A Study of Maroon Basin Neotectonics and Erosion Using Geomorphometric Techniques

In the regions with the active tectonics, the geometry and evolution of the river systems are sensitive to the surface uplift rate. The simply-folded belt of Zagros has been developed during the late Cenozoic era, and is still active as it is affected by the tectonic activity of the Arabian-Iranian shortening processes pertaining to plate boundary, since the widespread seismic activity in this region is an evidence. In a tectonically active region, geomorphic markers, such as alluvial fans, multiple river terraces and some other geomorphic features are essential as a reference frame for the gauge deformations. Stream profile analysis is a more stable parameter in the tectonic studies than the river terraces. By using digital elevation models (DEMs), such analyses would become easier, faster, and more precise. The study area is located in the southwestern Zagros Simply-Folded Belt (ZSFB) in southwestern Iran.
THEORETICAL FRAMEWORK: Geomorphometric analyses were done by using Digital Elevation Model in this study and some parameters such as concavity and drainage steepness were calculated. The Tectonic Uplift rate of the main stream of the catchment was calculated based on the geomorphometric analysis. The hypsometry curve showed that this catchment is an old one, so erosion is more progressive than the tectonic activity. The uplift rate in the middle of the catchment is higher. Also, the isobase maps were analyzed to yield more accurate understanding about the erosional condition of the catchment in its history. The spatial distribution of the stream height (isobase map) is a useful proxy for investigating the geologic or tectonic processes. Drainage networks are commonly organized according to the Strahler stream order. Streams of similar orders are of similar geological age, and are related to similar geological events. Hence, the interpolation of the isobase lines, connecting streams with a similar order, produces a surface resulting from the same erosional events.
The hypsometric curves have been used to infer the developmental stage of the drainage network and also it is a powerful tool to differentiate between the tectonically active and inactive areas. The curve is created by plotting the proportion of total basin height against the proportion of total basin area. Convex hypsometric curves characterize the young slightly eroded regions; The S shaped curves characterize the moderately eroded regions; concave curves point to the old, highly eroded regions. Streams of similar orders are of similar geological age and are related to similar geological events. Hence, the interpolation of isobase lines, which connects streams with a similar order, produces a surface resulting from the same erosional events. Isobase lines represent the erosional surfaces formed due to the recent tectonic and erosional events. Studies suggest that the isobase maps are prepared by interpolating the elevation at the location of the 2nd and the 3rd order streams. Sharp changes in the isobase map indicate the possible location of the faults and/or lithological contrasts.
Results show that the Khayzi anticline is a flat part in the isobase map, meaning that this anticline is younger than the other parts of the study area. The quantitative SL indices linked to the relative rock resistance described above with field observations suggest that, along the southern part of the Maroon River, the values of the SL index show a variable distribution. The highest and perhaps the most anomalous values of the index are along the Maroon River on its pass from Khayiz anticline. Hypsometry analysis is based on investigating the shape of the basin hypsometric curves which is convex. The hypsometric integral of the Maroon river basin is about 0.22, which means that this basin is an old one. The analyses suggest that as the basin is in the old stage, so the erosion processes are more influent that the tectonic ones. The incision map or the local relief is used to identify the regions of high gradients. The Maroon River is studied using the stream power law. This is a three-segment stream. The two knickpoints show the tectonic activity.
CONCLUSIONS AND SUGGESTIONS: As the stream goes down, the sharp change in the geomorphic indices shows gradual changes in the lithology and tectonic activity. The northern part of the region has low steepness values and because the steepness is directly related to the uplift rate, it means that the region has undergone less deformation processes on the northern section, compared to the other parts.