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.     

沁水盆地南缘中-新生代构造变形与构造应力场

沁水盆地南缘自中生代以来,主要经历了印支期、燕山期、喜马拉雅期三期构造活动的影响。通过对地表露头的断 层面擦痕、纵弯褶皱及共轭节理系的研究,获得了古构造应力场信息。在研究区东部 NNE 向的太行山断裂带内,逆冲挤压 构造非常明显,与其相伴发育的不对称背斜构造表明其主压应力方向为 110°;中部的 EW 向正断层、地堑系可能是印支期 近 SN 向挤压作用下形成的逆冲构造经历了新生代构造反转作用而产生的,新生代伸展作用非常显著,伸展方向为 26°, 249°,347°;西部边界由近 SN 向断裂组成,存在新生代近 EW 及 NEE-SSW 向伸展运动的擦痕证据,伸展方向为 94°,72°。 区内发育 NNW-SSE,NW-SE,NE-SW,NEE-SWW,近 SN 等几个方向的共轭节理系,表明存在过燕山期 NW-SE 向的水平 挤压构造应力场和喜山期 NE-SW 向水平挤压构造应力场,近 EW 向水平挤压应力场可能是在这两期主要构造应力场转换过 程中形成的。     

Paleo-stress orientations from calcite twins in the North Pyrenean foreland, determined by the Etchecopar inverse method

During the last decade, it has been shown that accurate analyses of calcite twinning in thin section may allow computation of the paleo-deviatoric stress tensor associated with this deformation. Following from the work of Larroque and Laurent (1988), and Lacombe et al. (1989), this is a new application of the Etchecopar inverse method. Weakly deformed limestones from about 150 to 200 km north of the Pyrenean chain (South France) were studied. The Etchecopar inverse method, which can be used on a microcomputer, is comparable to the method of analysis of striated fault planes proposed by Etchecopar et al. in 1981, as it determines the principal stress orientations and the stress ellipsoid shape ratio φ = (σ₂ − σ₃)/(σ₁ − σ₃). The Etchecopar method using calcite twins has been selected for this study because it is suitable for the determination of polyphase deformation in coarse-grained limestones (Lacombe et al. 1989).

Ten samples of oolitic limestones, cemented with sparry calcite, from the Bajocian (170 Ma) and the Oligocene (30 Ma) were studied. For each of them, only one or two stress tensors were determined: the first is characterized by a principal compressive stress axis σ₁ which is horizontal and approximately N-S. Local departures from this orientation have been observed and are interpreted as local stress perturbations. For the second, which was defined in the Oligocene, but occurred only locally in the Jurassic limestones, the position of σ₁ is nearly vertical; the direction of extension σ₃ is either NE-SW or undefined into the horizontal plane (σ₂ = σ₃); this radial extension is interpreted as the result of two or more superposed extensive deformation phases with vertical σ₁. The N-S compression was never found in the Oligocene limestones, and from its orientation, it is assumed to correspond to the Pyrenean deformation. These results are compared to the more complex deformation pattern obtained from classical microtectonical studies (Arthaud and Choukroune, 1972; Bonijoly and Blès, 1983; Granier and Blès, 1988; Blès et al., 1989). Only the major tectonic events are recorded by calcite twinning. Finally, the suitability of calcite twin analyses for the determination of complex polyphase deformation is discussed.     

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.     

罗布泊盆地新构造变形数值模拟分析

综合罗布泊盆地新构造研究相关成果, 运用数值模拟实验方法, 采用两种模型, 对罗布泊盆地新构造活动进行数值模拟研究, 直观展示盆地的应力状态与位移特征, 再现罗布泊盆地新构造变形序列, 查明运动学特征。数值模拟结果一方面展示出晚新生代以来罗布泊盆地先后主要经历了渐新世末期—早更新世晚期近南北向构造挤压作用控制下的盆地近东西向伸展断陷与早更新世晚期以来北东—南西向构造挤压作用导致的盆地剪切变形两大阶段; 另一方面实验结果也显示, 在两种边界条件的控制下, 研究区地质单元的应力状态主要受地层岩性和断裂共同控制, 盆地内部呈现低应力状态, 在与最大主压应力相垂直的方向上产生伸展变形。盆地南边的两条主干断裂内部具有较高的剪应力, 而罗布泊盆地及其以东地区剪应力最小。位移大小明显受断裂控制, 从南西向北东位移逐渐减小, 指示孔隙流体从南西向北东运移。      

