【作者】 雷超；

【导师】 任建业； S. Willett；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2012， 博士

【摘要】 莺歌海-琼东南盆地位于南海西北部,是NW向大型红河走滑断裂带与NE向南海北部陆缘构造带的交会部位,莺歌海和琼东南盆地二者夹持的东北部区域是海南岛隆升剥露区,出露大面积花岗岩和玄武岩,琼东南盆地向东延伸通过西沙海槽进入南海的西北次海盆。本论文以大陆边缘盆地动力学理论为指导,以南海走滑伸展型和伸展型陆缘交汇区盆地构造相互作用和形成演化研究为切入点,通过地质、地球物理和低温热年代学的综合分析,结合计算机数值模拟,深入研究莺歌海-琼东南盆地新生代构造变形格局及其构造、沉积演化过程。本研究将有助于深化对莺歌海-琼东南盆地成盆动力学的认识,同时对大陆边缘盆地油气勘探具有重要的指导意义。论文的主要成果如下：1、通过大量的二维地震剖面和新近采集的三维地震资料的地质解释,在莺歌海-琼东南盆地古近纪充填序列中重新追踪、识别了T70层序界面,该界面具有“下削上超”的地震反射结构特征和区域性分布特点,并分隔了同裂陷阶段早期(55-32Ma)孤立的、呈NE向展布的断陷盆地群和同裂陷阶段后期(32-23Ma)规模较大的、呈近东西向展布断坳盆地；区域地层对比和古生物资料定年表明该界面发育的时代为32Ma,与南海海底扩张起始和红河断裂带开始走滑运动的时间基本一致。由此确定了该界面的发育是在红河断裂大规模走滑活动以前,古南海向南俯冲导致南海北部陆缘伸展,岩石圈减薄,最终导致南海洋壳出露事件的响应界面。2、详细的地震剖面构造-地层解释揭示红河断裂带东西两侧盆地具有显著的构造差异。红河断裂西侧是走滑伸展型莺歌海盆地,地震成像揭示出构成盆地中部的临高凸起的层序地层特征,确定临高凸起在15.5Ma发育了反转构造,地震反射界面具有典型的“上削下超”反射特征。盆地构造制图表明,反转构造向南逐渐消失,并转换为发育少量正断层的张扭背景下的深坳陷,而向北追踪显示,河内坳陷发育强烈压扭型反转构造,反转地层年龄在15.5-5.5Ma。因此,同一个时期同一条断裂带表现为NW区段压扭和SE区段张扭的特征,盆地挤压反转(盆地北部)和伸展沉降(盆地南部)之间转变的枢纽点具有逐渐向北迁移规律。而位于红河断裂带东部的琼东南盆地与莺歌海盆地的结构存在明显的差异,琼东南盆地主要发育与伸展相关的构造,全盆可划分为北部隆起区、中央坳陷区和南部隆起区3个一级构造单元,而中央坳陷规模较大,近一步将中央坳陷区划分为北部坳陷带、中央低凸起和南部坳陷带3个二级构造单元,同时,在陵水凹陷东部新识别出NW向地垒式隆起带,以该隆起带为界,琼东南盆地可以划分为西部伸展区和东部伸展区,因此,琼东南盆地显示出“南北分带,东西分块”的平面分布格局。3、在红河断裂带区域资料基础上,结合莺歌海盆地和莺歌海-琼东南盆地结合部地质和地球物理资料,查明了红河断裂在海域,尤其是莺歌海盆地和莺歌海-琼东南盆地的延伸展布特征。在莺歌海盆地红河断裂主要由三条断层组成,莺东、东方和1号断层。莺东和东方断层位于盆地的北部,向南断层规模逐渐减小,在莺歌海坳陷中部消失,随之出现了向南延伸进入莺歌海-琼东南盆地结合部的1号断层,断层截切了琼东南盆地2号等北东向断层,但在莺歌海-琼东南盆地结合部断层规模逐渐减小,以转换带的形式转变成与其倾向相反的中建东断层。对莺歌海盆地和莺歌海-琼东南盆地结合部红河断裂活动性研究后表明,红河断裂走滑活动主要集中在32-5.5Ma之间,而5.5Ma断层活动特征并不明显。莺歌海-琼东南盆地另一重要断层是2号断层,在平面上呈东西向从西往东横跨整个琼东南盆地,但2号断层在莺歌海-琼东南结合部被红河断裂带组成部分1号断层所切割。对2号断裂系统详细的地质构造解释和断裂活动定量计算,认为该断裂系统具有复杂的结构特征,从西到东可以划分为西段、中段和东段3个区段；断层最西段被在莺歌海盆地东南方向延伸的1号断层所切割,但是2号断层西段和中段断层样式类型相同,主要表现为单断式,局部台阶式断裂结构,控制乐东凹陷、陵水凹陷,松南凹陷,东段为右阶斜列式断裂系,控制了宝岛凹陷和长昌凹陷的发育。同时,对盆地断层及其控制的凹陷结构进行系统研究后,总结了盆地主要凹陷类型,可以划分为半地堑、地堑和复式地堑。半地堑可细化分为平直型、铲型、缓坡断阶、陡坡断阶、同阶断裂,地堑可细划分为简单地堑、基底双侧断阶、双侧断阶,复式断阶可以细化分为旋转断块和半地堑-地堑交互断阶。4、通过对盆地全区地震反射剖面的详细解剖,莺歌海盆地底辟构造十分发育,共发育18个具有一定规模的底辟构造,并查明与底辟构造相关的构造主要有气烟囱构造、与底辟相关的断层和古底辟喷口等构造。根据底辟构造的形态特征,可将底辟构造划分为“三类五型”,即深埋型、浅埋型、夭折型、喷口型和塌陷型。通过对红河断裂莺歌海海域断层研究和盆地沉积速率计算,认为莺歌海盆地底辟构造形成主要原因可能是5.5Ma以来盆地基底沉降速率加快,岩石圈的拉伸导致高的地温梯度,驱使盆地深部烃源岩和碳酸盐埋藏加深并热解,释放丰富的气体和流体,同时红河提供的丰富的细粒沉积物,高速堆积在莺歌海坳陷,促使盆地深部超压系统进一步的形成并最终超压系统内泥流沉积物刺穿上覆地层,形成底辟构造。5、本次研究对海南岛低温热年代学数据空白区进行了补充样品并测试,报道了对海南岛岩石样品进行(U-Th-Sm)/He定年测试结果,(U-Th-Sm)/He年龄主要集中在16-35Ma,但年龄数据在25-30Ma较多。同时,对现有所有海南岛低温热年代学数据采用高斯线性反演剥蚀速率的方法,确定了在35Ma以来海南岛不同构造部位隆升剥露速率变化,结果表明海南岛35Ma以来剥蚀速率都较小,在0.05-0.2km/Ma之间,并且通过现今昌化江流域范围,估算了海南岛向莺歌海盆地提供沉积物的速率在0.3-0.4km3/Ma之间,表明海南岛向莺歌海盆地沉积物供给速率较小。6、在详细的地层划分基础上,通过对各个时期莺歌海盆地沉积物量进去压实回剥计算,获得了精度更高的莺歌海盆地各个时期初始沉积时沉积物总体积,并结合海南岛低温热年代学数据反演获得的各个时期海南岛向莺歌海盆地提供的沉积物剥蚀量,估算了莺歌海盆地来自红河的沉积物量,进一步从定量的角度证实了莺歌海盆地主要为来自红河的沉积物充填。并与青藏高原隆升和季风气候变化进行对比,认为长江袭夺红河时间在渐新世-早中新世之间,但最有可能是渐新世；同时,我们注意到盆地5.5Ma以来红河断裂带在莺歌海盆地停止了走滑活动,但盆地沉积物量突然增加,这可能与上新世以来全球气候变化频率增加有关。7、在南海西北次海盆洋脊延伸方向洋陆转换带新采集的二维长电缆深反射地震剖面资料构造-地层分析的基础上,采用挠曲悬臂梁模型和挠曲回剥模型算法,分别计算了上地壳、地壳和整个岩石圈拉伸系数,实验结果表明,研究区洋陆转换带盆地岩石圈发生了与深度相关的拉伸变形过程,并且随深度增加,拉伸量逐渐变大,该结果较好地解释了南海北部盆地自5.5Ma以来发生的盆地加速沉降现象。据此结合南海北部洋陆转换带盆地发育过程的特点,将洋陆转换带盆地演化划分为陆内裂陷阶段、裂后热沉降阶段和裂后加速沉降阶段。8、结合现有文献资料的总结和本次莺歌海-琼东南盆地研究认识,认为红河—越东—Lupar线断裂是东南亚地区的一个重要的构造界线,该界线划分出两个具有显著不同构造特征,经历了不同演化过程的区域构造变形区。在该界线的西侧为经典的印度—亚洲大陆碰撞所产生的挤出—逃逸构造区,而在该界线的东侧主要受古南海俯冲及其所引起的区域构造变形场的控制,为古南海俯冲拖曳构造区。