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1.
Transpressional deformation has played an important role in the late Neoproterozoic evolution of the ArabianNubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km-long, NW-oriented brittleductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike-slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along-strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure-shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple-shear dominated. These domains are comparable to splay-dominated and thrust-dominated strike-slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike-slip and thrustsense shear zones. The earlier fabric(S1), is locally recognized in low strain areas and SW-ward thrusts. S2 is associated with a shallowly plunging stretching lineation(L2), and defines ～NW-SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ～NNW–SSE tight-minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub-parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation in fold zones. Dextral ENEstriking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW-to NNW-striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss-cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike-slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strikeslip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian-Nubian Shield during agglutination of East and West Gondwana. 相似文献
2.
The Greiner shear zone in the Tauern Window, Eastern Alps, changes from a zone of distributed (dominantly sinistral) shear in supracrustal rocks to a series of narrow, gully forming dextral splays where it enters basement gneisses. Within these splays, granodiorite is transformed into quartz‐poor biotite and/or chlorite schists, reflecting hydration, removal of Si, Ca and Na, and concentration of Fe, Mg and Al. Stable isotope analyses show a prominent increase in δD and a decrease in δ18O from granodiorite into the shear zones. These changes indicate significant channelized flow of an externally derived, low‐δ18O, high‐δD fluid through the shear zones. The shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the Greiner zone and the stable isotope data support alteration via serpentinite‐derived fluid. Monazite in schist from one shear zone yields spot dates of 29–20 Ma, indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the Alpine orogeny (c. 30 Ma). We suggest that Alpine metamorphism of serpentinites released large amounts of high‐δD, low‐δ18O, Si‐undersaturated, Fe + Mg‐saturated fluids that became channelized along prior zones of weakness in the granodiorite. Infiltration of this fluid facilitated growth of chlorite and biotite, which in turn localized later dextral strain in the narrow splays via cleavage‐parallel slip. This dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the Eastern Alps. This study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis. 相似文献
3.
中西非裂谷系是沿中非剪切带及邻区发育的一系列中新生代裂谷盆地,其成因机理一直存在争议。中西非裂谷系的构造演化主要经历了三个演化阶段,其中在早白垩世进入强烈断陷期,是盆地形成的重要阶段。以早白垩世中西非裂谷系的地质背景为基础,运用弹性力学有限元数值模拟方法,通过应力场和应变场的分析,为中西非裂谷系形成的力学机制提供依据。模拟结果表明,早白垩世非洲大陆内部走滑和伸展作用并存,中非剪切带不是所谓的"转换断层",而是与中西非裂谷系同时形成和发育的构造。中西非裂谷系是在中新生代泛大陆裂解时期,非洲板块绕西北非地块逆时针旋转,非洲内部不同地块在统一构造应力场作用下,由于伸展和走滑的差异作用形成和发育的。 相似文献
4.
超高压变质岩的折返过程是陆陆碰撞边界演化的关键问题。南倾的花凉亭-弥陀剪切带位于南大别低温-超高压变质
带和中大别中温-超高压变质带之间,矿物拉伸线理倾伏向为SE,逆冲和走滑分量大致相等。电子背散射衍射分析表明：
花凉亭-弥陀剪切带大多数样品的石英组构记录了上盘向NW的剪切变形,反映了中大别超高压变质岩向SE的快速折返,
而部分样品的石英具有上盘向SE的剪切指向,与早白垩世花岗岩穹隆发育导致的区域伸展有关。对前人的岩石学和年代学
成果进行总结,发现大别山进变质和超高压变质峰期/退变质的锆石U-Pb年龄从南往北逐渐变新,南大别和中大别在215~
225 Ma同时经历了高压榴辉岩相退变质作用,在191~195 Ma经历了绿片岩相变质作用。超高压变质岩的白云母和黑云母的
40Ar/39Ar年龄靠近郯庐断裂时偏年轻,可能受到郯庐断裂活动的影响。南大别和中大别变质峰期温压的等值线与花凉亭-弥
陀剪切带的走向斜交,反映了超高压变质岩的斜向折返。因此,南大别低温-超高压变质带在~236 Ma最先开始折返,之后
中大别和北大别依次发生快速折返,具有不同折返速率和折返角度的构造岩片通过韧性剪切带调节相对运动。 相似文献
5.
