白云凹陷断裂特征及对构造与沉积控制的作用

南海北部珠江口盆地白云凹陷的地震资料分析显示,该区域自始新世以来断裂系统十分发育.断层表现出张性或张扭性特征并具有多期活动的特点.在平面上,断裂主要为NWW、近EW和 NE向.根据断层平面展布及组合形态,可将它们分为平行断层系、雁列断层系和树枝状断层系3种组合形式.根据断裂发育时间及规模,可将断裂的活动期次划分为以下几个阶段：剧烈活动期（Tg—T8）、较强中等活动期（T8—T6）、平静稳定期（T6—T2）、再度活化期（T2—T1）.断裂发育的时间及特点对凹陷的构造演化和沉积过程起着重要的控制作用.     

南海珠江21Ma深水扇特征及控制因素

通过对珠江口盆地白云凹陷三维地震资料解释、钻井、测井及岩心资料的观察和描述,对21 Ma发育的深水扇特征、沉积模式及控制因素进行研究。结果表明:岩心上发育正递变层理、鲍马序列和滑塌变形等多种典型重力流构造,指示了沉积物为半深海环境下的重力流沉积;地震资料上可识别出水道、水道堤岸复合体、朵体等典型深水扇构型;21 Ma深水扇沉积模式为陆架边缘三角洲-峡谷-深水扇的沉积模式,是在珠江口盆地的构造格局、相对海平面变化、坡折带演化、断裂系统的形成及古珠江三角洲的物源供给能力等多种因素的控制和有效配置下形成的。     

Distribution and identification of the low-velocity layer in the northern South China Sea

The low-velocity layer (LVL), closely related with tectonic activities and dynamic settings, has always been a hot topic in the deep crustal structure studies. The deep seismic (OBS/OBH) and onshore-offshore experiments have been extensively implemented in the northern South China Sea (SCS) since the 1990s. Six seismic profiles were finished on the northern margin of SCS by domestic and international cooperations. The features of crustal structures were revealed and five velocity-inversion layers were discovered. Among them three LVLs with 3.0—3. 5 km·s-1 velocity are located in the sedimentary structure (2.0—6.0 km in depth and 2.0—4. 6 km in thickness) of the Yinggehai Basin and Pearl River Mouth Basin. They were identified by the reflective and refractive phases for their shallow depth. The other two LVLs with 5.5—6.0 km·s-1 velocity generally existed in the middle crust (7.0—18.0 km in depth) with an about 2.5—6.0 km thickness in the transitional crustal structure of the northeastern and northwestern SCS. They were detected by the refractive phase from their overlain and underlying layers. We explored the possible tectonic formation mechanisms combining with previously reported results, which provided evidence for the formation and evolution of SCS.     

Characteristics of hydrocarbon accumulation and exploration potential of the northern South China Sea deepwater basins

Although the huge potential of the northern South China Sea deepwater basins has been proven by a series of discoveries that followed the exploration breakthrough of well LW 3-1-1, recent drilling and other studies have demonstrated the uniqueness and complicated nature of hydrocarbon accumulations of the deepwater basins there. Based on a review of previous work and the latest exploration activities and studies, the purpose of this paper is to discuss the critical controls for hydrocarbon accumulations in the deepwater basins of the northern South China Sea. A terrestrial-marine transitional coal-bearing source rock is proposed to be the primary source rock for the deepwater basins. A marine source rock, which was first identified as contributing to hydro-carbon generation in this region, probably plays a significant role in the deep-and ultra-deep water basins south to the Pearl River Mouth and Qingdongnan basins. The shelf margin delta depositional systems in the Baiyun Sag, sourced from the Pearl River, are currently primary exploration targets in the deepwater part of the Pearl River Mouth Basin, whereas the western Red River delta-ic-submarine fan depositional systems, initially proven by drilling, are the possible major exploration reservoirs in the Qing-dongnan deepwater areas. Current deepwater exploration targets at the large-sized structural traps and deep and ultra-deep areas in the south of the Pearl River Mouth and Qingdongnan basins will be the future exploration focus. Deepwater exploration activities and relevant fundamental studies, supporting and promoting each other, are of great importance to the national energy supply of China, the basic regional studies of the South China Sea, advancements in technology, and development of related deepwater industries, and will safeguard national sovereignty and territorial integrity.     

