渤海湾盆地济阳坳陷新生代裂后不整合、加速沉降事件及其成因浅析  

Cenozoic post-rift unconformity and the accelerated subsidence events of the Jiyang Depression,Bohai Bay Basin and preliminary analyses on their original mechanism

作　　者：郭兴伟[1] 施小斌[1] 丘学林[1] 吴智平[2] 杨小秋[1] 

机构地区：[1]中国科学院边缘海地质重点实验室 [2]石油大学地球资源与信息学院,山东东营257061

出　　处：《地球物理学报》2007年第2期455-464,共10页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(40676041;40204006);国家973项目(G2000046701);中国科学院南海海洋研究所与广州地球化学研究所边缘海地质重点实验室基金项目(MSGL0511);广东省自然科学基金(5300970)资助

摘　　要：为了考察渤海湾盆地济阳坳陷新生代裂后不整合及加速沉降事件并探讨其成因机制,利用悬臂梁模型和二维挠曲回剥模型的正反演模拟,对济阳坳陷2条NS向剖面新生代的构造演化进行了重建.正演计算表明,要反映14Ma的盆地结构,需要叠加断陷阶段及裂后不整合时期发生的构造抬升事件,叠加的构造抬升量在坳陷东北部比西南部大;反演计算表明,要恢复到14Ma的盆地结构,按照断层估算的拉张系数产生的热沉降不足以恢复当时的古水深,如果要通过人为增加构造沉降以恢复到14Ma的古水深,那么坳陷东北部比西南部需要更大的沉降量.结果说明,济阳坳陷在新生代发育时,除了水平伸展产生的岩石圈被动减薄外,可能还叠加了垂向因素引起的岩石圈主动减薄;14Ma以来发生的裂后加速沉降有从坳陷东北部向西南部推进的趋势.分析表明除了水平伸展诱发软流圈热扰动及随后快速热衰减外,岩石圈拆层作用、岩石圈地幔交代作用等主动因素,也会产生裂后不整合及加速沉降事件.To investigate the events of post-rift unconformity and accelerated subsidence in the Cenozoic Jiyang Depression, Bohai Bay Basin, and discuss on their original mechanism, a forward model of flexural cantilever model and a reverse model of 2-D flexural backstripping model were employed to rebuild the Cenozoic tectonic evolution of two seismic lines trending in NS in the Jiyang Depression, The forward modeling showed that, to rebuild the geometrical structures of the two lines at 14 Ma, uplift events that produced sgn-rift and post-rift unconformities should be included in the model, and the uplift amplitude in the northeast is higher than in the southwest. While the reverse modeling showed that the amount of the thermal subsidence, based on the stretching factors deduced from the faults. is not enough to restore the paleo-bathymetry at 14 Ma. Excess subsidence should be added ,and the amplitude of the excess subsidence in the northeast should be larger than in the southwest. The results suggest that during the development of the Jiyang Depression. The lithosphere might be thinned not only passively by horizontal extension. but also thinned actively by some vertical factors. and the accelerated subsidence since 14 Ma has a trend of propagating from the northeast to the southwest. The analyses also indicate that ,in addition to the passive factor of horizontal extension, by which the asthenosphere was perturbed thermally and then experienced quick thermal decay, some other active factors, such as lithosphere delamination and mantle lithosphere metasomatism, can be candidate mechanism for the post-rift unconformity and the accelerated subsidence.

关 键 词：渤海湾盆地 济阳坳陷 悬臂梁模型 挠曲回剥 裂后不整合 加速沉降 数值模拟 

分 类 号：P314[天文地球—固体地球物理学]