Crustal wide-angle reflection imaging along Lianxian-Gangkou profile in Guangdong province,China

A 400 km-long wide-angle seismic experiment along Lianxian-Gangkou profile in South China was carried out to study contact relationship between southeast continental margin of Yangtze block and northwest continental margin of Cathaysia block. We reconstructed crustal wide-angle reflection structure by the depth-domain pre-stack migration and the crustal velocity model constructed from the traveltime fitting. The wide-angle reflection section shows different reflection (from crystalline basement and Moho) pa...     

Frozen subduction in the Yangtze block: insights from the deep seismic profiling and gravity anomaly in east Sichuan fold belt

The Sichuan basin is the main part of the middle-upper Yangtze block, which has been experienced a long-term tectonic evolution since Archean. The Yangtze block was regarded as a stable block until the collision with the Cathaysia block in late Neoproterozoic. A new deep seismic reflection profile conducted in the eastern Sichuan fold belt (ESFB) discovered a serials of south-dipping reflectors shown from lower crust to the mantle imply a frozen subduction zone within the Yangtze block. In order to prove the speculation, we also obtain the middle-lower crustal gravity anomalies by removing the gravity anomalies induced by the sedimentary rocks and the mantle beneath the Moho, which shows the mid-lower crustal structure of the Sichuan basin can be divided into eastern and western parts. Combined with the geochronology and Aeromagnetic anomalies, we speculated the Yangtze block was amalgamated by the West Sichuan and East Sichuan blocks separated by the Huayin-Chongqing line. The frozen subduction zone subsequently shifted to a shear zone accommodated the lower crustal shortening when the decollement at the base of the Nanhua system functioned in the upper plate.     

太行山东缘汤阴地堑地壳结构和活动断裂探测

采用深、浅地震反射和钻孔地质剖面相结合的探测方法,对太行山东缘汤阴地堑的地壳结构和隐伏活动断裂进行了研究.结果表明,该区地壳厚度约36~42 km,莫霍面从华北平原区向太行山下倾伏.汤阴地堑是一个受汤东断裂控制的半地堑构造,其基底面形态与莫霍面展布呈"镜像"关系.汤东断裂是1条继承性的隐伏活动断裂,该断裂向上错断了埋深约20 m的中更新世晚期地层,向下延伸至上地壳底部.综合分析深地震反射和已有深地震宽角反射/折射剖面结果,发现深地震反射剖面上的中-下地壳强反射层和壳幔过渡带反射,与深地震宽角反射/折射剖面上出现的中-下地壳正负速度梯度变化层有着较好的对应关系,这表明本区中-下地壳和壳幔过渡带可能为一系列速度递变层或高低速物质的互变层,埋深约15~16 km的强反射带为上地壳与中-下地壳的转换带,壳幔过渡带的底界为地壳与地幔的分界.研究结果为深入理解该区的深部动力学过程、分析研究深浅构造关系、评价断裂的活动性提供了依据.     

云南思茅—中甸地震剖面的地壳结构

云南思茅—中甸宽角反射/折射地震剖面切割松潘—甘孜、扬子和华南三个构造单元的部分区域. 我们利用初至波和壳内反射波走时层析成像获得地壳纵波速度结构. 在获得新的地壳速度结构模型基础上,利用地震散射成像思想和低叠加次数的叠前深度偏移方法重建了研究区的地壳、上地幔反射结构. 综合分析研究区地壳P波速度模型和壳内地震反射剖面发现：沿测线从北至南地壳厚度从约50 km减薄至35 km左右,地壳厚度的减薄量主要体现在下地壳,剖面北段下地壳厚度约为30 km,剖面南段下地壳厚度仅为15 km左右;上地幔顶部局部位置P波速度值偏低,一般为7.6～7.8 km/s,反映出云南地区是典型的构造活动区的特点.剖面沿线地壳内地震反射发育,其中莫霍强反射出现在景云桥下方;在景云桥弧形断裂带8～10 km深处出现宽约50 km的强反射带.     

