南海北部陆缘区中特提斯构造演化研究

通过对南海及周边地区特提斯构造遗迹的综合分析，并与东亚、东南亚地区特提斯构造对比，认为南海北部陆缘区存在可以进行东、西向对比的中特提斯构造。相应的中特提斯洋因北巴拉望－礼乐－南沙地块与华南大陆边缘在白垩纪中期的碰撞而关闭。南海北部陆缘区中特提斯构造向西可以与加里曼丹的Metratus缝合线和苏门答腊的Woyla缝合线对比，向东经台湾海峡、琉球群岛与日本佐用带对比。南海北部陆缘区中特提斯构造的确认对正确解释南海北部陆缘区地壳结构在东西向和南北向的差异、重新认识华南陆域内地质构造演化以及对南海北部陆缘区油气资源勘探均具重要意义。     

加里曼丹岛和马来半岛中生代岩相古地理特征及其构造意义

印支运动以后,在现今的南海及其周围存在过2个古海洋,其中晚侏罗世一早白垩世消失于南海北部陆缘区、北巴拉望-礼乐滩-南沙地块以北的古海洋为“中特提斯”,而早第三纪期间消失于南沙地块以南沙捞越一带的古海洋为“古南海”。它们的结束时间和消失的古地理位置完全不同。对它们的正确识别和区分,对目前进行的南海周边地区中一新生代构造演化研究极为重要。对马来半岛、加里曼丹岛中生代岩相古地理资料的整理和分析结果支持如下结论：中特提斯洋的延伸是从苏门答腊的Woyla缝合线,过婆罗洲的Meratus缝合线。然后绕西南婆罗洲地块至加里曼丹岛的西北(Lupar带或者Boyan带),进入南海西南角(南沙-礼乐滩-北巴拉望地块等以北),再接南海北部陆缘区内的中特提斯缝合线。该区中生代海相地层的分布明显受构造演化的控制,整体趋势是向南退缩。印支运动以前、早-中三叠世的海侵广泛分布于古特提斯带及以南地区,涉及华南,中南地块,马来半岛及以南地区;印支运动基本结束了古特提斯带的海侵,因此晚三叠世一早侏罗世的海侵主要限于中特提斯海域及以南地区,如与中特提斯洋相邻的陆域,包括华南的湘赣粤海湾晚三叠世一早侏罗世的海侵、中南半岛东南部早侏罗世的海侵以及新加坡早侏罗世的海相地层。白垩纪海相地层主要分布于中特提斯以南地区,如加里曼丹岛。     

南海西北部新生代沉积基底构造演化

在综合分析地质、地球物理、地球化学、古生物学等多方面资料的基础上,将南海西北部海域控制新生代主要沉积盆地的基底划分为5个区:北部湾古生界断堑基底区、莺歌海古生界走滑拉分基底区、琼东古生界断陷基底区、西沙北古生界裂谷基底区、西沙南古生界走滑伸展基底区.通过区域地质分析,初步重建了该海域的大地构造演化历史.该海域新生代沉积基底在前新生代时期与其北面陆上云开地区和其南面的南沙地区同处于特提斯构造域中,经历过古特提斯和中特提斯的发育历程,晚古生代以来可初步分为5个阶段:(1)D-P₁,古特提斯东段多岛洋体系发育阶段;(2)P₂,中特提斯(古南海)开始出现、古特提斯开始消减阶段;(3)T-K₁,古特提斯东段多地块缝合阶段;(4)K₂-N₁1,现代南海形成、中特提斯(古南海)消亡时期;(6)N₁2以来南海扩张停止、澳大利亚板块向北俯冲挤压阶段.     

南海南部海区前陆盆地形成与演化

将南沙地块南缘与加里曼丹—巴拉望地块作为一个构造演化的整体进行研究,对南海南部构造边界的蛇绿—混杂岩及岩浆岩的分布和岩性,以及南海南部前陆盆地的构造与沉积特征加以描述、分析,发现前陆盆地系统的形成时间是自西南往东北,逐渐由晚始新世末—早中新世—中中新世,与南边的俯冲碰撞带形成时间相对应,认为南沙地块南缘与加里曼丹—巴拉望地块之间经历了一个与古南海消亡息息相关的连续演化的过程。     

