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1.
We have used a coupled thermo-mechanical finite-element (FE) model of crustal deformation driven by mantle/oceanic subduction to demonstrate that the tectonic evolution of the Lachlan Fold Belt (LFB) during the Mid-Palaeozoic (Late Ordovician to Early Carboniferous) can be linked to continuous subduction along a single subduction zone. This contrasts with most models proposed to date which assume that separate subduction zones were active beneath the western, central and eastern sections of the Lachlan Orogen. We demonstrate how the existing data on the structural, volcanic and erosional evolution of the Lachlan Fold Belt can be accounted for by our model. We focus particularly on the timing of fault movement in the various sectors of the orogen. We demonstrate that the presence of the weak basal decollement on which most of the Lachlan Fold Belt is constructed effectively decouples crustal structures from those in the underlying mantle. The patterns of faulting in the upper crust appears therefore to be controlled by lateral strength contrasts inherited from previous orogenic events rather than the location of one or several subduction zones. The model also predicts that the uplift and deep exhumation of the Wagga-Omeo Metamorphic Belt (WOMB) is associated with the advection of this terrane above the subduction point and is the only tectonic event that gives us direct constraints on the location of the subduction zone. We also discuss the implications of our model for the nature of the basement underlying the present-day orogen. 相似文献
2.
根据波茨坦地磁场模型(POMME6.2),研究喜马拉雅东构造结周围地区地壳磁异常的空间分布、磁异常随高度的衰减特征.利用二维小波变换方法对地表磁异常进行分解,分析小波细节组合和逼近信号的异常特点.讨论磁异常与地质构造的联系.结果表明,研究区内地壳磁异常分布相当不均匀.喜马拉雅—东构造结—龙门山—大巴山地区分布着较强的负磁异常;四川盆地为正磁异常,其他地区磁异常较弱.东构造结对周围地区磁异常有重要影响,它及其周围地区的地壳磁异常都是在负磁或弱磁异常背景上,叠加着中短波长的正负磁异常.这些中小尺度磁异常由中、上层地壳磁性物质产生,走向与地质构造基本一致.沿金沙江、红河断裂带分布着清晰的弱磁异常带.龙门山断裂带、丽江—小金河断裂带和红河断裂带是磁异常强弱过渡带.青蒇高原中部东西向的磁异常,在东构造结弧顶地区呈弧形分布.青藏高原中部和滇中地块带状、团状磁异常具有相同的衰减规律. 相似文献
3.
Early Cretaceous sinistral shearing and associated folding in the South Kitakami Belt, northeast Japan 总被引：1，自引：0，他引：1
Migiwa Sasaki† 《Island Arc》2003,12(2):92-109
Abstract Early Cretaceous structural development of the southern part of the South Kitakami Belt, northeast Japan, is discussed through precise structural mapping and the measurement of semiquantitative strain. The mapping and measurement revealed that wide north- to northeast-trending sinistral shear zones occupied by the 'slate' with higher strain than the surrounding rocks run from the axial part to the western limb of major synclines, with the wavelength of 5–10 km. The major synclines with a U-shaped rock distribution opening to the south are interpreted to be drag folds along the sinistral shear zones. These structures were modified by a second stage of Early Cretaceous sinistral shearing characterized by localized high-temperature mylonite zones along the rim of some of the 120 Ma granitoids that cut the major folds and baked the 'slate' in the older shear zones mentioned above. The rocks of the South Kitakami Belt, which had undergone two stages of shearing, were rapidly exhumed before the deposition of the Late Aptian–Albian Miyako Group. Finally, a restoration model is presented of the Early Cretaceous sinistral displacement and deformation in the study area. 相似文献
4.
大别造山带是全球最大的碰撞造山带之一,三叠纪时期,扬子板块深俯冲至地幔的200km处,经历了超高压变质作用。白垩纪早期,该造山带发生了强烈的伸展和垮塌,以及大规模的后造山地幔源岩浆侵入和火山活动。本研究收集了大别造山带及其邻区(29°~34°N、114°~119°E)的震相资料,采用双差层析成像技术,对大别造山带地壳结构进行反演,研究地壳结构与后造山地幔源岩浆侵入和火山活动之间的关系。结果显示,大别造山带中上地壳存在低速结构,该低速结构可能是熔融的幔源侵入物质,由于俯冲板片断裂,或下地壳/岩石圈发生拆沉,导致软流圈物质上涌至地壳底部、侵入地壳中,形成大别造山带地壳中的低速结构;同时,合肥盆地显示为低速区,可能是受浅部沉积层影响。研究中横切大别山的4条剖面显示,该地区下方存在北向倾斜高速结构,该高速结构可能是襄樊-广济断层,或者是扬子板块向华北板块下方俯冲的遗迹。 相似文献
5.
