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Knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern China and adjacent areas. In this study, we integrated the datasets from the TAIGER (TAiwan Integrated GEodynamic Research) and ATSEE (Across Taiwan Strait Explosion Experiment) projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Three seismic profiles were resolved, and the longest profile was 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. In total, data from 40 shots, 2 earthquakes, and approximately 1,950 stations were used; 15,612 arrivals were selected among three transects. Using these data, we determined the complex crustal evolution since the Paleozoic era , involving the closed Paleozoic rift basin in central Fujian, the Cenozoic extension due to the South China Sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen. The shape of the Moho, which also reflects the crustal evolution, can be summarized as follows: ~ 30 km deep to the west of Fujian, deepening toward central Fujian (~ 35 km), becoming shallower toward the Taiwan Strait (~ 28 km), deepening again toward the mountain belt of Taiwan (~ 42 km), and becoming shallower toward the Pacific Ocean (~ 10 km). [ABSTRACT FROM AUTHOR]

Taiwan’s mountain belt is an ideal location to address major questions regarding mechanisms of lithospheric deformation in convergent settings, mountain building processes from oceanic subduction to continental subduction, and post orogenic extension. In the northeast of this belt, the Ilan Plain is a triangular, deltaic plain characterized by a flat topography close to the sea level, and surrounded by the high mountains of the Hsuehshan Range to the northwest, and the Central Range to the southeast. Its eastern coast faces the western tip of the Okinawa Trough, the back-arc basin of the Ryukyu subduction zone. In this study, we analyzed the present-day surface deformation of the Ilan Plain, aiming at deciphering its relationships with basement faults and the regional geodynamic setting. Our approach is mainly based on surface vertical displacements revealed by Persistent Scatterer Interferometry Synthetic Aperture Radar (PSI), which indicate that there is an area of active subsidence (∼18 mm/yr) located in the southern part of the plain in probable connection with active basement faults and in agreement with previous geodetic measurements and existing geophysical data. Our PSI results also suggest that the subsidence occurring in the Ilan Plain has moved from north to south during Quaternary in relation with extrusion of the belt due to the westward propagation of the Okinawa Trough through the Taiwan Mountains. [ABSTRACT FROM AUTHOR]

Highlights: [•] Onset of Taiwan foreland basin development at 4.4Ma, younger than that proposed in some previous studies. [•] Three rapid subsidence events at 4.4–4, 2–1.8 and 0.45Ma in Taiwan foreland basin. [•] Tectonostratigraphic model for back-and-forth migration of the basin margin in the distal part of Taiwan foreland basin. [•] Slower migration rate of the forebulge in the early stage than that of the steady migration of the orogenic belt. [ABSTRACT FROM AUTHOR]

The offshore area of northern Taiwan is currently in an extensional regime, known for a post-collision area of the Taiwan mountain belt that has formed due to the oblique collision of the Philippine Sea Plate against the Eurasian continental margin since the late Miocene. The active collision has undergone a progressive migration of the Taiwan mountain belt from the northeast to the southwest direction. After the relaxation of the compressional stress due to the westward subduction of the Philippine Sea Plate, the northern Taiwan orogen has collapsed together with the opening of the southern Okinawa Trough. Here, we show the transitional process from compressional to extensional regime in the area off northern Taiwan and reconstruct the tectono-sedimentary evolution by using multi-channel reflection seismic data. We process and interpret multi-channel seismic profiles and use borehole data to determine the ages of sedimentary units and stratal surfaces/unconformities. Based on the seismic facies, we have recognized two distinctive domains separated by the Offshore Shanjiao Fault (OSF): a shelf basin to the northwest and a collapsed zone to the southeast. The tectono-sedimentary evolution off northern Taiwan since the late Miocene can be described in 4 stages. (1) The compressional structures off northern Taiwan were formed during the collision period starting around 6 Ma, a series of folds-and-thrusts aligned in the NE-SW direction. (2) Due to the oblique collision, some NW-SE-trending strike-slip faults were developed across the collision belt to accommodate the differential displacements between two adjacent segments of the folded belt. (3) During the transition from compressional to extensional regime at about 2.7 Ma, a post-collisional erosion and subsidence occurred in the collapsed zone to form the basal unconformity. This post-collisional collapse is associated with the opening of the southern Okinawa Trough, a back-arc basin, due to the westward migration of the Philippine Sea Plate subduction beneath the southern Ryukyu arc. (4) The offshore area of northern Taiwan has subsided continuously with sediment accumulation since the early Pleistocene (~2.0 Ma), accompanying the rifting of the southern Okinawa Trough. [ABSTRACT FROM AUTHOR]