深反射大炮揭示的青藏高原侧向碰撞带地壳骨架结构

青藏高原东南缘处于印度板块与欧亚板块碰撞的侧翼,揭示该地区的岩石圈结构有助于完整理解青藏高原碰撞造山的动力学过程,对构建大陆碰撞成矿理论框架至为关键.本研究对横过青藏高原侧向碰撞带的一条深反射地震剖面的15个大炮资料,进行了针对性静校正、去噪等处理和单次叠加成像,结果剖面显示了侧向碰撞带岩石圈结构的骨架特征：（1）双程走时（TWT）8~10 s的强反射（Tc）将地壳分为上、下两层;Tc可能是大型滑脱构造的拆离面,其存在使上地壳的变形与下地壳解耦;（2）Moho间断面反射（Tm）为3~4个同相轴的窄带反射波组,横向不连续,与深大断裂交汇处被错断,但断距不大;（3）在兰坪—思茅地块下方TWT21 s和扬子克拉通西缘下方TWT22~24 s存在相向倾斜的反射波组（TL）;以Tc、Tm和TL构成的骨架结构,定性地描绘出剖面下方岩石圈地幔以汇聚为主、地壳块体以侧向滑移为主和上地壳为薄皮逆冲或滑脱的分层动力学模式.该岩石圈变形样式明显不同于以正向碰撞挤压、地壳缩短垂向增厚为主的"冈底斯模式".     

The crustal structure under Sanjiang and its dynamic implications: Revealed by seismic reflection/refraction profile between Zhefang and Binchuan,Yunnan

The Sanjiang area in southwest China is considered as a tectonic intersection belt between the Tethys-Alps and the western Pacific, and has endured three-phase evolution processes: Proto-Tethys,Paleo-Tethys and Meso-Tethys[1―4]. In this area, its tectonics and struc- ture are extremely complicated, and intensively extru-sive deformation and faults are widely developed[1―3]. For that, the area is considered as the ideal na- ture-laboratory to study the evolution of Paleo-Tethys and also …     

Crustal structure of Gondwana- and Yangtze-typed blocks: An example by wide-angle seismic profile from Menglian to Malong in western Yunnan

Ancient Tethyan vestige extends from Alps, Kaebaiqn Mountain and eastward through Turkey, IranAfghanistan, and the middle and north of Tibetan Plateau, then turns to western Yunnan and Sichuan, andfinally ends at Zhongnan Peninsula. The PaleoTethyan is supposed as one eastward opened Oceanand superposed by tectonic deformation in the latestage of the late Mesozoic to Paleocene of Cenozoicand covered by Mesozoic and Cenozoic deposits. The Sanjiang region in southwestern China is in the…     

用地震走时反演长白山天池火山地区的二维地壳结构

应用一种同时获得地壳上地幔二维速度结构和界面形态的地震走时反演算法，对在长白山天池火山区L1剖面获得的人工地震折射和宽角反射走时数据进行反演，得到了该剖面的地壳上地幔二维速度结构和构造．结果表明:长白山天池火山口下方中下地壳存在一倒三角状的低速体，壳内反射界面和莫霍面一致呈下凹形态，幅度2～6km不等，形成一个地壳根，推测是长白山天池火山系统．最后将所得结果与SEIS83正演试错模拟结果进行了比较．      

2-D crustal structure of Changbaishan-Tianchi volcanic region determined by seismic traveltime inversion

IntroductionTrial-and-error forward modeling of wide-angle seismic reflection/refraction traveltimes for 2-D velocity structure is extremely time-consuming, even for experienced data interpreters. For wide-angle seismic reflection/refraction experiments that consist of numerous shots along a single line, it is quite difficult through repeated trial-and-error forward modeling to construct a 2-D model that fits the data within acceptable limits (Cerveny, et al, 1977; ZHANG, et al, 200 . In ad…     

南岭-武夷交汇区的深部背景及地壳泊松比

为研究南岭-武夷交汇区深部动力学过程提供深部背景资料和科学依据,本文利用远震P波接收函数H-κ叠加和共转换点（CCP）叠加两种方法获取了研究区66个宽频带流动台站及24个固定台站下方的地壳厚度、泊松比和Moho面起伏形态,揭示了扬子地块与华夏地块地壳结构及泊松比变化特征,给出了南岭和武夷之间一条莫霍凸起带的高分辨图像.

