Cenozoic tectonic stress evolution on the southern margin of the Songliao Block constrained by multi-source stress data

The northern Yanbian region, located at the southern margin of the Songliao Basin, contains multiple near-E–W, NE–SW, and NW-trending fault structures. Because of a lack of stress distribution data spanning multiple Cenozoic geological periods, the temporal evolution of the regional tectonic stress field remains poorly characterized. In this study, hydraulic fracturing measurements, focal mechanism solutions, and imaging logging data were integrated to reconstruct the Cenozoic-to-present tectonic stress evolution of the region. Tensile fractures preserved in basalts of different ages from five boreholes were statistically analyzed using imaging logging data to constrain the orientations of paleo-extensional stress. Their trends correspond to the NW–SE, near-E–W, NE–SW, and NEE–SWW directions. Hydraulic fracturing data show that the shallow crust is dominated by horizontal compression, with S_Hmax trending NEE–SWW to NE–SW, and that the shallow stress regime is mainly characterized by thrust faulting, locally transitioning to thrust-strike-slip conditions with depth. In contrast, focal mechanism inversion indicates that the deeper stress field is dominated by a thrust-strike-slip regime. Our results indicate that the extensional orientation recorded by basalt-hosted fracture sets underwent a stagewise deflection from NW–SE to near-E–W, then to NE–SW, followed by a relatively minor late-stage adjustment toward NEE–SWW. This pattern suggests a multi-stage, nonmonotonic evolution of the regional tectonic stress field since the Cenozoic. The Dunhua and Wangqing areas on the southern margin of the Songliao Block effectively preserve this evolutionary sequence, providing crucial insights into the long-term regional tectonic dynamics of the northern Yanbian region.