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1.
南沙地块构造格局及其演化特征 总被引：17，自引：5，他引：12
将南沙地块及其周边地块置于统一的地球动力学背景下,根据地球物理、地层展布、构造变形等特征,确立了南沙地块的一级构造边界,提出南沙地块的演化与古南海及现今南海的演化密不可分。古南海分隔了南沙地块和加里曼丹—巴拉望地块,随着古南海由西南往东北的剪刀状南向俯冲封闭和现今南海的张开,南沙地块和加里曼丹—巴拉望地块之间先后在始新世—晚中新世发生B型俯冲、A型俯冲及碰撞作用,形成沙捞越俯冲碰撞带,并在该带北侧形成南沙地块前陆盆地区、南沙地块隆起区及南海深海盆3个构造单元。 相似文献
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西南次海盆位于南海渐进式扩张的西南端,共轭陆缘结构和残留扩张脊保留完整,是研究南海深部结构和动力学机制的关键区域。前期研究发现,西南次海盆洋陆过渡带较窄、同扩张断层发育、地震反射莫霍面不清晰、具有慢速扩张等特征。然而,由于不同探测方法获取的地壳结构具有多解性,使得西南次海盆洋陆转换过程、慢速扩张洋壳结构与增生模式以及龙门海山岩石性质与地幔成因机制等基础科学问题尚存争议。为此我们建议在西南次海盆开展地质取样获取海山岩石样品,确定其年龄与性质,分析扩张后海山形成的深部动力过程;并对关键构造部署高精度的地震反射/折射联合探测,结合岩石物理分析,对西南次海盆进行构造成像和物质组成参数正反演,以实现壳幔尺度的地震学透视,为探索西南次海盆洋陆转换过程和洋壳增生模式提供重要的地球物理证据,以丰富和完善南海的动力学演化模式。 相似文献
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Shaoru Yin Weiwei Ding Derek E. Sawyer Ziyin Wu Yong Tang 《International Geology Review》2020,62(7-8):887-907
ABSTRACT Based on approximately 11,000 km of seismic reflection data collected across the South China Sea oceanic basin, we describe the sedimentary filling characteristics of the basin since its Oligocene opening, as well as connections between this history and contemporaneous regional tectonic events. The seismic lines are spaced ~50 km apart, and the data are tied to International Ocean Discovery Program (IODP) Expedition 349 drilling data. Basin filling occurred in three phases, with basin-wide mean sedimentation rates increasing through time. During the Oligocene to middle Miocene, sediments accumulated primarily in the northern East and Northwest Sub-basins, with a mean basin-wide sedimentation rate of 8 m/m.y. The presence of these deposits over deep basement floor indicates that seafloor spreading initiated in these northern regions. During the late Miocene, deposition occurred primarily in the Northwest Sub-basin and partly in the southern East Sub-basin, with a mean basin-wide sedimentation rate of 30 m/m.y. Basin filling during this time seems to have been linked to slip reversal of the Red River Fault and collision of the North Palawan Block with the Luzon Arc. During the Pliocene and Pleistocene, sediments accumulated rapidly in the northeastern and southern East Sub-basin and the Southwest Sub-basin. The mean basin-wide sedimentation rate was 70 m/m.y. Basin filling during this phase seems to have been associated with the Taiwan and North Palawan collisions, SCS subduction along the Manila Trench, and Tibetan Plateau uplift. Gravity flow deposits predominate throughout the basin fill. 相似文献
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Post-spreading transpressive faults in the South China Sea Basin 总被引：1，自引：0，他引：1
The South China Sea was formed by seafloor spreading during the late Oligocene to the mid-Miocene. After the cessation of spreading, compression due to the northwestward-moving Taiwan–Luzon Arc and strike–slip motion have been occurring on the South China Sea's eastern and west margins, respectively. However due to limited survey coverage, little is known about the tectonics in the oceanic basin of the South China Sea. Satellite altimetry-derived bathymetric data in a 2′ × 2′ grid shows not only a young seamount chain along the E–W-trending spreading axis of the South China Sea Basin, but also three previously unmapped NW- to NNW-trending segmented linear features. These features are topographic highs, rising 300–600 m above the surrounding sea floor, 10–30 km wide and 300–500 km long. Bathymetric and seismic reflection data reveal that they are strike–slip fault zones, in which folds of various amplitude and patterns have developed. These basin-wide transpressive fault zones, and the young volcanism, may be the result of ongoing NNW convergence of the Taiwan–Luzon Arc following the cessation of seafloor spreading in the South China Sea. The NNW-trending strike–slip fault at longitude 116°E is considered to be the boundary between the Eastern Subbasin and the SW Subbasin. 相似文献
