虹湾东缘雁列式月岭构造带形貌特征与成因模式研究

月岭作为月海中一种广泛分布的线性构造,多表现为褶皱逆冲推覆为主的构造样式,且具雁列式展布。因此,月岭对月表区域乃至全月的构造应力分析有着非常重要的指示作用,但其成因机制不清。虹湾是中国嫦娥绕月探测工程研究的重点区域,区域内最明显的线性构造是虹湾东缘呈雁列式展布的月岭构造带,对这一月岭构造带的研究将有助于了解虹湾地区的区域应力特征和构造演化过程。文中通过对虹湾东缘雁列式月岭构造带的高分辨率影像进行解译并与其他区域对比分析,结合虹湾地区已有地质资料和前人提出的相关构造演化模式及目前最新的研究成果,认为虹湾东缘雁列式月岭构造带受虹湾撞击坑坑缘基底和表面玄武岩性影响,虹湾撞击盆地沉降引起的径向挤压应力和表面熔岩流导致的挤压应力由于方向与大小的差异,共同导致该月岭构造带呈类似走滑剪切中右阶左行的形貌特点。在此基础上讨论了此月岭构造带的演化过程,并根据月岭与撞击坑的交切关系,发现虹湾东缘月岭构造带在哥白尼纪仍在继续活动。     

鄂尔多斯盆地东南部中生界地层节理发育特征与古应力场

鄂尔多斯盆地东南部中生代地层中发育有六组节理(E-W、N-S、ENE-WSW、NNW-SSE、WNW-ESE、NNE-SSW),并且构成三期的正交节理系统(E-W与N-S、ENE-WSW与NNW-SSE、WNW-ESE与NNE-SSW).三期正交节理系统形成的先后期次为:E-W向和N-S向两组节理最早形成,WNW-ESE向和NNE-SSW向两组节理为第二期形成,ENE-WSW向和NNW-SSE向两组节理则最晚形成.E-W向、N-S向和ENE-WSW向三组节理的节理间距指数(FSI)分析结果表明,节理间距的发育程度除了受岩层厚度控制外,还受区域应力场的控制.E-W向、N-S向和ENE-WSW向三组节理的节理间距率(FSR)值分布范围指示不同组节理在区域上发育程度具有差异性.此外,E-W向的优势节理组的FSR值有超过间距与层厚比值的临界值,而非优势组的SN向节理的FSR值则全部小于临界值,表明E-W向和N-S向两组节理组成最早一期的正交节理系统.盆内中生代地层中的三期正交节理系统,所对应的古应力场分别为:(1)晚侏罗世盆地处在近E-W向的挤压环境下,形成了第一期正交节理系统,为E-W向和N-S向两组节理;应力来源于古太平洋板块向欧亚板块俯冲所产生的NW-SE向的挤压分量.(2)晚白垩世时,来自于古太平洋板块俯冲产生的NW-SE向挤压应力形成了第二期正交节理系统的WNW-ESE向和NNE-SSW向两组节理.(3)晚白垩世末至新生代,印度板块向欧亚板块下的俯冲产生NE-SW向的远程挤压应力,形成第三期正交节理系统的ENE-WSW向和NNW-SSE向两组节理.     

1.9-1.8 Ga old strike-slip megashears in the Baltic Shield, and their plate tectonic implications

The tectonic evolution of the ca. 2.0-1.75 Ga old Svecokarelian fold belt is reviewed, and evidence is presented for large-scale intraplate strike-slip movements along ductile megashears. After the formation of the Kola collision suture and the neighbouring Granulite-Tanaelv thrust belt around 1.9 Ga ago, dextral shearing was initiated along N-S trending megashears. Subsequent anticlockwise rotation of the initially NNE-SSW oriented principal compressive stress caused dextral shearing along a NW-SE trending megashear and reversal in the sense of shearing in the N-S trending ones. Further anticlockwise stress rotation (to a total of about 120°) brought an end to sinistral shearing along the N-S megashears around 1.8 Ga ago and caused reversal to sinistral slip along the NW-SE megashear. Both the older (1.9-1.85 Ga) and younger (1.84-1.8 Ga) parts of this evolution are recorded within the Karelian province and its southwestern margin, where consolidation of the lithosphere took place shortly after 1.9 Ga ago. In the Svecofennian province, where crustal accretion did not start until around 1.9 Ga ago, the older movements may have caused synaccretional crustal folding, but with increasing consolidation, the deformation was concentrated along megashears. Although it is still not possible to interrelate the function of active subduction zones and intraplate megashears. the evolution traced so far provides support for plate tectonic interpretations of the Early Proterozoic geodynamics of the Baltic Shield.     