莺歌海盆地位于挤出—逃逸构造区东北侧边界上,其发育机制为印支地块沿红河断裂带大规模挤出,并小幅度顺时针旋转作用控制下发育的一种特殊的、规模最大的盆地类型—走滑—旋转型盆地。琼东南盆地和南海位于古南海俯冲拖曳构造区,它们的发育和演化古南海俯冲所引起的区域拉伸作用的控制,以形成EW向或NE向伸展盆地为主要特征。9、以区域构造事件为背景,分析并讨论了莺歌海-琼东南盆地的构造演化过程,确定了莺歌海-琼东南盆地新生代的演化阶段,可划分为同裂陷阶段(55-23Ma)和裂后热沉降阶段(23-0Ma),同裂陷阶段可划分为断陷幕(55-32Ma)和断坳幕(32-23Ma),裂后热沉降可划分为裂后热沉降幕(23-5.5Ma)和裂后加速沉降幕(5.5-0Ma)。盆地断陷幕为分散的NE向展布的弥散孤立湖盆断陷群,主要受古南海向南俯冲导致南海北部陆缘岩石圈减薄的影响；而自32Ma年以来,红河断裂在印支地块挤出逃逸过程中开始活动,莺歌海-琼东南盆地演化的主控构造因素具有明显差异的构造特征,莺歌海盆地转变为主要受红河走滑断裂构造活动控制,而琼东南盆地的演化仍是古南海持续向南俯冲、南海的扩张和洋脊跃迁起主导控制作用；在盆地裂后热沉降幕时期,莺歌海盆地发育典型的反转构造,并且挤压和伸展之间枢纽点具有从南向北逐渐迁移的特征,而琼东南盆地作为拉伸盆地,形成了受盆地岩石圈热冷却控制的构造地层特征；而5.5Ma以来,莺歌海和琼东南盆地都发生了基底沉降速率突然加快,形成的沉积物可容纳空间汇集了来自红河方向突然增加的沉积物,沉积物可容纳空间的增加可能与岩石圈深度相关的拉伸作用有关。更多还原

【Abstract】 The Yinggehai Basin (YGHB) and Qiongdongnan Basin (QDNB) are in the Northwest corner of the South China Sea positioned at a juncture between a strike-slipping zone and a extensional zone. The basins lie at the southern termination of the largest Tibetan strike-slip zones, the Red River Fault, and are the principal repository of materials eroded from the Red River drainage. The basins are flanked to the East by an oceanic ridge and border the Nansha area to the South, which is being subducted underneath the Borneo Block. Hainan Island, located between the YGHB and QGNB, is composed primarily of granites and basalts. In our study, a combination of geological, geophysical and low-temperature thermochronological methods are used to unravel the basins’history in greater detail. We studied the structure and evolution of the basins and explored the relationships between tectonics, erosion and climate of the peripheral area, which will enrich our knowledge about geodynamics and petroleum geology in Southeast Asia. The highlights of this Ph.D. thesis are shown as follows:1. A key tectonic sequence boundary, T70, was identified in the YGHB and QDNB based on the tectonic-stratigraphy interpretation of a number of available high-resolution seismic datasets. A series of small-scale, NE-SW trending, fault-bounded grabens developed extensively below this boundary. On the contrary, above the T70boundary, the depocenters are trending NE-SW, W-E and SWW-NWW from east to west of the basin. Larger-scale, partly fault-controlled depressions are superimposed clearly over underlying, faulted-bounding grabens on seismic profiles. Analysis of genetic type and geometry of graben-boundary faults, which underlie the T70boundary, indicates that these structures were formed by NW-SE extension. However, above the boundary, the partly fault-controlled depressions extended nearly N-S. We also report that the T70sequence boundary exists in both basins. Dating the sequence boundary by correlation of the regional sequences and biostratigraphical data reveals that it was formed at32Ma, which is consistent with the timing of the initiation of ridge spreading in the South China Sea and onset of sinistral movement along the Red River Fault. Therefore rifting on the northern continental margin of the South China Sea is considered to be a result of proto-South China Sea subduction underneath the Borneo Block. After the initiation of Red River Fault, evolution of the YGHB and QDNB show striking differences, as revealed by