南海和苏禄海的构造地层地体及拆离断层

自１９９７年以来,联邦德国地球科学和资源调查局（ＢＧＲ）从南海,苏禄海地区的采集的地球科学数据连同可利用的商业钻井和大洋钻探计划（ＯＤＰ）的井位资料一起作为综合数据进行了编辑和解释,用已解释的地震剖面对综合地层,岩性资料进行讨论和对比,以地层和构造分析的基础,把南海和苏禄发别划分为５个和４个主要的构造地层地体。南沙岛礁区（危险地块）,礼乐滩,巴拉望－西北婆罗洲海槽及巴拉望岛是晚白垩世－早古新世期间     

南海围区中、新生代古地磁特征与南海地质构造演化

南海的形成和构造演化的研究表明:早—中三叠世,印支微板块与华南微板块相隔约8个纬度,两者于晚三叠世碰撞成统一大陆。古新世—早渐新世,华南微板块向南漂移了约9.5个纬度;中渐新世一早中新世,它则向北漂移了约8个纬度。此一漂移对南海的第二期S—N向扩张起了重要的控制作用。菲律宾岛弧的两期大规模的逆时针旋转(40多度和20多度)恰好分别与太平洋板块运动方向的改变和南海海盆洋壳向东发生俯冲相对应。南海的扩张活动与周缘块体的相互运动有关。     

华南中生代岩相变化及海相地层时空分布

在搜集大量资料的基础上，分析了华南中生代地层时代、岩性、岩相对比关系，重点综述了中生代海相地层的时空分布特征。受所处构造部位的控制，华南中生代岩相时空变化总体上可分为3个区：东区(闽西南-粤东-粤北-粤中)、中区(粤西-桂东)、西区(滇西-滇东南)。中区在早三叠世以后完全隆升成陆，仅局部有山间盆地碎屑沉积。海相地层集中于东西两区，但存在明显的东西差异：海侵时间在东区为早三叠世、晚三叠世-早侏罗世和早白垩世，西区为中三叠世和中侏罗世；海侵方向在东区来自东南，西区则为中特提斯滇缅海的-部分。晚三叠世-早侏罗世的粤东海盆发育厚达5000m的海相和海陆交互相沉积，可能向南延伸到台西南盆地和南沙群岛东部，但它与南海西部围区的同时代海盆并不直接相通。     

南海北部中生代沉积模式

南海东北部与西北部海域均分布有中生代地层,地震勘探揭示南海北部中生界东、西之间在地震相及沉积充填结构上存在明显差异,东部中生界为双层结构,而西部为单层结构.东部中生代地层由海相及海陆过渡相侏罗系与陆相白垩系组成,而西部则由陆相白垩系构成,缺失侏罗系.从海水入侵方向看,南海北部中生界与特提斯域无关,可能更受太平洋域的影响.侏罗纪古太平洋边缘海盆在南海北部主要分布在珠江口盆地东部及台西南盆地,从早侏罗世到晚侏罗世海盆范围逐渐缩小;白垩纪南海北部整体抬升,除台西南盆地东部接受海相沉积外,白垩纪南海北部以小型断陷盆地为特征,在断陷盆地内接受陆相河湖相沉积.南海北部在中生代时期位于特提斯构造域与太平洋构造域的交接部位,东部中生界双层结构、西部单层结构的沉积模式进一步明确濒太平洋构造域的对南海北部中生界的控制作用,同时东部将是中生代油气勘探的有利区域.     

南海北部白垩系发育特征及构造意义

通过综合分析研究发现,晚中生代时期南海北部构造隆升带存在随时间由北向南逐步迁移:中晚侏罗世广东沿岸开始逐步隆升,大部分地区遭受剥蚀,火山碎屑岩发育,而南海北部则接受了滨浅海相到深海相沉积;早白垩世隆升带向海迁移,广东沿岸发育山间盆地,接受河湖相沉积,在南海北部深海相沉积消失,仅存在海陆过渡相沉积;进入晚白垩世,南海海域整体发生抬升,广东沿岸地区山间盆地范围扩大,陆相地层发育,以陆相洪积扇及河湖相沉积为特征,南海海域大部分地区缺失上白垩统,但在潮汕坳陷发育了一套杂色砂泥岩夹砾岩沉积,含蒸发岩,砂岩中的锆石FT年龄均在75 Ma左右,故地层形成时间应在75 Ma之后,由于上覆新生代地层的约束,该套地层应属晚白垩世,此时潮汕坳陷属前陆盆地,礼乐盆地、巴拉望及民都洛均位于潮汕坳陷南侧或西南侧,属于隆升山脉的一部分。     