南海潮汕坳陷前第三纪盆地结构地球物理研究

通过对珠江口盆地潮汕坳陷地质、地球物理条件的分析,采取针对性的综合地球物理研究方法,对地震资料难以解决的前第三系盆地结构及中生界的分布进行了综合物探研究,确定了盆地的重力和磁性基底深度,首次获得了全区中生界的分布,并对盆地内的断裂、火成岩分布及构造区划作了推断,提出了该坳陷为弧前盆地的认识,为该区勘探部署和进一步研究提供了依据.     

Lithospheric thermal-rheological structures of the continental margin in the northern South China Sea

Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their "thermal" lithospheric thicknesses are evaluated based on the basalt dry solidus, and their rheological structures are evaluated with linear frictional failure criterion and power-law creep equation. "Thermal" lithosphere is about 90 km in thickness in shelf area, and thins toward the slope, lowers to 60-65 km in the lower slope, ocean crust and Xisha Trough. In the mid-west of the studied area, the lithospheric rheological structure in shelf area and Xisha Islands is of four layers: brittle, ductile, brittle and ductile. Because of uprising of heat mantle and thinning of crust and lithosphere in Xisha Trough, the bottom of the upper brittle layer is only buried at 16 km. In the eastern area, the bottom of the upper brittle layer in the north is buried at 20 km or so, while in lower slope and ocean crust, the rheological structure is of two layers of brittle and ductile, and crust and uppermost mantle form one whole brittle layer whose bottom is buried at 30-32 km. Analyses show that the characteristics of rheological structure accord with the seismic result observed. The character of rheological stratification implies that before the extension of the continent margin, there likely was a ductile layer in mid-lower crust. The influence of the existence of ductile layer to the evolution of the continent margin and the different extensions of ductile layer and brittle layer should not be overlooked. Its thickness, depth and extent in influencing continent margin's extension and evolution should be well evaluated in building a dynamic model for the area.     

Velocity structure of the crust and uppermost mantle in the boundary area of the Tianshan Mountains and the Tarim Basin

A portable 3-component broadband digital seismic array was deployed across the Tianshan orogenic belt (TOB) to investigate the lithospheric structure. Based on receiver function analysis of the teleseismic P-wave data, a 2-D S-wave velocity profile of the boundary area of the TOB and the Tarim Basin was obtained at the depths of 0--80 km.Our results reveal a vertical and lateral inhomogeneity in the crust and uppermost mantle. Four velocity interfaces divide the crystalline crust into the upper, middle and lower crust. A low velocity zone is widely observed in the upper-middle crust. The depth of Moho varies between 42 and 52 km. At the north end of the profile the Moho dips northward with a vertical offset of 4--6 km, which implies a subduction front of the Tarim Basin into the TOB. The Moho generally appears as a velocity transitional zone except beneath two stations in the northern Tarim Basin, where the Moho is characterized by a typical velocity discontinuity. The fine velocity structure and the deep contact deformation of the crust and upper most mantle delineate the north-south lithospheric shortening and thickening in the boundary area of the TOB and the Tarim Basin, which would be helpful to constructing the geodynamical model of the intracontinental mountain-basin-coupling system.     