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The process of Cenozoic sea-land changes in the northern South China Sea(SCS)controlled the sedimentary filling pattern and played an important role in the petroleum geological characteristics of the northern marginal sedimentary basins.Under the control of the opening process of the SCS,the northern SCS Cenozoic transgression generally showed the characteristics of early in the east and late in the west,and early in the south and late in the north.The initial transgression occurred in the Eocene in the Taixinan Basin(TXNB)of the eastern SCS,while the transgression occurred until the Pliocene in the Yinggehai Basin(YGHB)of the western SCS.International Ocean Discovery Program(IODP)expeditions(Expeditions 367/368)revealed that the initial transgression of the SCS basin occurred at approximately 34 Ma,which was the initial opening time of the SCS.The period of drastic changes in the sedimentary environment caused by large-scale transgression corresponded to the opening time of the southwestern subbasin(approximately 23 Ma),which also represented the peak of the spreading of the SCS.The sea-land transition process controls the distribution of alternating continent-marine facies,marine facies source rocks and reservoirs in the basins.The marine facies source rocks of the basins in the northern SCS have a trend of gradually becoming younger from east to west,which is consistent with the regional process of gradual transgression from east to west.Regional sea-level changes were comprehensively influenced by SCS opening and global sea-level changes.These processes led to the early development in the east and south and late development in the west and north for the carbonate platform in the SCS.Carbonate platforms form another type of"selfgenerating and self-accumulating"oil-gas reservoir in the northern SCS.The sea-land transition controlled the depositional filling patterns of different basins and laid the foundation of marine deposits for oil and gas resources.The source-reservoircap assemblage in the northern SCS was controlled horizontally by provenance supply and sedimentary environmental changes caused by sea-land transition and vertically by the tectonic evolution of the SCS and regional sea-level changes. 相似文献
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为了阐明南海由陆向洋的过渡带内构造活动的时间 空间迁移过程,本文以两条跨南海东部共轭被动陆缘和南海西南部共轭陆缘的两条长剖面为基础,进行精细的构造解释和分析,在南海洋陆转换带内确定了出Tb、SD、PD和Bi四个一级层序界面,并以这4个一层序界面为界,将南海陆缘划分为：早期断陷盆地(Tb—SD)、晚期拆离盆地(SD—PD)和断坳转换盆地(PD—Bi)。通过对同一剖面不同构造单元带内同构造地层的分析,发现构造活动时代由陆向洋逐渐变年轻;通过对比不同剖面同一构造单元带内的同构造地层发现,构造活动时代沿着海底扩张迁移的方向逐渐变年轻。因此,在南海扩张期间,岩石圈的伸展变形不仅表现为向洋方向的迁移,同时表现为向海底扩张方向的迁移。 相似文献
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南海是西太平洋海域最大的边缘海,然而南海扩张终结后动力学过程研究仍较为薄弱.通过构造变革界面识别、褶皱冲断带沉积记录等方面的系统研究,揭示南海南部和东部陆缘在南海后扩张期的演化历程.研究表明南海南部和东部边缘经历了多个微板块从俯冲到碰撞的演变历程,形成了陆-陆碰撞、弧-陆碰撞、洋-弧俯冲等多个特征迥异的板块边界.南海南部陆缘属于古南海俯冲拖曳构造区,婆罗洲西北沙捞越-曾母地块率先碰撞,随后经历了婆罗洲东北沙巴-南沙地块碰撞、西南巴拉望-卡加延岛弧碰撞.南部多个微板块碰撞导致古南海呈剪刀式从西向东逐渐关闭和消亡,总体形成了以微地块碰撞、深海槽发育和造山带前缘巨厚沉积充填为特色的碰撞陆缘.东部陆缘属于菲律宾海俯冲-碰撞构造区,南海东部洋壳自中新世开始向菲律宾海板块俯冲,弧-陆碰撞仅局限于东部陆缘南北两端.澳洲-印度板块、菲律宾海板块与欧亚板块相互作用控制了南海边缘海闭合过程,南海正在进行的关闭过程主要集中在东缘和南缘,东缘呈现了以南海洋壳消亡为特征的闭合过程,而南缘则呈现以微陆块碰撞为特征的古南海闭合过程.显然,南部后扩张期陆缘演变可为边缘海闭合过程研究提供极佳的范例,同时对我国海洋权益保护和南海大陆边缘动力学研究具有重要意义. 相似文献
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洋-陆过渡带是理解大陆岩石圈破裂和海底初始扩张的关键位置,但是在南海北部地区仍然存在关于相关地质过程的诸多疑问.通过近年开展的国际大洋发现计划航次以及深部地质地球物理探测,取得以下4个方面的认识.（1）南海北部的洋-陆边界一般与自由空间重力异常的正-负值过渡位置对应,而更加准确地限定需要结合反射、折射地震资料.稳定大洋岩石圈生成与大陆岩石圈最终破裂之间的洋-陆过渡边界的位置比以往认为的还应往深海盆方向移动.（2）洋-陆过渡带代表了远端带构造作用减弱和岩浆作用逐渐增强的区域.陆坡地壳发育扩张后岩浆底侵、洋-陆过渡带发育同破裂期岩浆喷出结构和侵入反射体.（3）在中生代的古俯冲带弧前区域,新生代的断裂沿着早期的构造开始活动,岩石圈多处发生强烈的共轭韧性剪切作用.随着大陆岩石圈的进一步拉伸减薄,部分靠陆一侧的裂谷中心停止张裂,成为夭折裂谷,以台西南盆地南部凹陷、白云凹陷、西沙海槽为代表,而南海陆缘异常伸展和最终破裂的地方集中在南侧裂谷中心.夭折裂谷下亦发现地幔蛇纹石化,进一步反映了较弱的同破裂岩浆活动.（4）南海初始洋壳的增生沿着大陆边缘走向具有显著的变化,南海东北部洋-陆过渡带下伏地幔明显抬升和部分蛇纹石化,地震纵、横波速度以及折射波衰减特征都支持此观点,反映南海东北部是一个贫岩浆型大陆边缘.未来,南海北部洋-陆过渡带有望成为南海“莫霍钻”的理想备选钻探区. 相似文献
