Rupture Property of the 1927 Gulang Ms8.0 Earthquake and Numerical Simulation of Rupture Mechanism     

Zheng Wenjun Yuan Daoyang Zhang Dongli He Wengui Guo Hua Liu Baichi 《中国地震研究》2005,19(4):409-419

INTRODUCTIONThe1927GulangMS8.0earthquake is a severe earthquake followed the HaiyuanMS8.5earthquake of1920inthe Qilian Mt._Hexi Corridor earthquake zone.The most severely hit region wasaround Gulang and Liangzhou(the present Wuwei)of Gansu Province,with a…  相似文献   

Tectonothermal evolution of the Lesser Himalaya, Nepal: Constraints from ⁴⁰Ar/³⁹Ar ages from the Kathmandu Nappe     

Kazunori  Arita  R. David  Dallmeyer Akira  Takasu 《Island Arc》1997,6(4):372-385

Abstract The Himalaya is a fold-and-thrust wedge formed along the northern margin of the Indian continent, and consists of three thrust-bounded lithotectonic units; the Sub-Himalaya, the Lesser Himalaya, and the Higher Himalaya with the overlying Tethys Himalaya from south to north, respectively. The orogen-scale, intracrustal thrusts which bound the above lithotectonic units are splays off an underlying subhorizontal dkcollement, and show a southward propagating piggy-back sequence with an out-of-sequence thrust. Among these thrusts, the Main Central Thrust zone (MCT zone) has played a major role in Himalayan tectonics. The MCT zone represents a shear zone which has accommodated southward thrusting of the Higher Himalayan crystalline thrust sheet over the Lesser Himalayan sequence for ～140 km. The Kathmandu Nappe in central Nepal has been transported over the Lesser Himalayan metasediments along the MCT zone, and is locally separated from the Higher Himalayan thrust sheet in the north by an out-of-sequence thrust. ⁴⁰Ar/³⁹Ar ages have been determined for one whole-rock phyllite and six muscovite concentrates from metasedimenta-ry rocks and variably deformed granites in the Kathmandu Nappe. These ages range from 44 Ma to 14 Ma, and suggest a record of both Eo-Himalayan (Eocene) and Neo-Himalayan (Miocene) tectonothermal events in the Tertiary Himalayan orogeny. The Miocene event was associated with translation along the MCT zone. No tectonothermal event of the Late Miocene to Early Pliocene ages have been reported near the MCT zone in southern Lesser Himalayan crystalline nappe or klippe, although such events have been documented within and around the MCT zone in the northern root zone of the Higher Himalaya. This suggests that out-of-sequence thrusting may have occurred between 14 Ma and 5 Ma, probably during the period 10-7.5 Ma. Since then the frontal MCT zone below the Kathmandu Nappe has been inactive, but the MCT zone in the northern root zone has remained active. The rapid increase in denudation rates of the Higher Himalaya since the Late Miocene may have been caused by ramping along the out-of-sequence thrust at depth.  相似文献   

The relation between grain size and Ar/Ar date for Alpine white mica from the Siviez-Mischabel Nappe, Switzerland     

Michelle J. Markley  Christian Teyssier  Mike Cosca 《Journal of Structural Geology》2002,24(12):21

Variations in Alpine white mica ⁴⁰Ar/³⁹Ar dates from the cover units of the Siviez-Mischabel Nappe relate to regional variations in the thermal history of the nappe. We focus on three regions within the nappe: the central Siviez-Mischabel (CSM), the southern Siviez-Mischabel (SSM), and the eastern Siviez-Mischabel (ESM). Our approach weaves together observations of quartz and mica textures in thin section, the variation of ⁴⁰Ar/³⁹Ar date with grain size, considerations of the effective diffusion dimension (EDD) of argon in white mica, and a comparison of dates with diffusion model results. In the CSM, pressure solution of quartz and dislocation glide in mica accommodated Alpine deformation. Dates record mica growth during nappe emplacement from 40 to 36 Ma and do not vary with grain size. In the SSM and ESM, both mica and quartz show textures associated with dynamic recrystallization, and dates decrease with grain size. In the SSM, dates also agree with the timing of nappe emplacement, but in the ESM, dates significantly post-date the timing of nappe emplacement. A comparison of dates with diffusion model results supports inferences from rock fabrics that the SSM experienced higher peak temperatures than the CSM, even though dates from both units approximate the timing of mica growth. Dates obtained from the ESM, however, do not compare well with simple models, and the thermal evolution of this region of the nappe, in the neighborhood of the Simplon Fault Zone, is not well understood.  相似文献   

Late Cretaceous exhumation history of an extensional extruding wedge (Graz Paleozoic Nappe Complex, Austria)   总被引：1，自引：1，他引：0  