库车坳陷脆性构造序列及其对构造古应力的指示

在对野外脆性构造(主要是节理和断层) 大量观测的基础上, 根据它们与应力的关系, 讨论了库车坳陷白垩纪末期以来的古构造应力时空变化.结果表明, 在库车坳陷脆性构造中, 早期隆升作用形成的主要发育在中生界的NEE-SWW向系统节理被晚期同构造期的在中生界与上第三系均发育的NNW-SSE向和NW-SE向节理切割并改造, 这是对区域上构造应力场在进入新近纪时从弱伸展变化到强烈挤压这一过程的响应.基于断层滑动分析的古应力反演结果显示, 此时盆山边界处以近N-S向伸展应力状态占主导, 而坳陷内部则表现为近N-S向和NW-SE向挤压应力状态.说明在进入新近纪后, 最大主应力(σ₁) 方向从垂向变成水平, 应力场发生了转变.此后的天山快速垂向隆升是库车坳陷北缘和内部应力状态存在差异的原因.      

Pre-Quaternary orogen-parallel extension in the Southern Apennine belt, Italy

The Southern Apennine fold and thrust belt differs from other parts of the peri-Tyrrhenian orogen. In most of the peri-Tyrrhenian belt, hinterland extension is oriented at a high-angle to the orogen axis and appears to be related to rifting and formation of oceanic crust within the Tyrrhenian basin. The Southern Apennines share the late-stage development of normal faults related to the opening of the Tyrrhenian Sea, but also experienced an episode of extension parallel to the strike of the tectonic belt. The orogen-parallel extension was apparently formed in response to the increase in length of the deformed belt during arcuation. Arcuation ostensibly was related to asymmetrical rifting in the hinterland, which was greater in the Southern Tyrrhenian Sea than in areas to the north, and proportionately greater shortening in the frontal parts of the southern belt as compared to regions in the north. During arcuation, extension was spatially concentrated within structural domains and was accomplished by displacement on low-angle detachment faults cutting through a previously imbricated thrust stack. During the Miocene-Pliocene, NNW-SSE extension in the interior of the Southern Appennine belt formed coveally with ENE-WSW shortening in the foreland. Longitudinal extension ceased in the Pleistocene, when younger high-angle normal faults formed in response to the easterly migration of Tyrrhenian Sea rifting and NE-SW extension associated with lithospheric stretching.     

鄂西利川齐岳山高陡背斜带的古应力分析

鄂西利川地区位于湘鄂西构造带与川东构造带的过渡部位,叠加褶皱发育,地处两大构造带分界处的齐岳山高陡背斜带断裂发育。本文以利川地区褶皱和断裂为研究对象,在野外观测和分析的基础上,采用断层滑动数据反演方法,对构造应力场进行了恢复;结合区域构造演化历史,提出该区侏罗纪以来经历了五期构造应力作用,从早到晚分别为:北西-南东向挤压(J3-K1)、近东西向挤压(K1)、近南北向挤压(K1-K2)、北西-南东向引张(K2)和北东-南西向挤压(E3)。该区侏罗纪以来构造变形序列的建立,为深入认识齐岳山高陡背斜带地质灾害形成的地质背景提供了构造地质学证据。     

Tectonic stress regimes,rift extension and transform motion: The South Iceland Seismic Zone

