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Records of the thermal-age path of orogenic rocks are crucial in understanding subduction and collisional processes between a continent and an arc. Tectonic events and thermochronological data of the Taiwan Orogen have been extensively investigated. We use the zircon U Pb youngest ages as the (initial) subduction age, the Raman Spectroscopy of Carbonaceous Material, 40Ar/39Ar age of mica porphyroblasts, whole-rock Lu Hf isochron age and thermal results as prograde peak metamorphic condition during subduction and basal accretion, and the apatite fission-track data for cooling age of the Taiwan Orogen to illuminate the subduction and collisional processes between the Eurasian Plate and the Luzon Arc. The Hsuehshan Range Nappe in the west of the Taiwan Orogen, whose subduction was initiated at 12 Ma, reached peak metamorphism with a temperature of ~250 °C to 490 °C at a depth of 8 km during the interval 6–2.5 Ma, mainly by basal superimposed accretion. The isothermal dwelling during peak metamorphism condition of the Hsuehshan Range suggests that tectonic underplating through basal superimposed accretion contribute significantly to the formation of the Taiwan Orogen, and led to a sudden increase of subduction and décollement depths, and slow downward thickening of the orogenic wedge and mountain root growth. Located in the east of the Taiwan Orogen, the Yuli Beltsubduction was initiated at 15.4–16 Ma, and attained peak metamorphism at a depth of 40 km, with a temperature of 550–560 °C and a pressure of 10.5–13 kbar during the interval 12.2–4.4 Ma due to basal superimposed accretion. The exhumation of the Hsuehshan Range commenced at ~2.5 Ma, which is later than that of the Yuli Belt at ~3.4 Ma. Such distinct and different thermal-age paths of the Hsuehshan Range and the Tananao Complex indicate that different tectonic wedges in the Taiwan Orogen are formed through different subduction and accretional processes. [Display omitted] • The different tectonic wedges in the Taiwan Orogen have the different thermal-age paths. • The different thermal-age paths of the Hsuehshan Range and the Tananao Complex indicate that they are formed through different subduction and accretional processes. [ABSTRACT FROM AUTHOR]

In this study, we use provenance analysis to shed light on the Neogene evolution of river drainage and sediment dispersal in eastern Asia as a consequence of the Himalayan orogeny and topographic rise of the Tibetan Plateau. As an attempt to envisage how sediment‐routing systems operated in the past, and to identify the ultimate source of siliciclastic detritus originally generated in mainland China and now incorporated in, and recycled from, the western Taiwan accretionary prism, we have used Raman spectroscopy of detrital garnet in modern river sands and upper Neogene sandstones, complemented by detrital‐zircon geochronology and by petrographic and heavy‐mineral analysis. Garnet grains are relatively abundant and largely represented by almandine with various percentages of pyrope molecules in Yangtze sand as in western Taiwan sandstones and modern river sand derived from them. Instead, they are rare and largely represented by grossular or andradite in the sand of the Pearl River and of coastal rivers of SE China facing the Taiwan Strait. This finding supports the result of detrital geochronology, which documents a sharp difference between U‐Pb age spectra of Pearl River and coastal SE China zircons (characterised by a Paleozoic‐Mesozoic triple peak) and Yangtze and western Taiwan zircons (characterised by prominent Neoproterozoic, Paleoproterozoic, and latest Archean clusters). The Pearl River and minor rivers facing the Taiwan Strait are thus ruled out as ultimate sources of upper Neogene sandstones exposed today along the western front of the Taiwan fold‐thrust belt. In the envisaged scenario, sand mostly supplied by the paleo‐Yangtze River was entrained for ~ca.1,000 km southward by longshore currents and deposited on the Chinese passive margin before being accreted along the front of the Taiwan orogen since ~6 Ma. Littoral sand drift represents a major factor of long‐distance sediment transport in modern shelves and needs to be taken into full account in source‐to‐sink studies and paleogeographic reconstructions. [ABSTRACT FROM AUTHOR]