our study.2. From tectono-stratigraphical analyses of seismic profiles in the YGHB, we observed that each tectonic unit of the basin had a different deformation history. The Yinggehai Depression, located in the southern part of the basin, is characterized by an extensional lithosphere, thermal cooling and copious mud diapirs. However, on the Lingao Uplift, a very important structure dividing the basin into the Hanoi and Yinggehai Depressions, an inversed sequence boundary was identified on our seismic profiles. We dated the sequence boundary from drill core data at15.5Ma. However, in the Hanoi Depression, the inversed structures formed between15.5and5.5Ma. In our study, we noted that the structures of the QDNB are very different from those of the YGHB. High-quality seismic reflection data enabled us to divide the QDNB into three, first-order structural units, namely Northern Uplift, Central Depression and Southern Uplift. In addition, between Linshui Sag and Songnan Sag we recognized a NW-SE trending grabens and horsts belt, which separates the basin into the Eastern Extension Zone and Western Extension Zone. Moreover, at the junction of YGHB and QDNB, the Zhongjian Uplift, No.1and Zhongjiandong Faults are the main tectonic units in our investigation. At the juncture, the offset of No.1Fault decreases from north to south and gradually disappears, and Zhongjianzhong Fault appears and exhibits an opposite dip direction.3. The Red River Fault system in the Northwest corner of the South China Sea is investigated in detail by combining regional geological data and available seismic profiles. The fault system was interpreted to be composed of three segments:the Yingdong, Dongfang and No.1Fault. In the region of the Lingao Uplift, the Yingdong and Dongfang Faults are typical listric faults. Further south, the two faults disappear and a new fault, No.1Fault, with steeper dip is imaged on the seismic profiles. At the conjunction of YGHB and QDNB, the No.1Fault cut off the No.2Fault of the QDNB and extends southwards. In the middle of the junction zone, the newly described Zhongjiandong Fault with an opposite dip direction than that of the No.l Fault was distinguished on seismic profiles. In addition, we studied the strike-slip Red River Fault system in the YGHB, which has been active during the period of32-5.5Ma. After5.5Ma, no prominent activity is observed in the basin. No.2Fault is the largest-scale fault in the QDNB, streching from west to east. A quantitative, geometric analysis of the No.2Fault system was undertaken in our study and we divided the No.2Fault into three segments. The West and Middle Segment of the No.2Fault are characterized as single fault controlling the evolution of the Ledong, Linshui and Songnan Sags. The East Segment of the No.2Fault was features a dextral oblique fault system, which controls the development of Baodao and Changchang Sags. In addition, the sags in the QDNB can be grouped into half-graben, graben and compound graben types, which can be further divided into ten subtypes.4. In order to better understand how and why the diapirs formed, we compiled regional, high-resolution2D and3D seismic reflection data, as well as drilling