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1.
Mesozoic tectono-magmatic activities in South China:Retrospect and prospect   总被引：9，自引：0，他引：9  
The South China Block was formed through the collisional orogeny between the Cathaysia Block and the Yangtze Block in the Early Neoproterozoic.The northern,western and southern sides of the South China Block were affected by disappearance of the Paleo-Tethyan Ocean during the Paleozoic.The southern and northern sides of the South China Block were respectively collided with the Indo-China Block and North China Block in the latest Paleozoic to form the basic framework of the Eastern China.The Eastern China has been affected by the westward subduction of the Pacific Plate since the Mesozoic.Therefore,the South China Block was influenced by the three major tectonic systems,leading to a superposed compound tectonics.The comparative study of the Mesozoic geology between the South China Block and its surrounding areas suggests that although the Mesozoic South China Block was adjacent to the subduction zone of the western Pacific,no juvenile arc-type crust has been found in the eastern margin.The main Mesozoic geology in South China is characterized by reworking of ancient continental margins to intracontinental tectonics,lacking oceanic arc basalts and continental arc andesites.Therefore,a key to understanding of the Mesozoic geology in South China is to determine the temporal-spatial distribution and tectonic evolution of Mesozoic magmatic rocks in this region.This paper presents a review on the tectonic evolution of the South China Block through summarizing the magmatic rock records from the compressional to extensional tectonic process with the transition at the three juncture zones and using the deformation and geophysic data from the deep part of the South China continental lithosphere.Our attempt is to promote the study of South China’s geology and to make it as a typical target for development of plate tectonic theory.  相似文献   

2.
Time range of Mesozoic tectonic regime inversion in eastern North China Block   总被引：49，自引：9，他引：49  
An important tectonic inversion took place in eastern North China Block(NCB) during Mesozoic, which caused a great lithosphere thinning, reconstruction of basin-range series, powerful interaction between mantle and crust, a vast granitic intrusion and volcanism, and large-scale metallogenic explosion. The time range of the Mesozoic tectonic regime inversion in the eastern North China Block is one of the key issues to understand mechanism of tectonic regime inversion. Our updated results for recognizing the time range are mainly obtained from the following aspects: structural analyses along northern and southern margins of the NCB and within the NCB for revealing tectonic inversion from compression to extension and structural striking from -EW to NNE; geothermic analyses of the eastern sedimental basins for a great change of thermal history and regime; basin analysis for basin inversion from compression to extension and basin migration from -EW to NNE; petrological and geochemical studies of volcanic roc  相似文献   

3.
From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.  相似文献   

4.
For the first time on the Chinese mainland, long-range wide-angle seismic reflection/refraction profiling technology has been applied to seismic wave phases from different depths and with different attributes within the various blocks of the North China Craton to characterize the structure of the crust and upper mantle lithosphere. By comparative analysis of the seismic wave phase characteristics in each block across a 1500-km-long east-west profile, we have identified conventional Pg, Pci, PmP and Pn phases in the crust, made a clear contrast between PL1 and PL2 waves belonging to two groups of lithospheric-scale phases, and produced a model of crust-mantle velocity structures and tectonic characteristics after one- and two-dimensional calculations and processing. The results show that the thickness of the crust and lithosphere gradually deepens from east to west along the profile. However, at the reflection/refraction interface, seismic waves in each group show obvious localized changes in each block. Also, the depth to the crystalline basement changes greatly, from as much as 7.8 km in the North China fault basin to only about 2 km beneath the Jiaodong Peninsula and Taihang-Lüliang area. The Moho morphology as a whole ranges from shallow in the east to deep in the west, with the deepest point in the Ordos Block at 47 km; in contrast, the North China Plain Block is uplifting. The L1 interface of the lithosphere is observed only to the west of Taihang Mountains, at a relatively slowly changing depth of about 80 km. The L2 interface varies from 75 to 160 km and shows a sharp deepening to the west of Taihang Mountains, forming a mutation belt.  相似文献   

