Expansion of the South China Sea basin:Constraints from magnetic anomaly stripes,sea floor topography,satellite gravity and submarine geothermics

The widely distributed E-W-trending magnetic anomaly stripes in the central basin and the N-Etrending magnetic anomaly stripes in the southwest sub-basin provide the most important evidence for Neogene expansion of the South China Sea.The expansion mechanism remains,however,controversial because of the lack of direct drilling data,non-systematic marine magnetic survey data,and irregular magnetic anomaly stripes with two obvious directions.For example,researchers have inferred different ages and episodes of expansion for the central basin and southwest sub-basin.Major controversy centers on the order of basinal expansion and the mechanism of expansion for the entire South China Sea basin.This study attempts to constrain these problems from a comprehensive analysis of the seafloor topography,magnetic anomaly stripes,regional aeromagnetic data,satellite gravity,and submarine geothermics.The mapped seafloor terrain shows that the central basin is a north-south rectangle that is relatively shallow with many seamounts,whereas the southwest sub-basin is wide in northeast,gradually narrows to the southwest,and is relatively deeper with fewer seamounts.Many magnetic anomaly stripes are present in the central basin with variable dimensions and directions that are dominantly EWtrending,followed by the NE-,NW- and NS-trending.Conversely such stripes are few in the southwest sub-basin and mainly NE-trending.Regional magnetic data suggest that the NW-trending Ailaoshan-Red River fault extends into the South China Sea,links with the central fault zone in the South China Sea,which extends further southward to Reed Tablemount.Satellite gravity data show that both the central basin and southwest sub-basin are composed of oceanic crust.The Changlong seamount is particularly visible in the southwest sub-basin and extends eastward to the Zhenbei seamount.Also a low gravity anomaly zone coincides with the central fault zone in the sub-basin.The submarine geothermic distribution demonstrates that the southwest sub-basin has a higher geothermal value than the central basin,and that the central fault zone is defined by a low thermal anomaly.This study suggests that NW-SE expansion of the southwest subbasin is later than the N-S expansion of the central basin with the sub-basin extending into the central basin and with both expansions ending at the same time.The expansion of southwestern sub-basin,similar to the Japanese Sea,is likely caused by left-lateral strike slip on the central fault zone in the South China Sea,which may have significance for finding oil and gas in this region.

On the Co-Variability between Climate Indices and the Potential Spread of Seasonal Climate Simulations over South African Provinces

This study investigates the co-variability between measures of the spreads in the ensembles of seasonal climate simulations and large scale climate indices. Spreads in the ensembles of seasonal simulations (of rainfall and near surface air temperature) from an atmospheric model, over South African provinces, are quantified with the de-trended anomalies of standard deviation (StdDev) and the distance between the 90th and 10th percentiles (RoP) of the simulations. Results indicate that, on seasonal time scales, measures of spread significantly co-vary with observed global sea surface temperatures (SST) far and near. This suggests that the climate factors controlling the degree to which the seasonal climate may be precisely forecast over the South African provinces may both be locally and remotely based. Results also indicate that all significant predictors of spread—El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Benguela Niño (BGN) and Southwest Indian Ocean Index (SWI), are of tropical origin;they co-vary significantly with measures of spread on seasonal time scales over a number of provinces and seasons, particularly during the rainfall onset and peak periods, as well as during the cold season. Nevertheless, responses of measures of spread to climate predictors are relatively small, either indicating that predictor-spread relationships are more complex in nature than can be represented by the traditionally simple climate indices, or indicating that controls on ensemble spread are weak. Therefore, there may be limits to the extent to which year-to-year variations in the predictability of seasonal climate over South Africa provinces might be understood.

