پديد آورندگان :
رجبي، معصومه نويسنده دانشگاه تبريز Rajabi, M. , شيري طرزم، علي نويسنده Shiri Tarzam, A.
كليدواژه :
مورفومتري , ناوديس , طاقديس , گنبد نمكي شمال غرب , تكتونيك نمكي
چكيده لاتين :
Introduction
Evaporative deposits and their accompanying salt domes covered 25% of continents’ surface, and this value reaches to 50% in Northern hemisphere. Evaporative deposits don’t have much density difference in the surface parts of earth, but when these deposits are placed at a depth of 700 meters above ground, those deposits along with salt have high density due to compactness, while salt due to compactness maintains its original density. Density difference provides the driving force for salt diapirism and the formation of salt domes.
Salt domes are landforms that in spite of their importance, little have been discussed by the geomorphologies. Considering Salt domes of Iran, a noticeable number is located in the North West of Iran. Of the 60 identified salts in the region, 48 cases are real salt domes and have created morphs with measurable dimensions. Most salt domes of Iran’s North West are related to Upper Red formation with Miocene age, some domes are related to Qom Formation with Oligo – Miocene age and only one dome is related to Lower Red formation with Eocene age. The evaporative formations and salt domes resulted from these formations like other tectonic structures of the region are affected by Tabriz fault in the northwest - southeast direction and have been stretched in central Iran toward the mountains of Ararat. In this study, it is attempted to determine the role of host folds on the quantitative features of salt domes located within these folds and to identify how much these salt domes are affected by faults in the region. To do this, the salt domes located in the North West of Iran are classified into the two groups according to the type of host fold, these two groups are: salt domes within synclines or their borders and salt domes within anticlines. Also, the amount and type of relationship between the quantitative characteristics of each group with region faults are studied and then the characteristics of both groups are compared.
Materials and Methods
by the use of field and documentary methods and the application of geological maps, topography, aerial photos, satellite images, GPS, meter and clinometers, the original data such as the length of axial line and salt domes, relative height, area, perimeter and distance from Tabriz fault and the nearest fault were extracted and then morphometric parameters of domes like the elongation coefficient, circularity coefficient, rising coefficient of salt domes and faults’ density were calculated.
To analyze data, the domes were divided into the two groups: domes within synclines and domes within anticlines. Also, the quantitative data of each group were prepared in a table called morphometric parameters s. At first, scatter diagram, regression line, the type and amount of correlation between morphometric parameters of each group were determined and analyzed by the use of SPSS software and then the quantitative parameters of the two groups were compared.
Discussion and Results
Most classifications regarding domes are based on the salt structure of these salt domes. In this study, the salt domes of Iran’s North West based on host folds are classified as domes within synclines and domes within anticlines. From47 identified salt domes in the North West of Iran, 29 domes were located within anticline structures or their borders, mainly in mountains’ front and upon faults or in low distance from faults. These domes have a monocline structure. 18 salt domes were within anticlines, far from faults and in the mountains. These domes often have anticline structure. Comparing the morphometric parameters of two groups shows that salt domes within synclinesin comparison to salt domes within anticlines have low area, and relative height but they have high elongationcoefficient and rising coefficient. Salt domes within synclines are far from faults and salt needs to raise surface layers in order to come up to the surface. This cause the high area for anticlines domes. On the other hand, the presence of tensional joints in the surface of anticlines accelerates water erosion and reduces the height of the domes. Consequently, the rising coefficient of domes decreases. In synclinal salt domes which are located on faults, salt simply is injected in fault direction without raising upper layers and occupies a low area. Therefore, these domes have high elongation and rising coefficient.
Conclusion
Although the process of salt domes exposition like other regional tectonic factors such as faults, folds and magmatic follows the process of Tabriz fault, but the morphometric parameters of salt domes within synclines in comparison to salt domes within anticlines are more affected by faults. Therefore, they have low area but high elongation and rising coefficient. In some cases apparently, there is no connection between a parameter and faults, which shows the effect of other factors such as magmatism in the formation of salt domes in the region.