雨海地区月岭分布特征及控制因素分析

月岭是月球表面上最常见的线性构造之一,大多分布于被玄武岩充填的月海之中。虽对于月岭成因的观点不一,但多数月岭具有明显的挤压变形特征,其展布形式有单列、组或群(常见)、网状或雁列状等。月岭的形成和展布既受到月海盆地构造的控制,又受到区域应力状态的影响。文中以雨海为研究区域,利用美国环月球巡逻者(LRO)的宽视角影像(WAC)数据和激光高度计(LOLA)数据对雨海地区的月岭构造进行解译和提取,对月岭进行分类和统计分析,结合雨海盆地构造特征以及月岭构造的样式解析,并运用沙箱构造物理模拟方法对月岭的形成和分布进行模拟实验,讨论了雨海地区影响月岭形成和分布的主控因素。结果表明,月岭是挤压体制下形成的;盆地构造是控制月岭类型Ⅰ分布的主要因素;月岭类型Ⅱ的分布主要受区域构造应力控制,其走向主要反映区域构造的最大主应力方向。综上推断,雨海地区月岭形成于近东西向最大主应力并受到雨海盆地构造的控制,表现为月岭类型Ⅰ和月岭类型Ⅱ的综合样式。     

青藏高原南北向地堑系的实验研究

青藏高原南北向正断层及与其伴生的地堑是当前的热门话题。对其成因的认识分歧颇大,它们与高原隆升的关系则还处于推论阶段。本文用模拟实验的方法检验了其中的主要观点,结果表明:南北向正断层及与其伴生的地堑是南北向挤压的结果,是在挤压中期横张裂隙的基础上发展起来的。因此,它不代表高原已抬升到了最大高度后的塌陷,而是伴随高原隆升过程中的产物。     

Variability in Early Amazonian Tharsis stress state based on wrinkle ridges and strike-slip faulting

We present evidence for a decrease in the magnitude of Tharsis-circumferential compressive stress during the Late Hesperian to the Middle Amazonian based on chronologic changes in the predominant style of faulting in southern Amazonis Planitia. Using high-resolution MOLA topography, we identify a population of strike-slip faults that exhibit Middle Amazonian-aged displacements of regional chrono-stratigraphic units. These strike-slip faults are adjacent to an older population of previously documented Late Hesperian-aged thrust faults (wrinkle ridges). Along-strike orientations of these thrust and strike-slip faults reveal the Tharsis-radial stress to be the area's most compressive remote principal stress and that this stress orientation and magnitude persisted throughout the Late Hesperian to the Middle Amazonian. We show that the change in the predominant style of faulting from thrust faulting to strike-slip faulting during this time requires a decrease of the Tharsis-circumferential compressive stress to a magnitude less than lithostatic load, with negligible change in stress orientation.     

Strain distribution within arcuate diapiric ridges of silicone putty

Twenty crescent-shaped diapiric models of silicone putty were made in two high-capacity centrifuges. The strain distribution within the models was studied by means of coloured rectangular elements, a method which led to large errors at random locations. Most elements affected by large errors could be identified in repeated experiments.The deformation pattern within the central segment of the diapiric ridges is dominated by two large regions of contrasting principal strain normal to the radial symmetry plane (axial plane of the crescents). This principal strain is tensile near the concave boundary of a ridge and compressive near the convex boundary of a ridge.Within the radial symmetry plane, the orientation pattern of long axes of the total-strain ellipses resembles an open fan which diverges toward the crest of the diapiric ridge. In the high-amplitude models, there is a narrow crestal region in which the long axes are subhorizontal. A similar region has been noted in comparable models of cylindrical diapiric ridges.In one of our models (WMS 20), the arcuate hinge line has pronounced culminations at both ends of the diapiric ridge. This results in a strong crestal depression at the radial symmetry plane where the strain analysis was performed. Accordingly, the characteristic region of tensile normal strain occupies most of the radial section.     

