DISTRIBUTION OF UPLIFT ALONG THE EASTERN FLANK OF THE CENTRAL RANGE IN TAIWAN: INFERENCES FROM GEOMORPHIC ANALYSES

Mass redistribution by erosion represents a governing force in the tectonic evolution of orogenic systems and this process makes the steepest landscapes associated with regions of rapid rock uplift and it could exert a primary control revealing the uplift evolution. The eroded materials from the orogens are generally carried away by the numerous rivers originated in the mountain belts. Therefore, these rivers and their longitudinal profiles record the changes in landscape. Based on this theory, parameterization of the information of the streams could reveal meaningful geological information in the active tectonic regions. This study choses 18 drainage basins in the eastern flank of the Central Range in Taiwan as the study area, which is the oldest part of Taiwan and recorded complex uplift history. Although many geodetic measurements have been recently applied to reveal the uplift rates in the Taiwan island, they are often difficult to obtain the uplift history of larger time scale. In order to understand this complex history and the relationship between the geomorphology and tectonics, two geomorphic analyses, Stream power bedrock incision model and Drainage basin asymmetry method, have been applied. In Stream power bedrock incision model, the evaluated normalize steepness index (ksn) of each drainage basin is directly proportional to uplift rate of each drainage basin. Whereas in Drainage basin asymmetry method, the calculated asymmetry factor (AF) of each drainage basin is developed to detect tectonic tilting transverse to flow within each drainage basin. The results reveal that there are two obviously relative high uplift zones: the northern-and the central part of the eastern Central Range. The identified high uplift zones coincide with the high uplift zones identified from modern uplift rate obtained by triangulation network survey data, and long-term denudation rate inferred from zircon fission-track data. The fast uplift rates in these two zones could be attributed to the impinging basement highs of Taiwan orogen, the Kuanyin and Peikang highs. The subsidence of the Ilan Plain promote serious incision in the very northern part of the study area and couple with high annual precipitation in the same area, the erosion might feedback to the orogenic system and promote further uplift.