安徽巢湖大型平卧褶皱研究

巢湖平卧褶皱由一个背斜和一个向斜组成,枢纽呈NNE向,轴面微向NWW平卧背斜根部倾斜。卷入褶皱的地层为上震旦统至上三叠统,厚达3.1km。褶皱分布面积约380km~2,波长9km,波幅18km。后期直立褶皱叠加于平卧褶皱之上,褶皱缩短量达19.17km,缩短率约53.7％,褶皱受控于大玵台阶状滑脱断层。褶皱地层由NWW往SEE运动,是一种变动滑脱褶皱。     

Mega arrowhead interference patterns in the central part of the Yanshan Orogenic Belt,North China

The Chengde-Pingquan region is located in the central part of the Yanshan Orogenic Belt (YOB). At Daheishan and Pingquan in the central YOB, thrusts and folds of variable trends are displayed in 2 km-scale fold interference patterns. Detailed field mapping was conducted to decipher the geometry of these two superimposed structures. Map-view geometry and stereonet plots for outcrop-scale folds indicate that the superimposed structures form arrowhead interference pattern where NW-SE-trending F₁ folds are refolded by later ENE-WSW F₂ folding. After remove the effects of later faulting, restored map-views of the superimposed structures show that when the F₁ folds have inclined axial surfaces but with no an overturned limb, an arrowhead interference pattern (here called modified type-2 pattern) can form. Our field data and reinterpretation of the findings of previous studies suggest that five major shortening phases have occurred in the Chengde-Pingquan region. The first two phases, which formed the superimposed folds, occurred earlier than the Late Triassic (D1) and during the Late Triassic to Early Jurassic (D2). These two phases were followed by three deformation phases that are mainly characterized by thrusting and strike-slip faulting, which strongly modified the large-scale fold interference patterns.     

赣东北前震旦纪陆内叠加褶皱

江南古陆与华夏古陆拼接带北西侧前震旦纪地层中存在着近东西向褶皱叠加在早期近南北向褶皱上的现象,这是怀玉地块向西拼贴、华夏古陆向北西碰撞拼接过程中构造应力向陆内传递时形成的构造变形系统。叠加褶皱与拼接带具有成生联系,且各自代表了不同构造部位的变形特点。这一构造系统形成于前震旦纪,可能与格林威尔(Grenville)造山运动相当。     

复合褶皱数学模型的应用

为便于对褶皱构造的几何形态进行描述、概括和实际应用，在划分出两个基本类型褶皱的基础上，用数学方程式对五种叠加褶皱进行了表述，这样，利用计算机可以快速准确地获得叠加褶皱的具体形态。     

断层调整与控制作用下的叠加构造变形:以贵州地区燕山期构造为例

褶皱叠加方式与其形成的构造现象极为复杂。常见3种叠加方式为共轴叠加、横跨叠加和斜跨叠加。如果地质体均一,断层不发育,即会形成理想型叠加褶皱的构造样式。如果发育区域性大型断层,在不同方向的区域应力场作用下,加上地质体的不均一,就会在不同的区块内形成更为复杂的叠加褶皱与构造组合。贵州境内自古生代-中生代先后发育了5条切割基底的区域性断裂,至早中中生代,这些断层将区内切割为6个主要构造块体。在三叠纪之后的燕山构造运动期间,发生了强烈的构造叠加变形,早燕山期与晚燕山期区域应力场方向不同,使得不同区域断层的性质、位移发生变化,断层的多次活动起到了应力释放与调整作用,再加上块体地质结构的不均一性与软弱层的滑脱作用,最终在不同区块内发生了不同的褶皱叠加作用,形成了不同的褶皱构造样式与构造组合。     

甘肃古浪地区石炭系羊虎沟组层内褶皱特征及其对煤层的控制作用

本文探讨的是见于甘肃古浪地区石炭系羊虎沟组含煤建造中普遍发育的层间褶皱特征、形成机制及其对煤层储聚的控制作用,研究发现石炭纪地层中的层内褶皱具有多方位的褶皱枢纽,具非共轴叠加褶皱形态,经历了早期B形和晚期A形褶皱演化过程,最终形成AB复合型褶皱,此类褶皱普遍控制了该套岩层中煤层的储聚。本文在分析了该类褶皱的几何形态特征及其变形控制条件的基础上,探讨了它的形成演化机制和控煤特征。     