Abstract The complexity of the young Taiwan orogen mainly resulting from arc‐continent collision is manifold. As the Moho and crustal properties are crucial to unravel the still‐debated orogenic models, we adopt a H‐V stacking method jointly utilizing P and S receiver functions for simultaneously reliable determination of crustal thickness and average P‐ and S‐wave velocity, their ratio (Vp/Vs), and bulk sound speed (Vb) beneath 50 stations in Taiwan and offshore islands. Results indicate the Moho is inclined from ∼20 km in the north and west coastal areas to ∼47 km in the midwest of the Central Range (CR), and abruptly elevated >25 km at the eastern edge of the CR and adjacent collision suture zone. The uplifted Moho along with exclusively high Vp/Vs (2.1) suggest the subducted Eurasian crust may have been exhumed and compositionally modified by the accreted ophiolite complex of oceanic affinity during forearc basin closure. Our Moho mostly lies in the depths of the sharpest positive velocity gradient, a few to a dozen kilometers shallower than the Vp = 7.5 km/s isosurface assumed in the tomographic models. The unusually thin crust (∼20 km) with high Vp/Vs (1.9–2.0) is observed in the northern Taiwan volcanic zone, plausibly attributed to the post‐orogenic extensional thinning and induced melting in the sublithospheric mantle producing magmatic fluids trapped in the crust. Moreover, Vb apparently decreases from the coasts to the middle CR coinciding with the thickest crust, implying the crust under the central mountain range is more compressible and easily deformed/thickened by ongoing collisional compression.

The complexity of the young Taiwan orogen mainly resulting from arc‐continent collision is manifold. As the Moho and crustal properties are crucial to unravel the still‐debated orogenic models, we adopt a H‐V stacking method jointly utilizing P and S receiver functions for simultaneously reliable determination of crustal thickness and average P‐ and S‐wave velocity, their ratio (Vp/Vs), and bulk sound speed (Vb) beneath 50 stations in Taiwan and offshore islands. Results indicate the Moho is inclined from ∼20 km in the north and west coastal areas to ∼47 km in the midwest of the Central Range (CR), and abruptly elevated >25 km at the eastern edge of the CR and adjacent collision suture zone. The uplifted Moho along with exclusively high Vp/Vs (2.1) suggest the subducted Eurasian crust may have been exhumed and compositionally modified by the accreted ophiolite complex of oceanic affinity during forearc basin closure. Our Moho mostly lies in the depths of the sharpest positive velocity gradient, a few to a dozen kilometers shallower than the Vp = 7.5 km/s isosurface assumed in the tomographic models. The unusually thin crust (∼20 km) with high Vp/Vs (1.9–2.0) is observed in the northern Taiwan volcanic zone, plausibly attributed to the post‐orogenic extensional thinning and induced melting in the sublithospheric mantle producing magmatic fluids trapped in the crust. Moreover, Vb apparently decreases from the coasts to the middle CR coinciding with the thickest crust, implying the crust under the central mountain range is more compressible and easily deformed/thickened by ongoing collisional compression. Plain Language Summary: Taiwan is known for one of the most seismically hazardous and rapidly growing orogens in the world. The mountain building processes would involve the crustal deformation and disturbance of the boundary between the crust and underlying chemically distinct mantle, called the Moho, with sudden jumps in seismic velocities. Therefore, it is of vital importance to constrain the Moho depth and crustal velocity variations across Taiwan for advancing our understanding of orogenic and seismotectonic processes in Taiwan. We jointly use the arrival times of seismic phases converted at the Moho from direct P‐ and S‐ waves of distant earthquakes and their associated reverberations to robustly determine the Moho depth and average seismic velocities of the crust beneath permanent broadband seismograph stations across Taiwan. Our results indicate that the Moho is inclined toward the central Taiwan mountain ranges, and uplifted swiftly across the collision suture between the Eurasian continental margin and the Luzon arc of Philippine Sea Plate. The most thickened crust in the central Taiwan orogen reveals the lowest average bulk modulus or the highest compressibility, implying the crust therein is weaker and less resistant to compressional deformation. Key Points: Lateral variations of the Moho and average crustal velocities in Taiwan first studied by H‐V stacking of joint P and S receiver functionsThe Moho lying in the sharpest positive velocity gradient zone, not on the isovelocity surface assumed in prior tomographic modelsVariations of average Vp/Vs and bulk velocity providing key constraints on crustal composition and compressibility in the Taiwan orogen [ABSTRACT FROM AUTHOR]