Deformation of oceanic lithosphere near slow-spreading ridge discontinuities

Transform and non-transform discontinuities that offset slow spreading mid-ocean ridges involve complex thermal and mechanical interactions. The truncation of the ridge axis influences the dynamics of spreading and accretion over a certain distance from the segment-end. Likewise, the spreading system is expected to influence the lithospheric plate adjacent to the ridge-end opposite of the discontinuity. Tectonic effects of the truncated ridge are noticeable in for example the contrast between seafloor topography at inside corners and outside corners, along-axis variations in rift valley depth, style of crustal accretion, and ridge segment retreat and lengthening. Along such slow-spreading discontinuities and their fossil traces, oceanic core complexes or mega-mullion structures are rather common extensional tectonic features. In an attempt to understand deformation of oceanic lithosphere near ridge offsets, the evolution of discontinuities, and conditions that may favor oceanic core complex formation, a three-dimensional thermo-mechanical model has been developed. The numerical approach allows for a more complete assessment of lithosphere deformation and associated stress fields in inside corners than was possible in previous 3-D models. The initial suite of results reported here focuses on deformation when axial properties do not vary along-strike or with time, showing the extent to which plate boundary geometry alone can influence deformation. We find that non-transform discontinuities are represented by a wide, oblique deformation zone that tends to change orientation with time to become more parallel to the ridge segments. This contrasts with predicted deformation near transform discontinuities, where initial orientation is maintained in time. The boundary between the plates is found to be vertical in the center of the offset and curved at depth in the inside corners near the ridge–transform intersection. Ridge–normal tensile stresses concentrate in line with the ridge tip, extending onto the older plate across the discontinuity, and high stress amplitudes are absent in the inside corners during the magmatic accretionary phase simulated by our models. With the tested rheology and boundary conditions, inside corner formation of oceanic core complexes is predicted to be unlikely during magmatic spreading phases. Additional modeling studies are needed for a full understanding of extensional stress release in relatively young oceanic lithosphere.     

Compressive Tectonics around Tibetan Plateau Edges

Various earthquake fault types, mechanism solutions, stress field, and other geophysical data were analyzed for study on the crust movement in the Tibetan plateau and its tectonic implications. The results show that numbers of thrust fault and strike-slip fault type earthquakes with strong compressive stress near NNE-SSW direction occurred in the edges around the plateau except the eastern boundary. Some normal faulting type earthquakes concentrate in the Central Tibetan plateau. The strikes of fault planes of thrust and strike-slip faulting earthquakes are almost in the E-W direction based on the analyses of the Wulff stereonet diagrams of fault plane solutions. This implies that the dislocation slip vectors of the thrust and strike-slip faulting type events have quite great components in the N-S direction. The compression motion mainly probably plays the tectonic active regime around the plateau edges. The compressive stress in N-S or NE-SW directions predominates earthquake occurrence in the thrust and strike-slip faulting event region around the plateau. The compressive motion around the Tibetan plateau edge is attributable to the northward motion of the Indian subcontinent plate. The northward motion of the Tibetan plateau shortened in the N-S direction encounters probably strong obstructions at the western and northern margins.     

En echelon fractures in a dextral shear zone - tectonic heritage for a hydrothermal cave (Budapest, Hungary)

Microtectonic study of brittle structures in the József Hill Cave, Budapest, highlights the connection between different phases of fracturing and cave formation. E-W trending dextral faults (second order Riedels) and NW-SE oriented tension fractures developed in a ENE-WSW trending dextral shear zone as a result of WNW-ESE directed compression. Ascending thermal water dissolved cave galleries and created barite veins along these fractures. The first stage of cave formation as inferred from timing of fracturation from the regional stress field was Oligocene-Early Miocene. Between the Middle Miocene and Quaternary new N-S to NE-SW trending normal faults were formed by ESE-WNW extension. Pleistocene differential uplift resulted in the reactivation and enlarging of fault zones, dominantly the E-W trending older Riedels. These recent tectonic events enhanced the original en echelon geometry of the older cave corridors.     

Gravity induced near-surface stresses in long-symmetric ridge-valley systems

Patterns of near-surface gravity and tectonically-induced stresses within ridge-valley systems greatly illuminate our understanding of important geodynamic processes as well as design of experiments to elucidate them. This paper presents analytical results derived for a number of geometrical configurations and range of mechanical properties of a ridge-valley system using the elastic solution of McTigue and Mei. The study reveals (i) the presence of non-zero compressive stresses near the ridge crests, which decrease with increasing Poisson's ratio (μ) and reduce to zero at ridge crests for μ=0·5 and that (ii) the central tensional regime characterizing a valley becomes narrower due to the presence of two ridges; and decreases with increasing μ, becoming compressive at depth. For all geometrical parameters considered, all components of stress show concentration at the outer flanks of the ridges and increase with depth approaching a standard state of stress.     