Microstructural study of a natural slip zone: quantification and deformation history 总被引：4，自引：0，他引：4
Microstructure of a natural slip zone was comprehensively examined using a combination of images captured systematically by optical microscopy (OPM) and backscattered electron microscopy (BEM) techniques. Microstructural features identified on these images were processed and evaluated using an advanced image analysis system, which proved that quantitative analyses could considerably enhance the understanding of shear behavior of slip zones. It was found that variations of porosity, abundance of platy clay particles and alignments of particles are significant indicators revealing nature of deformation processes. These indicators show that global mechanical behavior of the investigated slip zone can be conceptualized as that of normally consolidated clayey soils under drained conditions.
The geometric patterns of the microstructure of the slip zone are similar to the S–C fabrics seen in tectonic shear zones. It is suggested that combined progressive bulk simple shear and pure shear modes enable to realistically reconstruct the kinematic history of the slip zone, through which particle movements and microstructural evolution were accomplished via various types of particulate flows. The results of this study show that clay mineralogy plays a more important role in the development of the slip zone than abundance of clay-size particles, while both clay mineralogy and relative proportions of each particle size fraction control the response of particles to shear deformation. Among the fractions present in the slip zone, fine silts are the strongest indicator of global shear stress characterized by their highest degree of alignment, whereas clay particles are the weakest. Highest degree of shape preferred orientation is also found within fine silt domains. 相似文献
6.
Overburden soil beds situated above a fault are often deformed by propagation of bedrock thrusting from the fault during large earthquake. The deformed beds formed a triangular shear zone. This coseismic faulting often causes damage to underground tunnels located in the shear zone. The present research studies the deformation behavior of the overburden soil beds and the tunnel, the associated mechanism and the impact on the safety of tunnel linings induced by a large blind thrust slip. Based on sandbox experimental and numerical studies, it is found that results from numerical analysis are in agreement with the sandbox model tests with regard to growths of the shear zones within the soil beds, location of the tunnel in this shear zone and deformations of the tunnel. The potential major shear zone may be bent or bifurcated into two sub-shear zones owing to existence of a tunnel inside the shear zone. Furthermore, the occurrence of back-thrust faulting will threaten the safety of nearby structures. It was also identified that stiffness of the soil and the fault dip angles are among the major factors controlling the configuration of shear zones, the stresses within the soil, and the loads on tunnel linings. Based on the identified mechanisms, the strategies for hazard prevention are accordingly suggested and discussed. 相似文献
7.
《Australian Journal of Earth Sciences》2013,60(6):983-999
We present new data on the field geology and late thermal evolution of the Redbank Thrust system in the Arunta Block of central Australia. Geochronological and field data from the Speares Metamorphics are also used to relate the thermal evolution of the Redbank Thrust system to the structural evolution of the region. We show that several stages in the evolution might be discerned. An originally sedimentary sequence was intruded by mafic intrusions and then deformed during partial melting to form the principal foliation observed in the region (D1). This sequence was then folded during D2 into upright folds with north‐ to northeast‐plunging fold axes. These events are likely to correlate with the Strangways and/or Argilke and Chewings Orogenies known from previous studies. Subsequently, the Redbank Thrust was initiated during D3. This event is recognised by deflection of the host rocks into the shear zone and might therefore have been associated with a component of strike‐slip motion. It occurred probably at or before 1500–1400 Ma. Subsequent north‐over‐south thrust motion in the Redbank Thrust formed the intense mylonitic fabric and folded the mylonitic fabric during D4 into asymmetric folds with shallow fold axes. New 40Ar/39Ar K‐feldspar ages from three samples collected from variably deformed branches of the Redbank Thrust and undeformed rocks in the Speares Metamorphics suggest that most parts of the Redbank Thrust system cooled relatively slowly after metamorphism and deformation in the Mesoproterozoic so that the D4 thrusting might have been very long‐lived. Minimum ages of the K‐feldspar age spectra show that the entire region cooled below 200°C by approximately 300 Ma. Apatite fission track ages from nine samples show that cooling through the apatite partial annealing zone occurred during Cretaceous time (ca 150–70 Ma) and modelled cooling histories are consistent with the cooling rates obtained from the K‐feldspar data. They indicate that final exhumation of the Redbank Thrust system occurred probably in response to erosion, possibly driven by rifting around the margins of Australia. 相似文献
8.