Morpho-tectonic study on late-stage spreading of the Eastern Subbasin of South China Sea

Three NE-trending linear structural zones with different strikes are present in the Eastern Subbasin of the South China Sea. They are distributed in the 350-km-wide central region of both sides of the Scarborough seamount chain, representing a morphological indication of the basement faulting. These three zones correspond respectively to three spreading episodes: the magnetic anomalies 6c -6a (24-21 Ma), 6a - 5e (21 - 19 Ma) and 5e - 5d (5c) (19 - 16 Ma). Instability, subsection and asymmetry characterize the seafloor spreading of the subbasin. The spreading directions change in a continuous way in each of the zones, but abrupt changes by 3°-5° occur when crossing the boundary between the zones, reflecting that the spreading direction has evolutionary characteristics of both gradual and sudden changes. NW-trending transform faults of the spreading become progressively densely distributed from the east to the west, cutting the NE-trending zones into several segments, between which the strikes of the NE-trending zones have marked changes. Such features indicate that the spreading axis is associated with subsection along the strike. Around 21 Ma (magnetic anomaly 6a), there was an important event of spreading acceleration, with the full rate rapidly increasing from 30.54 km/Ma to 42.88 km/Ma. This rate increment event corresponds to the sudden changes in the spreading characteristics of basement faulting, sedimentation, volcano activities, etc. The asymmetry of spreading over the eastern part of the Eastern Subbasin is generally larger than that over the western part, and the spreading rate is markedly larger on the southern side than on the northern side. As a result, the oceanic basin is wide in the east and narrow in the west, forming a significantly asymmetric pattern.

Cenozoic Volcanism in South China Sea and Its Vicinity and South China Sea Spreading

The rock series, rock types and Sr-Nd isotopic dating of the Cenozoicvolcanic rocks in the South China Sea are similar to those in its vicinity. On the basis of thespreading age of the South China Sea, the Cenozoic volcanic rocks are divided into three stages: thepre-spreading stage, the spreading stage and the post-spreading stage. The deep processcharacteristics of the asthenosphere and lithosphere may be inferred from the study on primarybasaltic magma. The top layers of the asthenosphere both in the spreading stage and in thepre-spreading stage are closer to the earth surface than that in the post-spreading stage. From thepre-spreading stage to the spreading stage, the top layer of the asthenosphere decreased in depth,while the amount of interstitial partial melts increased. The evolution of the primary basalticmagma shows a progressive evolution sequence of the rifting volcanism and a faster lithosphericspreading velocity. From the spreading stage to the post-spreading stage, the top layer of theasthenosphere gradually increased in depth, but the amount of interstitial partial melts decreased.The evolution of primary basaltic magma shows a retrogressive evolution sequence of the riftingvolcanism and a gradual decrease in the lithospheric spreading velocity. The depth recognized by thestudy on the Cenozoic volcanism demonstrates the deep environment for the formation and evolutionof the South China Sea.

The propagation of seafloor spreading in the southwestern subbasin,South China Sea

On the basis of the summary of basic characteristics of propagation, the dynamic model of the tectonic evolution in the South-western Subbasin (SWSB), South China Sea (SCS), has been established through high resolution multi-beam swatch bathymetry and multi-channel seismic profiles, combined with magnetic anomaly analysis. Spreading propagates from NE to SW and shows a transition from steady seafloor spreading, to initial seafloor spreading, and to continental rifting in the southwest end. The spreading in SWSB (SCS) is tectonic dominated, with a series of phenomena of inhomogeneous tectonics and sedimentation.

Intraseasonal oscillation features of the South China Sea summer monsoon and its response to abnormal Madden and Julian Oscillation in the tropical Indian Ocean

