中南-礼乐断裂发育特征及其发育机制

Zhongnan-Liyue Fault (ZLF) recorded important information about the multi-period spreading and the transform of magnetic anomalies in South China Sea (SCS) and coordinated the magnetic anomalies difference among the northwest, east and southwest sub-basins and their relative motion. Consequently, ZLF played a key role during the Tectonic evolution of SCS. Up to now, there are still debates about the location, direction and fault feature of the ZLF, due to the poor qualities of seismic profile and anomalies of gravity and magnetic. And there are seldom discusses about the developmental stages and mechanism of ZLF. But basing on the recent high precision data of seismic , gravity and magnetic anomalies, we found that the internal deformation characters of the ZLF shows a north-south segmentation, and its width and trending are also different from north to south..Therefore, this application will systematically analysis the internal deformation, spatial distribution, fault properties and its developmental stages of ZLF basing on the whole basing most high accuracy seismic, gravity and magnetic and multi beam topography data. And then the development mechanism of the ZLF in the South China Sea will be revealed by analogue modeling and debate its impact during the multi- period seafloor spreading. That will help us to understand the spreading mechanism of SCS and its tectonic evolution history, also contribute to a better understanding of the conjugate development characteristics in the northern and southern of SCS.

中南-礼乐断裂是协调西北次海盆与东部次海盆北部、西南次海盆与东部次海盆之间的磁异常差异及相对运动的大断裂。它记录了南海海盆多期次扩张及磁异常发生分叉转折的重要信息，在南海形成演化的动力学机制中起了关键性作用。由于海盆调查程度低，重、磁、震资料质量欠佳，导致对该断裂的具体位置、走向、长度及性质等认识，至今仍有分歧，且甚少讨论其发育时期及机制。申请者基于最新的高精度地震及重磁资料，发现该断裂内部变形呈现南北分段性，宽度和走向也有差异。因此，本申请拟基于覆盖全海盆最新高精度地震、重磁及多波束地形地貌等资料，系统地剖析和确定中南-礼乐断裂内部构造变形、空间展布、断裂性质及发育时期；然后利用物理模拟方法，研究该断裂的发育机制，探讨其在南海多期次扩张过程中所起的影响。这将有利于我们清楚地认识南海扩张方式及其构造演化史，也有助于更好地认识南海南北陆缘共轭发育特点。

中南-礼乐断裂带是协调西北次海盆与东部次海盆、西南次海盆与东部次海盆之间相对运动的大断裂，在南海形成演化中起了关键作用。本申请基于南海海盆最新地震、重、磁及地形等资料，系统剖析了中南-礼乐断裂带的时空间展布特征、断裂性质及深部结构；然后利用物理数值模拟方法，研究了该断裂的发育机制。同时，研究了南海海盆洋中脊断裂带和中沙地块南部断裂带的时空展布及其发育机制。结果表明：（1）中南-礼乐断裂带在海盆中由北至南具有明显的分段性。北段（西北次海盆与东部次海盆北部之间）断裂带宽15km，由经纬度18°N,115.5°E向17.5°N,116°E呈NNW向分布。南段（西南次海盆与东部次海盆之间）断裂带宽约60~80km，由中沙地块东侧向礼乐地块西侧呈NNW向展布。该断裂发育于晚渐新世至中中新世，上新世停止发育。断裂早期为转换断裂，后期叠加走滑。断裂带对其东西两侧次海盆的地质构造具有控制作用，推测该断裂带至少是一条地壳级断裂。断裂带的发育机制受控于海盆不同的运动速率及先存软弱带的控制。（2）中沙地块南部陆缘构造属性为非火山型被动大陆边缘：地壳性质从西北向东南由减薄陆壳向洋陆过渡壳再向正常洋壳变化。中沙地块南部发育4组阶梯状向海倾的深大正断裂，主要发育时期为晚渐新世到中中新世。断裂早期发育与南海东部次海盆近NS向扩张有关，后期遭受挤压变形、与菲律宾海板块向南海的NWW向仰冲有关。（3）南海海盆洋中脊断裂带分为西南次海盆段和东部次海盆段，断裂带的走向与洋中脊的走向近平行，分布在洋中脊两侧，为正断层。该断裂带在东部次海盆呈近EW走向，在西南次海盆呈近NE走向，主要发育于晚渐新世到中中新世时期，晚中新世以后为继承性活动。该断裂带的发育机制受控于东部次海盆的近EW向和西南次海盆NE向扩张作用。上述研究有利于清楚地认识南海扩张方式及其构造演化史，也有助于更好地认识南海南北陆缘共轭发育特点。