西南三江构造体系突出表现为以昌都-兰坪-思茅地块为中轴的不对称走滑对冲构造,次为与走滑断裂相伴的伸展滑脱、走滑拉分盆地构造体系,再次为块体内部的近北东、北西向走滑断裂系.西南三江造山带构造体系演化分为挤压收缩变形、走滑深熔热隆、走滑剪切伸展、走滑剥蚀隆升等4个阶段.自晚白垩世开始,印度板块与欧亚板块碰撞,西南三江造山带... 相似文献
9.
We use numerical simulations to investigate the evolution of sheath folds around slip surfaces in simple‐shear‐dominated monoclinic shear zones. A variety of sheath fold shapes develops under general shear, including tubular folds with low aspect ratio eye patterns and tongue‐like structures showing bivergent flanking structures in sections normal to the sheath elongation, which may potentially lead to confusing shear sense interpretations. Not all investigated monoclinic flow end‐members lead to the development of sheath folds sensu stricto (folds with apical angle <90°). The aspect ratio of the eye patterns, Ryz, correlates with the ratio between the principal strain in the Y‐direction and the smaller of the principal strains in the X–Z plane, and thus it could be used in strain analysis. 相似文献
10.
大青山伸展拆离断层运动学涡度研究及构造指示意义 总被引：3，自引：1，他引：2
在华北北缘的大青山伸展拆离断裂带叠加在中生代逆冲断层之上,其韧性剪切带在变质核杂岩南北两侧出露,运动学指向为上盘向南东向拆离.运动学涡度分析表明,大青山拆离断层剪切带早期(较高温)简单剪切分量不断增加直至简单剪切;拆离断层总体平均涡度Wm简单剪切分量沿拆离断层上盘运动方向增大,与韧性剪切带先垂向颈缩、后水平伸展的被动式... 相似文献
11.
Jonas B. Ruh 《地学学报》2017,29(3):202-210
Numerical experiments on evolving accretionary wedges usually implement predefined weak basal décollements and constant strength parameters for overlying compressed sequences, although fluid pressure ratio, and therefore brittle strength, can vary strongly in sedimentary basins. A two‐dimensional finite difference model with a visco‐elasto‐plastic rheology is used to investigate the influence of different simplified fluid pressure ratio distributions on the structural evolution of accretionary wedge systems. Results show that a linear increase in fluid pressure ratio towards the base leads to toeward‐verging thrust sheets and underplating of strata, while simulations with a predefined décollement form conjugate shear zones supporting box‐fold‐type frontal accretion. Surface tapers are in agreement with the critical wedge theory, which here is modified for cases of varying fluid pressure ratio. Furthermore, the numerical results resemble findings from natural examples of accretionary wedges. 相似文献
12.
The tectonic evolution of the Mont Blanc range with regard to its cooling and exhumation history has been discussed and debated over many years and is still controversial. Recently, several low-temperature thermochronology studies have determined the cooling history of the massif in considerable detail and various tectonic models proposed to explain the young and fast exhumation signal established from these studies. Here we present detailed field data from the wider Mont Blanc area and assess possible exhumation processes in terms of these field constraints. Our observations indicate that none of the major faults or shear zones around the Mont Blanc massif (i.e. Mont Blanc shear zone, Mont Blanc back-thrust, Penninic thrust) was active in Late Neogene times and that young exhumation is therefore not controlled by movements along these structures. We demonstrate that the position of Mont Blanc in the bend of the western Alps plays an important role in its tectonic history and that simple 2D models are insufficient to explain its evolution. Interference between NW–SE compression and orogen-parallel extension along the Rhône-Simplon fault system resulted in a complex regional structural pattern, with strike-slip movements on both sides of the Mont Blanc massif. Young brittle faults are predominantly strike slip without significant vertical offset. The young (<2 Ma) rapid exhumation of Mont Blanc is more broadly distributed and cannot be directly linked to discrete faults bounding the massif. The mechanisms driving this recent accelerated exhumation must similarly be of broader scale. 相似文献
13.
