Inversion of the Paleogene Chinese continental margin and thick-skinned deformation in the Western Foreland of Taiwan

New structural data, available seismicity data together with mechanical constraints on the Eurasian continental lithosphere and reconstruction of paleostress trajectories are combined in order to re-assess and discuss the dominant deformation mode (thin-skinned vs thick-skinned) in the Western fold-and-thrust belt of the active Taiwan collision zone. Serial balanced cross-sections and computed paleostress tensors suggest that structural styles and stress trajectories at the front of the Taiwan mountain belt may vary rapidly along-strike depending on the presence of pre-orogenic Paleogene troughs in the Chinese continental margin (Taihsi and Tainan basins) that are favourably oriented to be reactivated and inverted. In localities of the western foreland, where basin inversion and thick-skinned basement-involved shortening predominate, the crustal seismic activity is important and characterized by strike-slip faulting. In these domains of the fold–thrust belt, the stress deviations with respect to the regional transport direction are also important. By contrast, in domains of significant syn-orogenic subsidence, a thin-skinned style of deformation may be prominent due to the lack of available pre-existing features. The seismic activity is limited to few major faulted boundaries such as the active Chelungpu–Sani thrust, and the stress deviations are limited. The timing of deformation at the belt front seems to be independent of the structural styles, so that frontal folds are active since probably 0.5 Ma. However, in inner parts of the Western Foothills of Taiwan, where superimposed thick-skinned and thin-skinned deformation are required, out-of-sequence thrusting occurs to maintain the topographic profile. Finally, we suggest that kinematics and structural styles of the western fold–thrust belt are controlled by the mechanics of the Eurasian continental margin in agreement with a recent study. At the scale of the orogen, the limited shortening amounts across the WF and in the Central Range as well as the absence of continental HP-rocks better support a thick-skinned collision model for Taiwan.