Vladimír Bezák Josef Pek Ján Vozár Miroslav Bielik Jozef Vozár 《Studia Geophysica et Geodaetica》2014,58(3):473-488
Electrical resistivity of the Earth’s crust is sensitive to a wide range of petrological and physical parameters, and it particularly clearly indicates crustal zones that have been tectonically or thermodynamically disturbed. A complex geological structure of the Alpine nappe system, remnants of older Hercynian units and Neogene block tectonics in Western Slovakia has been a target of recent magnetotelluric investigations which made a new and more precise identification of the crustal structural elements of the Western Carpathians possible. A NW-SE magnetotelluric profile, 150 km long, with 30 broad-band and 3 long-period magnetotelluric sites, was deployed, crossing the major regional tectonic elements listed from the north: Brunia (as a part of the European platform), Outer Carpathian Flysch, Klippen Belt, blocks of Penninic or Oravicum crust, Tatricum and Veporicum. Magnetotelluric models were combined with previous seismic and gravimetric results and jointly interpreted in the final integrated geological model. The magnetotelluric models of geoelectrical structures exhibit strong correlation with the geological structures of the crust in this part of the Western Carpathians. The significant resemblance in geoelectrical and crustal geological structures are highlighted in shallow resistive structures of the covering formations represented by mainly Tertiary sediments and volcanics. Also in the deeper parts of the crust highly resistive and conductive structures are shown, which reflect the original building Hercynian crust, with superposition of granitoids or granitised complexes and lower metamorphosed complexes. Another important typical feature in the construction of the Western Carpathians is the existence of young Neogene steep fault zones exhibited by conductive zones within the whole crust. The most significant fault zones separate individual blocks of the Western Carpathians and the Western Carpathians itself from the European Platform. 相似文献
6.
The Shabogamo Intrusive Suite comprises numerous bodies of variably metamorphosed gabbro which intrude Archean and Proterozoic sequences at the junction of the Superior, Churchill, and Grenville structural provinces in western Labrador. Combined Sm-Nd and Rb-Sr systematics in two bodies, ranging from unmetamorphosed to lightly metamorphosed, document a crystallization age of about 1375 m.y., and suggest that both bodies crystallized from magmas with similar Nd and Sr isotopic compositions. This age is in accordance with the existence of a regional magmatic event in the Churchill Province at approximately 1400 m.y.Rb-Sr systematics in two bodies of amphibolite-grade gabbro suggest a regional metamorphic event at about 950 m.y., corresponding to the waning stages of Grenville activity. Sm-Nd systematics in these high-grade bodies are affected to a much lesser degree than Rb-Sr.Initial ratios for143Nd/144Nd and87Sr/86Sr are lower and higher, respectively, than bulk earth values at 1375 m.y. Both these displacements are in the direction of older crustal material at 1375 m.y., and a model is proposed to produce the Shabogamo magma by mixing a mantle-derived magma with a partial melt of crustal rocks (approximately 4: 1 by volume). Young volcanic rocks with anomalous Nd and Sr isotopic ratios, which have previously been taken as evidence for “enriched” mantle, may be interpreted similarly. 相似文献
7.
Sren Gregersen 《Journal of Geodynamics》1986,6(1-4)
Some very pronounced crustal inhomogeneities have been found in the North Sea and in Greenland, in regions which were adjacent to each other before the opening of the North Atlantic Ocean by sea-floor spreading. Some of these regions of inhomogeneities are zones of relatively high seismicity, while others are aseismic. In the North Sea, the Viking Graben has earthquakes, while its southern continuation, the Central Graben, is almost aseismic. In eastern Greenland, there are only few earthquakes near the Mesozoic graben, while there is a prominent earthquake zone at the coast line in north-eastern Greenland. It is concluded that, superposed on the apparent similarities in the two regions, some differences in stress conditions or crustal weakness patterns must exist. 相似文献
8.