结果显示：（1）研究区内地壳厚度平均值为31.2 km,泊松比平均值为0.23,总体呈现薄地壳、低泊松比的特点.地壳厚度从西北往东南由厚变薄,与区域地壳伸展特征相一致.（2）在韶关-赣州-吉安-南昌一线存在条带状薄地壳结构,平均值为28 km,呈南西-北东向展布,对应的泊松比值略微升高.推测地壳减薄带的形成可能与来自南海方向的地幔热流上涌有关.（3）江南造山带的泊松比整体偏低,存在两处平均值小于0.21的区域.华夏地块内地壳厚度与泊松比之间存在弱的负相关,表示随着地壳厚度的增大,铁镁质的下地壳厚度在整个地壳厚度中所占的比例减小.

     

High-resolution crustal structure of the Yinchuan basin revealed by deep seismic reflection profiling: implications for deep processes of basin

The Yinchuan basin, located on the western margin of the Ordos block, has the characteristics of an active continental rift. A NW-striking deep seismic reflection profile across the center of Yinchuan basin precisely revealed the fine structure of the crust. The images showed that the crust in the Yinchuan basin was characterized by vertical stratifications along a detachment located at a two-way travel time(TWT) of 8.0 s.The most outstanding feature of this seismic profile was the almost flat Mohorovicˇic′ discontinuity(Moho) and a high-reflection zone in the lower crust. This sub-horizontal Moho conflicts with the general assumption of an uplifted Moho under sedimentary basins and continental rifts, and may indicate the action of different processes at depth during the evolution of sedimentary basins or rifts.We present a possible interpretation of these deep processes and the sub-horizontal Moho. The high-reflection zone, which consists of sheets of high-density, mantlederived materials, may have compensated for crustal thinning in the Yinchuan basin, leading to the formation of a sub-horizontal Moho. These high-density materials may have been emplaced by underplating with mantlesourced magma.     

安徽贵池矿集区深部精细结构——来自综合地球物理探测结果的认识

安徽贵池矿集区是长江中下游成矿带中重要的铜多金属矿集区,随着浅表找矿难度的加大,急需了解矿集区深部结构为深部找矿提供深部找矿提供指示.为揭示贵池矿集区深部地壳结构格架、控岩、控矿构造和岩浆系统的空间结构,深化对成矿作用的认识,在该区实施了两条长度各约60 km垂直于构造走向的反射地震和MT探测剖面,通过对MT数据有针对性的去噪和反演,获得了研究区10 km以浅的地电结构;通过对反射数据的层析反演静校正、叠前保幅多域去噪、精细速度分析和叠前时间偏移等处理,获取了该地区地壳结构的地震成像剖面.结合区域地质构造背景和针对性处理的区域重磁数据,对两条综合探测剖面的反演处理结果进行了分析与解释,研究发现了本区地层的构造反射特征、地壳结构特征和Moho特征,厘定了盖层与基底之间的区域滑脱面、中下地壳滑脱面和Moho面的深度和形态.发现了地壳上冲和俯冲的反射特征,可能是华夏块体与扬子块体晋宁期发生板内碰撞的痕迹.高坦断裂是一个深达地壳级的断裂,其南北两侧具有不同的重磁特征、电性结构特征和地震反射特征,该断裂可能是深部流体上涌的通道,岩浆和地幔热液沿断裂上涌并沿地层和裂隙侵入中上地壳,形成岩基或岩体,或与围岩发生强烈矿化作用形成贵池矿集区多金属矿床.     

Crustal structure of northeastern Tibetan plateau and Ordos block: Waveform interpretation of the Maqen-Jingbian seismic refraction profile

The Maqen-Jingbian wide-angle seismic reflection and refraction experiment was carried out in 1998, which aims at determining detailed structure in the crust and top of the upper mantle and understanding structural relation between the northeastern Tibetan plateau and the Ordos block. The 1-D crustal models inferred by waveform inversion show strong variations in crustal structure, which can be classified into four different types: ① an Ordos platform with the Proterozoic crust and two high-velocity layers in the northeast section, ② a transitional crust between the northeastern Tibetan plateau and the Ordos block across the Haiyuan earthquake zone, ③ the Qilian orogenic zone in the central part, and 4 the Qinling orogenic zone in the southwestern section. The Moho depth increases from ~42 km to ~62 km from the NE part to the SW part of the profile. The crystalline crust consists of the upper crust and lower crust in northeastern Tibetan plateau. There is an obviously low P-wave velocity layer dipping northeastward, which is 12–13 km thick, at the bottom of the upper crust in Qinling orogenic zone and Haiyuan earthquake zone. The lower crust is characterized by alternating high and low P-wave velocity layers. Beneath Ordos block, i.e., the NE part of the profile, the crust shows quite a smooth increase in P-wave velocity down to the Moho at a depth of about 42 km.     

