郯庐断裂带安徽浮山段晚第四纪以来活动新发现

A NEW DISCOVERY OF ACTIVITY OF FUSHAN SECTION OF THE TAN-LU FAULT ZONE IN THE LATE QUATERNARY

郯庐断裂带淮河以南段第四纪地层分布不均,断层新活动研究存在一定的困难。在苏皖交界地区多次实地踏勘发现,淮河南侧的安徽浮山段断层发育于NNE向条形岗地的边缘,对第四纪地层和地貌仍有一定的控制作用。在浮山段开挖的三塘探槽、浮山南剖面等均显示,断层错断了晚第四纪地层,表明该段断裂晚更新世以来仍存在较强的活动。综合地层年代样品测试结果,浮山段断层最新活动时代可达全新世早期,最近1次古地震事件发生在(10.6±0.8)^(7.6±0.5)ka BP之间。探槽及剖面揭露的断层表现为正右旋滑动特征,这或是断层所在区域局部构造应力场复杂性的表现。

The east branch fault of Tan-Lu fault zone extends from Fengshan Town of Sihong County on the north shore of the Huaihe River in Jiangsu Province,into Fushan Town of Mingguang City on the south shore of Huaihe River in Anhui Province. The landform changes from Subei plain on the north of Huaihe River to Zhangbaling uplift area on the south of Huaihe River. The terrain rises gradually with larger relief amplitude. The Fushan section of the Tan-Lu fault zone is located in Ziyang to Fushan area of Mingguang City. The fault is shown in the satellite image as a clear linear image,and the fault extends along the east side of a NNE-trending hillock. In this section the Quaternary strata are unevenly distributed,which causes some difficulties in the study of recent fault activity.In recent years,the author has found that the fault of the Fushan section of the Tan-Lu fault zone on the south of the Huaihe River still has a certain control effect on the landform and the Quaternary strata. Based on satellite imagery and geological data,we select the appropriate location in the Fushan section to excavate the Santang trench Tc1 and Fushannan trench Tc2,and clean up the Fushannan profile Pm,which reveals rich phenomena of recent fault activity. Santang trench reveals three faults,and the faulting phenomenon is obvious. One of the faults shows the characteristic of right-lateral strike-slip normal faulting; Fushannan profile reveals one fault,with the same faulting behavior of right-lateral strike-slip normal fault. Comprehensive stratigraphic sample dating results indicate that the fault dislocated the middle Pleistocene strata,late Quaternary strata and early Holocene strata. All our work shows that the fault of Fushan section has intensive activity since late Pleistocene,and the latest active age can reach early Holocene. The latest earthquake occurred at( 10. 6 ± 0. 8) ^( 7. 6 ±0. 5) ka BP. The faults exposed by trenches and profiles show the characteristics of right-lateral strike-slip normal faulting,which reflects the complexity of the tectonic stress field in the area where the fault locates.