New subduction channel triggered by buoyant blocks during the arc-continent collision beneath Taiwan: Seismic evidence from P-wave tomography

The initiation of subduction zones has remained a contentious and unresolved issue due to the extraordinary forces required and the scarcity of realistic examples. Taiwan, a prominent arc-continent collision zone characterized by dual-slab subduction systems, offers a unique opportunity to investigate subduction polarity reversal (SPR) between the Eurasian and Philippine Sea plates, i.e., a process considered a key mechanism for forming new subduction channels. In this study, we utilize high-resolution 3-D seismic tomography to delineate the detailed morphology of the Eurasian plate and assess the potential for new subduction zone initiation driven by SPR. Our findings reveal significant deformation of the Eurasian plate influenced by the buoyant and rigid Kuanying and Peikang Highs, including slab break-off beneath northern Taiwan and lateral rupture beneath central Taiwan. We propose that the presence of a rigid and buoyant block within a pre-existing subduction zone facilitates SPR, ultimately triggering the formation of a new subduction system during an arc-continent collision.