Late Cenozoic changes in the intensity of the East Asian Summer Monsoon (EASM) are reconstructed using both terrestrial and marine proxy records; however, proxies from terrestrial (e.g., loess, pollen, and pedogenic isotopes) and marine environments (e.g., foraminifer assemblages and geochemistry) commonly display large discrepancies both in the direction and timing of changes in the EASM. In part, these discrepancies reflect long-term changes in paleogeography that are independent of climate variations. We assess the influence of a rapidly uplifting orogen on EASM records by comparing temporally constrained gamma-ray, δ13C org , hematite/goethite, and magnetic susceptibility records from Late Miocene–Early Pleistocene strata of the Taiwan Western Foreland Basin to time-equivalent EASM proxy records in the South China Sea (SCS). Prior to the emergence of modern Taiwan (∼6.3–5.4 Ma), sediment in the SCS was largely derived from Eurasia and transported into the Pacific Ocean. Following its emergence and southwest migration of the collision zone ∼5.4 Ma, proto-Taiwan became a major sediment source to the SCS. The uplift and southwest migration of Taiwan and northwest migration of the Luzon volcanic arc resulted in the formation of southwest-flowing deep- (1500–2500 m water depth) and bottom-water (>2500 m water depth) currents and the SCS Branch of the Kuroshio Current. Together these currents transported sediment from Taiwan towards the SCS. Increased sediment input from Taiwan is recorded as a decline in hematite/goethite values in sediment records from the northern and central SCS. By ∼3.2 Ma, continued southwest migration and growth of the Taiwan orogen resulted in the formation of the Taiwan Warm Current, which remobilized some sediment from Taiwan towards the East China Sea. Despite strengthening of deep-water currents during the Late Pliocene–Early Pleistocene, relative sediment input from Taiwan to the wider SCS decreased. Consequently, relative contributions from Eurasia and Luzon increased. In the southern SCS, where the Mekong River has dominated sedimentation since the Late Miocene, proxy records show no influence from the Taiwan orogen and instead reflect environmental changes in Mainland Southeast Asia driven mainly by monsoon variability. Our results show that a rapidly uplifting orogen has the potential to significantly impact paleoclimate records >1000 km away from the collision zone. This highlights the influence of shifting sediment sources on paleoclimate proxy records, which must be considered in interpreting past climate change from the sedimentary record. • Taiwan orogenesis is linked to South China Sea climate proxies. • Rapid orogenesis can drive shifts in sediment source and ocean currents. • Tectonic activity is the dominant control on proxies prior to ∼3 Ma. • After ∼3 Ma, proxies reflect enhanced monsoon strength related to glaciation. [ABSTRACT FROM AUTHOR]

The Okinawa Trough (OT) is a large sink of sediments supplied by the East Asian continent. Identifying the provenance of the OT sediments is key to reconstructing the temporal and spatial variations of the terrigenous supply to this area and is important for understanding the impact of paleoclimatic and paleoceanographic variability on the sediment supply to this marginal sea over the late Quaternary. In this contribution, we show that radiogenic strontium (Sr) and neodymium (Nd) isotopes allow to efficiently distinguish Yellow and Yangtze/Taiwan River detrital sediments, and can be used to reconstruct distinct changes in the provenance of the detrital fraction of marine sediments from the middle and northern OT since the last deglaciation. The Sr and Nd isotope signatures are compared to those of the potential sediment sources, namely the Yellow and Yangtze Rivers, the Taiwan orogen, and volcanic material from the OT and nearby islands, and the relative contributions of these sources are reconstructed. The Sr and Nd isotope compositions of the detrital fraction in the two sediment cores recovered from the middle and northern OT show that the sediments mainly originated from the Yangtze River between 18 and 10.5 ka, which was caused by low sea level and a widely developed channel system on the continental shelf. During the period between 10.5 and 7.0 ka, the rising sea level resulted in elevated Yangtze and Yellow Rivers sediment input into the OT. Simultaneously, large-scale volcanic activity also contributed significant amounts of material to the OT. During the last 7.0 ka, besides important contributions from the Yellow River, the intensification of the Kuroshio Current resulted in increased delivery of sediment from Taiwan to the OT. • Yangtze and Yellow River sediments can be distinguished with Sr Nd isotope. • Okinawa Trough (OT) sediments derived from the Yangtze River from 18.0 to 10.5 ka. • Yangtze and Yellow River contributed sediment to the OT from 10.5 to 7.0 ka. • Kuroshio Current control Taiwan sediment to the OT after 7.0 ka. • Yellow River sediment was transported to the OT by the coastal current in the last 10.5 ka. [ABSTRACT FROM AUTHOR]

