Mechanisms of block rotation and transrotational basin development in oblique convergent margins: Insights from the Longitudinal Valley, Taiwan

While the role of strike-slip faults as major seismogenic structures is well-established, the mechanical evolution of localized transtensional basins embedded within active convergent orogens remains a fundamental challenge in structural geology. The oblique plate boundary in Taiwan provides a premier setting to investigate how localized extension is accommodated within a dominant compressional regime. By integrating four seismic profiles, 33 borehole records, and five leveling surveys between 2018 and 2022, we reconstruct the 3D architecture of a major fault splay system (consisting of the Saoba and northern Yuli faults). Our analysis demonstrates that pre-existing basement-cover unconformities function as mechanical interfaces facilitating fault-tip migration along lithologic discontinuities. We identify a transrotational basin driven by clockwise rotation of inherited crustal blocks rather than simple fault-trace geometry. This process illustrates a mechanical pathway where secondary transtension is decoupled from regional shortening mediated by structural inheritance. These findings provide a generalized framework for deciphering block rotation and detachment-controlled faulting at oblique plate boundaries worldwide.