Mineralogy and geochemistry of sand dunes of the southern coast of the Caspian Sea

چکیده مقاله

Babolsar eastern coastal dunes have been developed along the southern coast of the Caspian Sea. The studied area is coordinated in N36°43' to N36°44' latitude and E52°44' to E52°52' longitude. The objectives of this research were to: Study mineralogy and geochemistry of sand dunes, to obtain chemical alteration index (CIA) and its relationship to climate and mineralogy, to determine the potential accumulation of heavy minerals and trace elements and to identify sedimentary processes, climate, source rock geochemistry and mineralogy of the deposits. In this research, 43 dune samples were collected from 4 different areas of coastal dunes, out of which 14 samples were analyzed using X-ray fluorescence method (XRF) for major oxides and trace elements. A comparison was made between sand dunes, river and beach. To increase the accuracy of the mineralogical study of sediments, 7 microscopic thin sections were prepared. The mineralogical analysis of the coastal sand dunes indicates that the average amounts of quartz, feldspar and rock fragments found in these samples are 29.56%, 7.42% and 63.02%, respectively. Much of the rock fragments were respectively sedimentary, volcanic, plutonic and finally metamorphic rock fragments with the lowest amounts. The abundance of carbonate sedimentary rock fragments in Babolsar coastal sand dunes can be caused by proximity to the carbonate source rock. The average amount of chemical alteration observed in coastal dunes of Babolsar was 89.39%, which is similar to coastal dunes of Miankaleh (=88.44%). It seems that warm and humid climates predominate in both of Miankaleh and Babolsar coastal sand dune areas. The concentration of TiO2, Fe2O3, MgO and heavy minerals in the coastal dunes of Babolsar were reduced eastward. This pattern of decreasing main oxides of iron, titanium and magnesium with the direction of prevailing winds in the area from west to east is in agreement and proves that the distribution pattern of major oxides which form dark heavy minerals in the sand dune samples have been more affected by the prevailing winds in the region.