南海北部大陆边缘洋陆过渡带构造研究
文献类型：学位论文
| 作者 | 高金尉1
|
| 学位类别 | 博士 |
| 答辩日期 | 2015-05-18 |
| 授予单位 | 中国科学院大学 |
| 授予地点 | 北京 |
| 导师 | 吴时国 |
| 关键词 | 南海 洋陆过渡带 多道地震反射剖面 重震联合反演 张裂 |
| 其他题名 | The continent-ocean transition zone at the northern margin of the South China Sea |
| 学位专业 | 海洋地质 |
| 中文摘要 | 相比于典型的被动大陆边缘的特征，南海北部陆缘具有特殊的构造和地层特征。这种差异可归因于由欧亚板块、菲律宾海板块和印澳板块相互作用引起的南海多幕构造运动和岩浆活动。基于多条穿过南海北部陆缘高质量的深反射多道地震剖面和最新的卫星重力数据，本文分析了南海北部陆缘洋陆过渡带内的构造、岩浆活动和深部反射特征，以研究南海北部陆缘的张裂类型和伸展机制。 研究区的构造演化明显可分为裂陷期和拗陷期两大阶段。在晚渐新世期间，整个南海北部陆缘都发生裂陷期的延迟现象，其表现是部分构造单元内的沉积速率未显著减小甚至有所增加和早中新世生物礁和浅水碳酸盐岩台地的发育。岩浆活动始终贯穿南海形成演化的过程中，南海北部陆缘强烈的火山活动发生于海底扩张末期或海底扩张停止以后。相比西北缘陆坡微弱的岩浆活动，与其相邻的西北次海盆、夭折裂谷以及西沙、中沙海区的岩浆活动却非常强烈，其主活动期为裂陷期（29.3-23.3Ma）。 南海北部陆缘洋陆过渡带向陆一侧边界位于陆架坡折或上陆坡向下陆坡转折处，向海一侧一般以围限前缘掀斜断块的向海倾的铲状正断层为界与洋壳区分，而局部地区（如西段Line07剖面）则以火山为界与洋壳区分，总体上呈NE-SW向展布，其范围由东向西逐渐收窄。洋陆过渡带在陆缘东段以受岩浆混染的裂陷期断陷和火山带（埋藏火山带）为特征，其范围超过200km；在中段一般以裂陷期断陷、受铲式正断层围限的构造低凸起和向海倾的掀斜断块带为特征，向西则以裂陷期断陷、受岩浆活动影响的构造低凸起、火山带和向海倾的掀斜断块带为特征，范围在220-265km之间；至陆缘西段，其范围收窄至69km左右，以裂陷期断陷为特征。 重震联合反演结果表明，南海北部陆缘下地壳高速层厚度在下陆坡之下厚达0.8-5km，而在东沙隆起附近地壳之下其厚度达到了6-10km，之后向两侧逐渐减薄，向西消失于白云凹陷之下，向东随过渡壳俯冲于吕宋岛弧之下。下地壳高速层广泛展布于南海北部陆缘东半部分的陆架和陆坡，这表明其范围与洋陆过渡带的范围并不重合，也意味着下地壳高速层并不是南海北部陆缘洋陆过渡带的必要标志。而陆架-陆坡区的火成岩和下地壳高速层的起源可能与被动上涌的软流圈的减压熔融有关，这种减压熔融作用导致了裂后期岩浆底侵和对地壳的侵位。 相比于两端元类型的岩浆匮乏型被动大陆边缘和火山型被动大陆边缘，南海北部陆缘是一个中间过渡的张裂模式，而且该模式更接近于岩浆匮乏型被动大陆边缘的特征。通过对南海南北共轭陆缘进行特征对比发现，南海北部陆缘洋陆过渡带大型控凹断层极为发育，而南部陆缘洋陆过渡带铲状断层可归并于主滑脱面或莫霍面上，这种构造差异现象可能是由南海新生代演化过程中地壳的随深度变化的差异伸展造成的，而导致这种差异伸展的深源机制很可能就是地幔岩石圈的破裂要早于陆壳。 |
| 英文摘要 | The northern margin of the South China Sea (SCS) has particular structural and stratigraphic characteristics that are somewhat different from those described in typical passive margin models. The differences are attributable to poly-phase tectonic movements and magmatic activity resulting from the interaction among the Eurasian, Philippine Sea and Indo-Australian plates. Based on several high quality crustal-scale multi-channel seismic reflection profiles and latest satellite gravity data across the northern SCS margin, this paper analyses the structures, igneous rock and deep crust of the continent-ocean transition zone (COT) at the northern margin of the SCS to study the patterns and model of extension there. The structural evolution of the northern margin of the SCS can be divided into the rifting and post-rifting stages obviously. During the Late Oligocene, continued high or even higher deposition rate in some depressions, Early Miocene organic reef and shallow water platform carbonates indicated a delay of rifting in the whole northern margin. Magmatic activities have occurred across the northern margin during the evolution of the SCS, and the volcanic activities intensely happened at/after the end of seafloor spreading. Compared with the very weak magmatic activities occurred in the slope of the northwestern margin of the SCS, the intruded/extruded magma, which chiefly happened in the 29.3-23.3Ma, was well developed in the Northwest sub-sea basin, aborted rift, Xisha, and Zhongsha area to the south. The results indicate that the COT is limited landward by basin-bounding faults near break in slope or between the upper