EXTENSIONAL AND COMPRESSIVE RATIOS AND TECTONIC EVOLUTION OF THE XIHU AND DIAOBEI SAGS
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摘要: 东海陆架盆地位于欧亚板块的东南边缘,具有东西分带、南北分块的格局,其中东部坳陷带包括福江凹陷、西湖凹陷和钓北凹陷。选择西湖凹陷11条、钓北凹陷2条地震剖面,采用平衡剖面技术,计算了西湖凹陷和钓北凹陷新生代不同演化阶段的伸缩率。伸缩率的分析表明,T50-T34西湖凹陷和钓北凹陷处于伸展状态,T34-T12西湖凹陷处于压缩状态,T34-T30、T30-T12钓北凹陷分别处于压缩、伸展状态,T12至今西湖凹陷和钓北凹陷区域沉降。始新世中期西湖凹陷进入挤压期,玉泉运动(T30)、花港运动(T20)和龙井运动(T12)3次挤压的强度不断加剧。结合盆地充填结构分析,钓北凹陷新生代经历了早中始新世地堑式断陷、晚始新世和渐新世坳陷、早中中新世断陷和晚中新世至今整体沉降的4个演化阶段;西湖凹陷新生代经历了古新世和早中始新世断陷、晚始新世和渐新世坳陷、早中中新世反转和晚中新世至今整体沉降的4个演化阶段。西湖凹陷和钓北凹陷构造演化有很大不同,这是东海陆架盆地南北分块的重要依据。Abstract: The East China Sea Shelf Basin lies in the southeast margin of the Eurasian Plate. It is characterized by the feature of east-west zonation and north-south blocking. The east belt of the depression includes the Fujiang Sag, Diaobei Sag and Xihu Sag. This paper selected 11 balanced cross-sections from the Xihu Sag and 2 from the Diaobei Sag. The extensional and compressive ratios of the Xihu and Diaobei sags in Cenozoic were calculated by using the technique of balanced cross-sections. The results showed that both the Xihu and Diaobei Sags were in a stretched state in T50-T34. However, they were different in other stages, for instance, the Xihu Sag was in a compressed state in T34-T12, while the Diaobei Sag in a compressed state in T34-T30 and in a stretched state in T30-T12. Both of them started subsiding since T12. The Xihu Sag had remained in compress since middle Eocene. The three tectonic movements:Yuquan (T30), Huagang (T20) and Longjing (T12), intensified the compression. Together with the history of basin filling, the Diaobei Sag could be divided into four evolutionary stages since Eocene:early-middle Eocene graben-type rifting, late Eocene and Oligocene depression, early-middle Miocene rifting and subsidence since late Miocene. Similarly, The Xihu Sag has also experienced four stages of evolution since Paleocene:Paleocene and early-middle Eocene rifting, late Eocene and Oligocene depression, early-middle Miocene reversion and subsidence since late Miocene. The Xihu and Diaobei sags are very different in terms of tectonic evolution that is the reason of the north-south zonation in the East China Sea Shelf Basin.
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