Tectonic activities along the eastern flank of the Central Range in the active Taiwan orogen inferred from river steepness index
Date Issued
2014
Date
2014
Author(s)
Chen, Yi-Wei
Abstract
The tectonic activity of the Taiwan orogenic belt has been well studied by different methods in various time scales, such as long-term (> 1 Ma) thermochronologic data and short-term (yearly to decadal) geodetic analysis. However, constrains on millennial-scale tectonic characteristics is limited, especially in the mountainous core of the island. Recent studies show the channel networks in active orogens reflect the pace at which landscapes respond to tectonic processes and provide a record of relative changes in rock uplift. Therefore, the purpose of this study is to figure out the millennial-scale tectonic characteristics in the mountainous core of Taiwan by using river steepness index (ksn), combining with knick point distributions.
This study analyzed 20 rivers along the eastern flank of the Central Range (ECR), and all of the rivers are the main trunk of each river system, defined as the major branch originated at the ridgeline of the Central Range and flowing perpendicular to the main structures and the strata. On the basis of the characteristics of knick point distributions and ksn, this study devides the rivers into 6 distinctive groups. At the northern and southern ends of ECR, group 1 and group 6 show graded river profiles with low ksn, and the ksn increases gradually toward the center of the orogen. Two groups with high ksn, i.e., high uplift rate, but with different uplift mechanisms are recognized: group 3 is influenced by the Central Range fault, the only major active fault in ECR, and group 5 is dominated by a steady uplifting process. It is noteworthy that the rivers of group 4 show ‘anti-knick points’, which are believed to be the results of the lowering of uplift rates.
The results show that the patterns of ksn are quite consistent with the patterns of tectonic evolution in Taiwan, where in the southern part the orogen is growing, but in the northern part the active collision and mountain-building have waned and the orogen is collapsing. Furthermore, the results not only enabled us to better identify the transition area between each collisional domain in the mountainous area of Taiwan, but also provide information to quantify relative rock uplift rates in the millennial time scale in the mountainous core of the island after calibrating with the results of triangulation measurements.
Subjects
河川陡峭度指標
遷急點
中央山脈東翼
河川下蝕
抬升速率
SDGs
Type
thesis
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