Mapping combined with structural analyses in the foreland edge of the metamorphic core of the Himalayas in SW Nepal highlights the existence of two north‐dipping shear zones with opposite sense of shear. Here, the metamorphic core is mainly affected by non‐coaxial top‐to‐the‐south sense of shear at temperatures between 450 °C and 550 °C that switch to a top‐to‐the‐north sense of shear at the top of the metamorphic core. We regionally correlate this upper shear zone with the South Tibetan detachment system. Ar‐dating on white mica indicates that both shear zones operated between 23 Ma and 17 Ma. Restoration of the folded South Tibetan detachment in far western Nepal yields a minimum dip‐slip distance of 190 km, compatible with predictions made by models of extrusion of a weak mid‐crustal channel. Our results support an orogenic model in which channel flow in the hinterland coexisted with thrust wedge mechanics in the foreland. 相似文献
14.
Chiara Montemagni Rodolfo Carosi Nicoletta Fusi Salvatore Iaccarino Chiara Montomoli Igor M. Villa Stefano Zanchetta 《地学学报》2020,32(3):215-224
Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two‐dimensional data. We describe a 3D approach based on the use of X‐ray micro‐computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non‐coaxial shearing. 40Ar/39Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow. 相似文献
15.
ZHANG Jinjiang ZHONG Dalai SANG Haiqing ZHOU Yong 《《地质学报》英文版》2006,80(1):79-96
Structural analyses show that the Ailaoshan-Red River shear zone （ASRRSZ） in Ailao Mountain is composed of three different deformational domains. These domains may represent three episodes of left-lateral slip experienced by the ASRRSZ. The first episode of such deformation occurred throughout the eastern high-grade belt of the ASRRSZ under a transtensional regime and produced L- type tectonites of amphibolite grade. The second episode of left-lateral slip formed high strain zones overprinting the high-grade belt. Its deformational mechanism is similar to simple shear and the deformed rocks are L-S mylonites of greenschist grade. The third episode of left-lateral slip took place chiefly in a western low-grade belt of the ASRRSZ. This deformation occurred in a transpressional regime, formed an overall structure pattern of a sinistral thrust system and produced phyllonites of low-greenschist grade. Geochronological data indicated that the three episodes of left-lateral slip happened before ～58-56 Ma, at least from ～27 Ma to 22 Ma and at ～13-12 Ma respectively. The first episode of slip in the ASRRSZ appeared to correspond to the initial collision of India and Asia at ～60 Ma. The second episode took place almost at the same time as the most intensive compression and uplift in Tibet. The latest event might represent a further eastward material flow in Tibet after ～16-13 Ma. Thus, the ASRRSZ of southeastern Asia probably experienced three main episodes of Tertiary left- lateral slip in the course of intracontinental convergence since the India-Asia collision. 相似文献
16.
矿物成分、特征地球化学组分对水在滑带形成中作用的指示意义:以三峡库区大型滑坡为例 总被引：5，自引：0，他引：5
弄清滑坡滑带抗剪强度降低的根本原因是滑坡形成机理研究和滑坡活动趋势预测的主要内容之一。水是滑带形成过程中导致其抗剪强度衰减的最活跃因素之一。三峡库区两个大型滑坡实例分析显示,滑带及其周围岩土矿物成分、地球化学成分的变化特征指示滑带形成与水-岩(土)物理、化学作用的方式及作用程度,从而证实矿物学、地球化学研究方法和理论是揭示滑带抗剪强度降低内在机理的有效途径之一。三峡库区黄土坡滑坡临江I#崩滑体和泄滩滑坡滑带土及其周围岩土矿物学、主量化学元素的含量变化特征指示:前者滑带形成过程中,滑带部位地下水因大气降水补给、地下水的氧化作用活跃,导致滑带土抗剪强度减低,其主要原因是其中泥灰岩碎屑的水解泥化作用、方解石溶解作用和伊利石向伊-蒙混层矿物的转化作用;后者滑带形成过程中,滑带部位地下水与外界水力联系较差、地下水的还原作用强烈,滑带部位长石化学风化、次生粘土矿物增多,可知由伊利石转化的伊-蒙混层矿物增多是导致滑带土抗剪强度衰减的主要原因。 相似文献
17.