The South Iceland Seismic Zone (SISZ) is located at the junction of three rift segments in southwestern Iceland. The presence of different types of faulting and of differently orientated subgroups in Upper Pliocene to Holocene formations indicate polyphase tectonism. We measured 736 minor faults at 25 sites. Two types of relationships between stress regimes are represented. The first type, named IDS (inhomogeneous data set), is characterized by the presence of two types of fault mechanisms, normal and strike-slip, consistent with a single direction of extension. The second type, named OSR (opposite stress regimes), is characterized by the presence of perpendicular directions of extensions for a single type (normal or strike-slip) of faulting. Because of contradictory chronological criteria, we infer that the OSR alternated during the brittle tectonic activity of the SISZ. Two stress regimes, primary and secondary, are characterized by directions of extension NW-SE and NE-SW, respectively. The general fracture pattern characterized for the primary stress regime in the SISZ includes NNE-SSW trending right-lateral strike-slip faults, conjugate ENE-WSW trending left-lateral faults and NE-SW normal faults. This distribution is quite consistent with a Riedeltype model of fault pattern in a left-lateral shear zone. The stress states characterized based on analysis of both the earthquake focal mechanisms and the recent faulting show great similarity in terms of stress directions. The main difference is the larger ratio of strike-slip motions representing 71 % of the total population in the case of earthquake focal mechanisms, whereas for the whole set of faults the proportion of strike-slip faulting was 50 %. We explain that a temporal evolution of the tectonic regime in the SISZ region, accompanied by a gradual change in stress field, starts with rift-type pure extension and progressively leads to development of preferentially strike-slip structures in the kinematic context of leftlateral transform motion.     

祁连山东南缘第四纪以来的隆升作用及动力学分析

祁连山东南缘隆升是来自印度板块挤压的远程效应与该区周边地块的存在及其活动的相互制约作用而产生的挤压隆升、伸展隆升和左旋走滑隆升共同作用的结果.标志性构造及主应力分析表明, 自早更新世以来, 隆升动力机制不断发生转换, 在早更新世早期以北东-南西向挤压为主, 中更新世早期至全新世早期以北东-南西向拉张、近东-西向的拉张为主, 全新世晚期以北西-南东向左旋扭动为主.根据湟水河阶地有关数据估算出的不同时段河谷下切速率为: 1.4 1× 103 ~ 36.4ka间平均速率较慢(0.11mm/a), 36.4ka至今较快(1.5 4mm/a), 其中10.5~ 3ka间最快(2.2 7~ 2.80mm/a), 显示该区自1.4 1Ma至今构造隆升具有越来越强烈的变化趋势.      

福建厦门地区中、新生代构造应力场研究

本文通过野外构造形变资料的研究,确定了厦门地区中生代的两期（侏罗纪、白垩纪）构造应力场及其主应力方向;利用最新一期共轭剪节理和震源机制解资料,确定了第四纪以来的构造应力场及其主应力方向。最大主压应力轴的优选方位分别为:侏罗纪SE138°,∠8°,白垩纪SW205,∠12°,第四纪以来NW312°,∠21°。 采用石英错密度法,估算了中生代古构造应力值,侏罗纪为88.5MPa,白垩纪为81.5MPa。利用岩石力学声发射技术,测定了现代构造应力大小,在标高为3——-151m（埋深为18——151m）的范围内,最大主压应力值为2.55——16.2MPa,最小主压应力值为1.1——10.1MPa。     

Crustal Stress in the northern North Sea as inferred from borehole breakouts and earthquake focal mechanisms

The regional stress field in the northern North Sea (offshore western Norway) has been studied through the acquisition and analysis of directions of maximum horizontal compression (_H) as extracted from borehole breakouts and from earthquake focal mechanism solutions.
The results indicate that the regional stress field is dominated by NW-SE compression, with good consistency between shallow borehole breakouts (2–5 km depth) and deeper earthquakes (10–25 km depth). The broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin, and the results are in good agreement with the western Europe trend found in earlier investigations.
The Tampen Spur region in the northern North Sea has been subjected to particularly complex deformation, with two dominating fault directions trending NW-SE and NE-SW. From Tampen Spur in the west to the Sogn graben in the east an anomalous stress field is indicated, with NE-SW oriented maximum horizontal compressions. This anomaly is clearly seen both in the borehole breakout data and in the earthquake data. Possible sources for this anomaly are discussed, and include postglacial uplift and/or lateral variations in the physical properties of the crust.     

