--> Relationship among West Taiwan Foreland Basin Development, Inherited Extensional Structures and Taiwan Orogeny

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Relationship among West Taiwan Foreland Basin Development, Inherited Extensional Structures and Taiwan Orogeny

Abstract

Abstract

During the Plio-Pleistocene, the Eurasian and Philippine Sea plates obliquely converged and formed an orogenic belt, which imposed tectonic loading to deflex a rift–type continental margin and formed a foreland basin in western Taiwan. However, several tectonic problems are still controversial; not only the initial age of the foreland basin remains in debate also the process and evolution of the basin formation have not established yet. This study attempts to unravel the relationship among the process of the foreland basin development, character of the flexural basement and the Taiwan orogen activity.

Based on the results of the subsidence curves, isopach maps and basin flexural model, this study proposes a detailed evolutionary model of the foreland basin in northwestern Taiwan. During 5.6-4.4Ma, the study area was still on the pre-orogenic passive continental margin. During 4.4–3 Ma, mild uplift and subsidence happened in the distal part and the proximal part of the foreland basin, respectively, indicate the initiation of basin development. However, in contrast with the northern part of the basin, the southern part was still affected by pre-existing basin. During 3–2.1 and 2.1–1.6 Ma, the activity of the tectonic movement manifests the intense oblique collision causing the growing orogenic belt. After the period of 1.6Ma, the activity of collision started to wane and the sedimentary environment changed to fluvial system, indicating that the orogen and basin went into a steady-state.

The isopach map and the flexural modeling for each stage of tectonic development demonstrate that the trend of the forebulge has been moving westward and gradually changing its trend to be parallel with the orogen. Spatial variation in tectonic movement implies foreland basin development influenced by a dissimilar rigidity of the basement and continues southward propagating of the orogey. In addition, the strength of the basement increases insignificantly since it formed. This also indicates that the inhomogeneity of crustal strength only sheds effect on the initial foreland basin development. The flexural modelling shows that the orogen height becomes the key factor for the basin development when the orogen approached to the study area. However, the basin formation cannot only be explained mechanically by the surface loading; it is probably contributed partly by the buried loading.