5.
Plate subduction is an important mechanism for exchanging the mass and energy between the mantle and the crust,and the igneous rocks in subduction zones are the important carriers for studying the recycling of crustal materials and the crust-mantle interaction.This study presents a review of geochronology and geochemistry for postcollisional mafic igneous rocks from the Hong’an-Dabie-Sulu orogens and the southeastern edge of the North China Block.The available results indicate two types of the crust-mantle interaction in the continental subduction zone,which are represented by two types of mafic igneous rocks with distinct geochemical compositions.The first type of rocks exhibit arc-like trace element distribution patterns(i.e.enrichment of LILE,LREE and Pb,but depletion of HFSE)and enriched radiogenic Sr-Nd isotope compositions,whereas the second type of rocks show OIB-like trace element distribution patterns(i.e.enrichment of LILE and LREE,but no depletion of HFSE)and depleted radiogenic Sr-Nd isotope compositions.Both of them have variable zircon O isotope compositions,which are different from those of the normal mantle zircon,and contain residual crustal zircons.These geochemical features indicate that the two types of mafic igneous rocks were originated from the different natures of mantle sources.The mantle source for the second type of rocks would be generated by reaction of the overlying juvenile lithospheric mantle with felsic melts originated from previously subducted oceanic crust,whereas the mantle source for the first type of rocks would be generated by reaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts from subsequently subducted continental crust of the South China Block.Therefore,there exist two types of the crust-mantle interaction in the continental subduction zone,and the postcollisional mafic igneous rocks provide petrological and geochemical records of the slab-mantle interactions in continental collision orogens.  相似文献   

6.
Rayleigh wave phase velocities of South China block and its adjacent areas   总被引：2，自引：0，他引：2  
Using records of continuous seismic waveforms from 609 broadband seismic stations in the South China Block and its adjacent areas in 2010–2012, empirical Green's functions of surface waves were obtained from cross-correlation functions of ambient noise data between these stations. High quality phase velocity dispersion curves of Rayleigh waves were obtained using time-frequency analysis. These interstation dispersion curves were then inverted to build Rayleigh wave phase velocity maps at periods of 6–50 s. The results of phase velocity maps indicate that phase velocities at 6–10 s periods are correlated with the geological features in the upper crust. Major basins and small-scale grabens and basins display slow velocity anomalies; while most of the orogenic belts and the fold belts display high velocity anomalies. With the gravity gradient zone along Taihang Mountain to Wuling Mountain as the boundary for the phase velocity maps at period of 20–30 s, the western area mainly displays low velocity anomalies, while the eastern side shows high velocity anomalies. Phase velocities in the eastern South China Block south to the Qinling-Dabie orogenic belt is higher than that in the eastern North China Block to the north, which is possibly due to the differences of tectonic mechanisms between the North China Craton and the South China Block. The phase velocities at periods of40–50 s are possibly related to the lateral variations of the velocity structure in the lower crust and upper mantle: The low-velocity anomalies in the eastern part of the Tibetan Plateau are caused by the thick crust; while the Sichuan Basin and the southern part of the Ordos Basin display distinct high-velocity anomalies, reflecting the stable features of the lithosphere in these blocks. The lateral variation pattern of phase velocities in the southern part of the South China Block is not consistent with the surface trace of the block boundary in the eastern Yunnan Province and its vicinities. The phase velocities in the Sichuan Basin are overall slow at short periods and gradually increase with period from the central part to the edge of the basin, indicating the features of shallower basement in the center and overall stable lithospheric mantle of the basin. The middle and upper crust of the southern Ordos Basin in the North China Block is heterogeneous, while in lower crust and the uppermost mantle the phase velocities mainly exhibit high anomalies. High-velocity anomalies are widespread at the middle of the Qinling-Dabie orogenic belt, as well as the areas in southeastern Guangxi with Caledonian granite explosion, but its detailed mechanism is still unclear.  相似文献   

7.
The Qinling orogen was formed as a result of the collision between the North and South China blocks. The Qinling orogen represents the location at which the southern and northern parts of the Chinese mainland collided, and it's also the intersection of the Central China orogen and the north-south tectonic belt. There is evidence of strong deformation in this orogen, and it has had a long and complex geological history. We investigated the structure of the Moho in the southern Qinling orogen using large dynamite shot imaging techniques. By integrating the analysis of the single-shot and the move-out corrections profile, we determined the structure of the Moho beneath the northern Dabashan thrust belt and the southern Qinling orogen, including the mantle suture beneath Fenghuang mountain. The Moho is divided into two parts by the mantle suture zone beneath Fenghuang mountain:(1) from Ziyang to Hanyin, the north-dipping Moho is at about45–55 km depth and the depth increases rapidly; and(2)from Hanyin to Ningshan, the south-dipping Moho is at about 40–45 km depth and shallows slowly. The mantle suture is located beneath Fenghuang mountain, and the Moho overlaps at this location: the shallower Moho is connected to the northern part of China, and the deeper Moho is connected to the southern part. This may indicate that the lithosphere in the Sichuan basin subducts to the Qinling block and that the subduction frontier reaches at least as far as Fenghuang mountain.  相似文献   