The subduction flipping in the Taiwan region leads to complexities in the lithospheric structure. To better understand the arc‐continental collision process in this zone, we construct a 3‐D lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc. In the middle to lower crust, low velocities are mainly located beneath the Ryukyu Trough and the rifted basins in the Taiwan Strait, and high velocities are imaged in the Kuanyin and Penghu Platforms. Likely, the Kuanyin and Penghu Platforms act as relatively strong barriers that block the persistent westward advance of the western deformation front of the Taiwan mountain belt, as manifested by shape of the deformation front that withdraws to the east in the basement highs. In the mantle, high velocities are observed beneath the Central Range and Ryukyu Arc, which is interpreted as the two oppositely oriented slab subductions, that is, subduction of the Philippine Sea slab in the northeast Taiwan and Eurasian slab subduction in south Taiwan. Based on the vertical transects through our 3‐D model, we find that the subduction polarity has flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal. We also image significant low mantle velocities beneath the North Taiwan Volcanic Zone and Taihsi Basin, which may be related to the breakoff of the subducting Eurasian slab. In addition, we propose that the inherited weakness of the Taihsi Basin may have facilitated the slab breakoff in central Taiwan. Plain Language Summary: In this work we collect the seismic data recorded by seismic stations in and around the Taiwan orogen and build a high‐resolution lithospheric velocity model for an area including the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc by ambient noise tomography. The model exhibits low crust velocity anomalies in the Ryukyu Trough and rifted basins of the Taiwan Strait, and low velocities in the uppermost mantle beneath the North Taiwan Volcanic Zone and Taihsi Basin. Based on the tomographic images, we clearly find that the subduction polarity has been flipped in north Taiwan, and the tectonic framework in central Taiwan is in the process of subduction polarity reversal, which is in consistent with the geological observations. Key Points: A high‐resolution lithospheric model of the Taiwan Strait, Taiwan Island, and southwestern Ryukyu Arc is obtained from ambient noise tomographySignificant low mantle velocities related to the breakoff of the subducting Eurasian slab are observed under the NTVZ and THBSubduction polarity reversal is ongoing in central Taiwan; the lithospheric scale weak THB facilitates the slab breakoff in central Taiwan [ABSTRACT FROM AUTHOR]

The offshore basins in the East Asian Continental Shelf have undergone distinct tectono-geomorphic-sedimentary evolution since the Neogene, driven by complex interactions between tectonic and surface Earth processes. However, the contribution of the latter to the evolution of the offshore basins has been less studied. The landscape simulation software Badlands serves as an ideal tool to investigate the impacts of tectonic and surface processes on sedimentation as it simulates the sediment routing in a source-to-sink context. Focusing on the southern East China Sea Basin (ECSB) and the northern South China Sea Shelf Basin (SCSSB), two key components of the East Asian Continental Shelf, we used Badlands to reconstruct the tectono-geomorphic-sedimentary evolution since the Neogene. It revealed two-phase evolutionary processes: (1) the southern ECSB and the northern SCSSB were in the unified shelf environment and represented as an integral during the Early Miocene, though the northern SCSSB experienced anomalous subsidence due to the southward jump of the SCS mid-ocean ridge. The integrated southern ECSB and northern SCSSB experienced uplift and denudation since the Middle Miocene, under the influence of the Philippine Sea Plate extrusion. (2) Subsequently, the southern ECSB and the northern SCSSB were separated into two independent basins in the Late Miocene, when Taiwan Island was significantly uplifted due to the Philippine Sea Plate extrusion and the arc-continental collision. Then Taiwan Island experienced a multi-stage uplift characterized by southward and westward migration. It concluded that tectonics (i.e. Taiwan Orogeny and the subduction of the Philippine Sea Plate) primarily dominated the differential evolution of the southern ECSB and the northern SCSSB. Surface Earth processes (i.e. the intensification of the East Asian Monsoon and the sea-level fluctuation) are the secondary contributors. • The southern ECSB and the northern SCSSB were an integral during the early Miocene. • The integral was divided into two independent basins due to Taiwan Orogeny. • Taiwan orogeny is characterized by diachronous westward and southward migration. [ABSTRACT FROM AUTHOR]

Abstract Late Cenozoic orogen-derived sediments recorded in the pro- and retro-foreland basins on both sides of the Taiwan orogenic wedge provide important constraints on sediment provenance evolution, and further outline the exhumation and erosion histories of the orogenic belt. We present 172 sandstone petrographic data from seven representative regions on the pro- and retro-foreland basins, which we coupled with previous thermochronological data from the pro-wedge of the Hsuehshan Range and the retro-wedge of the Backbone Range to elucidate the source-sink relationships between a source orogenic wedge and its associated foreland basin. Our data analysis and estimation provide evidence that the initial depositional age of orogen-derived sediments in pro- and retro-foreland basins is consistent with the exhumation and erosion histories of the adjacent orogen, indicating that the Backbone and Hsuehshan Ranges started to build up at ~12 and 5–6 Ma, respectively. The diachronous onset of orogenic sediment deposition and orogenic uplift also suggest a tendency for progressively southward and westward migration of the foreland basin, and asymmetric exhumation and erosion of the orogenic wedge over time due to oblique collision. The timing of the onset of the Taiwan orogeny formed the retro-wedge of the Backbone Range at ~12 Ma, which is much older than the previously determined onset age of Taiwan mountain building of ~6 Ma. We divide the Taiwan orogenic evolution into two stages: the first stage comprises the extrusion and exhumation of the subduction wedge formed as the Yuli Belt of the Backbone Range prior to the collision during the middle Miocene. The second stage comprises the arc-continent collision, producing doubly vergent orogenic wedge extrusion, leading to a diachronous uplift history of the Hsuehshan and Backbone Ranges since late Miocene. Highlights • Geochronological and petrographic data constrain the exhumation history of orogeny. • The onset age of the Taiwan mountain building occurred at ca. 12 Ma. • Stage 1: exhumation in a subduction wedge since middle Miocene • Stage 2: collision produced by doubly vergent wedge extrusion since late Miocene [ABSTRACT FROM AUTHOR]

