dc.description.abstract | Taiwan sits at the convergent plate boundary between the Eurasian and the Philippine sea plate, and the Luzon arc collided northwestward with the passive Chinese continental margin of the Eurasian plate. Continuing and active mountain building processes makes Taiwan a modal locality for studying mountain building processes. The slate terrane of the Taiwan mountain belt including two geological units, the Hsuehshan Range(HR) and the Backbone Range slate belt(BRSB), both are composed by Eocene to Miocene passive margin sequences. Due to the contrasting characteristics of the two units, previous studied proposed different models to interpret the contact relationship between the Hsuehshan Range and the Backbone Range, including disconformity, fault, and plate suture. This study combines field observations, peak metamorphic temperature from Raman spectroscopy of carbonaceous material(RSCM), slickenside paleostress analysis and thin section microstructure to investigate the property of this boundary, and then reconstructing the tectonic evolution of the slate terrane. According to the field observations, the dip of foliation in the Hsuehshan Range is steeper than the Backbone Range slate belt, even a crenulation foliation in the Backbone Range slate belt. In this research, we found four fault outcrop, including brittle, brittle-ductile, and ductile shear zone outcrop. The slickenside paleostress analysis shows there are two event, early E-W extension and late NW-SE compression. According to RSCM results, the metamorphic temperature of the Hsuehshan Range(321~372°C) is higher than Backbone Range slate belt(223~280°C) and small region of mid-temperature(281~320°C) between them. We consider that the fault offset was responsible for the observed metamorphic temperature gap, and the mid-temperature region caused by near surface branch faults. According to the microstructure results, we found the coaxial pressure shadow in the Hsuehshan Range and the non-coaxial pressure shadow in the Backbone Range slate belt, representing different deformation pattern in the two regions. Combining all of the data, we propose the structure evolution of the research area. The strata of the Hsuehshan Range deposited in the passive continental margin Hsuehshan Trough, and the pelagic Miocene Lushan Formation subducted and get into the accretionary wedge in the late Miocene. Then the Hsuehshan Trough subducted and folded and also achieved the maximum metamorphic temperature under the orogenic wedge. In the end the Backbone Range Lushan Formation juxtaposed with inner Hsuehshan Range strata, the contact relationship between them is the Lishan Fault. Because of the Lishan Fault east vergent thrusting, the Hsuehshan Range was more exhumed ~3 km than the Backbone Range slate belt and exposes rocks with higher metamorphic temperature. | en_US |