By applying the OLR and wind data, rainfall data and the Madden and Julian Oscillation （MJO） index, the paper deals with in traseasonal oscillation features and interannual differences of the South China Sea （SCS） summer monsoon, distribution of its LF circulation and convection fields and rainfall, and path of summer monsoon ISO spreading, as well as impact of tropical IndoMJO on SCS summer monsoon ISO during 19792008. It is found that （1） there are three intraseasonal oscillations of the SCS summer monsoon Intraseasonal Oscillation （ISO） in summer （from May to August） in the climate normal. The SCS summer monsoon ISO goes through six phases （exclusive of weak phase） at every complete fluctuation： developing, the strongest, weakening, restraining, the weakest, and recovering. Due to tropical LC convection spreading to the east and north, the LR convection and circulation fields in the lst3rd and 4th6th phases present the antiphase in the Arabian SeaWest Pa cific latitudinal band. Its corresponding rain bands in the lst3rd and 4th6th phases als present antiphase roughly. The rain band, mainly in tropical regions in the south of 20N, moves eastward with LR convection shifting eastward, while the rain band moves northward with LR convection shifting northward in East Asia （EA） subtropical regions in the north of 20N. （2） The SCS summer monsoon ISO presents significant interannual variations in intensity. There are three stronger monsoon in traseasonal oscillations in summer in the strong SCS monsoon ISO year. The first two oscillations from the tropical Indian Ocean ISO spread northward to the Bay of Bengal first, and then to the South China Sea （SCS） along the 10-20N latitudinal band. They are strengthened there and stimulate the ISO moving to the north to form the tropical IndoISO. Finally they spread to South China （SC） by relay way in the longitudelatitude direction. Moreover, in the weaker SCS summer monsoon ISO, the oscillation weakens greatly and irregularly in intensity with the weaker ISO spreading in the longitudelatitude direction. In average conditions, the tropical Indian ISO spreads to the SCS by about 20 days （one half ISO periods）. （3） MJO1 （the first modal of MJO index provided by the CPC） averaged value in the lst2nd pentads of April has the negative correlation with the SCS monsoon ISO intensity. The tropical IndoMJO is slightly stronger in the subsequent May to August when it is more ac tive in the lst2nd pentads of April, and the ISO also spreads strongly to the SCS, so that the SCS summer monsoon ISO strengthens. Conversely, the SCS summer monsoon ISO weakens. The abnormal MJO in the lst2nd pentads of April contrib utes to a certain theory basis for us to predict the subsequent SCS summer monsoon ISO intensity and analyze the related re gions＇ abnormal rainfall.

Magnetic recording of the Cenozoic oceanic crustal accretion and evolution of the South China Sea basin

我们考察并且讨论一些在华南海(SCS ) 在磁性的数据上做的最近的科学调查结果。磁性的异例在中生代和新生代上忍受极其富有的信息构造进化。从磁性的异例计算的分析信号振幅很精确揭示的 3D 二上的中生代沉积序列的寡妇分布结合大陆人边缘，和他们也在在 SCS 海洋的外壳以内描绘以后阶段的 magmatism 和构造转变和带状配列被发现很有效。通过综合分析磁性，严肃和思考地震数据，我们在华南海大陆人边缘附近定义大陆海洋边界(圆块) ，并且发现圆块与一个转变地区与一致很好从对否定免费空气的严肃异例主要积极。COB 的这精确构画出为更好跟踪海洋的外壳导致的磁性的异例是批评的。几何上复杂的圆块和内部磁性的带状配列要求一个阵发性的洞模型，以及一个变换差错的介绍(这里作为 Zhongnan 差错制造了)在东方和西南亚盆之间在东方和西南亚盆以内，磁性的异例旁边地是相当连续的，在这些亚盆以内显示大变换差错的不存在。我们提高浅玄武岩的层经由一个通带过滤器引起的磁性的异例，并且认识到北大陆人边缘附近的多半最旧的磁性的异例根据磁性的时间规模 CK95 是 C12。在南部的大陆人边缘附近，磁性的异例是不太可认识的，异例 C12 看起来失踪。这些差别证明关于散布中心的寡妇的一种不均匀的开始式样，和北部分看起来比到南方有稍微更快传播的率。磁性的异例 C8 (M1 和 M2， 26 妈) 在海洋的盆以内代表重要磁性的边界，并且可能与在散布率和 magmatic 紧张的变化有关。为一条以前建议的山脉的磁性的证据在异例 C7 不是清楚的以后，跳。西南亚盆的年龄还得进一步被检验，最有利地与深拖引磁性的调查并且海洋钻。我们的磁性光谱最浅的居里削尖的学习表演在西南的亚盆的东方部分附近被定位，而在东方亚盆居里以内深度对传播的寡妇的北方更小，比到南方集中。居里深度的这个模式对地区性的热流动大小和以后阶段的暴烈的海底山分布一致，并且我们因此推想居里深度变化仔细与以后阶段的 magmatism，而非与外壳的年龄被联系。尽管在北大陆海洋转变地区(简易窄床) 附近定位的磁性的异例是相对安静的，自从概念上它与一个海洋的磁性的安静地区显著地不同，这个区域不是一个典型磁性的安静地区。相对安静的磁性的异例看起来在居里等温线与 shallowing 被联系并且在磁性的层，而是我们的全面观察变瘦建议保存得很好的厚中生代沉积岩石是为有磁力地安静的地区的主要原因。各种各样的低通行证的过滤水兵和在空中的磁性的异例和卫星的高类似磁性的异例清楚地证实那更深磁性的来源(在更低的外壳中并且最高披风) 有贡献到长波长的表面在区域的磁性的异例，当已经推断了从有磁力地 inversed 居里深度。近海华南磁性的异例(SCMA ) 在低通行证的过滤水兵和在空中的磁性的异例和卫星上变得更突出磁性的异例，在它下面显示很深深地埋葬的磁性的来源。

