【作者】 尚继宏；

【导师】 李家彪；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质， 2008， 博士

【摘要】 多波束全覆盖高分辨率海底地形地貌数据与高清晰地震剖面的联合解释,结合其他地球物理资料,可极大地提高海底构造分析的分辨率和立体解析能力,在研究海底区域构造上具有独特的优势,尤其对年轻海底构造和活动构造,近年来已经成为研究洋中脊、俯冲带、边缘海盆地构造和形成机制的重要手段。马尼拉海沟俯冲带作为正在活动的年轻构造带,是南海海盆重要的东部俯冲边界,对其构造及演化的研究是对南海构造演化研究中极为关键的部分。而南海作为西太平洋最大的边缘海盆之一,对其研究的深化与细化,又是了解整个东亚大陆边缘构造乃至整个西太边缘海成盆机制的关键。本论文基于对马尼拉海沟中段与北段多次调查所获取高精度精细多波束海底地形地貌资料与多条地震剖面资料,结合台西南海域已知数据的钻井资料及其它所搜集到的地球物理数据,对海沟中段及北段的俯冲带构造特点进行了深入的分析与对比。论文对马尼拉俯冲带的平面构造特征及深部三维构造特点进行了重点剖析,结合南海东部海盆张裂演化史、西菲律宾海盆运动史、台湾弧陆碰撞造山历史等,最终对马尼拉俯冲带中段及北段的地貌形态、构造成因及其形成、演化历史等进行了广泛的讨论,并获得了多项有益的研究成果,主要有以下几个方面:1.对马尼拉海沟俯冲带中段及北段的增生楔地形地貌进行了精细构造特征分析与对比,揭示了两处俯冲带的平面分带特征与深部分层特点,发现在俯冲带增生楔下构造带中普遍发育有圈闭盆地。通过对圈闭盆地的外在形态、所处位置、形成过程的构造地貌分析,确定了圈闭盆地的形成、发展、与消亡对应了增生楔的前端褶皱变形、中部逆冲断裂以及顶端推覆隆升这一构造动力学过程,同时也反映了增生楔从变形前缘到海脊构造区横向压应力不断增强的特征,代表了一种新型的增生楔发育模式。而这种圈闭盆地在俯冲带中、北两段均有发现,说明它是俯冲带区域增生楔发育的一种较为普遍的模式;2.构造地貌图上发现的俯冲带北段增生楔构造地貌中的NE至NNE向压性断裂带、向北逐渐加宽的增生楔构造带、增生楔顶部超厚沉积及大范围隆起等,均证明21°N附近的台湾南部海域是马尼拉俯冲活动与台湾造山运动共同作用区,同时具有洋壳俯冲与弧陆碰撞的特点。由于北段俯冲带受到台湾造山作用的影响,俯冲活动在地表的界限发生了很大的改变,变形前锋在马尼拉海沟消失后顺澎湖峡谷NW向延伸,在陆架区折向NE,并最终在台南附近上陆并与台湾西部山麓带相连。弧前盆地顺北吕宋海槽向北延伸,穿越台东海槽后与台湾陆上的台东纵谷相接。而作为俯冲带增生楔一部分的恒春海脊,同时也是台湾造山带的南延,同时具有俯冲带的逆冲推覆构造特点与造山带的碰撞隆升特点;3.马尼拉海沟中段及北段的地表形态及其延伸方向具有很大的不同:海沟在北段台西南海域沟底呈“V”字形下切,且蜿蜒状延伸直至隐没消失,而在吕宋岛西侧的中段则呈现出平坦顺直的地表形态。经分析,海沟中段地表形态主要受深部俯冲构造活动控制,而北段海沟受到台湾弧陆碰撞及中国大陆边缘超厚沉积影响,海沟深部俯冲控制作用相对减小,而受陆坡附近富含陆缘沉积物的海底浊流影响较大,在形态上显示出和中段完全不同的地貌特征;4.经地震、钻井等多种资料推断,马尼拉俯冲带形成于16Ma左右的中中新世初期。覆盖马尼拉海沟北段的多道地震剖面在南海北部陆缘区经过了台湾石油公司已知数据的钻井A-1B井,而相邻的几口钻井更是为地震剖面层序的标定提供了可供对比的资料。将陆缘区的地震层序向台西南海域进行延伸后,发现俯冲拆离面为中中新统/下中新统交界面,证明俯冲活动开始最早不会超过在中中新世初期。而地质构造资料证明,作为俯冲增生楔的恒春海脊形成年代在中中新世左右,由此对俯冲带的形成时间进行约束,推断出马尼拉俯冲带形成于16Ma左右的中中新世初期; 5.联系周边地体的演化历史进行综合分析后,推断马尼拉海沟俯冲带形成动力来源于菲律宾海板块的北西向运动,而与南海东部海盆的扩张没有直接因果联系。更多还原