南海北部陆缘反“S”型构造带及其对地震活动的影响 总被引：3，自引：0，他引：3
通过地形—地貌、断裂构造、地壳结构、中新生代沉积盆地、第四纪地质特征等分析,认为南海北部陆缘存在滨岸岛链、陆坡北缘和陆坡南缘三条反“S”型构造带,它们形成于晚第三纪,较“新华夏系”和“南海系”晚。上新世末期以来,反“S”型构造带的活动方式,对南海北部陆缘第四纪地质特征影响显著,同时控制了这一区域的地震活动方式和地震带展布,其中,“滨海地震带”和“雷琼地震带”同属于滨岸岛链带,“台西滨外地震带”和“东沙—海南地震带”同属于陆坡北缘带。 相似文献
9.
Crustal P-wave velocity structure in the northeastern margin of the Qinghai-Tibetan Plateau and insights into crustal deformation 总被引：1，自引：0，他引：1
Shuaijun Wang Baojin Liu Xiaofeng Tian Baofeng Liu Xianghui Song Xiaoguo Deng Yinan Sun Cejun Ma Yudong Yang 《中国科学:地球科学(英文版)》2018,61(9):1221-1237
The transitional area between the northeastern margin of the Qinghai-Tibetan Plateau, Ordos Block and Alxa Block,also being the northern segment of the North-South Seismic Belt, is characterized by considerably high seismicity level and high risk of strong earthquakes. In view of the special tectonic environment and deep tectonic setting in this area, this study used two seismic wide-angle reflection/refraction cross profiles for double constraining, so as to more reliably obtain the fine-scale velocity structure characteristics in both the shallow and deep crust of individual blocks and their boundaries in the study area,and further discuss the seismogenic environment in seismic zones with strong historical earthquakes. In this paper, the P-wave data from the two profiles are processed and interpreted, and two-dimensional crustal velocity structure models along the two profiles are constructed by travel time forward modeling. The results show that there are great differences in velocity structure,shape of intra-crustal interfaces and crustal thickness among different blocks sampled by the two seismic profiles. The crustal thickness along the Lanzhou-Huianbu-Yulin seismic sounding profile(L1) increases from ~43 km in the western margin of Ordos Block to ~56 km in the Qilian Block to the west. In the Ordos Block, the velocity contours vary gently, and the average velocity of the crust is about 6.30 km s-1; On the other hand, the velocity structures in the crust of the Qilian Block and the arclike tectonic zone vary dramatically, and the average crustal velocities in these areas are about 0.10 km s-1 lower than that of the Ordos Block. In addition, discontinuous low-velocity bodies(LVZ1 and LVZ2) are identified in the crust of the Qilian Block and the arc-like tectonic zone, the velocity of which is 0.10–0.20 km s-1 lower than that of the surroundings. The average crustal thickness of the Ordos Block is consistently estimated to be around 43 km along both Profile L2(Tongchuan-Huianbu-Alashan left banner seismic sounding profile) and Profile L1. In contrast to the gently varying intra-crustal interfaces and velocity contours in the Ordos Block along Profile L1, which is a typical structure characteristic of stable cratons, the crustal structure in the Ordos Block along Profile L2 exhibits rather complex variations. This indicates the presence of significant structural differences in the crust within the Ordos Block. The crustal structure of the Helan Mountain Qilian Block and the Yinchuan Basin is featured by "uplift and depression" undulations, showing the characteristics of localized compressional deformation.Moreover, there are low-velocity zones with alternative high and low velocities in the middle and lower crust beneath the Helan Mountain, where the velocity is about 0.15–0.25 km s-1 lower than that of the surrounding areas. The crustal thickness of the Alxa Block is about 49 km, and the velocity contours in the upper and middle-lower crust of the block vary significantly. The complex crustal velocity structure images along the two seismic sounding profiles L1 and L2 reveal considerable structural differences among different tectonic blocks, their coupling relationships and velocity structural features in the seismic zones where strong historical earthquakes occurred. The imaging result of this study provides fine-scale crustal structure information for further understanding the seismogenic environment and mechanism in the study area. 相似文献
10.