8.
Using arrival data of the body waves recorded by seismic stations, we reconstructed the velocity structure of the crust and upper mantle beneath the southeastern edge of the Tibetan Plateau and the northwestern continental margin of the South China Sea through a travel time tomography technique. The result revealed the apparent tectonic variation along the Ailao Shan-Red River fault zone and its adjacent regions. High velocities are observed in the upper and middle crust beneath the Ailao Shan-Red River fault zone and they reflect the character of the fast uplifting and cooling of the metamorphic belt after the ductile shearing of the fault zone, while low velocities in the lower crust and near the Moho imply a relatively active crust-mantle boundary beneath the fault zone. On the west of the fault zone, the large-scale low velocities in the uppermost mantle beneath western Yunnan prove the influence of the mantle heat flow on volcano, hot spring and magma activities, however, the upper mantle on the eas  相似文献   

9.
The Dabie Mountain is the collisional orogenic belt between the North China Block and the Yangtze Block. As the eastern segment of the central-China orogenic belt, its tectonic framework is corresponding to the Qinling orogenic belt as a whole[1]. The NHB in northern part of Dabie Orogen is regarded as the joint belt between the Yangtze Block and the North China Block, and roughly corresponds to the north Qinling belt of the Qinling orogenic belt, which separated the Tongbai-Dabie hig…  相似文献   

10.
Mantle xenoliths brought up by Cenozoic volcanic rocks onto the earth‘s surface may provide direct information about the upper mantle beneath the volcanic region. This paper presents the study on mantle xenoliths collected from Haoti village, Dangchang County, Gansu Province, western China. The main purpose of the study is to gain an insight into the thermal structure and rbeology of the upper mantle beneath the region. The results show that the upper mantle of the region is composed mainly of spinel lherzolite at shallower depth (52-75km), and garnet iberzolite at greater depth (greater than 75km), instead of harzburgite and dunite as proposed by some previous studies. The upper mantle geotherm derived from the equilibrium temperatures and pressures of xenoliths from the region is lower than that of North China, and is somewhat closer to the Oceanic geotherm. The crust-mantle boundary is determined from the geotherm to be at about 52km, and the Moho seems to be the transition zone of lower crust material with spinel iberzolite. If we take 1280℃ as the temperature of the top of asthenosphere, then the fithospbere-asthenosphere boundary should be at about 120km depth. The differential stress of the upper mantle is determined by using recrystallized grain size piezometry, while the strain rate and equivalent viscosity are determined by using the high temperature flow law of peridotite. The differential stress, strain rate and viscosity profiles constructed on the basis of the obtained values indicate that asthenospberic diapir occurred in this region during the Cenozoic time, resulting in the corresponding thinning of the lithosphere. However, the scale and intensity of the diapir was significantly less than that occurring in the North China region. Moreover, numerous small-scale shear zones with localized deformation might occur in the iithospberic mantle, as evidenced by the extensive occurrence of xenoliths with tabular equigranular texture.  相似文献   

11.
Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling orogenic belt in a crocodile-mouth shape.  相似文献   

12.
秦岭造山带岩石圈电性结构及其地球动力学意义   总被引：11，自引：2，他引：11       下载免费PDF全文
秦岭造山带三维电性结构特征的详细研究结果，结合其他多种地球物理和地质资料分析发现，自中新生代以来，尤其是晚近时期华北和扬子两地块向秦岭造山带持续陆内俯冲过程中，由于南秦岭岩石圈向北挤入作用，秦岭造山带的后陆冲断褶带和北秦岭厚皮叠瓦逆冲带，现今处于岩石圈叠置加厚与拆沉作用的初始期；与之相反，南秦岭正在经历拆沉－底侵的物质再循环作用，佛坪一带可能发育新的地幔柱；此外，在造山带北、南深部边界与内部不同岩石圈块体之间还伴随强烈的不同性质的走滑作用和物质侧向传输．最后探讨了秦岭造山带构造拆沉与巨厚岩石圈并存以及走滑构造作用等的地球动力学意义．  相似文献   

