依兰‒伊通断裂带晚中生代走滑与伸展构造变形及其应力场

Late Mesozoic Strike-slip and Extensional Structural Deformation and Stress Field in the Yilan-Yitong Fault Zone

NE走向、延伸超过900km的依兰‒伊通断裂带是中国东北地区重要的大型断裂构造。然而关于该断裂带起源型式、伸展变形特征以及初始断陷时间长期以来存在较大分歧。本文对依兰‒伊通断裂带起源期和伸展构造变形规律、变形时间以及应力场特征进行了详细的野外调查、火山岩锆石U-Pb定年以及断层擦痕位移矢量反演研究。结果表明,依兰‒伊通断裂带在尚志隆起以及白垩纪‒古近纪地堑外侧保存着左行走滑断层或韧性剪切带,代表了其起源期构造。根据前人研究成果及未变形火山岩的年龄(125 Ma),限定起源时间为晚侏罗世初‒早白垩世初。早白垩世中期之前依兰‒伊通断裂带转变为伸展变形,南段控制发育的叶赫地堑具有典型的断陷盆地特征。在出露的花岗岩基底及地堑内下白垩统均可见一期NE走向正断层发育。应力场反演结果表明,依兰‒伊通断裂带起源期左行走滑活动是在近S-N向(偏NNW向)的挤压应力场作用下发育,晚期又叠加了NW-SE向的拉张应力场作用,导致该断裂带转为正断活动。本文认为太平洋区伊泽奈崎板块早白垩世初向东亚大陆下平板俯冲,随后俯冲板片后撤导致强烈的弧后伸展,是依兰‒伊通断裂带晚中生代左行走滑与伸展活动的动力学成因。

The ca.900 km leng NE-striking Yilan-Yitong Fault Zone is an important fault zone in Northeastern China,and controlled the development of a petroliferous graben with a large length-width ratio.However,the original pattern,extensional deformation characteristics,and initial rifting time of this fault zone are still controversial.In this paper,we report detailed field investigation,zircon U-Pb dating results of the volcanic rocks,and inversion of fault-slip data on the first-stage and extensional deformation characteristics,deformation time and stress field of the Yilan-Yitong Fault Zone.The results show that the first-stage structures in the Yilan-Yitong Fault Zone include the sinistral strike-slip faults or ductile shear zones in the Shangzhi uplift and outsides of the Cretaceous-Paleogene grabens.Combining the previous research results and the age of undeformed volcanic rock in this paper,the first-stage motion time is limited to the Early of the Late Jurassic to the Early of the Early Cretaceous.The Yilan-Yitong Fault Zone developed into extensional deformation before the Middle of the Early Cretaceous.The Yehe Graben controlled by the southern segment has typical characteristics of a rifted basin.A phase of NE-striking normal faulting can be observed in the exposed granitic basements and the Lower Cretaceous of the Yehe Graben.The inversion results of the paleo-stress field show that the sinistral strike-slip motion of the Yilan-Yitong Fault Zone was produced by the nearly N-S compression.And then it was superimposed with the NW-SE extensional stress field in the late period,leading to the normal motion of the fault zone and the formation of the Early Cretaceous grabens.The rapid,low-angle,oblique subduction relative to the eastern Asian and the subsequent retreat of the Izanagi Plate were the dynamic cause of the sinistral strike-slip and normal motion of the Yilan-Yitong Fault Zone in the Late Mesozoic,respectively.