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Abstract:
The eastern piedmont of the Helan Shan has experienced many tectonic activities since the Late Pleistocene. Previous studies have focused on the tectonic activity of it by various methods including geomorphic parameters. Hack profiles and stream length-gradient index(SL) are also parameters reflecting regional tectonic activity, which have not been applied in the eastern piedmont of the Helan Shan. In this paper, Hack profile and SL were extracted from the Hongguozigou to Zihuagou in the eastern piedmont of the Helan Shan to explore regional tectonic activity, the steepness index(ksn) and the hypsometric integral(HI) were extracted to verify their results. With the help of ArcGIS and MATLAB program TopoToolbox 2, 12 rivers in the study area were extracted from DEM data, and then Hack profile and SL were obtained by ArcGIS and Excel. ksn and HI were extracted by ArcGIS and MATLAB program for auxiliary verification. The results show that the distribution of equilibrium slope index(K) from Hack profile has a different trend from the peak distribution of standardized stream length-gradient index(SLK). The K value is generally higher in the southern part of the region than the northern part, while the high value of the SLK gradually decreases from north to south. The results of HI and ksn correspond to the distribution of K value, which are higher in the southern than the northern on the whole. And the distribution trend of the peak of ksn is similar to the high value of SLK. In general, HI and ksn verify the results of the K value and SLK respectively. Combined with the previous research results and the characteristics of the parameters, this paper believes that the different trends, the south of the K is higher than the north and the north of the SLK is higher than the south, may reflect the tectonic activity characteristics of the eastern piedmont of the Helan Shan at different time. The Hack profile reflects the tectonic activity in a later period from the macro scale, while the SL parameters retain the record of the tectonic activity in the longitudinal of the channel in a relatively earlier period from the micro scale. In previous studies, one argue that the tectonic activity of the eastern piedmont of the Helan Shan is greater in the north than the southern part, the other thinks the south is greater than the north. This paper believes that they may reflect the characteristics of different time. Combined with previous studies, since the Late Cenozoic, the northern part of the Helan Shan has been uplifted and its tectonic activities have gradually weakened from north to south. While since Late Quaternary, the Helan Shan has experienced differential uplift, showing tectonic activity is higher in the southern than that in the northern. Hack profile and SL parameters may also be able to explore regional tectonic activity characteristics from the perspective of time.
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