Geochemical approaches to the provenance and tectonics of the Quaternary sediments of Sagalak-sar wetland

Seventy- four surface and subsurface sediment samples from the SaghalakSar bog were investigated to decipher their tectonic setting and provenance. The Al2O3 content showed positive correlation with MgO, Fe2O3, and K2O while it showed negative correlation with TiO2 and SiO2, suggesting that clay minerals and mica were major hosts for these elements. Average K2O values were higher than average Na2O levels, reflecting that k-feldspar was proportionally more abundant than plagioclase in the source rock. A decrease in K2O with an increase in Na2O in the northwest bog could be interpreted as alteration of rocks, suggesting possible effect of sodium feldspar on the source rock. A strong increase in MgO and Fe2O3 relative to average upper continental crust was consistent with mafic source rock. The results of comparing the major-element oxides with the S (SiO2 / 10)-CM (CaO + MgO)- NK (Na2O + K20) diagram showed that the sediments had been subjected to weathering, and were derived from magmatic rocks, Shoshonite, Dacite, Monzonite, and Gabbro (usually intermediate composition) at the Alborz magmatic zone. Based on Binary plot of SiO2 versus Al2O3+Na2O+K2O indicated semi-arid climatic condition. Binary plot of Fe2O3+MgO versus Al2O3/SiO2 and TiO2, log (K2O/Na2O) versus SiO2, and ternary diagram of trace elemental, Th, Sc, La, and Zr, it seems that the sediments originated first from a marginal Back Arc basin and then from a magmatic arc in the active continental margin. Finally, during the Quaternary, they went through a recycle of sedimentation after weathering and transport to the Saghalak-Sar Bog