南海的破裂不整合与各次海盆的海底初始扩张年代

Initiation ages of sea-floor spreading in different subbasins of the South China Sea represent the central challenges of the ‘South China Sea Deep’ research. Characteristics of breakup unconformities of different margin types have been the subject of increasingly intense study of the evolution of continental margins. This research attempts to: (1) establish the regionally chronological framework, using regional seismic profiles tied to borehole data from the ocean drilling and hydrocarbon exploration and a comprehension study of different types of continental margins along the Atlantic ocean, to; (2) recognize breakup unconformities based on architectural styles and spatial-temporal distribution patterns of regionally important unconformities, which are obtained by zone-by-zone analysis from the outer, distal, necking domains to the proximal domain; (3) investigate the lateral variations in the intensities of breakup unconformities in each tectonic domain along the depositional strike of the continental margins; (4) reveal ages and spatial-temporal evolution patterns of breakup unconformities in the South China Sea; (5) identify the chronological relationships between the continent and the ocean, on the basis of the chronological comparison between breakup unconformities and adjacent upper bounding surfaces of the oceanic crust; (6) reveal ages and spatial-temporal evolution models of breakup unconformities recognized in the South China Sea, based on the recognition of characteristics of lateral variations in the intensities of breakup unconformities and their associated spreading versus non-spreading zones; (7) infer the seafloor spreading process based on analyzing the onlaping patterns atop the oceanic crust; and (8) establish spatial-temporal evolution models of seafloor spreading and breakup unconformities in a magma-poor marginal sea with slowly spreading anomalies (South China Sea).

南海各次海盆的初始扩张年代是南海深部过程研究中最具挑战性的问题，不同类型大陆边缘的破裂不整合特点及其与海底初始扩张时期的关系是当前国际上大陆边缘演化研究中的前缘热点问题。拟结合对大西洋两岸不同类型陆缘的类比分析，利用南海的区域地震剖面和大洋、石油钻孔资料建立区域等时地层格架。从外部域、远端域、缩颈域向近端域逐带分析区域不整合的结构特征及纵向变化规律，识别出破裂不整合。在各构造域平行大陆边缘方向分析破裂不整合强度的横向变化特征，揭示南海破裂不整合的时代及时空演化规律。将各破裂不整合与最近的洋陆边界的洋壳顶面进行等时对比，确定二者之间的年代对应关系。根据各破裂不整合强度的横向变化特征识别出与其对应的主扩张区和非扩张区，根据洋壳顶面超覆分析确定海底扩张方式，进而揭示南海破裂不整合和各次海盆初始扩张事件的时代及时空演化规律，建立边缘海贫岩浆慢速扩张陆缘型的南海扩张及破裂不整合时空演化模式，

对南海与大西洋两岸和红海-亚丁湾的典型富岩浆型和贫岩浆型被动陆缘进行对比分析，明确了不论是富岩浆型还是贫岩浆型，其破裂不整合的形成时期都大致与岩石圈完全破裂、大洋初始扩张的时期相对应，在不同构造域破裂不整合具有不同的表现形式，不都是“断陷-拗陷转换面”。.利用近万公里区域地震剖面，及十余口大洋钻井和部分石油探井资料，建立起从南海洋盆及陆缘统一的区域等时地层格架，完成了南海的破裂不整合识别对比和构造域划分，揭示了破裂不整合平行陆缘在相同构造域中形成时代的差异，及其垂直陆缘在各构造域中的结构特征和形成时代的变化规律。.利用地震资料对中南-礼乐转换断层的展布进行了厘定。指出以其为界，其东侧的东部次海盆共轭陆缘在近端域和颈缩域破裂不整合为T7（32Ma），而在陆缘隆起域、耦合域则发育T7和T6（23Ma）“双破裂不整合”。此外还发现在早期扩张洋壳之上发育有T6破裂不整合，其下为半地堑，为慢速扩张的显著标志。23Ma洋中脊跃迁使其抬升遭受剥蚀。而在中南-礼乐断裂以西的西南次海盆共轭陆缘及西部陆缘则只发育T6破裂不整合。T6分布最为广泛，是南海作为统一洋盆扩张的产物。.提出根据洋壳上覆地层超覆分析来确定洋壳年代进而恢复海底扩张历史的方法。据此在北部洋陆转换带的U1500至U1503间发现T6与洋壳反射面之间发育有600米以上半地堑沉积，经与外緣隆起上的U1501对比认定其中间有T7，并据沉积速率推测洋壳年龄可能在40Ma上下。这意味着南海初始扩张的时代有可能在晚始新世。.此外分别刻画了渐新世和中新世的南海海盆的洋陆边界和古洋中脊的空间展布。揭示了南海洋盆纵向跃迁、横向渐进式扩张的演化历史。.深入分析了南海洋盆演化对南海周缘发育“双破裂不整合”以及破裂不整合时代东西差异、南北差异的控制机理，建立了边缘海贫岩浆慢速扩张陆缘的破裂不整合时空演化模式，为揭示南海扩张演化历史提出基于地层沉积响应方面的证据。