钦杭成矿带和武夷山成矿带是华南大陆两个重要的成矿带,成矿作用主要发生于中生代陆内造山时期.地质研究表明,基底和地表断裂的特征对成矿过程有重要的控制作用,研究上地壳结构特征对成矿差异性特征的认识有重要的参考价值.为此,本文基于跨越钦杭、武夷山成矿带江西万载至福建惠安的NW-SE向深地震测深剖面初至波数据,利用有限差分走时反演方法,获得了钦杭、武夷山成矿带8 km深度范围内的上地壳P波速度结构,其主要特征为：（1）钦杭、武夷山成矿带上地壳P波速度横向非均匀特征明显,以5.8 km·s-1速度等值线作为基底参考面,发现剖面基底埋深较浅,约1.0~3.0 km;钦杭成矿带的基底埋深总体小于武夷山成矿带,分别为0.5~2.0 km和1.5~3.0 km;（2）P波高速区（速度正异常区）与地表出露的岩浆岩对应较一致,P波低速区（速度负异常区）与主要的断裂位置或沉积盆地对应较一致,绍兴—江山—萍乡断裂和政和—大浦断裂下方的低速特征显示两条断裂至少向深部延伸8 km以上,暗示两条断裂具备深大断裂的性质,推测绍兴—江山—萍乡断裂可能是扬子块体和华夏块体的边界;（3）综合已有的地质、地球物理资料,我们推测钦杭成矿带和武夷山成矿带上地壳P波速度的不同,反映了深部岩浆作用过程的差异,基底深度及断裂性质是造成两个成矿带成矿差异的重要因素. 相似文献
11.
Crustal velocity,density structure,and seismogenic environment in the southern segment of the North-South Seismic Belt,China 
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下载免费PDF全文 The southern segment of the North-South Seismic Belt in China is a critical region for earthquake preparedness and risk reduction efforts. However, limited by the low density of seismic stations and the use of single-parameter physical structural models, the deep tectonic features and seismogenic environment in this area remain controversial. Thus, a comprehensive analysis based on high-resolution crustal structures and multiple physical parameters is required. In this study, we applied the ambient noise tomography method to obtain the three-dimensional (3D) crustal S-wave velocity structure using continuous waveform data from 112 permanent stations and 350 densely distributed temporary stations in the southern segment of the North-South Seismic Belt. Then, we obtained the high-resolution 3D density structure through wavenumber-domain 3D gravity imaging constrained by the velocity structure. The low-velocity and low-density anomalies in the upper crust of the study area were mainly distributed in the Sichuan Basin and around Dali and Simao, while the high-velocity and high-density anomalies were primarily distributed in the Panxi region, corresponding to the surface geological features. Two prominent low-velocity and low-density anomalies were observed in the middle and lower crust: one to the west of the Songpan-Garzê block and Sichuan-Yunnan diamond-shaped block, and the other near the Anninghe-Xiaojiang fault. Combined with the spatial distribution of seismic events in the study area, we found that previous earthquakes predominantly occurred in the transition zones between high and low anomaly regions and in the low-velocity and low-density zones in the upper crust. In contrast, moderate-to-strong earthquakes mainly occurred within the transition zones between high and low anomaly regions and close to the high-velocity and high-density regions, often with low-velocity and low-density layers below their hypocenters. Fluids play a critical role in the seismogenic process by reducing fault strength and destabilizing the stress state, which may be a triggering factor for earthquakes in the study area. Additionally, the upwelling of molten materials from the mantle may lead to energy accumulation and stress concentration, providing an important seismogenic background for moderate-to-strong earthquakes in this area. 相似文献
12.
The Moho depth, crustal thickness and fault systems of the East Vietnam Sea (EVS) are determined by 3D interpretation of satellite gravity. The Moho depth is calculated by 3D Parker inversion from residual gravity anomaly that is obtained by removing the gravity effects of seafloor and Pre-Cenozoic sediment basement topographies from the free air anomaly. The 3D inversion solution is constrained by power density spectrum of gravity anomaly and seismic data. The calculated Moho depths in the EVS vary from 30–31 km near the coast to 9 km in the Central Basin. A map of the lithosphere extension factor in the Cenozoic is constructed from Moho and Pre-Cenozoic sediment basement depths. The fault systems constructed by the maximum horizontal gradient approach include NE-SW, NW-SE, and N-S oriented faults. Based on the interpretation results, the EVS is sub-divided into five structural zones which demonstrated the different characteristics of the crustal structure. 相似文献
13.
14.