Lineament analysis of Cannanore district and their implication on the tectonic evolution of the area

The Cannanore district and the adjoining areas mainly comprise of charnokites, gniesses, high and low-grade schists and various types of igneous intrusives. The lineament fabric of the region indicates that the NNW-SSE, NW-SE, ENE-WSW and NE-SW lineament directions are prominent. It is suggested that the area has undergone at least three distinct phases of tectonic activity. The NW-SE and ENE-WSW lineaments appear to have formed during the phase of NW-SE folding. The NE-SW lineaments may be the result of the cross-folding of the earlier folds. The NNW-SSE lineaments have been related to the Precambrian tectonic activity in South India.     

Tectonic stress regimes,rift extension and transform motion: the South Iceland Seismic Zone

Abstract

The South Iceland Seismic Zone (SISZ) is located at the junction of three rift segments in southwestern Iceland. The presence of different types of faulting and of differently orientated subgroups in Upper Pliocene to Holocene formations indicate polyphase tectonism. We measured 736 minor faults at 25 sites. Two types of relationships between stress regimes are represented. The first type, named IDS (inhomogeneous data set), is characterized by the presence of two types of fault mechanisms, normal and strike-slip, consistent with a single direction of extension. The second type, named OSR (opposite stress regimes), is characterized by the presence of perpendicular directions of extensions for a single type (normal or strike-slip) of faulting. Because of contradictory chronological criteria, we infer that the OSR alternated during the brittle tectonic activity of the SISZ. Two stress regimes, primary and secondary, are characterized by directions of extension NW-SE and NE-SW, respectively. The general fracture pattern characterized for the primary stress regime in the SISZ includes NNE-SSW trending right-lateral strike-slip faults, conjugate ENE-WSW trending left-lateral faults and NE-SW normal faults. This distribution is quite consistent with a Riedel- type model of fault pattern in a left-lateral shear zone. The stress states characterized based on analysis of both the earthquake focal mechanisms and the recent faulting sow great similarity in terms of stress directions. The main difference is the larger ratio of strike-slip motions representing 71% of the total population in the case of earthquake focal mechanisms, whereas for the whole set of faults the proportion of strike-slip faulting was 50 %. We explain that a témpora evolution of the tectonic regime in the SISZ region, accompanied by a gradual change in stress field, starts with rift-type pure extension and progressively leads to development of preferentially strike-slip structures in the kinematic context of left- lateral transform motion. © Elsevier, Paris     

Strain in an Archean greenstone belt of Minnesota

We measured strain at more than 60 locations in metasedimentary and metavolcanic rocks of the Vermilion district, an E-W trending Archean greenstone belt in Minnesota. Strain ellipsoid orientations and shapes correlate strongly with N-S location in the belt, but magnitudes do not. Flattening strains occur near the present Vermilion fault (which bounds the greenstone belt to the north) with constrictional strains to the south. The observed strain patterns can be mathematically modeled by deformation paths which produce the flattening strains (with west plunging λ₁ axes) by dextral shear of the constrictional strains (with east plunging λ₁ axes). Using reasonable geologic constraints, the shear plane must dip to the north with a subhorizontal shear direction. Structures throughout the district also indicate dextral shear. A geometrical finite element program uses the measured strains to destrain the rocks and find the configuration which most closely satisfies strain compatibility equations. The linear E-W strain patterns and minor rotations about horizontal axes during the deformation preclude origin of the greenstone belt by infolding and shear off the flanks of a rising granitic diapir. By accounting for rotations which result in the (deformed) curvature of the original surface, a true estimate of 50% N-S shortening across the belt can be made. The data and deformation models favor the origin of the Vermilion district rocks at a convergent margin, most likely as a N-dipping subduction zone complex with shallow slab dip. The origin of the constrictional strains remains enigmatic.     

