Writers : hashemi,Seyed mohammad؛Emami,Mohammad hashem؛Vousughi Abedini,Mansur
Refference : Proceeding Of The First Applied Geological Congress Of Iran
Publishing Year : 1386

Abstract :
Quaternary basalts are one of the last indicators of magmatism in Iran. Tabas basalts erupted during Quaternary near the great and active fault of Nayband in eastern Iran; and following their being fresh and not alternated, they represent useful data regarding the geological occurrences during Quaternary. The goal of this study is to investigate the basalts petrogenese, and to identify the techtonomagmatic environment of the region. These investigations indicated the contamination of basaltic magma with crust silisic magma- which was located in the rising rout of magma. This contamination have resulted a change in the characteristics of a number of basalts. For example, it has increased SiO2, and thus has changed the alkaline nature of some of the samples into Calc alkaline. More over, variation in the rate of Al2O3, Na2O, and K2O against the increase of SiO2 or MgO does not follow the normal or natural rules. In current geochemical petrologic classifications, the rocks formation, because of the increase of SiO2 in some samples, varies from olivine basalt to andesite. Normative mineral studies done with CIPW method shows the existence of maximum 8 percent of normative quartz in sub-alkaline samples, while the alkaline samples contain maximum up to 15 percent of normative nepheline. Investigating the geochemical behavior of rare elements Ce, Zr, and Nb proves the contamination of magma with crust rocks. The Nd and Sr isotops quantities indicate a depleted mantle source for these basalts which have contaminated with crust rocks while rising. These investigations show that the sub-alkaline samples have more contamination than alkaline samples.
Subject List : Contamination Crustal, Basalt