珠江口盆地构造变形特征与白云凹陷构造-沉积正演模拟研究

珠江口盆地构造演化与南海扩张运动之间的关系一直是众多研究者关注的重点,盆地内构造变形信息对南海多期次的扩张运动具有十分重要的指示作用。为研究珠江口盆地构造变形特征与白云凹陷构造演化,本文对横跨珠江口盆地的三条区域地震反射剖面及过白云凹陷沉积中心的地震反射剖面进行精细的构造解析,同时对白云凹陷主控正断层系统开展正演模拟研究。结果表明,过珠江口盆地东部、中部和西部的三条区域地震反射剖面都反映“三隆夹两坳”的结构特征;剖面对比发现盆地中部吸收的累计构造变形量最大,其中白云凹陷最为突出。对白云凹陷内的控凹正断层系统展开的2D-Move几何学正演模拟研究结果表明,该凹陷主要受控于三条北倾的铲形正断层,活动时间集中于T80～T70(约38～32 Ma)。结合白云凹陷反映的强烈活动时间和沉积分布特征,我们认为白云凹陷的形成可能与南海北部早期伸展作用相关,期间可能叠加了西北次海盆的扩张作用;西北次海盆扩张作用结束后,整个珠江口盆地构造演化都受到了东部次海盆扩张作用的影响。     

南海海盆海底扩张年代之探讨

根据海底地形地貌特征和区域构造走向,可将南海海盆分为三个次海盆：西北次海盆、西南次海盆和中央次海盆。通过地磁异常资料之分析对比,在中央次海盆中鉴别出５ｄ－１１号磁异常条带,推测其海底扩张年代为晚渐新世一早中新世（３２－１ＭａＢＰ）;在西南次海盆中鉴别出１８－１３号磁异常条带,推测其海底扩张年代为晚始新世一早渐新世（４２－３５ＭａＢＰ）。通过对穿过中央次海盆与西南海盆的地震反射剖面之分析,发现西南次     

中南-礼乐断裂带在南海海盆北部的时空展布与深部结构

中南-礼乐断裂带是协调南海各次海盆扩张的重要断裂.深入研究中南-礼乐断裂带时空展布和深部结构对于认识南海海盆多期次海底扩张和构造演化具有重要意义.本文主要基于深反射多道地震的精细剖析,结合重力、磁力与地形等地质与地球物理资料,揭示了中南-礼乐断裂带在南海海盆北部的时空展布特征、内部构造形变及其深部结构特征.结果表明:中南-礼乐断裂带在西北次海盆与东部次海盆之间宽约25~35 km,北延于珠江海谷西侧(18.7°N,115.5°E),南消失于中沙地块东北侧(17.2°N,116.0°E),主要呈NNW向延伸.该断裂带的主控断裂沿大型海山和侵入岩体分布,主要发育时期是渐新世至早中新世,中中新世至晚中新世为继承性活动,其内部断裂对早中新世及以前的地层具有控制作用,表现为正断层.深部结构上,中南-礼乐断裂带两侧Moho面埋深不一,两侧次海盆的沉积厚度和洋壳厚度存在明显差异,表明该断裂带至少是一条地壳级断裂,甚至可能是岩石圈级断裂.      

南海西南次海盆剪刀式扩张

南海西南次海盆的平面形态比较独特，是一个往北东开口、尖角指向西南的“V”字型海盆。正确认识其扩张运动学特征是研究南海新生代扩张与构造演化的关键一环。本文利用反射地震剖面、重力异常和磁异常资料、IODP大洋钻孔资料等，详细分析了西南次海盆的地质构造特征。研究结果揭示，次海盆边缘扩张期的上超层序自北东而西南特征相同，是海盆同一时间开启形成的沉积；作为西南次海盆与东部次海盆的构造分界，中南- 礼乐断裂带并非完全呈S—N向延伸，而是一条南、北两端均朝西弯曲、略呈弧形的断裂带，此为西南次海盆扩张期间呈扇形推移所导致；西南次海盆西部一条断层面西倾的断裂带在此分隔了扩张海盆区与过渡壳区，两区之上发育一套扩张期间沉积的层序，覆盖在扩张区的洋壳之上和过渡壳区的古近系之上，证实两区经历了同步拉张的过程。由此证实，西南次海盆的扩张运动学模式为“剪刀式扩张”。即海盆的扩张自北东而西南同时开启，扩张速率却自北东而西南逐渐减慢，导致越往西洋壳区越窄，使得海盆西部尖角区域成为有拉张而无扩张、面积较窄的过渡壳区，因而形成呈“V”字型展布的西南次海盆。     