data related to diapirs in the YGHB. Eighteen diapirs were identified in our study. The structures of gas chimneys, diapiric faults and palaeo-craters are genetically linked with diapirism. In this thesis, we propose, based on geophysical and geological observations, a three-stage model for diapirism:initiation, emplacement and collapse. During each stage, different diapiric types are described, including buried diapirs, piercing diapirs and collapsed diapirs. In addition, associated with large sediment supply from the Red River and large subsidence rate of YGHB, we suggest that a high paleogeothermal gradient to be the result of crustal thinning. Additionally, large volumes of sediment from the Tibetan plateau delivered by the Red River to the basin, majorly affect diapirism.5. The denudation history of Hainan Island aids in estimating the sediment flux from the island into the surrounding basins. However, the lack of low-temperature thermochronological data from Hainan Island obstructs us from studying the exhumation history in this region. Thus we collected rocks from places with scarce low-temperature thermochronological data. Ages from (U-Th-Sm)/He dating on Apatite range between35-16Ma. More specifically, most ages fall between30-25Ma. We used Gaussian the linear inversion method to study the topographic evolution and erosional history of Hainan Island since35Ma. The results from our numerical modeling show low erosion rates of0.05-0.2km/Ma on Hainan Island. Thus the sediments supplied from Hainan to the YGHB were calculated to be0.3-0.4km3/Ma, which is considered to be a small contribution compared to the total amount of sediments in the YGHB.6. Sedimentation rates within the YGHB are likely to be the most reliable record of changing erosion rates onshore, which in turn is linked to Tibetan Plateau uplift and monsoonal strength in SE Asia. We reconstructed sediment accumulation rates using a seismic framework and a better age control. This permits improved spatiotemporal constraints and enhanced stratigraphic resolution, with13separable stratigraphic units younger than23Ma. Considering the amount of sediments in the YGHB supplied by the Hainan Island, we estimated the sediments supplied by the Red River at different time intervals. Correlation with the event of Tibetan Plateau uplift and monsoon climate, we favor major headwater capture away from the Red River during the period between Oligocene and Middle Miocene, most likely the Oligocene. High rates of sediment accumulation since5.5Ma, even as tectonics appear to have slowed, suggest frequent climatic changes.7. We present one multichannel deep-penetration seismic reflection line collected during the late2000s. A numerical backstripping calculation using2D models of flexural cantilever and sediment decompaction were employed. The results demonstrate different stretching factors for the upper crust, the whole crust and the whole lithosphere, which indicate depth-dependent stretching occurred on the ocean-continent transition zone of the northern margin of the South China Sea. Compared with the faulting on the upper crust, the larger stretching factor of the whole lithosphere has an important