根据深反射地震资料识别南海北部洋陆过渡带

洋陆过渡带是被动大陆边缘的重要特征,对于理解大陆岩石圈破裂,随后的海底扩张及被动大陆边缘的形成与演化至关重要.前人通过重磁、地震等地球物理资料对南海北部洋陆过渡带进行过一些研究,但不同学者利用不同资料所确定的洋陆过渡带位置存在较大差异.本文基于高品质深反射地震剖面对南海北部洋陆过渡带进行重新解释,根据莫霍面快速抬升、地壳急剧减薄特征确定洋陆过渡带的分布范围.结果表明,南海北部洋陆过渡带位于大陆边缘减薄陆壳与正常洋壳之间,是受岩浆活动改造了的厚度急剧减薄的地壳,洋陆过渡带地壳深部发生岩浆侵入.减薄陆壳莫霍面平均埋深为21.9 km,地壳平均厚度约20.2 km;正常洋壳莫霍面平均埋深为12.0 km,地壳平均厚度为8.1 km,洋陆过渡带莫霍面埋深和地壳厚度急剧变化,其宽度大致介于46~99 km之间.南海北部磁异常条带和自由空间重力异常分布,验证了本文确定的洋陆过渡带范围的合理性.综合分析认为,南海北部洋陆过渡带的特征介于典型火山型与非火山型之间.

     

Crustal structure of northeastern Tibetan plateau and Ordos block:Waveform interpretation of the Maqen-Jingbian seismic refraction profile

The Maqen-Jingbian wide-angle seismic reflection and refraction experiment was carried out in 1998,which aims at determining detailed structure in the crust and top of the upper mantle and understanding structural relation between the northeastern Tibetan plateau and the Ordos block. The 1-D crustal models inferred by waveform inversion show strong variations in crustal structure,which can be classified into four different types:1 an Ordos platform with the Proterozoic crust and two high-velocity layers in ...     

The crust-mantle transition and the Moho beneath the Vogtland/West Bohemian region in the light of different seismic methods

The structure of the crust and the crust-mantle boundary in the Vogtland/West Bohemian region have been a target of several seismic measurements for the last 25 years, beginning with the steep-angle reflection seismic studies (DEKORP-4/KTB, MVE-90, 9HR), the refraction and wide-angle experiments (GRANU’95, CELEBRATION 2000, SUDETES 2003), and followed by passive seismic studies (receiver functions, teleseismic tomography). The steep-angle reflection studies imaged a highly reflective lower crust (4 to 6 km thick) with the Moho interpreted in a depth between 30 and 32 km and a thinner crust beneath the Eger Rift. The refraction and wide-angle reflection seismic studies (CELEBRATION 2000) revealed strong wide-angle reflections in a depth of 26–28 km interpreted as the top of the lower crust. Long coda of these reflections indicates strong reflectivity in the lower crustal layer, a phenomenon frequently observed in the Caledonian and Variscan areas. The receiver function studies detected one strong conversion from the base of the crust interpreted as the Moho discontinuity at a depth between 27 and 37 km (average at about 31 km). The discrepancies in the Moho depth determination could be partly attributed to different background of the methods and their resolution, but could not fully explain them. So that new receivers function modelling was provided. It revealed that, instead of a first-order Moho discontinuity, the observations can be explained with a lower crustal layer or a crust-mantle transition zone with a maximum thickness of 5 km. The consequent synthetic ray-tracing modelling resulted in the model with the top of the lower crust at 28 km, where highly reflective lower crustal layer can obscure the Moho reflection at a depth of 32–33 km.     

扬子块体与华北块体在海区的接触关系——来自上下源、长排列多道地震剖面的新认识

在新一轮南黄海区域地质地震调查工作中,针对地震地质条件和勘探目标,设计了新的地震资料采集技术方案——上下源延迟激发+长排列接收,获得了强反射界面之下的深部地层有效反射,揭示了千里岩断裂两侧分布着向南逆冲的构造推覆带.结合重力、磁力反演成果认为,千里岩隆起区为扬子块体与华北块体碰撞接触带,扬子块体向北运动与华北块体碰撞后楔入到华北块体之中.     