Abstract Geomorphic studies on the Taiwan orogen have long focused on the rapid erosion and efficient sediment transport in response to active tectonic uplift and frequent earthquakes/heavy rains. Little attention has been paid to the common low-relief surfaces in high mountains that appear to have been geomorphically stable for a long period of time. We undertook a study on a group of such gentle surfaces in Alishan, which consist of poorly drained hummocky slopes averaging 15° and as wide as 2 km. These gentle slopes are underlain by mass-wasting gravels 60–100 m thick, from which 22 radiocarbon dates >50 to 40 ka BP in age were obtained. Below these thick colluvial deposits are ~20° bedrock bedding planes apparently exposed by dip-slope failures. Combining these data reveals alternating hillslope erosion and deposition, along with episodic river downcutting, at a time scale of several 104 yr. We relate this temporal change in geomorphic processes to glacial-interglacial climate change. During the wet inter-/post-glacial periods characterized by frequent heavy rains, landslides/debris flows prevailed and rivers were capable of conveying most sediment eroded from hillslopes. Frequent debris flows combined with sufficient bedload sediments serving as tools for fluvial erosion caused rapid river downcutting. In contrast, the low river erosion/transport capacity during the dry last-glacial period allowed progressive deposition of thick colluvium on the preexisting, gentle bedding surfaces probably eroded during the last interglacial period. This study shows how glacial-interglacial climate change influenced the river/hillslope processes and landscape evolution of the Taiwan orogen. Highlights • Low-relief surfaces in the 2000-m high Alishan mountain are studied. • The surfaces are underlain by thick mass-wasting gravels dated >50 to 40 ka BP. • The coupling between river incision and mass movements are demonstrated. • The controls of glacial climate on geomorphic processes in Taiwan are shown. [ABSTRACT FROM AUTHOR]

To clarify the deep structure of the Taiwan Orogen formed by the collision between the Eurasian and the Philippine Sea plates, we determine a robust 3-D shear-wave velocity (Vs) model of the crust and upper mantle beneath the Taiwan Island and its surrounding regions by applying a novel joint inversion method to local and teleseismic P and S wave travel times, Rayleigh-wave phase velocities and S-wave receiver functions. A notable new feature revealed by our model is the morphologic variation of the subducting Eurasian slab along the orogen belt. Beneath South Taiwan, the subducting Eurasian slab is imaged as a continuous high-Vs zone down to ∼400 km depth with an obvious dip angle change at ∼70 km depth. Beneath Central Taiwan, the Eurasian slab is imaged as intermittent high-Vs anomalies in the upper mantle, whereas the Eurasian slab exhibits as a sheet-like high-Vs zone with a low dip angle down to only ∼100 km depth beneath North Taiwan. These results suggest that parts of the subducting Eurasian slab have been detached beneath the Philippine Sea east off the Taiwan Island, which may result in the remnant slab rebounding to underplate the upper plate and so promote mountain building on the Taiwan Island. • A 3-D Vs model of the Taiwan Orogen is derived from 4 kinds of seismic data. • Shape variations of the Eurasian slab are revealed along the orogen belt. • Parts of the Eurasian slab are detached beneath the Taiwan Orogen. [ABSTRACT FROM AUTHOR]

