Structural evolution of the Taiwan fold-and-thrust belt gleaned from balanced cross sections and tectono-metamorphic studies in the Central Range

Taiwan is situated along an active plate boundary between the Eurasian Plate and the Philippine Sea Plate, with a convergence rate at about 80 mm/yr. The convergence results in an ongoing mountain building that displays a structure particularly complex. This dissertation mainly focuses on the structural and tectonic evolution of the Taiwan fold-and-thrust belt and its eastern metamorphic Yuli Belt in the Central Range. The study involves geological mapping, cross-section construction and balancing, whole-rock geochemistry analysis, Raman spectroscopic geothermometry, and palaeogeographic reconstructions. (1) Three crustal-scale geological cross-sections at various latitudes of the Taiwan fold-and-thrust belt were constructed. The largely Eurasian basement overthrust the Cenozoic passive margin series and which are tectonically overlain by the upper-plate-derived Coastal Range series. The restoration of cross sections yields a minimum shortening of ca. 120 km in the Eurasian passive margin series, on top of which the accreted material was initially sitting, already subducted below the Philippine Sea Plate. (2) Fieldwork and structural analyses indicate three deformation phases in the Yuli Belt. Based on cross sections and a review of available P-T-t data, we suspect that blueschist-facies units could have been emplaced on top of greenschist-facies metasedimentary units along a thrust during a first deformation phase D1. (3) We integrated new and published Raman-spectroscopic measurements on carbonaceous matter from metasedimentary successions across the Tailuko and Yuli Belts and combined these results with new cross sections. We suggest that the Yuli Belt was initially emplaced on top of lower-grade Paleogene successions. Later, the nappe succession was overprinted by E-vergent backfolding of the Central Range and contemporaneous backthrusting along the Shoufeng Fault, leading to the presently observed synformal structure of the Yuli Belt.

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