郯庐断裂带北段的起源型式、时间与动力学背景研究

The Tan-Lu fault zone is the largest major fault zone in eastern China and an important window for understanding geodynamic processes in eastern China since Mesozoic. Origination of the northern segment of the Tan-Lu fault zone north of Shenyang is poorly investigated and remains controversial, restricting correct understanding for origination and displacement history of the whole Tan-Lu fault zone. In order to understand the origination mode, the first phase of structures of the Yilan-Yitong fault, the main fault in the northern segemnt, will be chosen for studies on their geometry, kinematics as well as deformation environment and methods. Ar-Ar dating of minerals from the shear zone mylonites and zircon U-Pb dating on Mesozoic plutons and dykes in the fault will be conducted for constraining its origination time. On the bases of the above studies and regional correlation, origination geodynamic setting and formation mechanism of the fault will be analyzed. The results will be used for testing previous views and models for the Tan-Lu fault zone obtained from studies in the middle and southern segments, which can help for further understanding about origination and displacement history of the whole fault zone. This project is also helpful for further understanding Mesozoic geodynamic processes in northeastern China, and can provide important information for further understanding continental geodynamic.

郯庐断裂带是中国东部规模最大的巨型断裂带，是认识中国东部中生代以来动力学作用过程的重要窗口。关于郯庐断裂带北段（沈阳以北）的起源，长期以来研究程度不高，认识上分歧较大，制约了对整个断裂带起源与平移历史的正确认识。本项目选择作为北段主干的依兰-伊通断裂第一期构造为研究对象，系统研究其几何学特征、运动学规律及变形环境与方式,以此确定其起源型式。通过剪切带糜棱岩内单矿物的Ar-Ar定年及其内中生代岩体与岩脉的锆石微区U-Pb定年限定其起源时间。在此基础上，通过区域对比，分析郯庐断裂带北段起源的动力学背景，明确其形成机制。将应用该项目的研究成果，检验依据郯庐断裂带中、南段研究所获得的已有认识与模式，进而完善对整个郯庐断裂带起源与平移历史的认识。该项目还将有助于加深对东北地区中生代动力学作用过程的认识，为深入理解大陆动力学提供重要的信息。

郯庐断裂带北段包括西支的依兰—伊通断裂带和东支的敦化—密山断裂带。关于郯庐断裂带北段的起源与演化，长期以来研究程度不高，认识上分歧较大，制约了对整个断裂带起源与平移历史的正确认识。本项目选择郯庐断裂带北段的依兰—伊通断裂带和敦化—密山断裂带为研究对象，通过构造与年代学研究，查明两者的起源、演化与平移距离。研究结果表明，这两条大型北东走向的断裂带皆起源于早白垩世初，起源时的活动方式为左行平移，起源期构造目前出露为走滑韧性剪切带，起源的动力为古太平洋板块低角度高速斜向俯冲作用。继早白垩世期间的伸展活动与断陷盆地发育，敦化—密山断裂带在早白垩世末再次发生了左行平移活动，目前以脆性平移断层型式存在。依兰—伊通断裂带在古近纪期间也转变为伸展活动，控制发育了依兰—伊通地堑。这一长度巨大的地堑形成于区域上南北向拉张作用中，属于斜向拉张或张扭性盆地，利用早期走滑断裂而形成。详细的研究表明，依兰—伊通断裂带左行平移距离为35 km，敦化—密山断裂带左行平移距离开为170 km，两者共同造成了华北克拉通北界205 km的左行平移。对比分析表明，郯庐断裂带南段起源于中三叠世，至早白垩初才在左行平移活动中扩展进展东北地区。该项目成果，完善了对整个郯庐断裂带起源与平移历史的认识，有助于加深对东北地区中生代动力学作用过程的理解。