پديد آورندگان :
خبازي، مصطفي نويسنده دانشجوي دكتراي ژيومورفولوژي، دانشگاه اصفهان , , سيف، عبداله نويسنده استاديار دانشكدهي علوم جغرافيايي و برنامهريزي، دانشگاه اصفهان , , معيّري ، مسعود نويسنده دانشيار دانشگاه اصفهان , , نوحه سرا ، مريم نويسنده كارشناس ارشد جغرافيا و برنامهريزي شهري، دانشگاه آزاد نجفآباد ,
كليدواژه :
تكتونيك فعّال , كواترنري , مخروطافكنه , دق سرخ , لندفرم
چكيده فارسي :
مخروطافكنهها يكي از مهمترين لندفرمهاي كواترنري شمرده ميشوند كه ميتوان از آنها بهعنوان پديدهايي ژيومورفيك، در شناخت ميزان فعّاليّتهاي تكتونيكي بهره جست. در اين پژوهش نخست، مخروطافكنههاي حوضهي آبخيز دق سرخ در ايران مركزي از نظر تعداد، مساحت و نحوهي پراكنش در ارتباط با ويژگيهاي فيزيكي حوضههاي آبريز بالادست، همچون مساحت، طول، ارتفاع كم، متوسّط و مطلق محاسبه شد. سپس تلاش گرديد بر اساس رابطههاي موجود، ارتباط معناداري ميان ميزان فعّاليّتهاي تكتونيكي و حجم مخروطافكنهها و مساحت حوضهي آبريز آنها برقرار شود. در گام بعد با استفاده از 6 شاخص ژيومورفيك، ميزان فعّاليّتهاي تكتونيكي منطقه (Lat) ارزيابي شد. پارامترهاي (S)، (R)، (h) با استفاده از نرمافزارهايArc GIS وAuto CAD بهدست آمد. نتايج پژوهش نشان داد، گرچه بين عوامل حجم مخروطافكنهها (V) و مساحت حوضهي آبخيز بالادست (BA)، ميتواند روابط معنادار بالايي وجود داشته باشد، اما در محدودهي مطالعاتي، مساحت حوضههاي بالادست مخروطافكنهها (BA) تاثير معناداري بر حجم آنها (V) ندارد؛ بنابراين با مطالعهي ويژگيهاي زمينشناسي، استخراج لايهها و رويهماندازي محدودههاي حوضههاي آبريز بالادست، محدودهي مخروطافكنهها و گسلها، مشخّص شد. بررسي ها نشان داد وجود گسل در حوضههاي بالادست مخروطافكنهها تاثير زيادي در افزايش حجم آنها ايفا كرده، بهگونهاي كه در هر حوضه، بالاترين مقدار عامل V مربوط به مخروطي است كه در حوضهي بالادست آن گسل وجود دارد. بنابراين عامل تكتونيك نقش اصلي در افزايش يا كاهش حجم مخروطافكنهها داشته و مساحت حوضهي بالا دست(BA) ، بهعنوان يك عامل فرعي شمرده ميشود.
چكيده لاتين :
Introduction
Morphology of alluvial fans with different levels might be recognized as an index from tectonic activities, because they reflect the amount of tectonic processes such as corrosion fault, displacement and folding over and next to the mountain front.
The watershed of Degh Sorkh is located in tectonic zone of Iran center. Building blocks in this part of Iran are the result of young Alpine tectonic process and the general process of the main buildings of geology in this zone are matched with the general process of tectonic zones in Sanandaj, Sirjan and Zagroos.
Methodology
The main purpose of the present article is to account the volume of alluvial fans and examination of their relationship with tectonic characteristics of DeghSorkh watershed. In order to achieve this, initially, articles, books and internal and external resources were collected by library research and it was recognized that among the methods of accounting the volume of alluvial fans, Church (1997) and Gills (2010) methods have high efficacy for estimation of the volume of alluvial fans. (Figures 1 and 2). In the next step, topographic maps of 1/50000 and satellite images of ETM+2008 for determining and bordering the studied watershed were used. The geology maps of 1/100000 and 1/250000 of the zone were digitized in Arc GIS space in order to extract the lithologic features, and the material of formations and fault layers. DEM of the area was used for some accountings. As the next step, the area of alluvial fans, sweep angle or the angle between two margins of alluvial fans on its head (S) and the radius of the alluvial fan or the horizontal distance between head and base of the cone (R) for 119 alluvial fans were drawn with the help of satellite images of ETM+2008, SID and survey. The mentioned data were given to Arc GIS 9.3 software and the sweep angle and alluvial fans radius were calculated. After giving the area of the alluvial fan to the software Arc GIS, the height difference of head and base of the alluvial fan (h) were calculated using topographic map 1/50000 and DEM of the zone. The calculation of alluvial fans volume was obtained based on the relation (1) (adopted from Church 1997: 107; and Jils, 2010: 321).
After calculating 119 alluvial fan volumes, the exit point of each fan (cone) was calculated and based on this we blocked the borders of the watershed of each alluvial fan. Therefore, we drew 119 watersheds (parcel) on the topographic maps and the area of each one was calculated.
Results and Discussion
The main purpose of the present study was to study and examine the relationship between the alluvial fans volume and the area of the upstream watershed, on the one hand, and the effect of active tectonic, on the other; therefore, it was attempted to calculate the geometric characteristics of the alluvial fans and to establish a significant relationship between tectonic activities and the volume of the alluvial fans and the area of their watershed. The findings of the present study indicated that although significant relationships could be existed between the mentioned variables (for example Mesabulaz, the international researcher has proved the correlation between the mentioned variables), in the studies area by the authors, the area of upstream watershed of the alluvial fans (BA) does not have a significant effect on the volume of the alluvial fans so that correlation coefficient between the two mentioned parameters for the watershed of Ardestan was 0,30, Barkhaled Abad0.05, Torogh Abiazan 0.007 and Degh Sorkh was zero. On the other hand, the volume of the alluvial fan is not just under the effect of the upstream watershed, but some other factors such as petrology, tectonic, climate and morphometric characteristics of drainage watersheds are effective in decrease or increase of alluvial fan volume. Therefore, studying the geology features of the studied area and extraction of the faults layer from the geology maps of 1/100000 and overlay of the upstream watershed areas, the area of the alluvial fans and the faults were determined that the existence of the fault in upstream watershed of the alluvial fans has significant effect on the increase of the volume of the fans so that, in each watershed, the highest amount of V parameter in related to the cone (fan) which is in the upstream watershed of that fault.
Conclusion
Calculating the geomorphic indices for evaluating tectonic activities shows that from a tectonic viewpoint, the northwest and southwest studied areas are more active than central and eastern parts of the watershed so that the index (Lat) is indicative of high activity in Torogh-abizan watershed, Bad-e Khaled Abad and also the amount of average tectonic activity in Ardestan and Degh Sorkh watersheds. Thus, according to the abovementioned points, it could be observed that tectonic factor has a major effect on increase or decrease of alluvial fan volume and the area of the upstream watershed (BA) is considered as a secondary factor.