Patterns of stress at midocean ridges and their offsets due to seafloor subsidence

The effect of the seafloor subsidence on the horizontal stress field is investigated by combining the finite element method with a formulation that allows us to compute the two-dimensional (2D) horizontal stresses arising from isostatically compensated vertical loads. The topographic load created by the elevation of midocean ridges relative to old ocean floor is shown to be a significant source of ridge-parallel tensile stresses. These may predominate over the ridge-perpendicular stresses and explain observations at midocean ridge offsets such as (1) oblique normal faulting at ridge-transform intersections trending up to 60° relative to the ridge axis, and (2) nontransform offsets consisting of structures oriented at 45° relative to the ridge trend. At midocean ridge overlaps, rotation of the ridge-parallel tensile stresses favours rift propagation at more than 45° relative to the ridge trend. It is suggested that propagating rift tips that bend abruptly lead to partially unlocked offsets, and as a result large overlaps may eventually start to rotate and evolve into a microplate.     

An analytical model of continental rift fault patterns

Two proposed mechanisms of rift initiation are crustal uplift alone and a combination of crustal uplift and regional horizontal extension. A three-dimensional, thick-plate, elastic analysis has been used to model the crustal stress state and the fault patterns associated with these mechanisms. Small ratios of uplift width to crustal thickness (<10) necessitate the thick-plate approach.For the crustal uplift model, the surface fault pattern is characterized by normal faults trending parallel to the major uplift axis at the uplift center and radial normal faults toward the ends of the major uplift axis. Zones of compressional structures (e.g., strikeslip and thrust faults) may develop at the periphery of the uplift. Superposition of regional horizontal tension with the stresses produced by crustal uplift eliminates the compressive stresses at the uplift periphery producing normal faults parallel to the major uplift axis at the uplift center and normal faults perpendicular to the major uplift axis at the uplift periphery.A comparison of these predicted fault patterns with the faults of the Rhine graben suggests that the combination of crustal uplift and regional horizontal extension contributed to the formation of that rift system. The stresses produced by crustal uplift promoted the formation of the central graben and the fan-shaped troughs toward the ends of the major uplift axes, while superposed regional horizontal tension eliminated the large compressive stresses at the uplift periphery promoting the normal faulting and dike intrusions observed on the Rhine graben flanks.     

中国第四纪的构造事件与应力场

在早、中更新世之间(０．７３ＭａＢ．Ｐ．)我国存在一次重要的构造事件，由此第四纪便分属两个构造期：喜马拉雅期(２３．３—０．７３ＭａＢ．Ｐ．)和新构造期(０．７３Ｍａ以来)。在这两个时期内，具有截然不同的构造应力场、不同的形成机制、不同的构造变形方式、方向、不同的扩张或缩短速度、不同类型的火山喷发、不同方向和不同位置的火山喷发带，并且也造成完全不同的构造地貌特征。     

山西太古代——中生代构造应力场

本文采用历史分析与力学分析相结合的原则,研究山西太古代至中生代五次主要构造运动的形变特征、主应力方向及分布规律。中太古代晚期（阜平运动）以SSW向挤压为主;晚太古代末期（五台运动）、早元古代末期（吕粱运动）和侏罗纪（燕山运动）受SE—SEE向挤压;白垩纪（四川运动）以SSW向挤压为特征。五次构造运动的最大主压应力均呈近水平方向。     

Regional stress and structure in relation to brown coal open cuts of the Latrobe Valley,Victoria

An interpretation of the origins of folds and joints, which affect the Tertiary Brown Coal Measures of the Latrobe Valley, leads to the proposal that the geological structures have been formed under a regional Late Tertiary NNW‐SSE compressive stress. Considerations of the pattern of measured in situ stresses and of interpreted stresses, derived from earth movements around open cuts and from earthquakes, indicate that a regional NNW‐SSE compressive stress is still in existence in the SE part of Australia at the present time.

It is proposed that the consistencies in the stress orientations reflect consistencies in the Late Tertiary to Recent global movements of the Australian plate.     

