Geodynamics of the Taiwan arc-arc collision

Abstract

Hsu and Sibuet (1995), on the basis of an overview of the satellite-derived marine gravity anomalies, postulated that the Ryukyu subduction zone extended before the formation of Taiwan a few hundreds kilometres south of its present-day termination, and that Taiwan resulted from an arc-arc collision rather than from an arc-continent collision. An analysis of the structure and timing of rifting in the basins of the Southeast Asia continental shelf offshore and onshore Taiwan shows that they are located within four belts parallel to the main China shoreline. Rifting occurred at the same time within basins belonging to each of these four belts and becomes younger oceanward for each belt. As a first approximation, the four rifting phases occurred during Paleocene, Eocene, Oligocene to Early Miocene and early Middle Miocene times to Present. Ridges with volcanic products are present between these belts. They seem to be the same age as basins located immediately northwest. We interpret these basins and associated ridges as relict backarc basins and arcs of the Ryukyu subduction system which were successively active since the early Tertiary. The geographic distribution of basins and ridges suggests that the Ryukyu subduction zone extended from Japan to southwest Taiwan from early Tertiary to Early Miocene times. During the early Middle Miocene, the southeast portion of the subduction zone facing the Tainan basin and the future island Taiwan became inactive. Southwest of the Tainan basin, the Pearl River basins are tensional basins formed during the rifting of the northern South China Sea margin. Consequently, the geology of the Southeast Asia continental shelf supports the existence of a former subduction zone with which the Luzon arc entered into collision in the Late Miocene. The kinematic evolution of the Southeast Asia region is compatible with such constraints. Such a detailed kinematic evolution of the collision between the Luzon arc and the former Ryukyu subduction zone is proposed both in plan views and in cross-sections. Collision started with the compression and uplift of the Hsüehshan trough backarc basins, where the continental crust and lithosphere were thin and weak, followed by the compression and uplift of the Luzon and Ryukyu arcs. The Lichi and Kenting melanges are explained in the framework of the arc-arc collision model.