13.
The Weihe Basin is the main component of the extrusion and escape shear zone between the ancient North China craton block in Ordos and the ancient Yangtze platform in Sichuan Basin, and carries the dynamic transmission from the main power source of the Qinghai-Tibet Block in the west to the North China and South China regions in the east. The basin itself plays multi roles in the east-west and north-south tectonic movement, and is an excellent site for studying the structural interlacing, dynamic transformation and transmission. At the same time, Weihe Basin is also a famous strong earthquake zone in China. Historically, there was a strong earthquake of magnitude 8 1/4 occurring in Huaxian County in 1556, causing huge casualties and property losses. In view of the special geological structures and the characteristics of modern seismicity activities in the Weihe fault-depression zone, it is necessary to carry out fine three-dimensional velocity structure detection in the deep part of Weihe Basin and its adjacent areas, so as to study the relationship between velocity structure and geological structural units and their evolution process, as well as the deep medium environment where earth￣quakes develop and occur. We investigate the S-wave velocity structure beneath Weihe Basin and its adjacent regions based on continuous background noise data and teleseismic data recorded by 257 broadband stations in Shaanxi Province and its adjacent regions and China Seismological Science Array Exploration Project, and by adopting seismic surface wave inter-station method and background noise cross-correlation method, a total of 10 049 fundamental-mode Rayleigh surface wave phase velocity dispersion curves in the periods of 5~70s are obtained. Firstly, using the average dispersion curve in this study area, we obtain the one-dimensional average S-wave velocity structure model of the study area, and then we apply the ray-tracing surface-wave-dispersion direct inversion method to obtain the S-wave velocity structure of the crust and uppermost mantle (3~80km) beneath Weihe Basin and its adjacent regions. The test results of a 1°×1° grid checker board show that the recovery is good, except for the areas east of 111° and south of 32° of the study area, where there is almost no resolution. The imaging results show that the velocity structure beneath each tectonic unit in the study area has a certain distribution rule, and there is a good correlation between surface geological structure and deep velocity structure. Based on the analysis of velocity slices at different depths and S-wave velocity structures of three profiles, and combined with existing geological structures, geophysics and other deep exploration research results, we obtain the following knowledge and conclusions:1)The thick sedimentary layer covering the top of Weihe Basin is the cause of low velocity anomaly in its shallow crust, the middle and upper crust of the basin are of low velocity structure, and the low-velocity zone extends about 25km, the Moho interface uplifts abruptly relative to both the Ordos Block and the Qinling orogenic belt on opposite sides, and high-speed materials from the upper mantle intrude into the lower crust, which may be related to the underplating of mafic-ultramafic materials from the upper mantle in Mesozoic-Cenozoic period; 2)The south Ordos Block is not a homogeneous whole, the low-velocity structure of the shallow crust in southern Ordos Block is thin in east and thick in west, which may be related to the overall tilting of the Ordos Basin since the Phanerozoic, as well as the differential uplift and strong and uneven denudation of the Ordos Block since the Late Cretaceous. The crustal structure of the south Ordos Block is relatively simple and homogeneous. There is no significant low-velocity structure in the curst of the block, which shows that the low-velocity structure in the crust does not penetrate the whole Ordos block. We speculate that the southern Ordos Block still maintains the stable craton property, and has not been reformed significantly so far; 3)The variation characteristics of deep structure of the Qinling orogenic belt reflect the deep crustal structure and tectonic deformation characteristics of the orogenic belt which are strongly reformed by land-land collision and suture between North China plate and Yangtze plate, intracontinental orogeny, uplift of Qinghai-Tibet Plateau and its northeastern expansion since the Late Hercynian-Indosinian period. The deep structure beneath the eastern and western Qinling orogenic belt is different and has the characteristics of segmentation. The low-velocity anomaly at the bottom of the lower crust of the orogenic belt may be affected by tectonic activities such as uplift and outward extension of the NE Tibetan plateau, and the analysis considers that there is little possibility of the existence of lower crustal circulation channel for the eastward flowing of Tibetan plateau materials in the Qinling orogenic belt. However, since the maximum depth from the inversion of this paper is 80km, which is located at the top of the upper mantle, our results cannot prove that there exists a mantle flow channel for the eastward flow of Tibetan plateau material beneath the Qinling orogenic belt.  相似文献   

