Structural Features And Evolution History Of The Dunhua–Mishan Fault Zone

The NE-striking Dunhua–Mishan Fault Zone has a length of ca.1000 km and a width of ca.10 km,which is one of two branches of the continental-scale,sinistral Tan–Lu Fault Zone in NE China.This important fault zone can provide insights into the MesozoicCenozoic tectonic evolution in northeastern China.However,both origin and evolution of the Dunhua–Mishan Fault Zone remains controversial as a result of tis long-term,complicated tectonic activities.Detailed field investigations and lab analysis indicate that the first movement?D₁? formed a series of NE–SW-striking ductile shear belts within the Dunhua–Mishan Fault Zone.These shear belts have steeply dipping foliations and gently dipping mineral elongation lineations.Both outcrop structures and microstructures provide evidence of sinistral motion within these shear belts which were generated by regional N–S compression.Microstructures and quartz c-axis fabrics of mylonites from the shear belts suggest deformation temperatures of 450–500 °C for the D₁ ductile shear belts.Combining a series of zircon U–Pb dates for deformed and undeformed igneous rocks in the shear belts with the geology of this region indicates that this phase of sinistral faulting formed during the earliest Early Cretaceous.It is suggested therefore that the Dunhua–Mishan Fault Zone originated in the earliest Early Cretaceous rather than the Triassic or Jurassic proposed before.It is this phase of sinistral displacement that made the Tan–Lu Fault Zone extended into NE China.The Dunhua–Mishan Fault Zone subsequently underwent an intense extensional event ?D₂? that produced many NE–SW-striking normal brittle faults and controlled the development of the Early Cretaceous rift basins during the rest of the Early Cretaceous.The fault-slip data demonstrate that this phase of regional extensional direction was NW–SE.Following the Early Cretaceous extension,the Dunhua–Mishan Fault Zone became the site of sinistral faulting?D₃? again.This phase of sinistral brittle faults cross-cut and have slightly different kinematics to the earlier ductile shear belts ?D₁? and also affect Early Cretaceous sediments.Some of sinistral faults reactivated the D₂ normal faults.The faultslip data indicate that the D₃ sinistral faulting took place under a tectonic regime of regional N–S compression.Combining our new zircon U–Pb data with previous results of zircon dating on rocks that pre-and post-date the D₃ faulting indicates that this event occurred between 102 and 96 Ma,most likely at the very beginning of the Late Cretaceous.The Dunhua–Mishan Fault Zone changed to the site of rifting and controlled the development of the rift basins during the Late Cretaceous ?D₄? and the Paleogene ?D₅? respectively.The fault zone was active as dextral normal faulting and became boundary faults of the rift basins during the two phases of extensional events.The two events mainly formed nearly E–W-striking normal faults inside of the basins that show features of a transtensional graben or half-graben during each period of the development of the basins.The fault-slip data show that both stress states of the two phases of rifting were nearly N–S extension.The unconformity between the Upper Cretaceous and Paleogene sediments in these basins recorded an inversion event and hiatus in deposition at the ends of the Late Cretaceous.The obtained U–Pb ages,?Hf?t?values,and two-stage model ages of zircons demonstrate that the Liaoyuan Accretionary Belt is present to the east of the Dunhua–Mishan Fault Zone.Comparison of the boundaries between the Liaoyuan Accretionary Belt and North China Craton on the both sides of the Dunhua–Mishan Fault Zone constrains a 170 km sinistral displacement along the fault zone.Considering the 35 km sinistral displacement along the Yilan–Yitong Fault Zone,as determined before,it is demonstrated that the northern segment of the Tan–Lu Fault Zone in NE China produced a 205 km sinistral offset of the northern boundaries of the North China Craton.Regional correlation indicates that the five-phases evolution history of the Cretaceous–Paleogene recorded in the Dunhua–Mishan Fault Zone resulted from regional dynamic action.The Cretaceous–Paleogene in the back-arc region of the active continental margin is characterized by the alternating compressional and extensional events that were driven by the subduction of the Paleo-Pacific plate.It is the alternation of subduction ways of the oceanic plate that resulted in alternating compressional and extensional events at the continental margin and the resultant polyphase evolution of the Dunhua–Mishan Fault Zone.