Metamorphic P–T trajectories of high –P rocks can well constrain the exhumation mechanism of rocks and thermal structure in a subduction zone. The Yuli Belt in eastern Taiwan is regarded as an ophiolitic mélange related to the subduction of the South China Sea Plate beneath the Philippine Sea Plate, but the metamorphic evolution of the high –P rocks therein is still controversial. Two glaucophane schists from the Tamayen block in the Yuli Belt, are chosen for detailed studies of petrography, mineral composition and phase equilibria modelling, and addressing the metamorphic evolution. The glaucophane schists show coarse-grained amphibole porphyroblasts that distribute randomly in a matrix consisting of amphibole, epidote, garnet, phengite, chlorite, albite and quartz. Amphibole porphyroblasts are characterized by core–mantle–rim zoning from sodic-, calcic- to sodic-amphiboles. Three metamorphic stages are recognized, involving prograde to the peak, post-peak decompression and subsequent cooling. The prograde to the peak stage is constrained to occur in lawsonite- and omphacite-bearing assemblages with the peak conditions of 2.1–2.3 GPa/530–560 °C on the basis of the garnet zoning and the maximum Si content in phengite. The post-peak decompression was first dominated by dehydration reactions with the expense of lawsonite and omphacite and producing glaucophane, followed by decompression in fluid-absent fields to 0.6–0.9 GPa/500–550 °C with the growth of calcic amphibole. The subsequent cooling is inferred from the regrowth of glaucophane that rims amphibole porphyroblasts. The glaucophane schists share clockwise P–T trajectories with evident isothermal decompression, and the peak conditions correspond to a low geothermal gradient of ∼250 °C/GPa, representing the metamorphic evolution within a mature subduction zone. The high- P rocks in the Yuli Belt experienced two exhumation stages: firstly, the rocks were isothermally exhumed via a matured subduction channel from ∼70 km to ∼30 km depth and incorporated into the base of the accretional wedge during 12–9 Ma; and then, further exhumation occurred through thrusting and erosion in response to the arc-continent collision started from ∼6 Ma. • Glaucophane schists (Taiwan Orogen) show peak P-T conditions of 2.1–2.3 GPa/530–560 °C. • They experienced a post-peak isothermal decompression to 0.6–0.9 kbar/500–550 °C. • They were firstly exhumed along subduction channel and then uplifted via thrusting. [ABSTRACT FROM AUTHOR]

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]

Serpentinized peridotite in the fore-arc has been observed in a number of subduction zones, including the northern Manila subduction zone which terminates northward in the Taiwan arc-continent collision. How this zone of serpentinization changes northward from the subduction of thinned continental lithosphere to full arc-continent collision in the Taiwan orogeny is not well known. In this paper we present 2-D gravity modeling along three P-wave (Vp) transects across the Taiwan orogeny. Two of these transects were collected with ocean-bottom seismometers. These two transects provide good constraints on the velocity structure to the west of, and on land, southern Taiwan. Conversion of Vp to density in this area allows us to model the gravity anomaly with very little misfit. Along the subduction zone, however, the velocity models are poorly constrained in the upper mantle, where an anomalous density unit has to be used in order to model the short wavelength gravity anomaly in this area. A third transect across central Taiwan that is derived from the TAIGER local tomography data, provides good control on the crust and upper mantle Vp structure that we use to place provide density constraints for modeling the gravity anomaly in this part of the collision zone. In order to model the short wavelength gravity anomaly across the Longitudinal Valley and the southern Longitudinal trough, an anomalous density block is required beneath the fore-arc region. We interpret that the source of this anomalous density material could be serpentinized fore-arc mantle, similar to what is interpreted for the northern Manila subduction zone farther south. Water released from the subduction of the extended crust of the continental margin results in the serpentinization of the fore-arc area and may be driving the uplifting of the high-pressure rocks. [ABSTRACT FROM AUTHOR]

Exposed in the Coastal Range of eastern Taiwan is a portion of the Luzon volcanic arc that has collided with the South China continent since 6 Ma, as well as syn-orogenic sedimentary rocks deposited on the arc and subsequently intensely folded and thrusted. This study sampled syn-orogenic mudstones for the measurement of anisotropy of magnetic susceptibility (AMS) at four sites on the sides of the range. The AMS fabrics reveal a contribution from burial compaction and, less significantly, tectonic shortening which varies slightly across the range. This lateral variation is considered as, for simplicity, a result of two-phase deformation because these rocks were involved in an eastward propagating back thrust system on the colliding arc. A new strain analysis method is developed to estimate the overall tectonic strain by unstraining the pseudo-strains with respect to the AMS measurements at each site with the knowledge about the distribution of the susceptibility ellipsoids in the unstrained state. Strain results reveal that shortening phases occurred before and after the folding, with a shortening ratio of 0.177–0.195 and 0.181–0.248, respectively. The post-folding shortening on the western side is sub-parallel to the range, and the pre-folding shortening on both sides is layer-parallel and nearly perpendicular to the range. Therefore, the mudstones underwent layer-parallel shortening, fold-related tilting and eventually orogen-parallel shortening after deposition. This sheds light on the complexity in deformation of the colliding Luzon arc. • Syn-orogenic mudstones in eastern Taiwan have composite magnetic fabrics. • A new method is developed to estimate strain from AMS data at a site. • Luzon arc mudstones underwent shortening before and after folding. [ABSTRACT FROM AUTHOR]