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Seismic imaging of the transitional crust across the northeastern margin of the South China Sea 总被引：23，自引：0，他引：23
Crustal structure across the passive continental margin of the northeastern South China Sea (SCS) is presented based on a deep seismic survey cooperated between Taiwan and China in August 2001. Reflection data collected from a 48-hydrophone streamer and the vertical component of refraction/reflection data recorded at 11 ocean-bottom seismometers along a NW–SE profile are integrated to image the upper (1.6–2.4 km/s), lower (2.5–2.9 km/s), and compacted (3–4.5 km/s) sediment, the upper (4.5–5.5 km/s), middle (5.5–6.5 km/s) and lower (6.5–7.5 km/s) crystalline crust successively. The velocity model shows that the thickness (0.5–3 km) and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the SCS. Furthermore, several volcanoes and igneous rocks in the upper/middle crust (7–10 km thick) and a high velocity layer (0–5 km thick) in the lower crust of the model are identified as the ocean–continent transition (OCT) below the lower slope in the northeastern margin of the SCS. A thin continent NW of the OCT and a thick oceanic crust SE of the OCT in the continental margin of the northeastern SCS are also imaged, but these transitional crusts cannot be classified as the OCT due to their crustal thickness and the limited amount of the volcano, the magma and the high velocity layer. The extended continent, next to the gravity low and a sag zone extended from the SW Taiwan Basin, may have resulted from subduction of the Eurasian Plate beneath the Manila Trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the SCS. 相似文献
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Age, thermal evolution and history of the Black Sea Basin based on heat flow and multichannel reflection data 总被引：2，自引：0，他引：2
A. Ya. Golmshtok L. P. Zonenshain A. A. Terekhov R. V. Shainurov 《Tectonophysics》1992,210(3-4):273-293
Multichannel reflection data (Tugolessov et al., 1985) have revealed two deeps in the basement topography of the Black Sea which are filled with sediments from 12 to 15 km thick. The deeps lack the “granitic layer” and are underlain by oceanic-type crust which we assume to be generated by seafloor spreading processes. The age of the deeps was interpreted previously, in a highly controversial manner, as being from the Paleozoic — Early Mesozoic to the Recent. In the paper, age estimations were undertaken using surficial heat flow data, assuming that they are related to deep-seated age-dependent heat flow generated by the cooling oceanic lithosphere, but that they are strongly distorted by the heating of continuously accumulating sediments as well as by additional heat input from radiogenic production within sediments. Using reliable thermophysical parameters of compacting sediments, the distorted heat flow in the sediments was evaluated numerically. This allowed us to estimate the age of the Black Sea deeps floor. The results show that the West Black Sea deep is 130 to 95 m.y. old, and the East Black Sea deep is nearly 110 m.y. old. These figures support an interpretation of the Black Sea deeps as remnants of a Late Mesozoic back-arc basin that evolved behind the Lesser Caucasian — Pontide island arc. The inferred Middle Cretaceous age of the deeps is the first estimate obtained quantitatively, and corresponds well with available heat flow and multichannel reflection data. 相似文献
12.
