Post-collisional and volcanic features of the Late Miocene-Pleistocene foreland area, northern offshore Taiwan

Based on multichannel seismic data northern offshore Taiwan, we revisited the post-collisional and volcanic features in the Late Miocene-Pleistocene wedge-top of the early Taiwan orogenic wedge. Seismic data transverse to wedge-top zone show the asymmetric and symmetric folds, along with blind thrusts and back thrusts. Seis-mic data parallel to the axis of the wedge-top zone show the volcanic features of poor stratified reflectors, forced fold and intrusive step of volcanic sills along and away from dominating normal fault structures. Since the volcanic extrusions and normal faults are probably associated events, we suggest that post-collisional extensional volcanism northern offshore Taiwan was probably formed along inherited primary and secondary fault structures. The wedge-top zone was formed at frontal part of the early Taiwan orogenic wedge in Late Miocene. Subsequent change of regional stress from convergence to extension led to the mountain collapse as well as primary and secondary normal faults. Thus, these post-collisional normal faults are mechanically weak, probably capable of providing pathways for the Pleistocene-present vol-canisms northern offshore Taiwan. The facilitation of post-collisional fault structures as transportation routes for deep material to migrate along may be important for the formation of the Quaternary volcanism extrusions northern offshore Taiwan.