南海西南次海盆构造特征及其沉积响应

本文对穿过南海西南次海盆的逾1000 km的多道地震测线CFT剖面进行了地震界面特征的识别和地震层序的划分,分段分析了拆离断层对其减薄陆壳的拆离作用。结合前人研究成果,对南海西南次海盆地壳结构特征开展了分析,并总结了其构造特征。西南次海盆在发生陆缘张裂—海盆扩张、洋壳出现—扩张后稳定沉积这一系列过程中,可划分为4个阶段的沉积响应：A阶段(古新世之前)——前裂谷阶段,表现为地壳在拉张应力下产生小的断层;B阶段（始新世—早渐新世）——陆缘的裂谷阶段,地壳在拉张应力下拉张减薄,A阶段产生的断层出现了旋转,出现了大型掀斜的拆离断层,沉积物为同裂谷沉积,该阶段以产生了破裂不整合结束;C阶段（晚渐新世—早中新世）——海盆扩张阶段,海盆开始扩张,张应力从陆缘转移到了洋盆;D阶段（中中新世以来）——海盆扩张结束以后,以一套稳定沉积为特征。     

从东海油气勘探谈台湾海峡油气地质

上海海洋地质调查局从1974年开始对东海进行了包括反射地震、重力、磁法、测深、浅地层剖面等多种疗法的综合调查,基本上建立了东海的新生代地层层序、构造分区及其构造演化历史。台湾海峡在地理上位于东海陆架的西南延伸部位,但其地质演化既具东海陆架盆地早第三纪构造演化的特点,又深受渐新世至中新世南海深海盆扩张的影响。根据地震资料和钻井资料之对比,台西盆地至少经历了古新世、始新世和中新世三次海侵,从而使其既区别于南海之珠江盆地,又有别于东海陆架盆地。     

南海西北次海盆构造演化的沉积响应

通过对南海西北次海盆新获得的地震资料进行综合解释和层序地层分析,揭示了海盆中的沉积对构造演化阶段的响应。始新世-早渐新世陆缘裂陷期,盆地以对称裂谷形式,发育地堑裂谷层序,沉积以近物源为特征,相变大,发育了冲积扇-扇三角洲-湖相沉积,沉积体系的配置受同沉积断裂控制明显,快速沉降和充分的物源供给决定了沉积体系的构成特征。晚渐新世海底扩张期,岩石圈破裂,陆缘进一步拉开并开始海底扩张,出现海相沉积,来自陆坡的陆架边缘三角洲越过陆坡进入海盆,在海盆内沉积了一套向海盆中部逐渐减薄的楔状地层,并伴有大量的火山碎屑沉积物。早-中新世以来热沉降期,随着构造沉降增大,相对海平面总体不断上升,进入深水盆地,形成陆架陆坡体系,大量的碎屑物质以重力流、深水底流等深水作用方式进入海盆;沉降晚期陆架-陆坡物源供应减弱,琼东南中央峡谷成为其主要的物质供应来源通道,在此期间二次海平面下降、回升的综合作用下,海盆内发育了多期以下切水道为特征的低水位域沉积体系。     

珠江口盆地裂后阶段性差异沉降及其成因机制*

位于南海北部陆缘的珠江口盆地裂后沉降特征不同于陆内典型断陷盆地。研究表明,盆地裂后期发生了阶段性有序差异沉降,可分为4个阶段: (1)渐新世早期(~33.9~27.2 Ma),以盆地整体缓慢沉降,大规模海侵为主要特征;(2)渐新世晚期(~27.2~23.0 Ma),以邻近西北次海盆的珠四坳陷强烈沉降为主要特征,差异沉降控制了陆架坡折带的发育和该时期陆架浅水和陆坡深水沉积环境的分布;(3)中新世早—中期(~23.0~10.0 Ma),陆缘强烈沉降区向北扩展至珠二坳陷,尤其是白云凹陷,导致陆架坡折带向北跃迁,并奠定了现今陆架浅水和陆坡深水的沉积格局;(4)中新世晚期—现今(~10.0~0 Ma),陆缘构造沉降逐渐减弱,陆坡由沉积区转变为沉积过路区,沉积物得以大量进入西北次海盆。渐新世2期快速沉降的初始时间,分别对应于南海扩张脊的跃迁,陆缘裂后沉降随扩张脊向南跃迁而向北扩展,并伴有岩浆作用的早强晚弱特点,而沉降量的大小则与裂陷期地壳的薄化程度正相关,反映了陆缘岩石圈经历了早期挠曲回弹的均衡调整和扩张脊跃迁导致地幔物质有序向南撤离而沉降的演化过程。珠江口盆地裂后有序差异沉降控制了陆架坡折带的发育,进而控制了浅水与深水两大沉积体系的展布。     

