南海东部海盆的张裂特征及扩张方式研究

IOCAS-IR > 海洋环流与波动重点实验室

	南海东部海盆的张裂特征及扩张方式研究
	李家彪
学位类型	博士
	2001
学位授予单位	中国科学院海洋研究所
学位授予地点	中国科学院海洋研究所
学位专业	海洋地质
关键词	构造地貌张裂特征扩张方式构造演化
摘要	构造地貌分析，结合地震剖面和磁异常对比已成为研究年轻海底扩张机制和构造演化的重要手段。利用南海东部海盆首次获取的多波束高分辨率全覆盖数据，进行构造地貌特征分析，通过张裂特征断面研究、条带磁异常识别和构造应力场分析，提出了东部海盆的扩张方式和成因模式，重建了南海海盆新生代多期次、多方向扩张的构造演化历史。东部海盆存在三组走向不同的北东向线性构造带，自中脊海山链向南、北两侧对称分布于约350km宽的中央区内，是张性深大断裂、基底断块和线性火山基底隆起在海底的反映。这三组构造带分别对应海盆三个扩张期：条带磁异常6a-6c (24-21Ma)、5e-6a (21-19Ma)和5d-5e (5c) (19-16Ma)。东部海盆扩张方式具有不稳定性、脉动式、分段性及不对称的特点。各扩张期内，线性构造走向呈连续变化，而各扩张期之间线性构造走向则均有3°-5°跃变，反映扩张方向存在渐变和突变的演化特点；与扩张同期的北西向平移断裂表现为转换断层，空间分布上呈由东向西逐步加密的特征，各段间北东向线性构造走向变化较大，反映扩张轴纵向延伸的分段性和不稳定性；在21Ma（磁异常序列6a）前后，存在一次重要的海底扩张增速事件，增速幅度达40%，从早期的30.54 km/Ma增加到晚期的42.88 km/Ma，对应基底断裂、沉积作用和火山活动等张裂特征的跃变：扩张速率普遍东部大于西部、南侧明显大于北侧，导致海盆扩张具有东宽西窄的特点，具有较强的不对称性。东部海盆识别出的大量线性火山岩带平行于扩张轴，主要分布在火山基底隆起和基底断块边界断裂上，强度北侧大于南侧，是扩张过程中海底持续经受张裂作用的产物，说明海盆的北西-南东向扩张是受构造张裂型扩张机制的控制，具有大西洋慢扩张型的构造特征。据此并结合海盆扩张方式和构造、沉积特征所提出的东部海盆不对称构造扩张成因机制模式，很好地说明了中脊两侧张裂构造密度、岩浆活动强度和海底扩张方式的差异。这种代表慢速扩张的不对称构造成因机制在中脊附近较大范围内出现断块活动和基底拆离构造，并诱导岩浆沿断裂再次侵位和喷溢，从而在西南海盆因岩浆再侵位而使条带磁异常复杂化，在东部海盆因断裂、岩浆活动形成了一系列线性火山岩带和不规则沉积中心。南海海盆断面特征研究表明，南海海盆东部和西部具有不同的张裂机制，东部以海底扩张为主，西部以地壳减薄和裂离为主。东部在海底扩张的过程中，早期活动主要集中在南海海盆北部，晚期活动主要表现在黄岩海山链南北约350km范围内的中央区，而西部的裂离作用导致了中沙—西沙地块、南沙地块与北京大陆边缘的分裂和西南海盆海底扩张的形成。南沙地块进一步向南迁移最终在中中新世晚期与南巴拉望和沙巴—沙捞越地块碰撞、团结，从而结束了南海海盆的大规模扩张的历史。自32Ma以来，南海东部海盆主要经历三个构造演化阶段：32-27Ma期间的近南北向扩张，24-16Ma期间的北西—南东向扩张，并进一步可分为三个亚扩张期，以及中中新世（15Ma）后海盆沿北西西向马尼拉海沟的倾斜俯冲。
其他摘要	Morpho-structural analysis, with its contrasting of seismic and magnetic data, has become one of important tools in the researches for the spreading mechanism and tectonic evolution of young seafloor. Making using of the full coverage multibeam data received from the East Basin of South China Sea (SCS) for the first time, through analyses of their morpho-structural characteristics, studies of the geotransect rifting patterns of SCS basin, contrast of the magnetic lineation and tectonic stress fields, the spreading mechanism of the Eastern Basin has been provided and the Cenozoic tectonic evolution history of the SCS Basin has been reconstructed. There existed three NE-trending linear structural zones, which are distributed symmetrically in the 350 km region of both sides from the ridge axis (central seamount chains) in the Eastern Basin, are the morphological representatives of the basement structures and correspond respectively to three spreading stages: 6a-6c(24-2 1Ma), 5e-6a(21-19Ma) and 5d-5e(5c)(19-16Ma). The seafloor spreading of the Eastern Basin has the characteristics of unstability, pulsation, subsection and asymmetry: the directions of spreading change continuously in zones and jump 3-5 degree between zones, spreading speed rapidly increase from 30.54 km/Ma to 42.88 km/Ma at 21Ma (6a). It is found that large amount of NE-trending linear volcanic zones, which parallel to ridge axis, are mainly distributed in the faults of basement uplift zones and basement blocks. The structural analyses of these zones with contrasting of the reflection seismic profiles, magnetic lineation anomaly and morphological zones show that the spreading mechanism is mainly controlled by tectonic rather than magma process, and the passive southward migration of spreading center and strong activities of basement detachment are main reason of structural asymmetry. Studies of the geotransect's characteristics of the SCS Basin show that the eastern part and western part of SCS Basin have different tectonic mechanism: the eastern part is mainly controlled by the seafloor spreading, and the west part mainly controlled by the crustal breaking-up and southward rifting. Such crustal breaking-up of the western part between Macclesfield Bank-Paracel Islands block and Spratley Islands block is so great that it leads to the spreading of the Southwestern Basin. From 32Ma, the Eastern Basin of SCS mainly went through three periods: rifting and spreading in S-N direction in period of 32-27Ma and in NW-SE direction in period of 24-16Ma which can be divided into three sub-stages, and after Middle Miocene (15Ma), the SCS Basin subducted obliquely into the Manila trench in the NWW direction.
页数	86
语种	中文
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/1101
专题	海洋环流与波动重点实验室
推荐引用方式 GB/T 7714	李家彪. 南海东部海盆的张裂特征及扩张方式研究[D]. 中国科学院海洋研究所. 中国科学院海洋研究所,2001.

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