Krenn Kurt  Fritz Harald  Mogessie Aberra  Schaflechner Johannes 《International Journal of Earth Sciences》2008,97(6):1331-1352

Late Cretaceous structures within the eastern Graz Paleozoic Nappe Complex define an extruding wedge with north-eastward directed thrusting in eastern portions and strike-slip shear along the margins. Stacking structures are overprinted by south-westward directed extension with low-grade metamorphic rocks in the hangingwall and high-grade basement rocks in the footwall. Pressure–temperature and structural data are obtained from successively opening quartz veins that record various stages of progressive deformation and metamorphism. Fluid inclusion data and related structures show that during extension isothermal decompression from ca. 550°C and 8 kbar down to ca. 450°C and 2 kbar was related to exhumation of rocks from deep crustal levels. The data point to a high geothermal gradient and explain condensed paleo-isotherms due to ductile normal faulting in the eastern areas of the Graz Paleozoic Nappe Complex. The investigated Late Cretaceous structural elements suggest that the Graz Paleozoic Nappe Complex decoupled from the surrounding basement units and operated as a large-scale extension–extrusion corridor that evolved prior to Miocene extrusion tectonics in the Eastern Alps.  相似文献   

古地磁与酒西盆地南缘推覆体     

黄华芳  郑国东等 《甘肃地质》1993,2(2):15-22

酒西盆地南缘晚古生代以来发育的典型冲断—褶皱推覆体隶属于北祁连构造带,自泥盆纪开始,它就拚接于华北板块边缘,成为其一部分,它所经历的构造变迁史是与华北板块紧密相连的,但与塔里木板块却是在二叠纪以后才联合到一起,联合部位在阿尔金断裂带。在伴随华北板块主体一同北向“漂移”的运动中,经历了3次较强烈运动阶段:(1)泥盆纪～石炭纪期间;(2)二叠纪～三叠纪期间;(3)第三纪～第四纪。并有过两个运动和缓时期:石炭纪～二叠纪期间和三叠纪～白垩纪。 推覆体多期推覆作用的发生对酒西盆地基底形态、范围、沉积物类型、有机质演化条件等均具有明显控制作用,进而给油气赋存亦带来极大影响。  相似文献   

沿雅鲁藏布江（东段）地区推覆与反向冲断构造的地质特征及其形成机制   总被引：1，自引：0，他引：1       下载免费PDF全文

郝杰  李齐 《地震地质》1996,18(1):30-36

沿雅鲁藏布江（东段）两岸至少发育着两套断裂系统。其一是断面北倾,由北向南远距离的推覆断裂系,发育着构造窗和飞来峰。该断裂系形成在洋－陆俯冲和陆－陆碰撞两个造山阶段（１００～２６Ｍａ）;其二是断面向南陡倾,由南向北逆冲,切割了早期的由北向南的推覆断裂系的反向冲断层系。该断裂系形成于碰撞造山阶段晚期（＜２６Ｍａ）的局部反向道冲作用或造山期后的重力伸展作用。上述两套断裂系的叠加造成沿江地区构造的复杂  相似文献   

Structural development of the Tso Morari ultra-high pressure nappe of the Ladakh Himalaya   总被引：2，自引：0，他引：2  