On the mechanics of basin formation in the Pannonian basin: Inferences from analogue and numerical modelling

We present the results of a thrust fault reactivation study that has been carried out using analogue (sandbox) and numerical modelling techniques. The basement of the Pannonian basin is built up of Cretaceous nappe piles. Reactivation of these compressional structures and connected weakness zones is one of the prime agents governing Miocene formation and Quaternary deformation of the basin system. However, reactivation on thrust fault planes (average dip of ca. 30°) in normal or transtensional stress regimes is a problematic process in terms of rock mechanics. The aim of the investigation was to analyse how the different stress regimes (extension or strike-slip), and the geometrical as well as the mechanical parameters (dip and strike of the faults, frictional coefficients) effect the reactivation potential of pre-existing faults.

Results of analogue modelling predict that thrust fault reactivation under pure extension is possible for fault dip angle larger than 45° with normal friction value (sand on sand) of the fault plane. By making the fault plane weaker, reactivation is possible down to 35° dip angle. These values are confirmed by the results of numerical modelling. Reactivation in transtensional manner can occur in a broad range of fault dip angle (from 35° to 20°) and strike angle (from 30° to 5° with respect to the direction of compression) when keeping the maximum horizontal stress magnitude approximately three times bigger than the vertical or the minimum horizontal stress values.

Our research focussed on two selected study areas in the Pannonian basin system: the Danube basin and the Derecske trough in its western and eastern part, respectively. Their Miocene tectonic evolution and their fault reactivation pattern show considerable differences. The dominance of pure extension in the Danube basin vs. strike-slip faulting (transtension) in the Derecske trough is interpreted as a consequence of their different geodynamic position in the evolving Pannonian basin system. In addition, orientation of the pre-existing thrust fault systems with respect to the Early to Middle Miocene paleostress fields had a major influence on reactivation kinematics.

As part of the collapsing east Alpine orogen, the area of the Danube basin was characterised by elevated topography and increased crustal thickness during the onset of rifting in the Pannonian basin. Consequently, an excess of gravitational potential energy resulted in extension (σ_v > σ_H) during Early Miocene basin formation. By the time topography and related crustal thickness variation relaxed (Middle Miocene), the stress field had rotated and the minimum horizontal stress axes (σ_h) became perpendicular to the main strike of the thrusts. The high topography and the rotation of σ_h could induce nearly pure extension (dip-slip faulting) along the pre-existing low-angle thrusts. On the contrary, the Derecske trough was situated near the Carpathian subduction belt, with lower crustal thickness and no pronounced topography. This resulted in much lower σ_v value than in the Danube basin. Moreover, the proximity of the retreating subduction slab provided low values of σ_h and the oblique orientation of the paleostress fields with respect to the master faults of the trough. This led to the dominance of strike-slip faulting in combination with extension and basin subsidence (transtension).     

Evolution of paleostress fields and brittle deformation of the Tornquist Zone in Scania (Sweden) during Permo-Mesozoic and Cenozoic times

