| dc.description.abstract | Taiwan is the junction of Eurasia Plate (EU) and Philippine Sea Plate (PSP). On the southwestern edge of the Coastal Range, eastern Taiwan, outcrops a special geological unit, Lichi Mélange. It’s the remaining product of the Taiwan arc-continental collision. It records the history of the entire arc-continental collision during the closure of the Luzon forearc basin. According to previous field investigations and paleostress studies of Lichi Mélange in the central part and southern part of the Coastal Range, the Lichi Mélange should originate from lower part of the forearc basin sequence with intensive shearing; the maximum principal stress axis has two main directions: one is parallel to the direction of plate motion of PSP (azimuth 335°), and the other is perpendicular to the structural lineation of the volcanic island arc (azimuth 315°). However, paleostress data is sparse in the southern tip of the Coastal Range, where Lichi Mélange outcrops extensively. There is no arc body buttressing on the eastern side of the mélange, and the onshore accreted arc is exposed north of the area, a different relationship between the Lichi Mélange and the volcanic arc than observed in the central to southern Coastal Range. Furthermore, there outcrop vast numbers of exotic blocks, including the Fukang Sandstone, in the southernmost tip of the Coastal Range. The stress regime in this area may be complicated due to the relative location of the arc body and the presence of exotic blocks. To understand the structural evolution of Lichi Mélange in this area, field observations, paleostress analysis and petrographic analysis are applied. The results show that the paleostress axis from north to south in the west side of the southern tip of the Coastal Range changed from northwest-southeast to northeast-southwest direction, and the paleostress axis in the Jia river drainage to the east is mainly north-south direction; such transformation of the paleostress direction may be related to the change in the relative position of the arc body. In addition, influences from presence of exotic blocks seem generally controlled by the contact geometry with the mélange matric. Numerous backthrust structures are documented through field investigations in the Jia river drainage, and may be the mechanism for extensive Lichi Mélange exposures in this area.
Key words: southern tip of the Coastal Range, Taiwan, Lichi Melange, Stress analysis, Petrographic analysis | en_US |