14.
从2013年3月至2014年11月,我们布设了一条延川—涪陵的流动宽频带地震台阵,剖面由70个流动台站组成,全长约900km,穿越华北克拉通、秦岭—大巴造山带和扬子克拉通东北缘陆内三大构造单元.利用记录到的远震波形资料,提取得到5638个远震P波接收函数,使用H-κ叠加扫描和CCP偏移叠加方法刻划了秦岭造山带与南北相邻地带的地壳厚度、泊松比以及构造界带.研究结果显示,(1)关于地壳厚度:地壳最厚的区域出现在大巴山,地壳厚度集中在47~51km之间,秦岭的地壳厚度相对大巴山较薄,且呈向北减薄趋势,集中在37~46km之间,渭河盆地地壳厚度为本区域最薄地带,在34°N左右处达到最薄为35km,剖面北侧的南鄂尔多斯盆地的地壳厚度变化缓慢,多为44km左右,南侧的四川盆地东北缘的地壳厚度向南缓慢减薄,集中在42~48km之间;(2)关于泊松比:使用接收函数H-κ叠加扫描法得到了沿剖面各台站下方地壳的平均纵、横波速度比VP/VS(κ),进一步计算得到泊松比σ,泊松比具有明显的横向分块特征,秦岭造山带的泊松比明显低于南北两侧区域,其小于0.26的泊松比表征着该区域地壳物质组分主要为酸性岩石,亦即其酸性长英质组分上地壳相对于基性铁镁质组分下地壳较厚,该区域没有高泊松比分布则表明不存在广泛的部分熔融.(3)关于构造界带:秦岭—大巴造山带与扬子克拉通的边界并非在勉略构造带,应向南移至四川盆地的东北缘,华北克拉通和扬子克拉通分踞秦岭—大巴造山带南、北两侧,且分别以较陡倾角向南和相对较缓的倾角向北俯冲于秦岭—大巴造山带之下,使得秦岭—大巴造山带呈不对称状扇形向外扩展与向上抬升的空间几何模型.秦岭和大巴山之间33°N附近存在分界面,两区域地壳厚度与泊松比特征各异.  相似文献   

15.
青藏高原东北部多尺度重力场及其地球动力学意义   总被引：6，自引：3，他引：3       下载免费PDF全文
由于受到SN和EW双向挤压作用的综合影响,处于年轻高原与古老地块交接区的青藏高原东北部岩石圈强烈变形,构造活动十分活跃.为了整体性地了解青藏高原东北部重力场和深部动力学机制,本文基于EGM2008全球重力场模型数据,利用小波多尺度分析获得不同尺度的重力异常信息;同时反演了研究区的地壳厚度;通过构建穿越龙门山造山带和西秦岭造山带两条剖面的岩石圈密度结构模型,分析了地壳上地幔内不同介质的分布特征.研究结果表明,青藏高原东北部岩石圈显示十分复杂的塑性体的特征,其重力异常走向多以EW或SSE为主,反映了高原岩石圈物质向东运移的趋势;地壳厚度由西向东逐渐减薄,边缘造山带深部并没有发现"山根"痕迹,结合该地区低重力的特征,推测西秦岭—松潘构造结岩石圈发生过大规模地幔流底侵作用;地幔流上涌的动力可能来源于印度板块向欧亚大陆板块俯冲,激发了地幔流体侧向移动,在扬子地台和华北地台附近受到坚硬岩石圈的阻挡而被迫上移,并因此造成龙门山与西秦岭的隆升.  相似文献   

16.
目前研究一般认为华南块体是由扬子块体和华夏块体在新元古代拼合形成,并同时形成位于扬子块体东南边缘的江南造山带.但是由于华南地区构造历史复杂,对于扬子块体与华夏块体的分界及构造属性仍存在较大争议.为了研究华南块体的地下速度结构及构造属性,我们利用块体交界处的九嶷山及其附近的流动和固定台网的地震波数据,采用地震背景噪声互相关方法反演研究区域2~40 s瑞利波群速度和相速度分布,并进一步得出了该区域地壳的精细三维S波速度结构.反演成像结果显示,扬子块体与华夏块体的地壳及上地幔的结构特征差异显著.10~20 km的S波速度分布图显示呈线性的、连续分布低速异常,可能为扬子块体与华夏块体的具体分界位置.结合华南地区地球化学研究结果和构造历史,该低速异常可能代表了来自上地壳的变质沉积岩,即沉积岩受到上地幔物质上涌或底侵作用的加热变质形成.成像结果对了解华南地区的构造演化历史提供了地震学约束.  相似文献   

