Anisotropic Deformation and Rotation Tectonics during Oblique Convergence: Examples from Northeastern Taiwan

Excellent exposures on wave-cut platforms display along the northeastern Taiwan coast a thick Oligocene succession that suffered low-grade metamorphism. The strata show anisotropic ductile-brittle deformation associated with the Late Cenozoic Taiwan mountain building event. Paleomagnetic analyses suggest probable contraction-induced remagnetization of remanent magnetization, taking place before rotation of the entire succession. Three deformation stages can be distinguished: (1) an early contraction stage that resulted in thrusting, regional tilting of strata and subsequent folding, together with remagnetization of remanent magnetization, (2) a second stage dominated by block rotation and drag folds accompanying progressive dextral shear thrusting, with dominoand bookshelf-type strike-slip fault systems as well as a variety of transpressional structures such as pressure ridges, restraining oversteps and rhomb horses and finally , (3) late transpression with little rotation represented by pop-up structures as well as penetrative pencil structure and fracture cleavage with a constant NNE-SSW orientation. This demonstrates an example of anisotropic deformation and rotation tectonics during oblique convergence at acollisional plate boundary.