南海中北部陆架-陆坡区新生代构造-沉积演化

南海中北部陆架-陆坡区作为南海地区的一个重要地质构造单元,记录了大陆张裂到海盆扩张的丰富信息。通过对研究区地震剖面的解释,分析了该地区新生代的构造与沉积特征,同时通过平衡剖面恢复工作,建立了新生代演化模型。研究显示南海中北部陆架-陆坡区新生代构造演化可以分为三个阶段：古新世—始新世的裂陷阶段、渐新世—早中新世的裂陷-坳陷过渡阶段以及中中新世以来的坳陷阶段。沉积环境经历了河流-湖泊、浅海和深海的演化过程。南海北部陆缘下NW-SE方向流动的地幔流的存在使得伸展活动具有由北向南发育的机制。同时陆坡区盆地（如白云凹陷）显示出韧性伸展的特征,这与地幔上涌热岩石圈伸展引起的该区域地壳强烈韧性减薄和颈缩变形相关。     

万安盆地构造沉降与沉积速率及其油气资源前景

万安盆地是南海重要的新生代含油气盆地之一,是较为典型的新生代走滑拉张盆地。根据对横穿盆地的地震反射剖面的平衡剖面模拟和构造沉降速率、沉积速率的计算,认为万安盆地曾经历了3次快速的构造沉降。2.6Ma以来,沉积速率最大。万安盆地的沉降与沉积速率和盆地构造演化过程密切相关,各构造演化阶段分别控制了盆地中油气的生成、运聚和保存等成藏条件与过程。     

http://www.sciencedirect.com/science/article/pii/S1674987111000491

Based on the interpretations of three seismic profiles and one wide-angle seismic profile across the Northwest Sub-basin, South China Sea, stratigraphic sequences, deformation characteristics and an extension model for this sub-basin have been worked out. Three tectonic-stratigraphic units are determined. Detailed analyses of extension show that the event occurred mainly during the Paleogene and resulted in the formation of half-grabens or grabens distributed symmetrically around the spreading center. Sediments are characterized by chaotic and discontinuous reflectors, indicating clastic sediments. Farther to the southwest, the sub-basin features mainly continental rifting instead of sea-floor spreading. The rifting would have been controlled by the shape of the massif and developed just along the northern edge of the Zhongsha-Xisha Block, rather than joined the Xisha Trough. After 25 Ma, a southward ridge jump triggered the opening of the Southwest Sub-basin. The NW-directed stress caused by the sea-floor spreading of the Northwest Sub-basin may have prevented the continuous opening of the sub-basin. After that the Northwest Sub-basin experienced thermal cooling and exhibited broad subsidence. The deep crustal structure shown by the velocity model from a wide-angle seismic profile is also symmetrical around the spreading center, which indicates that the Northwest Sub-basin might have opened in a pure shear model.     

Crustal Structure across the Northwestern Margin of South China Sea: Evidence for Magma‐poor Rifting from a Wide‐angle Seismic Profile

We present results from a 484 km wide-angle seismic profile acquired in the northwest part of the South China Sea (SCS) during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line (SO49-18) crosses the continental slope of the northern margin, the Northwest Subbasin (NWSB) of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary (Moho). Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 km. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oceanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body (velocities above 7.0 km/s) at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin (SWSB) reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 km. The Zhongsha Massif in between is extremely stretched with only 6–10 km continental crust left. Crustal velocity is below 6.5 km/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin.     

Tectonic Evolution of the Wanan Basin,Southwestern South China Sea

Quantitative studies on the extension and subsidence of the Wanan Basin were carried out based on available seismic and borehole data together with regional geological data.Using balanced cross-section and backstripping techniques,we reconstructed the stratigraphic deposition and tectonic evolution histories of the basin.The basin formed from the Eocene and was generally in an extensional/transtensional state except for the Late Miocene local compressoin.The major basin extension ocurred in the Oligocene and Early Miocene(before ~16.3 Ma) and thereafter uniform stretch in a smaller rate.The northern and middle basin extended intensely earlier during 38.6–23.3 Ma,while the southern basin was mainly stretched during 23.3–16.3 Ma.The basin formation and development are related to alternating sinistral to dextral strike-slip motions along the Wanan Fault Zone.The dominant dynamics may be caused by the seafloor spreading of the South China Sea and the its peripheral plate interaction.The basin tectonic evolution is divided into five phases:initial rifting,main rifting,rift-drift transition,structural inversion,and thermal subsidence.     

