Passive margins through earth history

The disastrous effects of the 1999 Chi-Chi earthquake in Taiwan demonstrated an urgent need for better knowledge of the island's potential earthquake sources. Toward this end, we have prepared a neotectonic map of Taiwan. The map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40-m resolution digital elevation model, augmented by geodetic and seismologic data. The active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the Eurasian continental margin have created two neotectonic belts in Taiwan. In the southern part of the orogen both belts are in the final stage of consuming oceanic crust. Collision and suturing occur in the middle part of both belts, and postcollisional collapse and extension dominate the island's northern and northeastern flanks. Both belts consist of several distinct neotectonic domains. Seven domains (Kaoping, Chiayi, Taichung, Miaoli, Hsinchu, Ilan, and Taipei) constitute the western belt, and four domains (Lutao-Lanyu, Taitung, Hualien, and Ryukyu) make up the eastern belt. Each domain is defined by a distinct suite of active structures. For example, the Chelungpu fault (source of the 1999 earthquake) and its western neighbor, the Changhua fault, are the principal components of the Taichung Domain, whereas both its neighboring domains, the Chiayi and Miaoli Domains, are dominated by major blind faults. In most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid-7 values.

https://fault.moeacgs.gov.tw/UploadFiles/files/MEETING/2009/C1_4.pdf

Neotectonic architecture of Taiwan and its implications for future large earthquakes

Interaction between surface and tectonic processes plays a key role in the structural evolution, kinematics, and exhumation of rocks in orogenic wedges. The deformation patterns observed in analog models show that strain partitioning has a strong impact on the vertical component of displacement of tectonic units, which in return favors erosion in domains of important uplift. Partitioning is controlled by tectonic processes and by climate-dependent surface processes, including erosion and sedimentation. The effects of partitioning include localization of deformed domains, exhumation above areas of deep underplating, and steady-state maintenance of wedges for long time periods. Simple models illustrate well how the morphostructural evolution of mountain belts is determined by these complex interactions.

Impact of erosion, sedimentation, and structural heritage on the structure and kinematics of orogenic wedges: Analog models and case studies

Well-documented stratigraphy and clearly defined geodynamics in Taiwan, where some of the best records on arc-continent collision have been preserved, offer a unique example for the study of collision belts worldwide. The oblique arc-continent collision in Taiwan caused a simultaneous and sequential migration of four tectonic processes. Beginning from 16 to 15 Ma, subduction of the South China Sea oceanic crust beneath the Philippine Sea plate resulted in volcanism in the Coastal Range and formation of an accretionary prism in the Central Range. Beginning in the latest Miocene–earliest Pliocene, the subduction was followed by initial arc-continent collision, as supported by the following: unroofing and erosion of the deformed accretionary prism, and deposition of sediments thus derived in the adjacent accretionary forearc (5 Ma) and slope basins (4 Ma); waning of volcanism (north, 6–5 Ma; south, 3.3 Ma); buildup of fringing reefs on the gradually quiescent volcanoes (north, 5.2 Ma; south, 2.9 Ma); arc subsidence by strike-slip faulting and the development of pull-apart intra-arc basins (north, 5.2–3.5 Ma; south, 2.9–1.8 Ma); thrusting of forearc sequences to generate a collision complex starting from 3 Ma; and clockwise rotation of the arc-forearc sequences (north, 2.1–1.7 Ma; south, 1.4 Ma). The collision propagated southward and reached southern Taiwan by 5 Ma, as evidenced by the successive deformation of the associated accretionary wedge en route. Afterward, the advanced arc-continent collision stage appeared in the earliest Pleistocene, as marked by the westward thrusting and accretion of the Luzon arc-forearc against the accretionary wedge (north, 1.5 Ma; south, 1.1 Ma) and exhumation of the underthrust Eurasian continent rocks (north, 2.0–1.0 Ma; south, 1.0–0.5 Ma). The final stage of the tectonic process, arc collapse-subduction, began by 1 Ma off the northern Coastal Range.

The geologic records compiled and presented in this study strongly support the scenario of a continuous southward migration of tectonic processes and a change in sediment source and structural style. Most importantly, the model has a broad potential for reconstructing and predicting the evolution of arc-continent collision through space and time.

Temporal and spatial records of active arc-continent collision in Taiwan: A synthesis

Provenance control on chemical indices of weathering (Taiwan river sands)

Marine observations offshore of Taiwan indicate intense deformation of the Luzon arc-forearc complex, with episodic eastward migration of the active deformation front across the complex. The Philippine Sea Plate (PHS) began colliding with the Eurasian continental margin in Pliocene time. Because of the obliquity of plate convergence, the collision has propagated through time from north of Taiwan to the south with the more advanced stages being presently observed to the north, whereas the subduction of the oceanic lithosphere of the South China Sea beneath the PHS occurs to the south. Offshore, the collision zone is characterized by deformation of the arc including the forearc region to the south. This active tectonic domain absorbs a significant amount of shortening between the Eurasia margin and the PHS, which is moving towards N 310° E at about 8 cm/yr relative to Eurasia. Swath bathymetry and backscattering data, together with seismic reflection and geopotential data obtained during the ACT cruise onboard the R/V L'Atalante, showed major north to south changes in the tectonic style in both the indenting arc and the host margin. In the southern domain, left-lateral transpression is recorded by deformed and folded series of the forearc domain that are unconformably overlain by collision-derived sediments of the Southern Longitudinal Trough (SLT). Today, the loci of deformation has jumped to the east and it is characterized by the growth of a sedimentary ridge (the Huatung ridge, rear portion of the former Manila oceanic accretionary wedge including forearc and intra-arc sequences), which overthrusts the basement of the island arc. In the northern domain, north of 22°30'N, active westward thrusting of the Coastal Range (remnants of the island arc and forearc basins) over the Lichi melange develops onland along the Longitudinal Valley. Offshore, at the base of the eastern slope, prominent fault scarps suggest an active eastward thrusting of parts of the arc (volcanic edifices and intra-arc or forearc sediments) onto the oceanic crust of the Philippine Sea Plate. It accounts today for part of the convergence. The

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Philippe Schnuerle

Papers

Arc-continent collision in Taiwan: New marine observations and tectonic evolution