پديد آورندگان :
محمدنژاد، وحيد نويسنده , , اصغري، صياد نويسنده استاديار دانشگاه اروميه ,
كليدواژه :
گسل قربيلك , گسل گرمسار , مخروط افكنه , مخروط افكنه ده نمك , مورفولوژي
چكيده فارسي :
اين پژوهش به بررسي شواهد و آثار گسل هاي فعال بر مورفولوژي مخروط افكنه هاي واقع در بخش خاوري گرمسار، به ويژه نحوه تحول مخروط افكنه بزرگ ده نمك مي پردازد. روش كار مبتني بر تحليل هاي كمّي و كيفي حاصل از تصاوير ماهواره اي و مدل هاي رقومي ارتفاعي، ويژگي هاي مورفومتري مخروط ها، اندازه گيري ميزان جابجايي كانال ها، ميزان بالاآمدگي رسوبات و تحليل شيب و نيمرخ هاي طولي و عرضي است. نقشه هاي توپوگرافي 1:25000، عكس هاي هوايي 1:55000، تصاوير ماهواره اي ETM و IRS و Aster، نقشه هاي زمين شناسي 1:100000 و داده هاي ارتفاعي رقومي ابزارهاي اصلي پژوهش را تشكيل داده اند. همچنين پيمايش هاي ميداني جهت بررسي و اندازه گيري شواهد فعاليت گسل ها در دو مرحله صورت گرفته است. نتايج نشان مي دهد كه گسل هاي گرمسار، سرخه كلوت و قربيلك اثرات اصلي و عمده اي بر روي مخروط افكنه ها گذاشته اند. فعاليت گسل هاي مذكور موجب بالا آمدن رسوبات مخروط افكنه اي و رسوبات اليگوسن زيرين شده است. همچنين فعاليت اين گسل ها موجب ايجاد سطوح مختلف بالاآمده، متروك ماندن سطح مخروط ها، جابجايي نقطه تقطيع آبراهه، بالاآمدگي رسوبات مخروط افكنه اي و جابجايي افقي شبكه زهكشي سطح مخروط افكنه ها و همين طور تاثير بر فضاي قابل دسترس مخروط افكنه ها شده است. مولفه قايم گسل گرمسار و قربيلك موجب شكل گيري سطوح قديمي و جديد (فعال و غير فعال) در سطح اغلب مخروط افكنه ها شده است. اين مخروط ها در واقع آثار و بقاياي مخروط افكنه بزرگ و واحدي به نام ده نمك است كه در اثر فعاليت گسل هاي گرمسار و قربيلك، طي دوره كواترنري، به شكل امروزي در آمده اند.
چكيده لاتين :
Introduction: When a river reaches from high gradient mountains to a low gradient plain, aggradations is occurred and Alluvial fans are built. At least five factors influence fan processes, including catchment bedrock lithology, catchment shape, neighboring environments, climate, and tectonics. Rocks of differing lithology yield contrasting sediment suites and volumes due to their variable response to weathering. Bedrock in desert settings is optimal for fan development, especially tectonically maintained mountain fronts, yields sediment in varying size and volume depending on: (a) the style of fracturing in proximity to faults, (b) the presence or absence of internal discontinuities such as bedding planes or foliation planes, and (c) the reaction to chemical weathering and non-tectonic types of physical weathering. Aeolian, fluvial, volcanic, lacustrine, or marine environments that border alluvial fans can impact fan processes by modifying the conditions of deposition. Fluvial environments, usually in the form of longitudinally oriented rivers, may affect fans by eroding their distal margins. Climate and its fluctuations affect water supply and vegetation cover. Without continued tectonics, fans may become minor or short-lived features. In this study, the evidences and impacts of the active faults are investigated in alluvial fans morphometry and morphology located at the east part of the city of Garmsar.
Materials and Methods: The method is based on the obtained qualitative and quantitative data. The quantitative data includes satellite image interpretation and digital elevation models, alluvial fan morphometry, channel displacement and rate of sediment uplift. longitudinal and cross profile and gradient analysis used to interpret the active fault effects on alluvial fans. Topography maps (1:25000), Aerial Photos (1:55000), ETM, IRS and Aster satellite image with 30, 15 and 5 m spatial resolution, geology maps (1:100000) and digital elevation models (50m pixel resolution) were utilized in this study. For such interpretation, ArcGIS, ENVI and Freehand software were utilized. Also, field work for investigation of evidences of faults activities were performed in two stages.
Results and discussion: This area is located between two geo-structural zones. Alborz zone in the north and central Iran zone in the south. There are four main Faults in this area. Garmsar fault is located at Alborz mountain front and affects the apex of alluvial fans, whereas Shahrabad, SorkheKalut and Gharabilak faults are located far from mountain front. Garmsar fault has caused the displacement of the main channel in fan apex, and therefore has changed the sedimentation position; while evidences of the three other faults activities are more, and has caused uplifting surfaces, derelict of fan surface, change of intersection point, uplift of fan sediment and lateral change of fan surface channels. The slope of most alluvial fans is 2-5 degree. The Deh Namak fan is the largest fan in the study area. This fan combined from several quaternary fans. Deh Namak fan are affected by four faults and reformate to present landform since quaternary. Four faults activities have caused Alluvial fan deposits uplifted about 9 m.
Conclusion: The findings show that Garmsar, Shahrabad, Garabilak and SorkheKalut faults were active in quaternary epoch and position of alluvial fans is affected by activities of these faults. Faults have had either lateral or vertical displacements. Findings show that the slope of all alluvial fans increases suddenly in the apex of fans. Therefore the longitudinal profiles of alluvial fans are in a concaved shape. This means that tectonic activities affect the evolution of alluvial fans in quaternary epoch. Investigations show that there is no statistical correlation among the variables that affect the alluvial fans. Generally, tectonic activities disrupt natural evolution of alluvial fans. Each fault has a different effect on alluvial fan evolution. Garmsar fault has caused the displacement of the main channel to the east of fan apex and has increased slope of this part. other fault have caused uplift of fan deposits, change the intersection point and reconstruction of new alluvial fans in the lower of this point. Deh Namak fan are affected by four faults and reformate to present landform since quaternary.