【Abstract】 Associative interpretation by all-covered high-resolution multi-beam topographical & geomorphic maps and high-definition seismic profiles with other geophysical data can promote resolution and stereo analytical capacities of submarine tectonics extremely. This method has special predominance in regional submarine tectonic research especially to young submarine tectonics and active submarine tectonics, and has been an important method in studying tectonics and formation mechanism of mid-ocean ridges, subducting belts and marginal basins. As an active young subducting belt, eastern Manila Subducting Belt (MSB) is one of the most important margins of South China Sea (SCS). Tectonic and evolutionary study to it is the key point in study to SCS. While as one of the biggest marginal basins of west Pacific, deepening and refining to the study of SCS is the key to understand the tectonic of East Asia continental margin and the formation mechanism of whole west Pacific basins.Based on high-resolution multi-beam topographical & geomorphic maps and multiple seismic profiles at middle and northern part of Manila Trench acquired by multi-time investigations, combining with data-known boreholes and other collected geophysical data of southwest Taiwan area, we analyzed and contrast the diving tectonic features deeply to the middle and northern part of Manila Trench. We placed focus on planar tectonic characteristics and deep 3D-tectonic features of the subducting belt, integrating with evolutionary histories of surrounding terrains such as rifting history of eastern sub-basin of SCS, kinetic history of West Philippine Sea crust and orogenic history of Taiwan arc-continent collision, and discussed extensively to the geomorphic appearance, tectonic origin, the formation and evolutionary history of middle and northern part of MSB at last. Multiple dominant research products had been obtained as followed:1. We analyzed and contrasted the delicate tectonic features of accretionary wedges at middle & northern part of MSB, disclosed the planar zonal features and deep layered characteristics of two regions, and found that the trapped basins were developed extensively in Lower Tectonic Zone of accretionary wedge. After morphostructure analysis to the tectonic appearance, emerging place and formation process of the trapped basins, we confirmed that the formation, development and extinction of trapped basins are corresponding to the tectonic dynamic process of front fold and deformation, mid thrust and break, top nappe and uplift of accretionary wedge respectively. It also reflected the feature of strengthened horizontal compression stress of accretionary wedge from deformation front to Ridge Tectonic Zone, and represented a new developing pattern of accretionary wedge. The trapped basins could be found both at northern part and middle part of MSB which demonstrate that it represents a widespread developing method of accretionary wedge at subducting belt;2. The NE to NNE compressive fracture zone, accretionary wedge tectonic belt widening to north, super-thick and large extent uplift at top wedge area, which were found on morphostructure map of northern part of MSB proved that the sea area at South Taiwan near 21°N is the interaction area between Manila subducting activity and Taiwan orogenic movement where it has characteristics both of ocean crust subduction and arc-continent collision. Because of the influence of Taiwan Orogenic activity to the northern part of MSB, the surficial bound of subducting activity had changed greatly. The deformation front extend NW along Penghu Canyon after the disappearance of Manila Trench, turned NE on Chinese continental shelf area, and connected to the western piedmont belt of Taiwan after getting on land at south of Tainan city. The fore-arc basin extended along North Luzon Trough and connected to Taitung Longitudinal Valley after crossing the Taitung Trough. As a part of accretionary wedge of MSB, Hengchun Ridge is also the extended area of Taiwan Orogen. It is characterized by the features of both thrust and nappe of subducting belt and collision and uplift of Orogen; 3. The surficial appearance and extended direction of northern and middle part of Manila Trench have great differences. The trench shows“V”-shape down-cut appearance in southwestern Taiwan sea area and extends meanderingly until its disappearance. But at the middle part of northwest Luzon Island, it shows flat and regular straight appearance. By analysis, we confirmed that the middle part of trench is controlled by deep subducting activity while northern part is influenced by Taiwan arc-continent collision and the sedimentation of Chinese continental margin. Therefore, northern part of the trench is influenced mostly by bottom turbidity current with abundant marginal sediments and less influenced by deep subducting activity. Thus it shows entirely different appearance against middle part.4. Deduced by seismic, borehole and other information, we are certain that Manila Subducting Belt formed at about 16Ma, that is, early stage of mid-Miocene. The multi-channel seismic profile crossing northern part of Manila trench passed by the“A-1B”borehole drilled by Taiwan Petroleum Corporation in slope area of northern SCS margin which the detailed strata information is known. Other adjacent boreholes can provide reference information for the strata determination to the seismic profile. Extending the stratigraphic sequence to the southwest area of Taiwan from continental margin, we found the detaching surface of the subducting belt is the interface between mid-Miocene and low-Miocene. This indicates that the subducting activity started not early than mid-Miocene. As the cretionary wedge of subducting belt, we know by geological tectonic information, the Hengchun ridge was formed at about mid-Miocene, so we deduced that the Manila subducting belt is formed at about early stage of mid-Miocene (16Ma) after constraint to its formation time by above information.5. The dynamic force of MSB formation is originated from NW movement of Philippine Sea Plate but has no straight causal relation with the spreading of eastern sub-basin of SCS.更多还原