The NW-SE oriented Sorgenfrei–Tornquist Zone (STZ) has been thoroughly studied during the last 25 years, especially by means of well data and seismic profiles. We present the results of a first brittle tectonic analysis based on about 850 dykes, veins and minor fault-slip data measured in the field in Scania, including paleostress reconstruction. We discuss the relationships between normal and strike-slip faulting in Scania since the Permian extension to the Late Cretaceous–Tertiary structural inversions. Our paleostress determinations reveal six successive or coeval main stress states in the evolution of Scania since the Permian. Two stress states correspond to normal faulting with NE-SW and NW-SE extensions, one stress state is mainly of reverse type with NE-SW compression, and three stress states are strike-slip in type with NNW-SSE, WNW-ESE and NNE-SSW directions of compression.The NE-SW extension partly corresponds to the Late Carboniferous–Permian important extensional period, dated by dykes and fault mineralisations. However extension existed along a similar direction during the Mesozoic. It has been locally observed until within the Danian. A perpendicular NW-SE extension reveals the occurrence of stress permutations. The NNW-SSE strike-slip episode is also expected to belong to the Late Carboniferous–Permian episode and is interpreted in terms of right-lateral wrench faulting along STZ-oriented faults. The inversion process has been characterised by reverse and strike-slip faulting related to the NE-SW compressional stress state.This study highlights the importance of extensional tectonics in northwest Europe since the end of the Palaeozoic until the end of the Cretaceous. The importance and role of wrench faulting in the tectonic evolution of the Sorgenfrei–Tornquist Zone are discussed.     

Geological and archaeological evidence of active faulting on the Martana Fault (Umbria–Marche Apennines,Italy) and its geodynamic implications

This paper examines the morphotectonic and structural–geological characteristics of the Quaternary Martana Fault in the Umbria–Marche Apennines fold‐and‐thrust belt. This structure is more than 30 km long and comprises two segments: a N–NNW‐trending longer segment and a 100°N‐trending segment. After developing as a normal fault in Early Pleistocene times, the N–NNW Martana Fault segment experienced a phase of dextral faulting extending from the Early to Middle Pleistocene boundary until around 0.39 Ma, the absolute age of volcanics erupted in correspondence to releasing bends. The establishment of a stress field with a NE–ENE‐trending σ₃ axis and NW–NNW σ₁ axis in Late Pleistocene to Holocene times resulted in a strong component of sinistral faulting along N–NNW‐trending fault segments and almost pure normal faulting on newly formed NW–SE faults. Fresh fault scarps, the interaction of faulting with drainage systems and displacement of alluvial fan apexes provide evidence of the ongoing activity of this fault. The active left‐lateral kinematic along N–NNW‐trending fault segments is also revealed by the 1.8 m horizontal offset of the E–W‐trending Decumanus road, at the Roman town of Carsulae. We interpret the present‐day kinematics of the Martana Fault as consistent with a model connecting surface structures to the inferred north‐northwest trending lithospheric shear zone marking the western boundary of the Adria Plate. Copyright © 2003 John Wiley & Sons, Ltd.     

Fault systems and paleostresses in the Vestfirdir Peninsula. Relationships with the Tertiary paleo-rifts of Skagi and Snaefells (Northwest Iceland)

Abstract

The Vestfirdir Peninsula of northwestern Iceland mainly consists of tholeiitic lava flows, 8–14 Ma old, gently dipping to the southeast. A detailed study of strike-slip and normal faulting allowed identification of two main paleostress regimes. Two sets of normal faults were recognized. The largest set trends ENE-WSW to NNE-SSW; the minor set trends NW-SE to WNW-ESE. Concerning the major extension, the reconstruction of paleostress trajectories shows a gradual change in trend from ESE-WNW, in the northern half of the peninsula, to NNW-SSE to the south. The minor extension also shows a gradual change from NNE-SSW to ENE-WSW trends, from north to south. The nearly constant perpendicularity between the major and minor trends of extension is accounted for by permutation of stress axes within the general pattern of extension related to oceanic rifting. The progressive azimuthal change of the major extension trend, from northeast to southwest across the peninsula, is interpreted as the expression of a change in trend of the extinct Skagi-Snaefells rift, a structure that cannot be reconstructed directly through geological mapping. The average trends of extension in the southern Vestfirdir Peninsula, N150°E, suggest a N60°E trend for the ancient Snaefells rift segment. Likewise, the N100–110°E trends of extension in northern Vestfirdir suggest a N10–20°E trend for the Skagi paleo-rift., © Elsevier, Paris     

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。