Timo Tiira Tomasz Janik Elena Kozlovskaya Marek Grad Annakaisa Korja Kari Komminaho Endre HegedŰs Csaba Attila Kovács Hanna Silvennoinen Ewald BrŰckl 《Pure and Applied Geophysics》2014,171(7):1129-1152
We have studied the lateral velocity variations along a partly buried inverted paleo–rift in Central Lapland, Northern Europe with a 2D wide-angle reflection and refraction experiment, HUKKA 2007. The experiment was designed to use seven chemical explosions from commercial and military sites as sources of seismic energy. The shots were recorded by 102 stations with an average spacing of 3.45 km. Two-dimensional crustal models of variations in P-wave velocity and Vp/Vs-ratio were calculated using the ray tracing forward modeling technique. The HUKKA 2007 experiment comprises a 455 km long profile that runs NNW–SSE parallel to the Kittilä Shear Zone, a major deformation zone hosting gold deposits in the area. The profile crosses Paleoproterozoic and reactivated Archean terranes of Central Lapland. The velocity model shows a significant difference in crustal velocity structure between the northern (distances 0–120 km) and southern parts of the profile. The difference in P-wave velocities and Vp/Vs ratio can be followed through the whole crust down to the Moho boundary indicating major tectonic boundaries. Upper crustal velocities seem to vary with the terranes/compositional differences mapped at the surface. The lower layer of the upper crust displays velocities of 6.0–6.1 km/s. Both Paleoproterozoic and Archean terranes are associated with high velocity bodies (6.30–6.35 km/s) at 100 and 200–350 km distances. The Central Lapland greenstone belt and Central Lapland Granitoid complex are associated with a 4 km-thick zone of unusually low velocities (<6.0 km/s) at distances between 120 and 220 km. We interpret the HUKKA 2007 profile to image an old, partly buried, inverted continental rift zone that has been closed and modified by younger tectonic events. It has structural features typical of rifts: inward dipping rift shoulders, undulating thickness of the middle crust, high velocity lower crust and a rather uniform crustal thickness of 48 km. 相似文献
15.
Oliver Ritter Ute WeckmannTim Vietor Volker Haak 《Physics of the Earth and Planetary Interiors》2003,138(2):71-90
The Namibian margin is dominated by the late Proterozoic to early Cambrian fold belts of the Damara Orogen, which wrap around and separate the Congo and Kalahari Cratons. This mosaic of relatively ‘soft’ fold belts and ‘hard’ cratons apparently controlled the path for the opening of the South Atlantic in the early Cretaceous. The continents split along the coast-parallel fold belts of the Damara Orogen while the inland fold belt (Damara Belt) was effected by extension and widespread igneous intrusion but never developed to the rift stage. This paper is concerned with the interpretation of magnetotelluric (MT) data along a 200 km NW-SE profile across the Damara Belt in NW Namibia. The regional, two-dimensional electrical resistivity model and the induction vector data exhibit three distinctive zones: (i) a generally very resistive upper crust which is typical for the granites and metasediments of the Damara Belt, (ii) two subvertical conductors in upper to mid-crustal levels which correlate with major tectonic zone boundaries and (iii) a highly conductive middle to lower crust in the southern part of the profile. The geometry of the conductive structures could reflect a regional shear system in which upper crustal listric faults pass into a detachment zone in the middle crust. We interpret the high electrical conductivity in terms of graphite (or other forms of mineralization) enrichment along the shear planes. This zone of crustal weakness may have originated in Pre-Damara times and had probably experienced several episodes of crustal reactivation before the intrusion of basaltic dike swarms during the Cretaceous rifting and magmatism associated with the opening of the South Atlantic. 相似文献
16.