Crustal structure of the southeastern margin of the Ordos Block

We use a profile made up of teleseismic receiver functions to study the crustal thickness and structure of the southeastern margin of the Ordos Block.The Mohorovii discontinuity(Moho) has been identified beneath all stations.Its depth gradually decreases towards the southeast,from about 43 km in the Ordos Block to ~30 km near the northern margin of the Qinling Orogen.Our results show clear lateral variations in the structure of the crust and the features of the Moho.Accordingly,the study region can be divided into four parts:(1) Beneath the Ordos Block,the Moho is visible and flat at a depth of ~40 km.The crustal structure is best characterized by stable cratonic crust.(2) In the Weihe-Shanxi Graben,the Moho is uplifted by about 3 km,which may be the result of upwelling of upper mantle materials.(3) Under the Xionger-Funiu Mountains,the Moho is flat at a depth between 36 and 33 km,but becomes shallower towards the southeast.(4) In the Hehuai Basin,adjacent to the northern margin of the Qinling Orogen,the Moho shows strong lateral variations with a mean depth of ~31 km.The crustal structure here is complex,which may indicate a complicated tectonic environment.Additionally,the Moho is clearly interrupted at two locations(beneath stations st11 and st18) near major tectonic boundaries.These results suggest that the structure of the deep crust along the southeastern margin of the Ordos Block has great lateral variability,which strongly affects the complex geological features on the surface.Furthermore,these results can help us understand the interrelationships of different parts of the southeastern margin of the Ordos Block.     

A deep seismic sounding profile across the Tianshan Mountains

The deep seismic sounding profile across the Tianshan Mountains revealed a two-layer crustal structure in the Tianshregion, namely the lower and upper crusts. Lateral variations of layer velocity and thickness are evidently shown. Low-velocity layers spread discontinuously at the bottom of the upper crust. The Moho depth is 47 km in the Kuytun area and 50 km in the Xayar area. In the Tianshan Mountains, the Moho becomes deeper with the maximum depth of 62 km around the boundary between the southern and northern Tianshan Mountains. The average velocity ranges from 6.1 to 6.3 km/s in the crust and 8.15 km/s at the top of the upper mantle. Two groups of reliable reflective seismic phases of the Moho (Pm1 and Pm2) are recognized on the shot record section of the Kuytun area. A staked and offset region, 20-30 km long, is displayed within a shot-geophone distance of 190-210 km in Pm1 and Pm2. Calculation shows that the Moho is offset by 10 km in the northern Tianshan region, 62 km deep in the south while 52 km deep in the north, and plunges northwards. In comparison with typical collisional orogenic belts, the structure of the Moho beneath the Tianshan Mountains presents a similar pattern. This can be used to explain the subduction of the Tarim plate towards the Tianshan Mountains. This intracontinental subduction is considered the dynamic mechanism of the Cenozoic uplifting of the Tianshan Mountains. The discovery of seismic phases Pm1 and Pm2 serves as the seismological evidence for the northward subduction of the Tarim plate.     

珠江口及北部湾盆地泥岩地球化学特点

通过地球化学研究表明,珠江口及北部湾盆地泥岩中稀土元素分布配分形式显示轻稀土元素较平稳,铕出现明显亏损的特点,与澳大利亚后太古代页岩（ＰＡＡＳ）的分布特点相似,但样品的稀土元素（ＲＥＥ）高于ＰＡＡＳ。在Ｔｈ－Ｈｆ－Ｃｏ三角图解中,所有样品均位于上地壳平均值的上方,远离地壳平均值和洋壳,说明珠江口、北部湾盆地沉积物母岩以来自上地壳偏酸性的岩石类型为主,地球化学判别分析结果表明珠江口盆地与北部湾盆地在     

珠江口盆地深水扇识别和油气成藏的关键要素

近年来在层序地层学理论的指导下,在珠江口盆地白云凹陷的地震剖面上识别出各种层序界面,并进一步识别出大量深水扇沉积体,这些深水扇体由众多的盆底扇、斜坡扇、低位楔和下切水道构成。盆底扇和斜坡扇多期叠加,平面上成朵叶状,并与下切水道相连。综合分析白云深水扇的成藏条件,得出控制深水扇成藏的关键要素有两点：（1）由断层、不整合面、横向连通的砂体以及流体底辟带组成的发达的输导格架,特别是能与深水扇相连的断层与流体底辟带,是深水扇油气成藏的关键所在;（2）油气运移的动力,盆地模拟结果表明,白云凹陷曾经历了三个地层压力演化旋回,超压的累积和释放对深部烃源岩的排烃并向深水扇体中运移起到了重要作用。     