公元前三千纪黍西传与欧亚大陆人群的文化交流

公元前2400年前后,沿着亚洲内陆山脉廊道,通过早期人群的移动、迁徙和交流,黍被带到了中亚地区。公元前2000年前后,黍快速传入印度河流域,并经由海上传播至阿拉伯半岛西南端和非洲东北部地区。公元前三千纪中叶和后半叶,两河流域、尼罗河流域、印度河流域处于早期城市文明发展的高峰,黄河流域也已步入早期文明阶段,人口增长和城市化进程加速了早期文明的扩张,推动了东西方人群的双向交流与互动,促进了黍的西传。

Relationship between Formation of Zhongyebei Basin and Spreading of Southwest Subbasin, South China Sea

The Zhongyebei （中业北） basin （ZYBB） is an NE-striking, narrow and small sedimentary basin superimposing the southern 1/2 segment of the proposed spreading axes of the SW subbasin of the South China Sea （SCS）. More than 4 500 m strata were identified in the Zhongyebei basin, including the Paleogene lower structure layer and the Neogene upper structure layer. The SW subbasin of the South China Sea has been regarded as an oceanic basin opened by seafloor spreading, as evidenced by the flat and deep （〉 4 000 m mostly） seafloor with linear magnetic anomalies, and by the shallow Moho depth of 〈 12 km as estimated from gravity modeling. The classic model of seafloor spreading predicts that sediments on the oceanic crust are younger and thinner towards the spreading axes. But in the southwestern segment of the SW subbasin, contradictions appear. Firstly, the thick sedimentation in the ZYBB is along the proposed spreading axes. Secondly, the sediments are thinner （500-1 500 m） and younger away from the proposed spreading axes. Thirdly, geological elements of the two sides of spreading axes develop asymmetrically in the southwestern SW subbasin. Two models, the early opening model and the limited modeling model, are suggested for resolving this paradox. The former suggests that the opening of the SW subbasin was in Late Eocene and earlier than the oldest sediment in the ZYBB. The latter proposes that the opening of the SW subbasin was limited to its northeastern portion, and did not extend to the southwest portion. The ZYBB is a rift basin survived from the spreading but subjected to severe syn-spreading magmatic disturbance. The SW subbasin and the ZYBB of the SCS provide a unique opportunity for studying the structural evolution and dynamic mechanism at the tip of a propagating seafloor spreading. Both models have unresolved questions, and further studies are needed.

南海《更路簿》文化传播研究

南海《更路簿》在元代已有雏形,形成于明代初期,并在明清及民国时期得到广泛使用。其文化价值在于它是南海渔民航海的重要法宝、我国自古以来管辖南海的重要证据和珍贵的非物质文化遗产。南海《更路簿》的文化传播途径包括历代渔民传承、学术研究、大众传媒等。对其传播存在的主体较少、传播渠道较窄等问题,提出扩大媒体对内传播和对外传播、加强全国学术层面的研究、建设《更路簿》博物馆和数据库、开展多种形式的宣传等路径,以提高南海《更路簿》文化的传播水平。

