Influence of multi-trend major fault reactivation during multiphase rifting: Beier Depression, Hailar Basin, NE China

Complex fault patterns associated with rift development in the Hailar Basin were largely influenced by the Mongolia-Okhotsk Ocean and Palaeo-Pacific tectonic regimes during the Late Jurassic to Early Cretaceous periods. Based on 3D seismic data from the Beier Depression in the Hailar Basin, we characterized the reactivation history of multi-trend major faults and examined the evolution of the Beier Depression during the Early Cretaceous period. NE-SW-, NW-SE- and ENE-WSW-oriented major faults originated from strike-slip-associated structures that were pre-existing fabrics and then were reactivated and propagated upward under extensional regimes in the Late Jurassic. During the syn-rift stage (K(1)t-K(1)n), the Hailar Basin was in a NNW-SSE- to NW-SE-oriented extensional setting, and major faults of all orientations were active. There was tectonic quiescence (K(1)n(1) (L)) between the syn-rift stages (a rifting transition stage). The short compression stage after the syn-rift stage caused regional compressional deformation. During the post-rift stage (K(1)d-K(1)y), the extension direction rotated to an E-W orientation, and a new population of N-S-trending faults formed together with the reactivation of NE-SW- and ENE-WSW-trending major faults. Structural analysis shows that the major ENE-WSW-trending major faults were polycyclic growth faults reactivated via an upward propagation mode and that the NE-SW-trending faults were dip linkage faults reactivated via a dip linkage mode. The reactivation intensity of the NE-SW-trending major faults was stronger than that of the ENE-WSW-trending major faults. These results demonstrate the differences in the evolution of the different trending faults in the same tectonic regime, and the complexity of the final fault patterns in the Beier Depression was produced by differences in the reactivation of major faults. The originate interpretation of the multi-trend major faults in the Hailar Basin provides new insights into fault generation, and the classification of fault growth also has useful implications for future research on multiphase rifts.