Recent progress of deep seismic experiments and studies of crustal structure in northern South China Sea

The South China Sea (SCS) is one of the largest marginal seas in the western Pacific. Its northern part has the features of a passive continental margin. The studies of deep crustal structure in this area are very important for understanding the tectonic nature, evolution history, basin formation of the northern margin, and the origin of the SCS. In the past decades, the deep seismic experiments of crustal studies in the northern SCS have gone through three stages, namely the sonobuoy, two-ship Expanding Spread Profile (ESP), and Ocean Bottom Hydrophone/Seismometer (OBH/OBS). Along the continental slope, the sonobuoy experiments provided useful information about the velocity structure of the upper crust, while the ESP data recorded for the first time the seismic signals from deep crustal structure and Moho interface. And the OBH/OBS profiles revealed the crustal structure in much greater detail. This paper first gives a brief historical review of these deep seismic experiments and studies, then a summary of the latest progress and important research results. The remaining problems and suggestions for further research work are presented as conclusive remarks.     

Deep structure at northern margin of Tarim Basin

In this paper, a 2D velocity structure of the crust and the upper mantle of the northern margin of the Tarim Basin （TB） has been obtained by ray tracing and theoretical seismogram calculation under the condition of 2D lateral inhomogeneous medium using the data of seismic wide angle reflection/refraction profile from Baicheng to Da Qaidam crossing the Kuqa Depression （KD） and Tabei Uplift （TU）. And along the Baicheng to Da Qaidam profile, 4 of the 10 shot points are located in the northern margin of the TB. The results show that the character of the crust is uniform on the whole between the KD and TU, but the depth of the layers, thickness of the crust and the velocity obviously vary along the profile. Thereinto, the variation of the crust thickness mainly occurs in the middle and lower crust. The Moho has an uplifting trend near the Baicheng shot point in KD and Luntai shot point in TU, and the thickness of the crust reduces to 42 km and 47 km in these two areas, respectively. The transition zone between the KD and TU has a thickest crust, up to 52 km. In this transition zone, there are high velocity anoma- lies in the upper crust, and low velocity anomalies in the lower crust, these velocity anomalies zone is near vertical, and the sediment above them is thicker than the other areas. According to the velocity distributions, the profile can be divided into three sections： KD, TU and transition zone between them. Each section has a special velocity structural feature, the form of the crystalline basement and the relationship between the deep structure and the shallow one. The differences of velocity and tectonic between eastern and western profile in the northern margin of the Tarim Basin （NMTB） may suggest different speed and intensity of the subduction from the Tarim basin to the Tianshan orogenic belt （TOB）.     

Three-dimensional crustal velocity structure of P-wave in East China from wide-angle reflection and refraction surveys

The 3-D crustal structure of P-wave velocity in East China is studied based on the data obtained by wide-angle seismic reflection and refraction surveys.The results suggest that a deep Moho disconti-nuity exists in the western zone of the study region,being 35―48 thick.High-velocity structure zones exist in the upper crust shallower than 20 km beneath the Sulu and Dabie regions.The cause of high-velocity zones is attributable to high-pressure metamorphic(HPM) and ultra-high-pressure metamorphic(UHPM) terran...     

Crustal P-wave velocity structure in Lower Yangtze region： Reinterpretation of Fuliji-Fengxian deep seismic sounding profile

A deep seismic sounding profile in this paper, from Fuliji in Anhui Province to Fengxian of Shanghai City, is located at eastern China (Fig. 1). The field work was jointly accomplished by the Chinese Geological and Mineral Bureau, the China Seismological …     

珠江口盆地西部生物礁与火山岩的辩证识别

探讨生物礁与火山岩等疑似礁体的辩证差异,厘清珠江口盆地西部浅层地震异常体的地质属性。从琼海24-2异常体所处地理环境出发,结合南海北部生物礁发育的大背景和珠江口盆地生物礁发育的演化规律,重点从生物礁发育所必备的各种地质条件及其地震响应特征进行辩证分析。结果表明琼海24-2异常体所处地理环境不具备生物礁发育的地质条件,地震反射特征具有明显的火山穿刺现象,且属后期破坏型火山活动,因此琼海24-2是受火山活动影响复杂化的异常体,不是生物礁,也不满足火山旁侧发育生物礁的模式,勘探风险较大。     