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。 相似文献
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南海张裂过程及其对晚中生代以来东南亚构造的启示——IODP建议书735-Full介绍 总被引：2，自引：1，他引：1
李春峰 汪品先 Dieter Franke 李家彪 许树坤 Peter Michael 周祖翼 翦知湣 李前裕 刘志飞 耿建华 木村学 阎贫 丘学林 王嘹亮 解习农 吴时国 吴能友 《地球科学进展》2009,24(12):1339-1351
南海的形成揭示了大陆边缘张裂和盆地形成的复杂模式,尽管已经进行了广泛研究,但是关于基底岩石和深海盆沉积层的精确年代数据还很缺乏,这使得对南海张裂年代的估计存在很大的误差,对张裂机制和历史的各种假设没有得到验证.同时只有对南海的张裂过程有了精确地分析与刻画,才能更好地理解西太平洋边缘海盆地的形成以及它们在印支块体受印度-欧亚板块碰撞而向东南挤出、青藏高原隆升中可能起到的作用.2009年正式提交的国际综合大洋钻探计划(IODP)建议书735-Full建议在南海深海盆内的4个站位上实施钻探.这4个站位分布在南海盆地4个不同的次级构造单元上(南海东北部、西北次海盆、东部次海盆和西南次海盆),这样的站位设计会确保完成本建议书的整体研究目标,即揭示南海的张裂历史和它对晚中生代以来东南亚构造的启示.位于南海盆地最东北部的站位有助于确定该区域地壳的属性和验证古南海是否存在,位于西北次海盆的站住可能会提供南海的最早张裂年代,另外2个分别位于东部次海盆和西南次海盆的站位将重点确定2个次海盆的绝对年龄、基底矿物成分与磁化率以及2个次海盆的相对张裂次序.这些站位的水深大约在2 910～4 400 m,钻探深度预计到海底以下大约700～2 200 m,总的钻透深度为5 959 m,其中5 359 m穿透沉积层,另外600 m或400 m钻入基底.所有这些站位的位置是由已有的地球物理观测数据所确定,目前计划收集更多的地质与地球物理数据以满足IODP对井位调查数据的要求. 相似文献
14.
There are numerous controversies surrounding the tectonic properties and evolution of the Proto-South China Sea(PSCS).By combining data from previously published works with our geological and paleontological observations of the South China Sea(SCS),we propose that the PSCS should be analyzed within two separate contexts:its paleogeographic location and the history of its oceanic crust.With respect to its paleogeographic location,the tectonic properties of the PSCS vary widely from the Triassic to the mid-Late Cretaceous.In the Triassic,the Paleo-Tethys and the Paleo-Pacific Oceans were the major causes of tectonic changes in the SCS,while the PCSC may have been a remnant sea residing upon Tethys or Paleo-Pacific oceanic crust.In the Jurassic,the Meso-Tethys and the Paleo-Pacific oceans joined,creating a PSCS back-arc basin consisting of Meso-Tethys and/or Paleo-Pacific oceanic crust.From the Early Cretaceous to the midLate Cretaceous,the Paleo-Pacific Ocean was the main tectonic body affecting the SCS;the PSCS may have been a marginal sea or a back-arc basin with Paleo-Pacific oceanic crust.With respect to its oceanic crust,due to the subduction and retreat of the Paleo-Pacific plate in Southeast Asia at the end of the Late Cretaceous,the SCS probably produced new oceanic crust,which allowed the PSCS to formally emerge.At this time,the PSCS was most likely a combination of a new marginal sea and a remnant sea;its oceanic crust,which eventually subducted and became extinct,consisted of both new oceanic crust and remnant oceanic crust from the Paleo-Pacific Ocean.In the present day,the remnant PSCS oceanic crust is located in the southwestern Nansha Trough. 相似文献
16.