大容量气枪震源陆地反射地震探测——以长江中下游铜陵地区为例

为了实验大容量气枪震源陆地水体流动激发反射地震探测效果,在长江中下游安徽省铜陵段,采用气枪船长江航道流动激发、沿江岸布设反射地震仪器接收的非纵弯线工作方式,得到了反映测线经过地区地壳深部结构和构造特征的反射地震数据。原始资料信噪比较低,但部分资料不同部位仍可辨认出来自地壳及莫霍面反射波组。就传播距离而言,地震波传播的水平距离最大可达21km,垂直深度可达30km以上。在数据处理中,根据原始资料特点,针对性采用了非纵弯线面元定义、三维层析静校正、叠前多域去噪及组合反褶积技术,最终得到的叠加时间剖面上具有丰富的壳内反射波组。结果显示,测线经过地区的地壳结构为双层结构,总厚度为30.0～36.0km。上地壳呈现隆坳相间的反射特征,下地壳存在多组叠层状弧型反射波组,莫霍面反射特征清晰,由2～3个反射同相轴组成,呈现SW端向NE段抬升的形态。剖面经过地区存在一个切穿下地壳和莫霍面的深部断裂,应该是长江深断裂的反映。研究结果充分说明,大容量气枪震源可应用于陆地流动水体地壳精细结构的深地震反射探测。     

四川盆地东西陆块中下地壳结构存在差异

四川盆地是中上扬子克拉通的主要组成部分.作为我国三大稳定克拉通之一,扬子克拉通经历了自太古代以来的长期演化,直到新元古代晚期与华夏板块发生碰撞拼合前,一直被认为是一个稳定的统一陆块.基底包括了新太古宙-新元古代岩层,其上广泛被新元古代晚期至显生宙地层覆盖,仅有~2.9—2.95 Ga基底岩石零星出露于四川盆地的西缘、西南缘和三峡地区,使得对于沉积盖层之下的中下地壳的性质和分布规模的认识十分有限.重力异常则能够宏观揭示区域结构特征.本文通过刨除沉积盖层和莫霍面起伏引起的重力异常而获得了中下地壳的重力异常,反映了四川盆地东西陆块中下地壳存在结构差异,结合深地震反射资料、航磁异常和地球化学资料,证实了该分界线位于重庆—华蓥一线,故而推测中上扬子克拉通在太古宙-古元古代可能存在东西两个陆核.     

六盘山断裂带及其邻区地壳结构

新生代期间,中国大陆西部受印度—欧亚板块碰撞和青藏高原隆升影响,以地壳缩短、增厚、陆内造山和强烈地震活动等为主要特征.在青藏高原东北边缘,高原物质侧向移动被鄂尔多斯地块所阻,在六盘山地区发育了一系列左旋斜冲断裂.断裂带周缘构造变形强烈,地震活动频繁,是研究青藏高原横向扩展控制大陆内部弥散变形的理想场所.本文对穿越青藏高原东北缘—六盘山断裂带—鄂尔多斯地块的宽角反射与折射地震资料使用层析成像和射线反演算法进行成像,获得了研究区地壳速度结构模型,其结果反映出六盘山断裂带两侧地壳结构、构造特征差异显著：1）上地壳层析成像结果显示鄂尔多斯盆地一侧地壳上部速度较低,等值线呈近水平状,具有典型的沉积盆地特征,而青藏高原东北缘一侧上地壳速度相对较高,横向变化剧烈,呈褶皱状,二者的分界为海原—六盘山逆冲走滑断裂;2）全地壳射线反演结果显示鄂尔多斯地块地壳速度梯度大,下地壳底部速度高由铁镁质物质组成,具有典型稳定古老克拉通的特征,青藏高原东北缘地壳速度总体较低,主要由长英质及长英-铁镁质过渡物质组成,具有典型造山带的特征,而六盘山断裂带下方地壳速度结构复杂,层面呈拱形,部分层出现速度逆转,为两个构造单元的接触过渡带;3）青藏高原东北缘一侧地壳厚度~50 km,鄂尔多斯地块地壳厚度~42 km,六盘山断裂带下方莫霍面发生叠置,揭示出青藏高原东北缘、鄂尔多斯地壳在六盘山下汇聚,较薄且刚性的鄂尔多斯地壳挤入较厚且塑性的青藏高原东北缘地壳中的构造模式.