苏北箕状断陷形成的动力学机制

苏北盆地由多个小型箕状盆地组成,过去一直用“拉线作用”和“裂谷盆地”理论解释其成因,但大量地震资料显示,新生界地层“楔状实体”的形成除沉积因素外,更主要的是因为多次不均衡抬升削蚀所造成,实际是一个早第三纪残留盆地。新生代构造现象既是中生代时期构造作用的延续,也是始新世以来复杂应力环境作用的结果。印支－燕山中期,中国东部只受到太平洋－库拉板块一种力源作用,地层形变强烈,受力方向单一,以NW,NWW向挤压或左行剪切为主,发育了大量逆冲推覆构造,始新世,由印度板块向欧亚大陆冲撞引发的NE向挤压力加入到本区,使苏北盆地从此处在因两大板块非均速推进而产生的二元交变动力环境：印度板块力源占主导时,产生“右旋扭动”力偶,使燕山早－中期逆断层复活反转的同时,由于中国西部大陆的不断抬升,本区总的以沉积作用为主,而太洋板块力源占主导时又产生“左行剪切挤压”,在整体抬升基础上,斜坡－凸起处的过多蚀进一步加强了箕状盆地结构。两种力源的时空交替实际形成了一个完整的“断－坳－隆”沉降－抬升构造旋回,利用裂变途径迹资料探讨了不同方向构的形成年代。

Dynamic Mechanism of Formation of Dustpan Subsidence, Northern Jiangsu

Subei Basin is composed of several small subbasin shaped like dustpan. Many authors had previously explained the origin of Subei Basin on the theory of pull apart basin or rifting basin. However, seismic information suggests that wedges of the Palaeogene strata formed mainly through imbalance uplifting and erosion beside the sedimentary reason. In fact, Subei Basin is a residual basin in the Palaeogene period.The tectonic phenomena happened in the Cenozoic are caused by both of the continuity of the Mesozoic tectonic processes and the complexity of Cenozoic stress field. During the end of Indosinian to middle Yanshan movement, eastern China was only effected by Pacific-Kula plate, then the strata were deformed strongly, and with the single direction of stress field,bearing the NW NWW compression direction or the left lateral shearing,lots of thrust nappe tectonics were formed in eastern China. Since the Eocene the compression force caused by collision of India Plate to Eurasia has been added to this region, Subei Basin is in alternative variable dualstic dynamic environment because of different move velocity for two plates.As the force source from India plate dominated, the force couple of right lateral twist emerged and led to the reverse faults of early middle Yanshan period to be reacted and reversed. The sedimentation dominated in this region, while the raising dominated in western continental of China. But as the force source from Pacific Plate dominated, the couple force of left lateral transpression appeared,then the whole uplifting of the basin occured, the slope and heave underwent erosion so that the dustpan structure got enhanced. Alternation of two force sources on the time and space completed a whole "fault subsidence depression uplift", i.e. the sedimentary erosion tectonic cycle.