南海大陆边缘盆地构造演化差异性及其与南海扩张耦合关系

南海大陆边缘盆地由于边界条件的差异,不仅形成了不同类型的陆缘盆地,如离散型、走滑-伸展型和伸展-挠曲复合型,而且这些盆地构造演化存在明显的非同步性。这些陆缘破裂过程与南海扩张作用过程呈现明显不一致性。研究表明,南海扩张时期南海南、北大陆边缘均形成了一系列裂陷盆地,然而,南海南部、北部大陆边缘盆地裂陷作用结束时间不同,北部大陆边缘盆地裂陷作用结束于23Ma或21Ma,而南部大陆边缘盆地裂陷作用结束于15.5Ma,显然北部大陆边缘盆地裂陷结束时间明显早于南部大陆边缘盆地。南海扩张停止后,南海南、北部陆缘仍表现出明显差异,北部陆缘仍以伸展作用为主,晚中新世以来出现快速沉降幕,而南海南部陆缘则以挤压作用为主,且其挤压时间及强度呈现南早北晚的特点,即南部曾母盆地明显早于南薇西盆地和北康盆地。南海南、北大陆边缘盆地形成演化的差异性,特别是构造转型差异变化,为新生代南海扩张的迁移性提供了有力的佐证,可以推断南海不同期次海盆扩张可能存在向南的突然跃迁。因此,本次研究梳理出的南海不同陆缘盆地张裂-伸展的非同步性可为南海洋盆扩张演化过程解释提供新的证据。

南海海盆扩张成因质疑

从板块构造学、地球物理学和地球动力学等角度,结合南海中央海盆及其周边的地质、地球物理资料进行综合分析论证,对南海“扩张成因”模式提出质疑.认为南海“扩张成因说”不能成立,其中的几个核心问题是:(1)数学理论模型的边界参数选取存在多解性,其结果与地质地球物理资料不符或相去甚远;(2)无法解释海盆区地球物理探测和研究所表明的地壳结构及岩性特征,也无法解释海盆区的断裂分布和岩浆活动特征;(3)地球动力学诸方面难以支持南海“扩张成因说”成立;(4)南海海盆周边不存在与南海“扩张成因”相关的相互强烈作用的地球物理和地质构造特征;(5)南海海盆不具备大规模扩张的空间.南海“扩张成因说”已严重阻碍对南海和周边的地质与地球物理研究工作的深入和发展,应该放弃.

南海新生代碳酸盐台地淹没事件记录的海底扩张

本文通过对南海 4个碳酸盐台地及其淹没事件的分析来阐明南海海底扩张的演化史。南海碳酸盐台地出现在最大海底扩张期 ,淹没事件出现在海底扩张和地壳下降速率进一步加快时期 ,因而它记录了海底扩张的阶段性和不均一性。南海共经历了早中新世晚期(距今 1 7± 0 5Ma)、晚中新世早期 (距今 1 0 0～ 8 2Ma)和上新世早期 (距今 3 4～ 3 0Ma)等 3次大的淹没事件 ,表明南海经历了 3次大的海底扩张 。

南海北部古俯冲带的位置及其对南海扩张的控制

为了确定南海北部古俯冲带的具体位置,作者利用美国LCT综合反演软件对收集到的重磁数据进行处理解释,结果显示在南海北部从台湾西南部到一统暗沙隆起,即沿南海海盆北部陆坡为一条布格重力异常水平梯度峰值带,指示了古俯冲带的具体位置;其北部的高磁异常代表了与之对应的古火山弧。深反射地震资料也验证了南海北部陆坡位置存在古俯冲带,钻井资料显示俯冲带存在的时代为晚侏罗世到早白垩世。据此绘制了南海地区晚中生代到现今的构造古地理演化图,指出南海的扩张应与晚中生代俯冲带这个先存的软弱带有关,南海海盆正是从古俯冲带的位置开始扩张。

琼东南盆地古近纪沉积充填演化及其区域构造意义

琼东南盆地是发育于南海西北部的新生代张性断陷盆地。始新统和早渐新统崖城组属过充填型或平衡充填类型,在盆地各个断陷内均具有砂岩-泥岩-砂岩三重沉积充填结构;晚渐新统陵水组在北部坳陷带属过充填及平衡充填类型,发育砂岩-泥岩-砂岩三重沉积充填结构,而在中央坳陷带则属由砂岩-泥岩二重沉积充填结构组成的欠充填型。古近纪盆地的沉积充填结构演化反映了始新世—早渐新世断陷阶段与晚渐新世断拗阶段的盆地演化历史,其中,晚渐新世盆地断拗阶段的发育是南海海底单期扩张过程的结果。

