郯庐断裂中段新生代右行走滑位移

Cenozoic Dextral Strike-Slip Displacement of the Middle Tan-Lu Fault Zone

依据走滑拉分盆地中盆地沉降(或抬升)速率与边界断层走滑速率之间的数值关系,通过对夹在郯庐断裂中段两分支断层间的潍北凹陷沉积埋藏史的恢复,间接求取郯庐断裂中段新生代右行走滑位移。潍北凹陷内不同构造位置4口井的埋藏史恢复结果表明:凹陷新生代经历了古近纪早、中期的快速沉降,古近纪末-新近纪初的抬升剥蚀和中新世以来的缓慢沉降3个阶段;各阶段的平均沉降速率分别为0.142 9、-0.072 8、0.032 5km/Ma。通过对太平洋板块与欧亚板块间俯冲速率和方向变化的分析推断,中新世中期(39.5Ma)太平洋板块由北西向俯冲转而变成正西向俯冲所产生的西南向应力分量是导致新生代郯庐断裂开始右行走滑的主要因素,且走滑活动持续至今。根据走滑活动发生和持续的时间,结合各个时期内潍北凹陷的沉降和抬升速率,计算出郯庐断裂中段新生代右行走滑位移量为15km左右。

According to the numerical relationship between subsidence（or uplifting） rate and boundary fault strike-slip rate in pull-apart basin,the Cenozoic dextral strike-slip displacement of the middle portion of the Tan-Lu fault zone is indirectly calculated by restoring subsidence history of the Weibei sag which is bounded by the two branch faults of the Tan-Lu fault zone.The subsidence history restoration of four wells located at different structural units shows the sag experienced Early to Middle Paleogene fast subsidence,Late Paleogene uplifting and Neogene to present thermal subsidence,and their averaged subsidence rate are 0.142 9 km/Ma,-0.072 8 km/Ma and 0.032 5 km/Ma respectively.Based on the analysis of the direction and velocity variation of the Pacific-Eurasia subduction,it is inferred the southwestward component of the westward compression stress between Pacific and Eurasia plate might be the main trigger for the dextral strike-slip movement of the Tan-Lu fault zone when the subduction direction changed from northwest to west at Middle Eocene（39.5 Ma）.Given the strike-slip movement started at Middle Eocene and sustained to the present time,jointly considered with the subsidence and uplifting rate of the Weibei sag,the Cenozoic dextral strike-slip displacement of the middle Tan-Lu fault zone is calculated to be about 15 km.