Hinge migration as a mechanism of superimposed folding

Paraffin wax analogue modelling of superimposed folding shows how early fold shape and orientation determine fold-axis orientation, type of interference pattern and mechanism of superposed folding. During two successive deformations, the behaviour depends on the angle between the first and second compression directions. (i) When they are perpendicular to each other, classic superposed folding with either domes and basins, or folds with vertical axes develop, depending on whether the earlier folds were open or closed. (ii) When the two compression directions are oblique, the earlier folds rotate. The degree of rotation depends on the angle between the first folds and the later compression direction and is proportional to the amount of strain. The orientations of the new folds are close to those of the earlier open folds. The final deformation pattern consists of domains where the orientations of the axes depend on whether the early folds were previously either open or closed. Many early folds are reused to become later folds by the mechanism of hinge migration.These results are consistent with the pattern of superimposed folding observed in the Devoluy structure of the French Alps. They show that simply by studying the directions of fold axes in areas of superposed folding, it is not possible to define compression directions. Moreover there is the possibility that superposed folding may go unnoticed if hinge migration has occurred.     

冀东高级变质区的构造特征──冀东太古宙地质问题讨论之三

按照韧性剪切带的发育程度，将区内划分为迁西群分布区的弱变形域和遵化群分布区的强变形带。根据各种形变特征，认为迁西群及遵化群分别存在三次及两次叠加褶皱，其中迁西期形成的为轴面南倾的东西向线状同斜褶皱；遵化期第一幕为北东向摆动的紧密线形倒转褶皱。由于边界条件的限制，叠加在迁西群上的褶皱，轴向转为近南北向。迁西期褶皱因属同斜而具简单层状体特征，故每个单体的叠加背向形并非三斜对称，主要部分也并非穹盆构造，而为ｗ形蛇形弯曲，不存在原生的穹隆或卵形群构造；遵化期第二幕表现为舒缓的东西向叠加褶皱。区内的主要构造样式为包括迁西群在内的由叠加褶皱及两组共轭韧性剪切带共同作用所形成的迂西－曹在卵形隆起区；遵化群的弧形褶皱群被密云－喜峰口－王厂左行平移韧性断裂带带动形成的宽城－遵化帚状构造亚区以及由遵化群形成的青龙王厂－迁安重熔片麻岩穹隆亚区。     

Episodic Mesozoic constructional events of central South China: constraints from lines of evidence of superimposed folds,fault kinematic analysis,and magma geochronology

ABSTRACT

The South China block (SCB), located in the convergence zones of the western Pacific subduction tectonic domain and Tethyan tectonic domain, has experienced complex tectonic processes, including the continent–continent collision caused by the closure of the Palaeo-Tethys Ocean, and the subduction of the Palaeo-Pacific plate. However, due to complex intracontinental deformation and abundant magmatism, there are serious divergences in the corresponding records of the tectonic transformation from Palaeo-Tethys to Palaeo-Pacific. We have analysed the map-scale superimposed fold system developed in central SCB and also inverted the palaeo-stress field based on the fault–slip vectors. On this basis, the deformation styles and superposition mechanism of two-stage folds were recovered to establish the tectonic stress field in early Mesozoic and tectono-magmatic events by combining the chronology of the accompanying syntectonic magma. The early E–W/WNW-trending folds and Triassic magmatic system were identified; these were controlled by the NE–SW-trending compressive stress field, to coordinate with the collisions between the SCB and the Indochina block in the southwest, and the North China block in the north. The late NE/NNE-trending folds superimposed on the early folds in an orthogonal way to form a large-scale dome-basin superimposed fold system, which were controlled by the WNW–ESE-trending compressive stress field. According to the strata relations involved in deformation and the chronology data of magmatic rocks, it could be determined that NE/ENE-trending folds would be formed during the Mid- to Late Jurassic, corresponding to the westward subduction events of the Palaeo-Pacific plate. The establishment of the large-scale superimposed fold styles and the identification of fold deformation in the Triassic and Jurassic are important for understanding the early Mesozoic tectonics of South China, and even for all East Asia continent. In particular, it can provide important temporal and spatial constraints to explain the complex deformation process and geodynamic settings of South China in the early Mesozoic.     

塔里木盆地塔北隆起叠加构造分析

对叠加构造变形构造,变形时序、叠加构造形成的地球动力学背景及其与油气关系的综合研究表明,塔北隆起的叠加构造可以划分出：以二叠纪为形成高峰期的北西－南东走向的挤压构造,以三叠纪为形成高峰期的北东－南西走向的挤压构造,主要形成于渐新世－中新世的拉张构造,这三期构造在空间上、时间上复合叠加,从而在塔北隆起形成了轮南构造带、南喀－英买力叠加褶皱带以及羊塔克－提尔根负反转构造带等叠加构造变形区。上述叠加构造变形区均是有利的油气勘探区。