Tectonic activity is intense and destructive earthquakes occur frequently in the northern section of the North-South Seismic Belt(NSSB). After the May 12, 2008 Wenchuan earthquake, the North-South Seismic Belt enters a new period of high seismicity. On July 22, 2013, the Minxian-Zhangxian earthquake occurred, which broke the 10-years seismic quiescence of magnitude 6 of the area, indicating an increasing trend of strong earthquakes in the region. Earthquake is the product of crustal movement. Understanding the dynamics of the process of crustal movement may provide basis for earthquake prediction. GPS measurement can provide high-precision, large-scale, quasi-real-time quantitative crustal movement data, that allows us to explore the evolution of crustal movement and its relationship with earthquake, thus providing the basis for determining the seismic situation. Since 2009, the density of mobile GPS measurement stations has significantly improved in the Chinese mainland, and moreover, the Wenchuan earthquake has brought about adjustment of the regional crustal deformation regime. So the introduction of the latest repeat GPS data is important for understanding the features of crustal movement in the northern section of the North-South Seismic Belt. In this paper, we obtained the GPS velocity field, fault profile and baseline time series and analyzed the dynamics of recent crustal movement in the northern section of the North-South Seismic Belt using the 1999a-2014a GPS data of mobile and continuous GPS measurement stations. The results show that: the Qilianshan Fault has a high strain accumulation background. There are locked portions on the Liupanshan Fault, especially in the region of Jingning, Pingling, Dingxi, Longxi. In 2004-2009a, the degree of locking of the Liupanshan Fault got higher. In 2009—2013a, crustal movement on the northern section of the North-South Seismic Belt weakened compared with 1999-2004, 2004-2009, and showed some features as follows: ① The velocity field weakened more markedly near the Qilian-Haiyuan-Liupanshan faults; ②The velocity decreased more significantly in the region north of Qilianshan-Haiyuan Fault than that of the south, resulting in enhanced thrust deformation on the Qilianshan Fault in 2009-2013a and the decreased sinistral shear deformation on the Qilianshan Fault and Haiyuan Fault; ③the velocity field decreased more remarkably at 50km west of Liupanshan Fault, compared to the east region, which led to the locked range on the Liupanshan Fault extending to the range of 100km near the fault zone during 2009-2013 from the previous locked range of 50km near the fault. The GPS baseline time series analysis also reveals a number of structural features in the region: Yinchuan Graben is continuing extending, and the extension in the west is stronger than that in the east. On the southern end of Yinchuan Graben, the deformation is very small. 相似文献
17.
本文利用天然地震面波记录和层析成像方法,研究了南北地震带及邻近区域的岩石圈S波速度结构和各向异性特征.结果表明南北地震带的东边界不但是地壳厚度剧变带,也是地壳速度的显著分界.其西侧中下地壳的S波速度显著低于东侧,强震大多发生在低速区内部和边界.青藏高原东缘中下地壳速度显著低于正常大陆地壳,在松潘甘孜地块和川滇地块西部大约25～45 km深度存在壳内低速层;这些低速特征与高原主体的低速区相连,有利于下地壳物质的侧向流动.地壳的各向异性图像与下地壳流动模式相符,即下地壳物质绕喜马拉雅东构造结运动,东向的运动遇到扬子坚硬地壳阻挡而变为向南和向北东的运动.面波层析成像结果支持青藏高原地壳运动的下地壳流动模型.南北地震带的岩石圈厚度与其东侧的扬子和鄂尔多斯地块相似但速度较低.川滇西部地块上地幔顶部(莫霍面至88 km左右)异常低速;松潘甘孜地块上地幔盖层中有低速夹层(约90～130 km深度).岩石圈上地幔的速度分布图像与地壳显著不同,在高原主体与川滇之间存在北北东向高速带,可能会阻挡地幔物质的东向运动.上地幔各向异性较弱且与地壳的分布图像显然不同.因此青藏高原岩石圈地幔的构造运动具有与地壳不同的模式,软弱的下地壳提供了壳幔运动解耦的条件. 相似文献
18.
F. Calamita M. Coltorti D. Piccinini P. P. Pierantoni A. Pizzi M. Ripepe V. Scisciani E. Turco 《Journal of Geodynamics》2000,29(3-5)
Analyses of structural and geomorphological data combined with remote sensing interpretation confirm previous knowledge on the existence of an extensional Quaternary tectonic regime in the Colfiorito area (Umbro-Marchean Central Apennines). This is characterized by a maximum principal axis of finite strain oriented approx. NE–SW, which is the result of a progressive deformation process due to pure and radial extension. Surface geological data, the crustal tectonic setting (reconstructed using a CROP 03 seismic reflection profile), and seismological data relative to the autumn 1997 Colfiorito earthquake sequence constrain the following seismotectonic model. We interpret the seismogenic SW-dipping low-angle normal fault pictured by seismic data as an inverted thrust ramp located in the basement at depth between 5 and 10 km. The surface projection of this seismogenic structure defines a crustal box within which high-angle normal faults are responsible for the deformation of the uppermost crust. The regional patterns of pre-existing basement thrusts therefore control the seismotectonic zoning of the area that cannot be directly related to the high-angle normal fault systems which cut through different crustal boxes; the latter system records, in fact, re-shear along pre-existing normal faults. Moreover, Quaternary slip-rates relative to high-angle normal faults in the Central Apennines are closely related to seismic hazard within each crustal box. 相似文献
19.