To better understand the establishment of subduction zones, considerable effort is required regarding various factors, such as the time of subduction initiation and the age of the slab's lithosphere. In this study, adakitic dikes (ca. 17.3 Ma: ε Nd of 7.4–7.9 and 206Pb/204Pb of 18.27–18.42) were recognized to crystallize along with the normal and enriched mid-ocean ridge basalt (N- and E-MORB)-like oceanic crust (ca. 17.8–14.1 Ma: ε Nd of 8.8–13.3 and 206Pb/204Pb of 17.71–18.22) in the East Taiwan Ophiolite (ETO). Given that the outcropping in ultramafic sequence, the distinct Nd–Pb isotopes, and the slight precedence than corresponding arc volcanism (≤ ca. 14.1 Ma), the origins of the ETO adakitic dikes are related to amphibolite-facies melting of the subducted slab beneath the Luzon forearc spreading center during subduction initiation. In this respect, we conclude that the sparsely exposed but isotopically heterogeneous E-MORB-type rocks (ε Nd of 8.8–10.2 and 206Pb/204Pb of 18.06–18.22) are Nb-enriched basalts and relate to the Nb-enriched slab melts derived from further melting of the hot eclogitic residuum of the young South China Sea subducted slab. In addition, the isotopic diversity of N-MORB-like samples can be attributed to the diking of adakitic and Nb-enriched slab melts beneath the Luzon forearc spreading center. Combined with the previously reported early Miocene uplift of the Zambales Ophiolite in the western Luzon, we infer an early Miocene induced-subduction initiation of the South China Sea and the delayed near-trench spreading of the Luzon forearc by <5 Myr. Compared to the absence of Nb-enriched slab melts and >20 Myr subducted slab in the genesis of the in-situ Izu-Bonin-Mariana (IBM) forearc and the voluminous Nb-enriched rocks and ca. 0 Myr subducted slab of the Central Palawan–Amnay ophiolites, the sparse Nb-enriched rocks and <15 Myr subducted slab of the ETO sequence invoke the governing factor of slab's lithosphere age during subduction initiation magmatism. We propose that the lack of Nb-enriched slab melts in the forearc chemostratigraphy of the Oman Ophiolite may indicate the subduction initiation of an old and cold oceanic plate. • Coeval adakitic & Nb-enriched dikes expose in the forearc-type East Taiwan Ophiolite. • Mid-Miocene East Taiwan Ophiolite is representative fragments of the Luzon forearc. • Luzon forearc was due to South China Sea Early Miocene induced-subduction initiation. • Slab's crystallization age is governing factor of subduction initiation magmatism. [ABSTRACT FROM AUTHOR]

Sponsored by the Chinese National Fundamental Research and Development Program in 2001, Guangzhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS), through the Luzon Arc, to the Huatung Basin and the Gagua Ridge. Based on high-resolution seismic data from this survey, combined with gravimetric and magnetic modeling, a systematic effort is made to the study of the regional geodynamics offshore southern Taiwan. By focusing particularly on precollisional tectonic interactions between adjacent geological units and their tectonic affiliations, this study can help reveal early arc-continent collisional processes that formed the Taiwan orogen. The construction of the Manila accretionary prism and its eastward progressive deformation indicate that the subduction of SCS have experienced multiple phases of increased activity. Active precollisional crustal shortening within the Northern Luzon Trough resulted in tilting of sedimentary layers at angles between 6° and 13°. But the shortening induced by tilting accounts for only a tiny part of regional total crustal compression. The eastern flank of the Luzon Arc appears to be more active than the rest, evidenced by active faulting and folding in the intra-arc basins on the eastern flank. Magnetic modeling/inversion shows that the Luzon Arc may have experienced multiple phases of magmatic activities, causing lateral magnetic inhomogeneity. Bouguer gravity anomalies and gravity modeling indicate that the Huatung Basin has anomalously higher crustal and upper mantle densities than those of SCS and the Luzon Arc. In addition, there is a large bathymetric difference between the Huatung Basin and the northeastern part of SCS basin. These observations argue against early hypothesis that the Huatung Basin and the northeastern part of SCS basin may once have belonged to one single oceanic crust, in part or in whole. The Gagua Ridge, as a sliver of uplifted oceanic crust, may be related to a transient northwestward subduction of the western Philippine plate. All evidences point to the argument that the region offshore southern Taiwan is experiencing multiple terrain amalgamation, which is a classical model for continental growth. [ABSTRACT FROM AUTHOR]