Abstract: The direct and feedback relationships between tectonics, climate and denudation are a matter of debate. A better understanding of these relationships requires quantifying rates of denudation in a wide range of climate and tectonic settings, as well as at various time and space scales. Because of an ongoing active collision implying high uplift rates and a climate prone to extreme rainfall events and frequent tropical typhoons facilitating strong erosion dominated by mass movements and high degree of fluvial transport, the Taiwan environment is highly dynamic. In this work, spatially-averaged denudation rates determined along the network of one of the major rivers in Taiwan (Lanyang River) from in situ-produced cosmogenic nuclides (10Be) measured in river-borne quartz minerals are compared to the erosion rates determined from the statistical analysis of modern sediment load data. Integrated over the last several hundreds of years, the denudation rate derived from in situ-produced 10Be concentrations averages 2 ± 1 mm/yr within the Lanyang watershed. Integrated over the last 50 years, the erosion rate given by modern sediment load data is 5–7 mm/yr within the same catchment area. The studied catchment being characterized by a relatively low-level of human activity, the discrepancy between the two rates is most probably due different sensibilities to high-frequency, stochastic erosional events (typhoons and earthquakes). The cosmogenic-derived denudation rates can thus be regarded as more representatives for quantifying erosion processes on the short-time scale, and be strictly compared to the long-term exhumation rates derived from low-temperature chronological data. [Copyright &y& Elsevier]

Abstract: This study aims at the recent activity and development of an active wrench fault, the Touhuanping Fault in northwestern Taiwan. Northwestern Taiwan has been proposed in a current situation between the mature to waning collision in terms of tectonic evolution. The main drainage in this area, the Chungkang River, flows close to the trace of the fault mentioned above. We examined various types of deformation of fluvial terraces along the Chungkang River as a key to understanding the nature and rate of the late Quaternary tectonics. The E–W trending Touhuanping Fault has long been mapped as a geological boundary fault, but its recent activity was suspected. Field survey revealed that its late Quaternary activity is recorded in the offset fluvial terraces. Our result shows dextral slip and vertical offset with upthrown side on the south, and activated at least twice since the emergence of terrace 4 (older terrace 3 with OSL date of ca. 80 ka). Total amount of offset recorded in the Touhuanping terrace sequence is 15 m for dextral and 10 m for vertical offset. Estimated recurrence time of earthquake rupture may be a few tens of thousand years. Uplift on the upthrown side of the Touhuanping Fault also resulted in the formation of drowned valleys which were graded to terrace 4. Other deformation features, such as back-tilting, westward warping, and a range-facing straight scarp, were also identified. A second-order anticline roughly parallel to the Touhuanping Fault is suggested to be the origin of the northward tilting on terrace 3; it could have resulted from a flower structure on the Touhuanping Fault at shallow depth. This may demonstrate that the buried segment of the Touhuanping Fault has also been active since 80 ka. In the northern study area, the westward warping at terrace 2 probably represents late Quaternary activity of another NE–SW trending Hsincheng Fault. [Copyright &y& Elsevier]

Abstract: The Philippine Sea Plate overrides the Eurasian Plate along the east-dipping Manila Trench between Taiwan and Luzon islands. From south to north, the plate convergence gradually evolves from normal subduction of the South China Sea lithosphere to initial collision of the Taiwan orogen. The subduction-related earthquakes become diffusive close to Taiwan; the accretionary prism is dramatically wider toward Taiwan. To understand the plate convergent features of this subduction-collision transition zone, we have analyzed twelve seismic reflection profiles across the Manila Trench between Luzon and Taiwan. The results show that the basement of northern South China Sea basin generally dips toward east and south. The northern Manila Trench accumulates more trench-fill sediments in the south than in the north. A sequence boundary t0 is suggested to distinguish the hemipelagic and trench-fill sediments. Probably due to the collision in Taiwan, the sequence boundary t0 displays more gentle slope or has been uplifted in the north. Structural analysis shows that the subducting crust in the northern Manila Trench area can be characterized by three distinctive zones: a normal fault zone (NFZ), a proto-thrust zone (PTZ) and a thrust zone (TZ). The NFZ is defined by the distribution of numerous normal faults in the top or upper portion of the subducting crust. The normal faults are gradually buried by trench-fill sediments when they are closer to the deep trench. It is suggested that normal fault may take place at the location where the crust starts to bend and induces gravity sliding of the upper sedimentary layers. Some buried normal faults could be reactivated to blind thrust faults because of stronger plate convergence near the accretionary prism. The PTZ is located between the NFZ and the frontal thrust of the accretionary prism; it contains blind thrust faults or folds instead of thrust faults. The successive distribution of the crustal structures of normal faults, blind thrust and thrust faults at the trench area suggests that the blind thrust faults develop along the location of pre-existing normal faults. The brittle deformation occurs at the lower part of the sedimentary layers probably because of stronger compaction and less water content; eventually blind thrust faults may propagate upward and become thrust faults at the seabed. [Copyright &y& Elsevier]

Recent observations of cleavage patterns, strain histories, and kinematics across the Taiwan mountain belt depict systematic orogen-scale variations with respect to the synorogenic divide and suggest that the pattern of cleavage development is a predictable consequence of orogen stresses and kinematics. In Taiwan, continental crust within the collision is accreted in the prowedge facing Asia, but is advected eastward into the east-verging retrowedge, where the most deeply exhumed rocks are exposed. Wedge mechanics predict a reversal in the direction of plunge of the principal compressive stress at the topographic divide between the opposing wedges. The observation of a single cleavage in western Taiwan suggests that the cleavage in the prowedge remains stable with respect to the stress orientation. In contrast, the existence of a second crenulation cleavage in the retrowedge is evidence for an abrupt change in stress orientation and unstable buckling of preexisting prowedge fabrics. Advection of a fabric across a topographic divide in a doubly vergent wedge provides an explanation for the occurrence of cleavage fronts and fans in natural systems such as Taiwan. [ABSTRACT FROM AUTHOR]