Tracking the subduction-collision transition in the Taiwan-Philippine-New Guinea regions: a simple structural scheme to assist kinematic reconstructions

In Southeast Asia, the contact between oceanic plates of Pacific affinity (Caroline and West Philippine seas) and the Eurasia and Australia plates of continental nature is rarely marked by high mountain ranges. Instead, it is characterised by fold-and-thrust belts involving volcanic arcs and slices made of continent-derived sediments. At every location, the tectonic style results from the oblique docking of the oceanic plates against the continental margins.

In this compressional setting, we identify two discrete systems developing the one after the other. The first system is marked by arcuate frontal thrusts bounded by oblique strike-slip lateral ramps, that are ubiquitous and vary in size from a few tens of meters to a few tens of kilometers. The regional convergence obliquity leads to a migration of the plates contact with consecutive tectonic periods of 1 to 2 Myrs, controlling the rapid triggering of subduction jumps that progressively change the location of the plates boundary over time. The second system corresponds to the onset of shear partitioning marked by the formation of a new subduction zone along which long, subparallel strike-slip faults form. Therefore, these new structures intersect previous ones, and the resulting sliver plate is affected by a margin-parallel stretching regime accommodating the progression of the docking and velocity variations during the convergence.

Thus, our study describes the evolution from one system to the other in Taiwan, Northern Philippines, Southern Philippines, Eastern Indonesia and Papua New Guinea. It also highlights important shifts that are necessary to discriminate small, Recent-to-Actual displacements imposed by GPS data (from 0Ma to 2Ma) from those deduced from longer-term motions documented along the main faults. In the frontal units of the Taiwan foothills or in the Luzon sedimentary wedge, recent tectonic slices typically disappear as we go backward in time by just a few Ma. In Southern Philippines, compression began in the latest Miocene–earliest Pliocene times with flat-and-ramp system, before being progressively replaced by the N–S Philippine Fault throughout the entire archipelago. In Eastern Indonesia and Papua New Guinea, the Sorong Fault also crosscuts Mid-Miocene docking structures marked by the flat-and-ramps features. Any regional reconstruction requires to unravel the two systems and date them carefully.