EVOLUTIONARY MODEL FOR THE TAIWAN COLLISION BASED ON PHYSICAL MODELING

2-D and 3-D physical modelling of lithospheric convergence in the Luzo n-Taiwan-Ryukyu region is performed with properly scaled laboratory mo dels. The lithospheric model consists of two parts, continental (the A sian Plate, AP) and oceanic (the Philippine Sea Plate, PSP). The ocean ic lithosphere has one layer, while the continental lithosphere includ es both mantle and crustal layers. The continental margin is covered b y sediments. A low-viscosity asthenosphere underlies the lithosphere. The opposing Luzon and Ryukyu subduction zones are initiated by inclin ed cuts made within the PSP. The subduction/collision is driven by a p iston, Pre-collisional intraoceanic subduction along the Luzon and Ryu kyu boundaries results in the formation of a transform zone between th em, with two tear faults at the ends. The PSP undergoes strong compres sion along this zone. Subduction of the Chinese margin under the Luzon boundary further increases the compression. Compressive stresses reac h the yield limit of the PSP in the arc area, which is a weak zone in the experiments. The plate fails at the western side of the arc along an eastward dipping fault, the Longitudinal Valley Fault. Underthrusti ng of the frontal wedge of the PSP along this fault results in the clo sure of the fore arc basin and is then blocked. The PSP fails at the o pposite side of the Luzon arc along the westward dipping fault. The fa ilure releases lithospheric compression in this region and results in the initiation of southward-propagating subduction of the PSP under no rtheastern Taiwan. The incipient subduction zone becomes part of the s outheastward-retreating Ryukyu subduction zone, which allows the Okina wa back arc rift to propagate into Taiwan. The Taiwan collision thus i ncludes the following succession of major processes over time, or from south to north: (1) an E-W shortening of the PSP in the Luzon arc; (2 ) a failure of this plate at the western side of the arc and the forma tion of the eastward-dipping Longitudinal Valley Fault (the transient plate boundary); (3) a closure of the fore arc basin and a rapid uplif t of the orogen; (4) a failure of the PSP at the eastern side of the L uzon arc partly overthrusting the orogen, and the initiation of westwa rd CNN-ward) subduction of the PSP; (5) and finally 'back arc' rifting in the rear of this incipient subduction zone (i.e. in northern Taiwa n). All these processes commence with some delay with respect to the p receding ones and propagate southwards.