南海珠江深水扇系统的沉积构造背景分析

从深水扇系统的观点出发,主要基于对最近所采集的穿越整个白云凹陷的700余公里长电缆深反射(深达14 s)地震资料综合解释,结合南海大洋钻探的成果,对南海珠江深水扇系统沉积的构造背景特征进行了综合分析.研究发现:白云主凹在早中新世-中中新世期间(即大约距今25～10 Ma)是一个因坳陷期盆地基底的持续沉降及其相关断裂活动而形成的南海北部陆缘上的斜坡内盆地;白云主凹这个"斜坡内盆地"有别于世界上其它位于被动大陆边缘背景中(如西非近海、巴西近海、墨西哥湾)的斜坡内盆地;海平面变化、沉积物通量变化、构造活动等地质营力都在斜坡内盆地的构造背景上对南海珠江深水扇系统在不同时期产生了不同程度的重要影响.简言之,斜坡内盆地成就了南海珠江深水扇系统.这为以后进一步全面深入研究南海珠江深水扇系统的形成机制、演化过程、结构特征等有着重要意义.     

珠江口盆地(东部)新近系珠江组碳酸盐台地沉积特征及其地震相特征

利用钻井、测井及地震资料,通过对珠江口盆地(东部)大量的岩心和薄片的观察鉴定以及对地震剖面资料的精细解释,进而探讨珠江组碳酸盐台地的沉积特征与地震响应特征.珠江口盆地(东部)碳酸盐岩由于古地貌及海侵时间的差异性,珠江组沉积序列,特别是碳酸盐台地的沉积厚度及发育时间,存在明显的差异性.碳酸盐台地沉积相带发育齐全,包括:开阔台地、台地边缘及其台地前缘斜坡3类沉积相.碳酸盐台地的地震相特征突出,易于识别.     

珠江口盆地白云北坡韩江组层序格架及富砂沉积体研究

通过钻井、测井、地震资料分析,并利用层序地层学、地震沉积学等方法,对珠江口盆地白云北坡韩江组的层序地层格架、体系域和富砂沉积体进行研究。结果表明:SQhj1层序体系域可四分为低位体系域(LST)、海侵体系域(TST)、高位体系域(HST)和下降体系域(FSST),SQhj2层序可划分出低位体系域、海侵体系域及高位体系域,其中低位体系域具有两期特征,可细分为LST1和LST2;SQhj1层序的FSST三角洲砂体和SQhj2层序的低位扇体是研究区重要的富砂沉积体,SQhj1层序FSST中的三角洲前缘近端坝、远端坝以及SQhj2层序LST1和LST2中的斜坡水道复合体、盆底扇以及低位楔三角洲前缘砂体等均为有利的富砂沉积体;SQhj1、SQhj2沉积层序发育演化受盆地古地貌、同沉积断裂及断裂坡折带、沉积物供以及海平面变化等因素的影响。     

Episodic rifting of continental marginal basins and tectonic events since 10 Ma in the South China Sea

Integrated study on the tectonic, basin filling and thermal evolution of the Tertiary basins on the northern margin of the South China Sea has indicated that the rift continental margin on the northern South China Sea is not a passive margin and that the western margin is characteristic of the transform-extension. Episodic rifting and the thermal events since 10 Ma in the area have been documented by the integrated analysis of dynamic process. It has been clarified that the tectono-thermal events have exerted a significant influence on basin features and hydrocarbon accumulation, and particularly, the westward collision of the Lusong Island Arc, the generation of densely spaced faults in the Pearl River Mouth Basin, the rapid subsidence, high heat flow and large-scale over pressure and thermal-fluid breakthrough in the Yinggehai and the Qiongdongnan basins have proved to be the important factors determining the formation of oil and gas in these basins.