南沙海区中生界岩相分布及构造特征

为了了解南中国海南部南沙群岛陆架-陆坡区中生代地层发育情况,作者通过综合分析该海区钻井、拖网及1987年以来采集的20000多公里的多道反射地震勘探等资料,得到了对该区中生界基本特征的如下新认识:空间分布上,南沙的中生界具有从北部的郑和-礼乐隆起南缘向南增厚的趋势;沉积岩相方面,东部三叠纪时为深海相,侏罗纪为浅海与三角洲相,白垩纪为浅海-内浅海相,而往西南部中生代的海水深度有变深的趋势;中-新生代变形上,在南沙西部的曾母盆地,中生界褶皱为复式的、非协调性的,南沙中部多为舒缓褶皱,东部仅在近巴拉望海槽地带出现小幅度的褶皱。结合围区中生界及特提斯构造域的发育特征,作者提出南沙地块上的海相中生界在大地构造上归属于残留在中特提斯洋北部减薄陆缘地壳上的中特提斯期海相沉积地层,是该海域油气资源勘探不可忽视的对象。     

Deep structures of the Palawan and Sulu Sea and their implications for opening of the South China Sea

Compared to the northern South China Sea continental margin, the deep structures and tectonic evolution of the Palawan and Sulu Sea and ambient regions are not well understood so far. However, this part of the southern continental margin and adjacent areas embed critical information on the opening of the South China Sea (SCS). In this paper, we carry out geophysical investigations using regional magnetic, gravity and reflection seismic data. Analytical signal amplitudes (ASA) of magnetic anomalies are calculated to depict the boundaries of different tectonic units. Curie-point depths are estimated from magnetic anomalies using a windowed wavenumber-domain algorithm. Application of the Parker–Oldenburg algorithm to Bouguer gravity anomalies yields a 3D Moho topography. The Palawan Continental Block (PCB) is defined by quiet magnetic anomalies, low ASA, moderate depths to the top and bottom of the magnetic layer, and its northern boundary is further constrained by reflection seismic data and Moho interpretation. The PCB is found to be a favorable area for hydrocarbon exploration. However, the continent–ocean transition zone between the PCB and the SCS is characterized by hyper-extended continental crust intruded with magmatic bodies. The NW Sulu Sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the Proto South China Sea (PSCS) is further constrained. With additional age constraints from inverted Moho and Curie-point depths, we confirm that the spreading of the SE Sulu Sea started in the Early Oligocene/Late Eocene due to the subduction of the PSCS, and terminated in the Middle Miocene by the obduction of the NW Sulu Sea onto the PCB.     

珠江口盆地的形成与南海的构造演化

南海地块在中生代早期与华南大陆边缘发生了一次陆陆碰撞,这一碰撞形成了研究地区中生代近EW向为主的构造格局,珠江口盆地及整个南海的演化都是在南海地块各块体裂离华南陆缘后发生的。盆地自晚白垩世以来,先后经历了不同构造方向的两期张裂阶段及张裂后沉降阶段。     

Seismic anisotropy surrounding South China Sea and its geodynamic implications

Several mechanisms have been proposed for the opening of the South China Sea. Here, we use SKS splitting analysis to investigate the mantle flow surrounding the South China Sea. We use a total of 23 seismic stations and 87 events. We applied spectral analysis and cluster analysis to find a stable splitting solution for each event. The main conclusions are: (1) In northern Vietnam, the NW–SE fast direction is parallel to the absolute plate motion as well as GPS observations with splitting times larger than 1 s, indicating a coupled lithosphere and mantle. In contrast, in southern Vietnam, the NE–SW fast direction suggests that the lithosphere and asthenosphere are decoupled. (2) The fast directions beneath the South China Block and central Taiwan are NE–SW and NS respectively, both parallel to surface deformations with splitting times greater than 1 s, indicating that mantle flow and surface deformation are related. (3) The observed NW–SE fast directions beneath Hainan Island reflect the India–Eurasia collision, and show no signatures of an upwelling mantle plume directly underneath Hainan Island. This implies that Hainan Island is tectonically closely related to the Red River Fault, not the South China Block. (4) In Borneo, the observed NE-SW direction is parallel to the Palawan Trench, consistent with flow associated with the inactive proto-South China Sea subduction system. The SKS splitting observations surrounding South China Sea cannot be explained by a single geologic process, with either the collision-driven extrusion model or the slab pull model fitting the data presented here.     