Yanghui Zhao Shaoru Yin Jiabiao Li Jie Zhang Hanghang Ding 《International Geology Review》2020,62(7-8):955-969
ABSTRACT The volume of seamounts is an essential indicator of the intensity of mantle convection during the evolution of the oceanic lithosphere. Drilling and dredging samples suggest volcanic seamounts are widely distributed in the oceanic basin of the South China Sea, and most of them were formed after cessation of seafloor spreading. By using an SRTM15_PLUS Digital Elevation Model with a 15-arc-second grid, we developed a spatial filtering method based on the Top Hat Transform to extract seamounts. With a combined analysis of basalt dating results from previous studies and gravity anomaly data, an accurate estimation of seamount volume and its spatiotemporal distribution have been obtained. In addition to an asymmetric distribution of the seamounts with a larger volume in the northern flank, clusters of seamounts can be observed at certain locations in the abyssal plain. Due to the consistency between the distribution of the seamount volume and the seafloor spreading features in the South China Sea basin, we propose the ridge jump may induce additional partial melting zones which account for the larger number of seamounts developed in the northern flank while the re-orientation of the extension during seafloor spreading dominated the distribution of post-spreading magmatism. Similar to other marginal basins, magmas formed by spontaneous partial melting would migrate through weak lithosphere where the extension direction changed, resulting in post-spreading magmatism in those lithospheric weak zones. 相似文献
17.
运用丰富的二维地震资料,通过构造结构与地层结构的分析,对礼乐盆地的盆地结构演化与转型过程及其对南海地区复杂动力学背景的响应特征进行研究。结果表明:受控于NNE、NEE、NW和近EW向的断裂体系,礼乐盆地现今构造格局表现为"两坳一隆"的结构特征;两个关键的区域角度不整合T70和T50将礼乐盆地新生界自下而上划分为三层结构:陆缘裂陷层、漂移裂陷层和前陆-拗陷层;响应于太平洋板块俯冲、印度-欧亚板块碰撞、新南海扩张、古南海消亡和菲律宾海板块楔入等一系列周缘板块重组事件,礼乐盆地的盆地结构演化及转型经历了三个阶段:陆缘多幕裂陷阶段,盆地结构受控于NNE和NEE向断裂体系,南北坳陷连通;漂移裂陷阶段,NNE和NW向共轭断裂体系控制盆地格局,中部隆起形成,分隔南、北坳陷;前陆-拗陷阶段,前陆盆地结构形成,随后盆地因热沉降进入拗陷沉积阶段。 相似文献
18.
西太平洋典型边缘海盆的岩浆活动 总被引：1，自引：0，他引：1
在发育有全球最大、最复杂的弧—沟—盆体系的西太平洋地区,集中了全球75％左右的边缘海盆(弧后盆地).根据磁异常条带年龄,这些边缘海盆可粗略分为3个扩张幕.主要根据DS-DP,ODP和IODP计划实施以来所获得的成果,结合其他海洋调查航次研究成果,系统阐述了分属3个扩张幕的西菲律宾海盆(第一扩张幕)、南海—四国海盆(第二扩张幕)和冲绳海槽(第三扩张幕)—马里亚纳海槽内的岩浆活动特点.西菲律宾海盆(扩张时代为65～35 Ma BP)从原先的赤道位置迁移至现今的位置,其内存在如似正常洋中脊玄武岩(NMORB)、洋岛玄武岩(OIB)及弧火山岩等多种岩石类型,其地球动力学背景分别与弧后扩张、地幔柱及火山弧等背景有关,其复杂的构造演化样式需要进一步研究;四国海盆(扩张时代为27 ～ 15 Ma BP)是由古伊豆—小笠原—马里亚纳弧(IBM)裂解形成的,其内除发育正常(N)—富集(E)的洋中脊玄武岩(NMORB-EMORB)外,还在扩张停止的同时出现了板内火山作用,形成了中K-超K碱性玄武岩.四国海盆的扩张模式并没有从岩石学和地质年代学角度进行明确制约,板内火山作用的地球动力学背景也不甚清楚.南海(扩张时代为32～15.5 MaBP)是由来自华南地块的一些微陆块向东南裂离后的海底扩张所形成,并在海底扩张后2 ～8 Ma出现板内火山作用,截止目前,并没有获取到洋壳基底样品,主要获取到了南海海山似OIB的玄武岩,未来需要从岩石学和地质年代学角度对南海海底扩张动力学和时代以及扩张期后的板内火山作用动力学背景进行进一步制约.马里亚纳海槽(扩张时代为5 Ma BP至今)为一年青的洋内弧后盆地,其北段处于裂解增进阶段,其内出露有似MORB(中南段)及介于似MORB与似岛弧岩石之间过渡类型的玄武岩(增进端);虽然在扩张时代上与马里亚纳海槽相当,但冲绳海槽(扩张时代为4 Ma BP至今)为一陆缘、初生弧后盆地,从西南往东北方向,不同区段处于不同的伸展发育阶段,西南段出露有似MORB岩石,中段岩石主要为玄武质岩石和流纹质岩石组成双峰组合,而东北段为中酸性火山岩.正在活动的马里亚纳海槽与冲绳海槽的岩浆作用研究应和其伴随的火山岛弧及其相邻的海沟处正在俯冲的洋壳板块结合起来,完整理解板块俯冲输入(subduction input)与弧及弧后输出(volcanic output)之间的关系,这将为揭示西太平洋地区构造演化提供重要证据.即将在西太平洋地区实施的IODP 349 ～ 352航次,为我国科学家提供了研究西太平洋地区构造演化的契机. 相似文献