slope and lower slope and is often bounded by seaward-dipping normal faults near the oceanic basin, whereas it is bounded by volcano in some area (e.g. Line07 seismic profile of the west segment). Generally, the COT extended from NE to SW with a gradually shallowing from east to west. The shallow anatomy of the COT at the northeastern margin with an extent in excess of 200-km is characterized by rift depression infected by magma and volcanic zone. And it is characterized by rift depression, structural highs bounded by listric normal faults and/or a zone of tilted faults blocks, whereas it is marked by rift depressions, a structural high affected by lava flow, a volcanic zone and a zone of tilted faults blocks instead to the west in the mid-northern margin with a width of 220-265-km. Further to the west, the shallow anatomy of the COT at the northwestern margin with a narrower width of 69-km is characterized by rift depression only. Gravity modeling revealed that a high velocity layer (HVL), with a 0.8-5-km thickness, is frequently present in the lower slope below the lower crust, and can be up to 6-10km below the crust of the Dongsha area, and then gradually thins to both sides below the lower slope and finally terminates at the Baiyun sag and subducts below the Luzon islands with the transitional crust. Our study shows that the HVL is widely located in the shelf and slope of the eastern portion of the northern SCS margin based on the available geophysical data, indicating that it is distributed essentially within the COT but is clearly not present everywhere in the COT. Thus, the HVL should not be considered as a necessary sign of the COT at the northern margin of the SCS. The magmatic rock located in the shelf and slope and HVL may be related to partial melting caused by the decompression of a passive, upwelling asthenosphere, which resulted primarily in post-rifting underplating and magmatic emplacement or modification of the crust. Compared with the typical magma-poor margins and volcanic margins, we propose that an intermediate mode of rifting was active in the mid-northern margin of the SCS with characteristics that are closer to those of the magma-poor margins than those of volcanic margins. Moreover, compared with the characteristics of the SCS conjugate passive margins, the large basin-bounding faults are well developed in the COT of the northern margin whereas the listric normal faults may merge into a main detachment fault in the deep crust or even the Moho in the COT of the southern margin. This structural difference may be controlled by the depth dependent lithospheric differential extensional deformation during the Cenozoic evolution of the SCS, which may result from the rifting mechanism of mantle lithosphere break-up before continental crust. |
| 学科主题 | 海洋地质与环境 |
| 语种 | 中文 |
| 源URL | [http://ir.qdio.ac.cn/handle/337002/22781]  |
| 专题 | 海洋研究所_海洋地质与环境重点实验室 |
| 作者单位 | 1.中国科学院海洋研究所 2.中国科学院大学 |
| 推荐引用方式 GB/T 7714 | 高金尉. 南海北部大陆边缘洋陆过渡带构造研究[D]. 北京. 中国科学院大学. 2015. |
入库方式： OAI收割
来源：海洋研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。