我国南海历史性水域线的地质特征

40a的海洋地质、地球物理实测研究表明,九段线不仅是显示我国南海主权的历史性水域线,而且总体上也是南海与东部、南部和西部陆区及岛区的巨型地质边界线。根据实测数据,本文将从地质成因、来源、演化的角度论述此南海历史性水域线的合理性。主要结论包括:历史性水域线的东段在地形上基本与马尼拉海沟一致,海沟西侧为南海中央海盆洋壳区,东侧为菲律宾群岛。根据国际地质研究的资料,菲律宾群岛始新世以前位于较偏南的纬度,后来于中晚中新世(距今16~10Ma)仰冲于南海中央海盆之上,因此菲律宾群岛是一个外来群岛。而黄岩岛在马尼拉海沟以西,是中央海盆洋壳区的一个岛礁,与菲律宾群岛成因不同。南海历史性水域线的南段在地形上基本与南沙海槽一致,伴随南沙地块由北部陆缘向南裂离,古南海洋壳沿此海槽以南俯冲至加里曼丹岛陆壳之下,因此南沙地块与加里曼丹陆块为两个来历不同的地块。南海历史性水域线西段的分布在地形上与越东巨型走滑断裂带基本一致,可能与西沙地块、中沙地块、南沙地块从南海北部陆缘向南滑移有关。南沙地块北缘陡直的正断层结构,突显中央海盆是拉裂形成,其基底和中新生代地层与北部珠江口盆地的地层结构可以对比,说明南沙岛礁原属我国华南大陆南缘,后因南海的形成裂离至现今的位置。     

Middle to Late Cenozoic tectonic events in south and central Palawan (Philippines) and their implications to the evolution of the south-eastern margin of South China Sea: Evidence from onshore structural and offshore seismic data

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan.     

Structural evolution of Malay Basin,its link to Sunda Block tectonics

The Malay Basin is located offshore West Malaysia in the South China Sea, within north central region of 1st order Sunda Block. The basin developed partly as a result of tectonic collisions and strike-slip shear of the Southeast Asia continental slabs, as the Indian Plate collided into Eurasia, and subsequent extrusion of lithospheric blocks towards Indochina. The Sunda Block epicontinental earliest rift margins were manifested by the Palaeogene W–E rift valleys, which formed during NW–SE sinistral shear of the region. Later Eocene NW–SE dextral shear of (2nd order) Indochina Block against East Malaya Block rifted open a 3rd order Malay Basin. Developed within it is a series of 4th order N–S en-echelon ridges and grabens. The grabens and some ridges, sequentially, host W–E trending 5th order folds of later compressional episodes. The Malay Basin Ridge and Graben Model explains the multi-phased structural deformation which started with, the a) Pre-Rift Palaeo/Mesozoic crystalline/metamorphic Basement, b) Synrift phase during Paleogene, c) Fast Subsidence from Late Oligocene to Middle Miocene, d) Compressional inversion of first Sunda fold during Late Miocene, and e) Basin Sag during Plio-Pleistocene with mild compressional episodes. The subsequent Mio-Pliocene folding history of Malay Basin is connected to the collision of Sunda Block against subducting Indian–Australian Plate. This Neogene Sunda tectonics, to some degree after the cessation of South China Sea spreading, is due to the diachronous collision along the 1st order plate margins between SE Asia and Australia.     

Stratigraphic division and depositional processes for the Mesozoic basin in Northern South China Sea

This paper divided the age of Mesozoic strata in the Northern South China Sea into epochs by the stratigraphic correlation between land and sea areas. A Mesozoic stratigraphic profile from South China to the northern continental slope of the South China Sea was constructed by ground and seismic surveys. The depositional process was illustrated by the chronostratigraphic framework of the Mesozoic basin, and the oil and gas exploration prospect was discussed. Results indicate that the depositional process from the initial transgression in the Late Triassic to the Mesozoic maximum flooding event that occurred in the Early Jurassic period formed a continuous transgression when the depositional environment varied from littoral to semi-closed gulf and shelf. After this maximum flooding event, a continuous marine regressive process developed, including seawater withdrawal from the South China epicontinental region at the end of the Early Jurassic period, seawater withdrawal to the outer shelf of the Northern South China Sea at the end of the Early Cretaceous period, and seawater withdrawal to the slope trough at the end of the Cretaceous period. Research achievement not only connects major Mesozoic geological events but also specifies the time nodes of such events. Thus, an investigation of this event is significant to the Mesozoic tectonic evolution study of the South China Sea and Paleo-Pacific Ocean.