南海构造演化模式:综合作用下的被动扩张

南海处于欧亚板块、印度-澳大利亚板块和太平洋板块的交汇处,地质作用十分复杂,至今未能建立一个普遍适用的演化模式,成为南海研究中亟待解决的问题。通过总结南海构造演化的主要模式,分析各模式建立的依据和存在的问题,发现通过一个动力源来研究南海的形成演化是片面的。从南海构造特征分析,结合国外有关大陆岩石圈破裂的研究成果,认为南海海盆主体经历了被动大陆张裂到海底扩张的演化过程。动力源主要是古南海向南俯冲的拖曳力,辅助于南、南东向的地幔流作用。南海北部陆缘广泛存在的高速层,可能是地幔流沿拉张减薄面底侵的结果,因而不同于地幔柱作用引起南海的打开。印度板块碰撞、楔入产生的地幔流,经太平洋俯冲板块的阻挡,最终发生南、南东向流动。印支地块的挤出则对南海西部的拉张具有重要影响。

南水北调东线江都泵站钉螺扩散情况现场观察

目的了解南水北调东线取水口抽调江水时钉螺能否进入输水河道孳生扩散。方法对泵站前水源河道、泵站拦污栅、泵站消力池滩地和渠首输水河道进行钉螺分布调查,采用打捞的方法检测水源河道漂浮物携带钉螺情况,结合水工建筑功能、调水量及有关河道水位资料,对钉螺通过泵站扩散可能性进行分析研究。结果江都泵站前水源河道查出钉螺面积185.28hm2,水源河道漂浮物调查发现钉螺主要在汛期吸附于漂浮物漂流扩散;泵站前拦污栅及泵站出水口消力池滩地及泵站后渠首输水河道均未发现钉螺。结论南水北调东线调水泵站水闸、拦污栅、水泵、消力池等水工建筑物具有阻挡、沉淀钉螺的作用,泵站消力池及输水河道因水体大,常年保持高水位运行,不适宜钉螺孳生。

南海北部陆缘深水盆地多边形断层几何特征及成因

基于高分辨3D地震资料研究得出,南海北部大陆边缘深水区的珠江口盆地白云凹陷、琼东南盆地华光凹陷、长昌凹陷和北礁凸起中新统普遍发育了延伸长度短、间距小、断距小、倾角大、受层序边界控制、平面呈多边形特征的小型伸展正断层,即多边形断层。借助区域相对海平面变化曲线、盆地构造和沉积演化、ODP钻井和深水油气井资料,探讨了南海北部多边形断层的形成机理。珠江口盆地白云凹陷和琼东南盆地华光凹陷多边形断层发育在海泛面对应的密集段上下,其形成受早期成岩过程中的压实脱水、黏土矿物相变脱水和生烃增压作用影响,可用超压泥岩水压破裂模型解释。琼东南盆地长昌凹陷和北礁凸起受复杂构造和沉积环境影响,多边形断层具有一定的定向性,地层岩性也较为复杂,除了受早期成岩过程中的压实脱水、水压破裂作用影响外,还受构造应力和重力扩展作用的叠加改造。

南海西南次海盆广角地震探测

2010年12月—2011年3月在南海西南次海盆开展了海底地震仪(Ocean Bottom Seismometer,OBS)探测,采用Sedis IV型、I-4C型和MicrOBS3种不同型号的OBS,以4×24.5L的大容量气枪为震源,获得了覆盖西南次海盆残留扩张脊的3D人工地震数据。从处理的地震数据可知,此次试验是一次比较成功的地震实验,OBS地震记录清晰、震相丰富,所使用的气枪有足够的能量输出,显示了其良好的工作能力。选取剖面1中的7台OBS进行了2D剖面处理。初步建模结果表明,南海西南次海盆地壳结构为普通洋壳,海山顶部沉积层很薄,莫霍面埋深较浅。

慢速-超慢速扩张西南印度洋中脊研究进展

西南印度洋中脊具有慢速—超慢速扩张速率和倾向扩张的特征,是全球洋中脊系统研究的热点之一,也是研究海底构造环境、热液活动、地幔深部过程及其动力学机制的重要区域。在前人工作的基础上较为详细地介绍了西南印度洋中脊的研究历史、地形划分、扩张速率及其构造特征,归纳了西南印度洋中脊热液活动及岩石地球化学特征,探讨了超慢速扩张洋脊和超镁铁质岩系热液系统的特殊性,并认为超慢速扩张洋脊广泛暴露的地幔岩及其蛇纹石化作用、超镁铁质岩系热液系统以及热液硫化物成矿作用是西南印度洋中脊今后研究的重要内容。