17.
The Qinling–Dabie–Sulu orogenic belt in east-central China is the largest high and ultrahigh pressure (HP and UHP) metamorphic zone in the world. The Dabie Mountains are the central segment of this orogenic belt between the North China and Yangtze cratons. This work studies the nature of the crustal structure beneath the Dabie orogenic belt to better understand the orogeny. To do that, we apply ambient noise tomography to the Dabie orogenic belt using ambient noise data from 40 stations of the China National Seismic Network (CNSN) between January 2008 and December 2009. We retrieve high signal noise ratio (SNR) Rayleigh waves by cross-correlating ambient noise data between most of the station pairs and then extract phase velocity dispersion measurements from those cross-correlations using a spectral method. Taking those dispersion measurements, we obtain high-resolution phase velocity maps at 8–35 second periods. By inverting Rayleigh wave phase velocity maps, we construct a high-resolution 3D shear velocity model of the crust in the Dabie orogenic belt.The resulting 3D model reveals interesting crustal features related to the orogeny. High shear wave velocities are imaged beneath the HP/UHP metaphoric zones at depths shallower than 9 km, suggesting that HP/UHP metaphoric rocks are primarily concentrated in the upper crust. Underlying the high velocity HP/UHP metamorphic zones, low shear velocities are observed in the middle crust, probably representing ductile shear zones and/or brittle fracture zones developed during the exhumation of the HP/UHP metamorphic rocks. Strong high velocities are present beneath the Northern Dabie complex unit in the middle crust, possibly related to cooling and crystallization of intrusive igneous rocks in the middle crust resulting from the post-collisional lithosphere delamination and subsequent magmatism. A north-dipping Moho is revealed in the eastern Dabie with the deepest Moho appearing beneath the Northern Dabie complex unit, consistent with the model of Triassic northward subduction of the Yangtze Craton beneath the North China Craton.  相似文献   

18.
利用155个宽频带流动地震仪记录的连续地震波形数据,通过有限频层析成像技术,反演获得了华南地区上地幔的高分辨率P波三维速度模型.结果显示,大致以江南造山带为界,研究区域南部的华夏块体的大部分区域上地幔存在一个清晰的低速异常构造,而研究区北部的扬子克拉通的大部分区域上地幔则存在高速异常结构,并且这些速度异常体都向下延伸到地幔转换带.一个重要的结果是在(27°N,118°E)处观测到通过410-km界面的上涌流,并且在上升的过程中逐渐向西和向北扩展,显示为华夏块体深部200～400 km深度的大范围低速异常,可能为华夏块体广泛分布的新生代岩浆活动提供深部来源.更重要的是华夏块体通过410-km界面上涌流在上涌的过程中向北延伸,越过江南造山带"侵入"到扬子克拉通的南部地区,造成了扬子克拉通较厚的岩石圈对应的高速异常体向南倾斜的假象.最后,位于117°E(郯庐断裂的南端)以东的扬子克拉通岩石圈已经被"活化",即被来自南部热的软流圈物质替而代之.同时,推断在华夏块体下方地幔转换带内低速异常体可能是与海南地幔柱有关.海南地幔柱和(27°N,118°E)410-km界面上涌流的关系还有待于今后更大范围地震台阵反演研究进行验证.  相似文献   

19.
对包含大别－苏鲁碰撞造山带在内的东经 １１２°－１２４°,北纬２８°－３９°区域进行地 震层析成像研究,重建其地壳及上部地幔的三维速度图像．结果表明：造山带岩石圈速度横 向不均匀性显著;大别造山带以商城－麻城断裂为界,东侧的大别地块与西侧红安地块在地 壳速度上是两个不同的速度块体;中地壳 １５-２５ｋｍ深度范围内存在低速带,与伸展滑脱构造 有关;南、北大别构造单元之下,莫霍面下凹,地壳内发育了速度为６．５－６．６ｋｍ／ｓ、向北倾斜的 相对高速体,与超高压变质岩体相对应;在大别－苏鲁造山带下方的上部地幔中存在向北倾 斜的板片状高速体,结合已有地质、地球化学证据推测,它是三叠纪俯冲的扬子地块的残留 体;俯冲板片在深部发生了断离．本文利用地震层析成像方法揭示的造山带岩石圈速度结构 细节,对研究与地表地质有关的地球动力学无疑是十分重要的．  相似文献   

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