effect on the fast subsidence recognized in recent years. In our study, three stages of basin evolution of the ocean-continent transition zone of the South China Sea were established. They are rifted continent stage, post-rifted thermal subsidence stage and post-rifted fast subsidence stage. This bears great significance for the geodynamics of the continental margins and deepwater petroleum exploration in the South China Sea.8. Based on regional tectonic and geophysical data, we support the tectonic model that SE Asia can be divided into a collision-extrusion tectonic province and a proto-South China Sea slab-pull tectonic province. These two tectonic provinces are separated by a transform boundary beginning with the Red River Fault extending southward along the Vietnamese margin and merging with the trench along the Lupar Line. We have further clarified the distinct structures, evolution and dynamic settings of the two tectonic provinces. The collision-extrusion tectonic province is considered to result from crustal shortening associated with the ongoing India-Eurasian collision, whereas the proto-South China Sea slab pull tectonic province was mainly driven by proto-South China Sea subduction toward the Borneo Block. Our focus areas, YGHB and QDNB, are situated along the junction of these two tectonic provinces.9. A new compilation of high-resolution2D seismic profiles tied to wells with biostratigraphic age control was used to better constrain the evolution of the YGHB and QDNB. We divided the Cenozoic evolution of the basins into four episodes, namely fault-controlled grabens episode (55-32Ma), fault-sag grabens episode (32-23Ma), post-rifted thermal subsidence episode (23-5.5Ma) and post-rifted fast subsidence episode (5.5-OMa). We recognized the offshore Red River Fault became active after32Ma. Before the onset of strike-slip, widespread crustal extension occurred across the northern continental margin of the South China Sea. Fault-bounded grabens developed at the bottom of the YGHB and QDNB. We noted the two basins have a very different evolution after32Ma. In the YGHB, fault-bounded grabens are typically overlain by successions deposited in a pull-apart regime dominated by the Red River Fault. After15.5Ma the basin experienced distinct structural inversion. In the Lingao Uplift, a clear unconformity was dated at15.5Ma, while after that time no erosion was documented in the geological and geophysical data. In the Hanoi Depression, a strong erosional unconformity was terminated at5.5Ma. In contrast, in the Yinggehai Depression, there is no evidence for inversion or erosion. A transition from extension to compression migrating from south to north between15.5and5.5Ma, known as zipper tectonism, indicates a reversal of slip sense along the Red River Fault. However, QDNB was interpreted as a typical extensional basin. The evolution of the QDNB before32Ma was similar to that of the YGHB. During the period of32-23Ma, the QDNB was controlled by lithospheric thermal cooling and faulting. Between23-5.5Ma, the basin was completely controlled by the lithospheric thermal cooling. The last tectonic episode was a fast subsidence event starting after5.5Ma.更多还原