عنوان مقاله [English]
Nearly two-thirds the area of the country is desert. Playa or holes as well as units from the desert area of Iran occupy substantially and Due to their economic and ecological potential and requires careful and thoughtful be evaluated. Meyghan is a playa. Playa undeniable importance of studying in Iran. The other side is located near the city Meyghan and geomorphological undeniable impact on the city and other nearby towns led to this research, studied watersheds. Overall, in this study, the landforms are identified. The active processes are assessed to identify areas Morphogenetic and morph tectonic. In the next stage due to a bug off and heritage areas Morphogenetic climate in the climate of the last glacial period, these territories will be determined in the past. Finally, based on changes in landforms checked. According to a survey by researcher of research on these topics in our country is very small compared with the world.
Area of study
The main central drainage basin of the 5 sub-basin - Qomroud, Ghare Chay, salt (Khoshkrud), Meyghan and is composed Kashan desert. Meyighan sedimentary basin that Taleghani (1375) referred to as Arak plain, covers an area of 5528 square kilometers, of which 2,000 square kilometers and 3528 square kilometers it plain to the heights overlooking the plain form. The basin of the lake with an area ranging up to 106 seasonal Meyghan square kilometers and the elevation 1660 to 1700 meters above sea level, Farah and Arak alluvial plain, alluvial fans and piedmont basin is a watershed contour Qom and cranberry tea with low-lying mountains to the south, east and north, with the hilly areas located in the west basin has emerged. Meghan with an area of 135 square kilometers, including 94 percent of the lake's salt level is the average height of 1675 meters above sea level and is located in the Alborz and Zagros Mountains, 15 km north and northeast of the city of Arak is located. It covers an area of 143 square kilometers of desert in the pits or Meyghan playa is located in the center of the basin and is surrounded by relatively high mountains. The closest town to Meghan is Arak. Desert surrounding villages at different distances relative to seasonal lake surrounded by Meyghan
Data and Methodology
Meyghan Basin based on DEM and topographic maps at a scale of 1: 50,000 has been set. To obtain changes in the Quaternary surface of the lake, the main component analysis (PCA) was used based on the correlation matrix. In this way, aimed at identifying the level that had arisen as a result of changes in mineralization. For this purpose, reflective bands of ETM image data 6 was used. To increase the spatial resolution panchromatic band with the same image sensor with a pixel size of 15 m were combined. Then they calculated the correlation matrix. Most correlation between the bands 1 and 2 are equivalent to 9699/0 is the ETM image.
6 persons, sensor-based component bands 1 to 7 ETM (with the exception of band 6) was calculated as the percentage share of each PC of total variance changes (or eigenvalues) were compared.
For the above analysis with higher accuracy can be performed, the same operation on the pictures) III IRS- P6 (LISS - with pixel dimensions of 27 meters and four reflective bands was carried out.
Levels obtained respectively from the inside out with areas of salt, gypsum and lime playa Meyghan have coincidence.
Satellite images of the area, a large lineaments in the basin Meyghan, are identifiable. There are three clauses that are based on the three sides of Meghan, shows that the desert is probably along three fault, and has fallen But Tabarteh and Talkhab in the marginal basins in the margins of tectonic uplift and fall Pasadenian for the middle section appears which results in the formation of sedimentary basins and independence Meyghan and ultimately create Meghan at its center the size of today.
Meyghan Lake drainage basin with an area of 5528 square kilometers, which is more water volume to get the last cold period that has been more widely. Given the existence of a considerable part of limestone, gypsum and salt compounds in the rocks of the basin, in cold periods of lower temperatures and more precipitation, these dissolved minerals and water flow the basin is drained by the end. With global warming and increased evaporation than precipitation, sedimentation and dissolved minerals and as a result Meyghan just a playa lake has evolved.
Given the existence of a considerable part of limestone, gypsum and salt compounds in the rocks of the basin, in cold periods of lower temperatures and more precipitation, these dissolved minerals and water flow the basin is drained by the end. With global warming and increased evaporation than precipitation, sedimentation and dissolved minerals and as a result Meyghan just a playa lake has evolved. Smaller level from the third component part of the evaporate deposits along the lake correspond with the field observations showed that the part with a maximum accumulation of gypsum. Field observations in addition to sediment gypsum, calcite and halite mineral zones with predominant accumulation around the lake showed. Open correspond with the dominant mineral calcite surface Meyghan biggest playa. This level may indicate that precipitation since the last cold period is higher or lower temperature than is the present time. Now as the wet and dry climatic fluctuations in lake levels Meyghan just changes the expanse of salt and gypsum appear wet and dry. The maximum difference in height between the deepest points of the lake with the greatest surface obtained from the above analysis, 7 meters. In general it can be said that whenever a more humid climate and rainfall was higher, the central part of damp and salt Meyghan, expanded and more dry periods soluble salts have precipitated; therefore, in zones around the lake as well as lime and gypsum salt deposits can be seen. In this way, aimed at identifying the level that had arisen as a result of changes in mineralization.