The North China Craton (NCC) witnessed Mesozoic vigorous tectono-thermal activities and transition in the nature of deep lithosphere. These processes took place in three periods: (1) Late Paleozoic to Early Jurassic (～170 Ma); (2) Middle Jurassic to Early Cretaceous (160–140 Ma); (3) Early Cretaceous to Cenozoic (140 Ma to present). The last two stages saw the lithospheric mantle replacement and coupled basin-mountain response within the North China Craton due to subduction and retreating of the Paleo-Pacific plate, and is the emphasis in this paper. In the first period, the subduction and closure of the Paleo- Asian Ocean triggered the back-arc extension, syn-collisional compression and then post-collisional extension accompanied by ubiquitous magmatism along the northern margin of the NCC. Similar processes happened in the southern margin of the craton as the subduction of the Paleo-Tethys ocean and collision with the South China Block. These processes had caused the chemical modification and mechanical destruction of the cratonic margins. The margins could serve as conduits for the asthenosphere upwelling and had the priority for magmatism and deformation. The second period saw the closure of the Mongol-Okhotsk ocean and the shear deformation and magmatism induced by the drifting of the Paleo-Pacific slab. The former led to two pulse of N-S trending compression (Episodes A and B of the Yanshan Movement) and thus the pre-existing continental marginal basins were disintegrated into sporadically basin and range province by the Mesozoic magmatic plutons and NE-SW trending faults. With the anticlockwise rotation of the Paleo-Pacific moving direction, the subduction-related magmatism migrated into the inner part of the craton and the Tanlu fault became normal fault from a sinistral one. The NCC thus turned into a back-arc extension setting at the end of this period. In the third period, the refractory subcontinental lithospheric mantle (SCLM) was firstly remarkably eroded and thinned by the subduction-induced asthenospheric upwelling, especially those beneath the weak zones (i.e., cratonic margins and the lithospheric Tanlu fault zone). Then a slightly lithospheric thickening occurred when the upwelled asthenosphere got cool and transformed to be lithospheric mantle accreted (～125 Ma) beneath the thinned SCLM. Besides, the magmatism continuously moved southeastward and the extensional deformations preferentially developed in weak zones, which include the Early Cenozoic normal fault transformed from the Jurassic thrust in the Trans-North Orogenic Belt, the crustal detachment and the subsidence of Bohai basin caused by the continuous normal strike slip of the Tanlu fault, the Cenozoic graben basins originated from the fault depression in the Trans-North Orogenic Belt, the Bohai Basin and the Sulu Orogenic belt. With small block size, inner lithospheric weak zones and the surrounding subductions/collisions, the Mesozoic NCC was characterized by (1) lithospheric thinning and crustal detachment triggered by the subduction-induced asthenospheric upwelling. Local crustal contraction and orogenesis appeared in the Trans-North Orogenic Belt coupled with the crustal detachment; (2) then upwelled asthenosphere got cool to be newly-accreted lithospheric mantle and crustal grabens and basin subsidence happened, as a result of the subduction zone retreating. Therefore, the subduction and retreating of the western Pacific plate is the outside dynamics which resulted in mantle replacement and coupled basin-mountain respond within the North China Craton. We consider that the Mesozoic decratonization of the North China Craton, or the Yanshan Movement, is a comprehensive consequence of complex geological processes proceeding surrounding and within craton, involving both the deep lithospheric mantle and shallow continental crust. 相似文献
20.
The paper presents an alternative consistent seismotectonic model of the Kaliningrad (Russia) September 21, 2004, earthquake according to which source zones of the two strongest shocks were confined to a N-S fault off the Sambiiskii Peninsula in the Kaliningrad region. A left-lateral deformation fractured a local crustal zone between the town of Yantarnyi and the settlement of Bakalino. The model was constructed with the use of a method developed by the authors for structural analysis of gravity and magnetic data. Initial materials are revised in terms of the EMS-98 macroseismic scale, and modified maps showing the shaking intensity in the NW part of the Sambiiskii Peninsula are compiled. 相似文献