多层滑带滑坡演化过程具有多级滑体相对运动、应力非连续性特点,由于不同层滑体间的相对运动,多层滑带滑坡内的推力分布形式往往比较复杂,亟需提出针对多层滑带滑坡的抗滑桩桩后推力分布计算方法。本文采用水平极限平衡法对多层滑带滑坡进行分析,根据水平微段极限平衡状态下的受力分析,可计算抗滑桩桩后每层滑体内的滑坡推力。在分析竖直方向的受力平衡时,需要考虑不同层滑体向下的受力传递,从而导致滑坡推力分布函数在滑带处存在突变。据此推导出了多层滑带滑坡的抗滑桩桩后推力分布函数,并通过数值模拟进行了工程案例验算分析,验算结果表明了该方法的可靠性。本文提出的多层滑带滑坡抗滑桩桩后推力分布计算方法,为多层滑带滑坡的防治理论提供了一定的参考。 相似文献
18.
Pressure variations in a magma reservoir may cause deformation at the surface and a redistribution of the stress in the surrounding rock. In this study, we use two‐dimensional numerical models and elaborate how magma chamber inflation and deflation affect the stress field around and surface displacement. We test how a pre‐existing normal fault near the magma reservoir may influence the pattern of stress. We demonstrate the possibility of initiating both normal and reverse slip on faults during the inflation of the magma reservoir. The Coulomb failure stress changes are calculated during the periods of pressure variation. An increase of Coulomb failure stress can be predicted above and below the magma chamber during increasing magma chamber pressure that may encourage earthquakes. This process can produce cracks and fault growth encouraging magma propagation along the cracked zone. A different distribution of the stress change is expected in the case of subsequent deflation of the overpressured magma reservoir. In this case, seismicity is expected on a plane at equal depth than the magma chamber, laterally offset from the extent of the magma chamber. Magma could propagate laterally from the magma reservoir into zones where cracks have been generated, but only if the resolved shear stress on the fault is small compared with the excess magma pressure. 相似文献
19.
本文概括性总结了天山东段大型推覆构造的基本特征。根据地质证据和同位素年龄,东天山存在早古生代末,晚古生代晚期和新生代三期推覆构造;根据推覆构造分布规律及构造背景,在平面上划分为五大推覆带、9个大型韧剪带;根据出露岩石的矿物变形相将东天山推覆构造划分为深、中深和浅三个深度层次;通过韧剪变形组构的观察分析,确定了多期韧性变形性质与运动方向。糜棱岩中超微构造、古应力及小构造变形缩短率测量统计,证明东天山推覆变形具有显著的地壳缩短增厚作用。新生代板块碰撞导致本区中新生代盆地基底向造山带A型俯冲,造山带向盆地推覆,其结果就构成了今日看到的镶嵌状盆地-山脉构造地貌景观。 相似文献
20.
Aeromagnetic signature of an exhumed double dome system in the SW Grenville Province (Canada) 
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下载免费PDF全文 Grégory Dufréchou 《地学学报》2017,29(6):363-371
Analysis of aeromagnetic data in the Grenville Province reveals the presence of two regional‐scale unmapped structural domes (the Morin and Mékinac‐Taureau domes) with an oval‐shaped magnetic pattern bounded by regional‐scale shear zones and a geometry that is similar to that produced in crustal flow models under extension, which predict two upright domes of foliation (double dome) separated by a steep shear zone. The Mékinac‐Taureau dome, a metamorphic core complex, and the Morin dome may have been exhumed by channel flow. Exhumation occurred by a combination of thrust, normal‐sense and wrench shear zones. The preservation of paragneisses in the Morin dome suggests that it underwent a lesser degree of exhumation than did the Mékinac‐Taureau dome. This study shows how the integration of local field information with magnetic data in a regional tectonic setting can reveal and delineate concealed gneiss domes and highlights a role for strike‐slip tectonics in the creation of regional structures involving the exhumation of deep crust. 相似文献