19.
Satellite Gravity Anomalies and Their Correlation with the Major Tectonic Features in the South China Sea 总被引：4，自引：0，他引：4
The South China Sea (SCS) is a region of interaction among three major plates: the Pacific, Indo-Australian and Eurasian. The collision of the Indian subcontinent with the Eurasian plate in the northwest, back-arc spreading at the center, and subduction beneath the Philippine plate along Manila trench in the east and the collision along Palawan trough in the south have produced complex tectonic features within and along the SCS. This investigation examines the satellite-derived gravity anomalies of the SCS and compares them with major tectonic features of the area. A map of Bouguer gravity anomaly is derived in conjunction with available seafloor topography to investigate the crustal structure. The residual isostatic gravity anomaly is calculated assuming that the Cenozoic sedimentary load is isostatically compensated. The features in the gravity anomalies in general correlate remarkably well with the major geological features, including offsets in the seafloor spreading segments, major faults, basins, seamounts and other manifestations of magmatism and volcanism on the seafloor. They also correlate with the presumed location of continental-oceanic crust boundary. The region underlain by oceanic crust in the central part of the SCS is characterized by a large positive Bouguer gravity anomaly (220–330 mgal) as well as large free-air and residual isostatic anomalies. There are, however, important differences among spreading segments. For example, in terms of free-air gravity anomaly, the southwest section of mid-ocean has an approximately 50 km wide belt of gravity low superimposed on a broad high of 45 mgal running NW–SE, whereas there are no similar features in other spreading segments. There are indications that gravity anomalies may represent lateral variation in upper crustal density structure. For instance, free air and isostatic anomalies show large positive anomalies in the east of the Namconson basin, which coincide with areas of dense volcanic material known from seismic surveys. The Red River Fault system are clearly identified in the satellite gravity anomalies, including three major faults, Songchay Fault in the southwest, Songlo Fault in the Northeast and Central Fault in the center of the basin. They are elongated in NW–SE direction between 20±30'N and 17°N and reach to Vietnam Scarp Fault around 16°30'N. It is also defined that the crustal density in the south side of the Central Basin is denser than that in the north side of the Central Basin. 相似文献
20.
为了探讨南海西缘结合带的构造贯通性, 在系统分析其地质-地球物理资料的基础上, 剖析了该带的分段性和深-浅部构造几何学特征, 对该带的哀牢山-红河-越东-万纳-卢帕尔各段进行了全面的构造几何学及构造运动学上的对比分析, 提出该带是一条相互贯通的走滑断裂系统, 其各部分在构造几何学上符合走滑构造的基本构架, 构造运动学上具有同时性, 浅部各段具有共同相连的深部的"根", 表现出明显的时空上的贯通性与构造上的一致性. 相似文献