Jean-Luc Epard  Albrecht Steck   《Tectonophysics》2008,451(1-4):242-264

A continental subduction-related and multistage exhumation process for the Tso Morari ultra-high pressure nappe is proposed. The model is constrained by published thermo-barometry and age data, combined with new geological and tectonic maps. Additionally, observations on the structural and metamorphic evolution of the Tso Morari area and the North Himalayan nappes are presented. The northern margin of the Indian continental crust was subducted to a depth of > 90 km below Asia after continental collision some 55 Ma ago. The underthrusting was accompanied by the detachment and accretion of Late Proterozoic to Early Eocene sediments, creating the North Himalayan accretionary wedge, in front of the active Asian margin and the 103–50 Ma Ladakh arc batholith. The basic dikes in the Ordovician Tso Morari granite were transformed to eclogites with crystallization of coesite, some 53 Ma ago at a depth of > 90 km (> 27 kbar) and temperatures of 500 to 600 °C. The detachment and extrusion of the low density Tso Morari nappe, composed of 70% of the Tso Morari granite and 30% of graywackes with some eclogitic dikes, occurred by ductile pure and simple shear deformation. It was pushed by buoyancy forces and by squeezing between the underthrusted Indian lithosphere and the Asian mantle wedge. The extruding Tso Morari nappe reached a depth of 35 km at the base of the North Himalayan accretionary wedge some 48 Ma ago. There the whole nappe stack recrystallized under amphibolite facies conditions of a Barrovian regional metamorphism with a metamorphic field gradient of 20 °C/km. An intense schistosity with a W–E oriented stretching lineation L₁ and top-to-the E shear criteria and crystallization of oriented sillimanite needles after kyanite, testify to the Tso Morari nappe extrusion and pressure drop. The whole nappe stack, comprising from the base to top the Tso Morari, Tetraogal, Karzok and Mata–Nyimaling-Tsarap nappes, was overprinted by new schistosities with a first N-directed and a second NE-directed stretching lineation L₂ and L₃ reaching the base of the North Himalayan accretionary wedge. They are characterized by top-to-the S and SW shear criteria. This structural overprint was related to an early N- and a younger NE-directed underthrusting of the Indian plate below Asia that was accompanied by anticlockwise rotation of India. The warping of the Tso Morari dome started already some 48 Ma ago with the formation of an extruding nappe at depth. The Tso Morari dome reached a depth of 15 km about 40 Ma ago in the eastern Kiagar La region and 30 Ma ago in the western Nuruchan region. The extrusion rate was of about 3 cm/yr between 53 and 48 Ma, followed by an uplift rate of 1.2 mm/yr between 48 and 30 Ma and of only 0.5 mm/yr after 30 Ma. Geomorphology observations show that the Tso Morari dome is still affected by faults, open regional dome, and basin and pull-apart structures, in a zone of active dextral transpression parallel to the Indus Suture zone.  相似文献   

秦岭─大别造山带及其南北缘地震层析成像   总被引：4，自引：1，他引：4       下载免费PDF全文

刘建华  刘福田  孙若昧  吴华  吴丹 《地球物理学报》1995,(1)

利用秦岭─大别造山带及其毗邻地区３１０个地震台站记录到的区域地震２３６００条Ｐ波到时数据，重建了该区地壳和上地幔三维速度图像。结果表明：１．秦岭─大别造山带及其毗邻地区地壳和上地幔存在显著的横向不均匀性，直至１１０ｋｍ深度处依然明显。２．地壳上部的速度图像与地表地质构造密切相关：造山带隆起区显著高速；盆地及坳陷区明显低速。由速度鲜明对比勾勒出的秦岭─大别造山带南界基本上位于扬子北缘主边断裂带上。３．中地壳的速度图像表明，造山带内部的一些低速区对应于一些大型推覆构造。４．４０＋０ｋｍ深度处的速度图像反映了该区莫霍界面深度的起伏。大致以１０７°Ｅ为界，以东地区地壳厚度小于４０ｋｍ，以西地区大于４０ｋｍ，且呈现出往西地壳逐渐加厚的趋势。５．位于滦川、商县、丹凤的北秦岭构造带，上地幔顶部出现低速异常，异常速度值约为７．３９—７．５５ｋｍ／ｓ。结合地球物理测深的结果，可能是由下地壳、上地幔顶部的热过程所致。  相似文献   

依据卫星遥感影像研究结果综论西南三江地区构造特征   总被引：1，自引：0，他引：1  

王铠元 《矿产与地质》1991,(Z1)

我国西南怒江、澜沧江、金沙江——红河流域通称三江地区.本课题属“西南三江地区大地构造问题及其与成矿关系的研究”二级课题的卫星遥感影像研究部分,利用遥感研究成果综论和探讨三江地区的构造特征.使用的遥感资料是美国第四号陆地卫星影像磁带所处理1/100万和1/50万假彩色MSS图像,其图像质量较好.另在丁青—泸水地段还进行了计算机多功能的处理(成图6幅),效果亦较好.专题共作有卫星影像彩色图片19幅,编缩了相应比例尺的构造解译图(24幅).通过卫星影像的解译和研究,综论了三江地区断裂构造的总格局,由5条主干断裂(一级断裂)组成一个NNW向中部紧缩狭窄,而向北、南部撒开的“哑铃棒状”格局.与主断裂紧密相伴的还有约30条呈NNW—NW向展布的二级和三级断裂以及为数不少的、规模大小各异的环状—似环状构造、推覆构造.还有15条活动断裂分布其间,组成了一幅极为复杂多变,但内容又十分丰富的构造景观.本文不仅对三江地区总格局作了阐述,还分别对主干断裂、二～三级断裂、活动断裂、环状—似环状构造、推覆构造等的影像标志、展布特征及相互关系都作了探讨,并讨论了三江地区断裂构造格局中几个争议较大的问题,还对遥感技术手段及其各种资料对本区构造研究效果作了综述.  相似文献   

Evolution, formation mechanism and kinematics of a contractional shallow shear zone within sedimentary rocks of the Northern Apennines (Italy)     

Andrea Brogi 《Eclogae Geologicae Helvetiae》2006,99(1):29-47

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