Review and New Insights on Foreland Tectonics in Western Taiwan

Abstract

Taiwan is located on the boundary between the Eurasian and Philippine Sea plates. As a result, foreland tectonics in western Taiwan can be divided into two domains: pre-orogenic extensional structures and those of the outer part of the fold-and-thrust belt that mingled with syn-orogenic normal fault reactivation. This paper proposes a synthetic model for foreland tectonics in western Taiwan, and advances possible mechanisms by which pre-existing normal faults might have affected the evolving thrust tectonics in foreland areas of western Taiwan.The sedimentary basins of pre-orogenic extensional tectonics are of two types-Paleogene and Neogene-which reflect two stages of continental rifting. Results from several studies have been synthesized to provide a tectonic map displaying the regional distribution of tectonic settings at different stages and the trends of normal faults in the basins. The similarity of the en echelon patterns of arrangement for both the Neogene and Paleogene tectonic and structural settings, as shown by the tectonic map, strongly suggests that the entire foreland area was influenced by regional dextral shear. We also provide a detailed description of structures in each tectonic setting, and propose a tectonic evolution model for Cenozoic basin architecture in western Taiwan.Among the pre-orogenic sedimentary basins, the Neogene ones, in which normal faults extend to the frontal areas of the fold-and-thrust belt in western Taiwan, open northeastward. Structural analysis of the thrust fault geometry indicates that, during development of the fold-and-thrust belt on the rifted continental margin in western Taiwan, the pre-existing normal faults in northwestern Taiwan were reactivated to form inversion structures of various types on different scales, depending on the angle between the strike of the normal faults and the direction of maximum compressive stress field. In southwestern Taiwan, where normal fault reactivation is absent from the eastern part of the foreland areas, pre-existing normal faults interacted with developing low-angle thrusts in the inner part of the fold-and-thrust belt. Normal fault reactivation, regardless of how it occurs, thus plays an important role in forming the deformation front of the fold-and-thrust belt. Based on this view, we propose that the orocline or tectonic arc of the island has been influenced more by normal fault reactivation than by the morphology of basement highs.

3D Geometry of the Chelungpu Thrust System in Central Taiwan: Its Implications for Active Tectonics

“…2a) show a great magnitude of displacement along the Chelungpu and ShuangtungHsiaomao thrusts and the restored length for the cross-sections would be sufficient to accommodate gradual thickening of the Lower Miocene from the HW of the Changhua thrust to that of the Shuangtung-Hsiaomao thrust. The reason that the normal fault, if it does exist, is to accommodate the thickened Pliocene rather than the Lower Miocene is based on research on regional tectonics of the undeformed areas to the west (Yuan et al 1989;Yang et al 1996bYang et al , 2006Lin et al 2003), which suggest that predominant normal faulting did not start until the late Miocene.…”

Tectonic Implications of Stratigraphy Architecture in Distal Part of Foreland Basin, Southwestern Taiwan

“…www.intechopen.com older phase primarily developed in the Paleogene period and ended in the Middle Oligocene [70,71,51,52], forming a regional unconformity across the entire area of passive margin of southeastern China Mainland [70,72]. However, the age of initiation of the postrift sequences varies everywhere in the newly formed post-rift basin.…”

“…In southwestern Taiwan, the age of the strata right overlying the regional unconformity is in NN1 zone [56]. The latest phase of the extensional tectonics initiated in the Middle to Late Miocene [73, 74, 70, 75 , 76, 77, 78, 71, 79, 51, 80] and formed two rifted basins separated by a basement high that stood nearly perpendicular to the front of thrust belt [80,52]. The study area in this paper is located right on the northern margin of the southern rifted basins (Figure 1).…”

“…Taiwan is located on the convergent plate boundary between the Eurasian and Philippine Sea plates; its tectonic belts are aligned from east to west: the island arc in the Coastal Range, the suture zone along the Longitudinal Valley Fault Zone, the inner mountain-building belt of high-grade metamorphism in the Basement Complex, the outer mountain-building belt of low-grade metamorphism in the Backbone and Hsuehshan ranges, the imbricate fold-and-thrust belt in the Western Foothills, and the foreland basin ( Figure 1, [50]). According to the model and definition of DeCelles and Giles [1], the coastal plain and its subsurface settings of southwestern Taiwan has been located in the distal part and the adjacent forebulge of the foreland basin system since the Late Neogene [23,51,52,53,50]. The present day forebulge is located on the central line of the Taiwan Strait [23,51,52].…”

“…According to the model and definition of DeCelles and Giles [1], the coastal plain and its subsurface settings of southwestern Taiwan has been located in the distal part and the adjacent forebulge of the foreland basin system since the Late Neogene [23,51,52,53,50]. The present day forebulge is located on the central line of the Taiwan Strait [23,51,52]. Owing to the paragenetic relationship between the foreland basin and the adjacent www.intechopen.com Tectonic Implications of Stratigraphy Architecture in Distal Part of Foreland Basin, Southwestern Taiwan 173 mountain belt, the stratal sequences, lithofacies and subsidence history of the basin, especially those in the distal part and the forebulge of the basin system, would not only record the evolutionary history of the basin itself but also provide the most crucial indicators to infer the kinematics of the mountain-building process.…”