Geodynamics of the Amirante Ridge and Trench Complex,Western Indian Ocean

The formation and evolution of the ～600 km long arcuate Amirante Ridge and Trench Complex (ARTC) is a significant geomorphic–structural feature in the Western Indian Ocean (WIO). The WIO contains evidence of at least two major magmatic episodes followed by continental rifting within the span of a little more than 20 million years. This involved the splitting of Madagascar from India at around 85 Ma and then separation between India and the Seychelles at 64–63 Ma as a possible consequence of two powerful volcanic eruptions from the Marion and Reunion hot spots, respectively. Formation and evolution of the ARTC represents this tumultuous period in the Indian Ocean, approximately between 85 and 60 Ma (Late Cretaceous–Early Tertiary).

We integrated geophysical, palaeomagnetical, and petrological data to examine three existing models that attempt to explain the formation of ARTC. In contrast, our study hints at several stages of extension and compression responsible for its formation. Our integrated data also suggest that the Carlsberg Ridge may have played a prominent role in the evolution of the ARTC that seems to have formed through a ridge-jump process after the conjugate spreading centres – Mascarene and Palitana ridges formed earlier during the India–Madagascar separation – ceased spreading because of violent eruption of the Reunion hot spot at around 65 Ma. The eruption disturbed the plumbing system of magma ascent, resulting in cessation of spreading along the conjugate spreading centres, forcing a ridge jump.

A collage of seismic refraction and reflection, free-air gravity, magnetic anomaly data, and Ar dating of rocks indicates that as the Carlsberg Ridge swept the Seychelles towards south, the crust between Madagascar and the Seychelles was increasingly compressed, with the abandoned northern Mascarene spreading centre absorbing the maximum stress. With continued compression, the western limb of the abandoned spreading ridge was thrust below the eastern limb to a limited degree. This partial subduction agrees with the gravity and seismic results. Our new study also accounts for the anomalous presence of 14 km-thick oceanic crust beneath the ARTC and its characteristic difference in petrology with other established subduction zones in the world.     

伊通盆地岔路河断陷西北缘断裂带构造特征研究

岔路河断陷是伊通盆地的一个二级构造单元,其西北缘断裂带是断陷的主控断裂,早始新世以来开始拉张,控制了最大厚度达五六千米厚的第三系地层沉积。但西北缘断裂带结构复杂,经历了挤压和拉张的多次转换,挤压较弱的地方能在露头和地震剖面上看到边界正断层,而挤压强的地方西北缘发育多条具有叠式特征的逆断层,地震剖面显示挤压应力主要来源于大黑山的隆起。结合地震资料和地层埋藏史等资料,可将西北缘断裂带的演化划分为6个阶段：①双阳-奢岭期拉张阶段;②奢岭期末挤压阶段;③永吉期拉张阶段;④永吉期末挤压阶段;⑤万昌-齐家期拉张阶段;⑥晚第三纪以来的挤压阶段。     

中国东部北黄海盆地东部坳陷岩浆活动特征及其与区域构造的耦合关系

如何深入了解中国东部北黄海盆地东部坳陷岩浆活动特征是目前研究的前沿之一.为探讨早白垩世异常剧烈岩浆活动的区域构造成因并揭示中国东部的构造动力学机制,利用井-震及岩浆岩测试资料,对北黄海盆地岩浆活动特征及其与区域构造的耦合关系进行研究.在空间上刻画了岩浆的侵入相、喷出相的地震反射特征及沿深大断裂展布的平面分布特征;在时间上划分出了包括早白垩世108~115 Ma、134~145 Ma在内的4期岩浆活动.结合区域地质分析认为早白垩世早期,伊泽奈琦板块沿北北西斜向俯冲于欧亚板块之下,太平洋板块向南西方向俯冲,板块剪切作用导致郯庐断裂带左旋走滑,使得盆地处于左旋伸展环境中,内部形成派生的北西向右旋、近南北向左旋的次级共轭断裂系并控制岩浆上侵底辟活动.经过综合分析,厘清了盆地岩浆活动及断裂演化过程与区域板块运动之间的耦合关系.      