A study of the behaviour of brittle rocks subjected to confined stress based on the Mohr–Coulomb failure criterion

In this study the relationship between brittle rocks’ behaviour and uniaxial compression stress is obtained based on the Mohr-Coulomb failure criterion and the behavioural characteristics of brittle rocks under uniaxial compression stress are investigated. According to the laboratory uniaxial compression tests on granite rocks, and also available results in the literature, required parameters in the study are obtained. It is indicated that the behaviour of brittle rocks which is affected by uniaxial compression is function of cohesion. In the other words, cohesion changes as the uniaxial compression increases. Also, in yield point where its stress is equivalent to the uniaxial compressive strength, the cohesion maximises. By suggesting a new viewpoint to the Mohr’s circle, normal stresses on failure plane, shear stresses tangential to the failure plane and hydrostatic stresses are investigated. Results show that, normal stress on the failure plane in yield point of the behavioural curve equals zero and shear stress tangential to the failure plane is maximum which is equal to the maximum rocks’ natural strength. Also, in this point the strength is equi-pressure, therefore the stress is of hydrostatic type.     

Vertical tectonic movements of the crust in transform fracture zones of the Central Atlantic

The most significant vertical movements of the oceanic crust in the Central Atlantic are characteristic of transverse ridges confined to transform fracture zones. These movements are also recorded in some local depressions of the Mid-Atlantic Ridge (MAR) and in older structures of deep-sea basins. The amplitude of such movements substantially exceeds that related to the cooling of lithospheric plates. Vertical movements can be driven by various factors: the thermal effect of a heated young MAR segment upon a cold plate, thermal stress, thermal energy released by friction in the course of displacement of fault walls relative to each other, serpentinization of the upper mantle rocks in the transform fault zone, and lateral compression and extension. The alternation of compression and extension that arises because of the nonparallel boundaries of the transform fracture zone and the unstable configuration of the rift/fracture zone junction was the main factor responsible for the formation of the transverse ridge in the Romanche Fracture Zone. The most probable cause of the vertical rise of the southern transverse ridge in the Vema Fracture Zone is the change in the spreading direction. In general, the fracture zones with active segments more than 100 km long are characterized by extension and compression oriented perpendicularly to the main displacement and related to slight changes in the spreading configuration. It is impossible to single out ambiguously the causes of vertical movements in particular structural features. In most cases, the vertical movements are controlled by several factors, while the main role belongs to the lateral compressive and tensile stresses that appear owing to changes in the movement of lithospheric blocks in the course of MAR spreading.     

层状岩体单轴和双轴压缩蠕变特性的数值试验

以绿片岩和大理岩组成的层状岩体为研究对象,采用FLAC3D对互层状岩体进行了单轴和双轴压缩蠕变试验的数值分析,在数值分析中考虑荷载方向与层理之间的几何关系、大理岩夹层的体积分数、应力水平等的影响。研究结果表明:单轴和双轴压缩条件下,随着夹层倾角由0°增加至90°,轴向和夹层倾斜方向的应变绝对值均呈先增大后减小的变化规律;随着大理岩夹层体积分数的增加,轴向压缩变形和2个侧向方向的膨胀变形量均有所减小。单轴压缩条件下,当轴向荷载方向垂直于层理时,轴向压缩变形均大于轴向荷载方向平行于层理时的轴向压缩变形;双轴压缩条件下,当轴向荷载方向垂直于层理、侧向荷载方向平行于层理时,轴向压缩变形最大,当轴向荷载方向平行于层理、侧向荷载方向垂直于层理时,轴向压缩变形最小。     

晋中南中新生代构造应力场演化及其动力学分析

中生代以来,晋中南经历了多期构造应力场的作用：印支期,在华北板块南北边缘造山带的强烈挤压作用下,形成了近南北方向的水平挤压应力场;燕山期,在西太平洋古陆与亚洲大陆的碰撞、拼贴作用下,形成了北西西—南东东方向的水平挤压应力场;喜山早期,受印度板块与欧亚板块碰撞作用的影响,形成了北东—南西方向的水平挤压应力场。新第三纪以来,随着裂陷沉降作用和断陷盆地深部塑性物质上涌底辟作用的增强,晋中南构造应力场演化为以北西—南东方向近水平伸展应力场为主,并且伴随着太行山和霍山的不断隆起,在晋中南东部的沁水含煤向斜中形成了局部挤压应力场。