The Philippine Sea Plate is converging against the Eurasian Plate near Taiwan at a velocity of 7–8 cm yr−1; this has caused the Taiwan orogenesis and induced abundant earthquakes. In this study we examine the corresponding change of gravitational potential energy (ΔGPE) using 757 earthquakes from the earthquake catalogue of the Broadband Array in Taiwan for Seismology (BATS) from 1995 July to 2003 December. Our results show that the variation of the crustal ΔGPE strongly correlates with the different stages of the orogenesis. Except for the western Okinawa Trough and southern Taiwan, most of the Taiwan convergent region exhibits a gain of crustal ΔGPE. In contrast, the lithospheric ΔGPE in the Taiwan region exhibits a reverse pattern. For the whole Taiwan region, the earthquake-induced crustal ΔGPE and the lithospheric ΔGPE during the observation period are and , respectively. The average rate of the whole ΔGPE in the Taiwan region is very intense and equal to , corresponding to about 1 per cent of the global GPE loss induced by earthquakes. [ABSTRACT FROM AUTHOR]

The active convergence between the northwest corner of the Philippine Sea Plate and the southeast margin of the Eurasian Plate has given rise to the Taiwan mountain-building and produced numerous earthquakes. Among the earthquakes, the 1999 Chi-Chi earthquake is the largest one recorded in the century. In this study, we examine the crustal gravitational potential energy (GPE) change in the Taiwan orogen caused by the Chi-Chi earthquake sequence, which was catalogued by the regional broadband seismometer array for a whole year. As a result, we find that the crust was going up and down randomly during the earthquake sequence, but an overall cumulative gain of the crustal GPE, +1.82×1016 J, was rapidly achieved in 1 month after the main shock. The crustal GPE was nearly still afterwards and reached +1.90×1016 J in 1 year. Spatially, although the main surface faulting has occurred in western Taiwan, the crustal GPE gain is mainly distributed in central Taiwan at the area where the existing crustal GPE is high and the existing lithospheric GPE is relatively low. The crustal GPE loss by the Chi-Chi earthquake sequence can also be observed and is generally distributed at both sides of the crustal GPE gain area. The crustal GPE gain mainly found in central Taiwan corroborates that the uplift of the Taiwan orogen is principally taking place in central Taiwan, rather than in the more hazardous western Taiwan. [Copyright &y& Elsevier]

The convergence between the Eurasian Plate and the Philippine Sea Plate results in rapid uplifting of the Taiwan Orogen. To study the mountain building in Taiwan, we present three transects of shear wave velocity across the Taiwan mountain belt with joint inversion of teleseismic Rayleigh wave H/V ratios and phase velocities derived from ambient noise tomography. The Particle Swarm Optimization algorithm is introduced into the joint inversion and is proved to be an efficient tool in solving the geophysical inverse problems. In determining the H/V ratios, cross-correlation techniques are used to reduce the non-great circle effects of the Rayleigh wave packets and to correct sensor misorientations. The cross-correlation techniques improve the accuracy of the H/V measurements, especially at the short periods. The observed up-to-middle crustal thickening in the central segment of the Central Range suggests lithospheric collision tectonism, whereas the lower crustal thickening in southern segment is proposed to be related to subduction of the Eurasian continental crust. In the north, however, no crust thickening is observed. The variations of the crust architecture along the axis of the Taiwan Orogen favor a close coupling relationship between mountain building and slab interactions in the mantle. Beneath the Central Range, the twist of the fate of the Eurasian continental crust from consumption in the south to collision in the central segment is proposed to be resulted from the slab breakoff beneath central Taiwan. • High-resolution shear wave velocity transects across the Taiwan Island from joint inversion. • Deflection of Rayleigh wave packet from the great-circle path. • Coupling of the mountain building with the subsurface slab interactions in Taiwan. [ABSTRACT FROM AUTHOR]

In their Comment to Resentini et al. (2020) , Mesalles et al. pointed out supposed fundamental inaccuracies concerning analytical aspects and the tectonic interpretation of fission-track data. This would invalidate the main conclusions of our study. Here we demonstrate that their criticism is ill-founded. [ABSTRACT FROM AUTHOR]

The interpretation of modern river apatite fission track (AFT) data of Taiwan by Resentini et al. (2020) presents some fundamental inaccuracies that call in question the main conclusions of the paper. The study aims at approximating source rock cooling histories by analysing erosional products, but ignores existing bedrock data in their maps and discussions. The allegedly "new" southern extension of the AFT reset zone is largely unconstrained by the presented data and ignores the local geology and stratigraphy of individual drainage basins. Notably, low grain counts (median=9) and catchment with various geological provinces, including orogenic derived sediments, question the significance of the dataset to characterise "single geological domains" as explained in the paper. Overall, the new data do not provide discriminating evidence for an earlier collision in the north of the island and thus do not support a southwardly propagation of collision. [ABSTRACT FROM AUTHOR]