Geodynamic evolution of the Vulcan Sub‐basin,Timor Sea,northwest Australia: A pre‐compression New Guinea analogue?

The Vulcan Sub‐basin lies immediately inboard of the incipient arc‐continent collision in the Timor Sea and comprises part of the Bonaparte Basin system, the northernmost basin on Australia's North West Shelf. Given the high level of preservation of its extensional fabric, the region can provide important analogues for the likely pre‐orogeny architecture of New Guinea, which enables a better understanding of the onset of, and response to, orogenesis. Structural restoration of regional, depth‐converted 2–D seismic lines shows that although the Late Jurassic Swan Graben is significant and contains a thick source‐rock section, the principal phase of crustal extension took place in the Triassic to Middle Jurassic. Within the Vulcan Sub‐basin, the southern Tilted Fault Block Domain records ～10% Triassic to Middle Jurassic extension, whereas <5% upper crustal extension has been measured in the northern Hourglass Domain. Similarly, while Jurassic extension in the Tilted Fault Block Domain is both deep and focused, the Hourglass Domain is expressed as a broad sag to the northeast, indicating a strong underlying basement influence on compartmentalisation. The Vulcan Sub‐basin shows four principal stages of evolution: (i) regional, evenly spaced crustal faulting and subsidence in the Triassic ‐ Middle Jurassic; (ii) focused faulting in the Late Jurassic that created grabens with uplift of the shoulders; (iii) regional subsidence from the Middle Valanginian; and (iv) minor extensional and contractional reactivation in the Mio‐Pliocene. The measured brittle extension is much less than that suggested by modelling of lithospheric subsidence, which suggests long wavelength distribution of strain in the ductile lower crust, with upper crustal extension mainly focused along the continent‐ocean boundary. Along the North West Shelf and on a smaller scale within the Vulcan Sub‐basin per se, the obvious, basement‐involved, rectilinear compartments defined by prominent offsetting of both extensional fault systems and abyssal plains have important implications for the development of the New Guinea orogen. Similar scale compartments are recognised in New Guinea and display different structural styles and hydrocarbon prospectivity. The transfer zones separating the compartments are the sites of the major copper‐gold deposits in New Guinea. Using the Vulcan Sub‐basin ‐ Timor area as an analogue, it can be seen that an arc could originally collide with a promontory, such as what is now Timor, and reactivate the lineaments allowing local extension and mineralisation. In addition, interpretation of the structure of the New Guinea Fold Belt may be aided by considering the effects of compression on the geometry of the Vulcan Sub‐basin and of the similar Carnarvon Basin and adjacent extended and broken Exmouth Plateau.     

The Earlier Spreading of South China Sea Basin due to the Late Mesozoic to Early Cenozoic Extension of South China Block： Structural Styles and Chronological Evidence from the Dulong-Song Chay Metamorphic Dome, Southwest China

INTRODUCTION Whatmechanismresultedinthespreadingof SouthChinaSeabasin(SCSB)?Wasitreallypro ducedbytheinteractionofperipheralplatesofthe SCSBorAilaoshan RedRiversinistralfault(Fig.1)? Figure1.AnoutlinetectonicmapofSouthChinablockandIndochinablock(modified…     

渤海海域渤南地区新生代断裂体系与盆地演化

利用现今丰富的三维地震资料,将地震剖面解释与相干切片分析相结合,对渤海海域渤南地区断裂发育与盆地结构 进行研究,明确了断裂体系及构造演化特征。结果表明：新生代郯庐断裂渤南段可分为东、中、西三支,并与受郯庐走滑 断裂影响的近EW向、NW向和NE向主干断裂体系共同组成了渤南地区网格状的构造格局;而区域应力背景的改变导致渤 南地区走滑和伸展作用的强弱发生了变化,使得构造演化可划分为左旋走滑-强伸展、右旋走滑-强伸展和弱走滑-弱伸展 三个阶段,第一阶段孔店组~沙四段郯庐断裂东支强烈活动,中支和西支活动微弱,NW向和近EW向大断裂活动形成了黄 河口凹陷和莱州湾凹陷的盆地格局;第二阶段沙三段~东营组走滑断裂三支及其他方向主干断裂均活动,NE向和近EW向 次级断裂开始发育,各盆地持续性伸展断陷;第三阶段馆陶组-明化镇组右旋走滑减弱,郯庐断裂中支和西支发育呈一系 列NE向雁列断层,东支及其他方向主干断裂附近次级小断层继续增多,各盆地转为了整体的坳陷。