession of the Lagonegro basin (southern Italian Apennines) has been carried out using ellipsoid-shaped reduction spots as strain markers. Most of the determined finite strain ellipsoids are of oblate type and show a peculiar distribution of the maximum extension direction (X), with maxima either subparallel or subperpendicular to the local fold axes. Using the strain matrix method, two different deformation histories have been considered to assist the interpretation of the observed finite strain pattern. A first deformation history involved vertical compaction followed by horizontal shortening (occurring by a combination of true tectonic strain and volume loss), whereby all strain is coaxial and there is no change in the intermediate axis of the strain ellipsoid. By this type of deformation sequence, which produces a deformation path where total strain moves from the oblate to the prolate strain field and back to the oblate field, prolate strain ellipsoids can be generated and may be recorded where tectonic deformation has not been large enough to reverse pretectonic compaction. This type of deformation history may be of local importance within the study area (i.e. it may characterize some fold hinge regions) and, more generally, is probably of limited occurrence in deformed pelitic rocks. A second deformation sequence considered the superposition of pre-tectonic compaction and tectonic strain consisting of initial layer-parallel shortening followed by layer-parallel shear (related to flexural folding). Also in this instance, volume change during tectonic deformation and tectonic plane strain have been assumed. For geologically reasonable amounts of volume loss due to compaction and of initial layer-parallel shortening, this type of deformation history is capable of producing a deformation path entirely lying within the oblate strain field, but still characterized by a changeover, during deformation, of the maximum extension axis (X) from a position parallel to the fold axis to one perpendicular to it. This type of deformation sequence may explain the main strain features observed in the study area, where most of the measured finite strain ellipsoids, determined from the limb regions of flexural folds, display an oblate shape, irrespective of the orientation of their maximum extension direction (X) with respect to the local structural trends. More generally, this type of deformation history provides a mechanism to account for the predominance of oblate strains in deformed pelitic rocks.