Acidic volcanic rocks in the Saveh quadrangle

Category Petrology
Group GSI.IR
Location 20th symposium on geosciences
Holding Date 16 April 2008

   General:
     Acidic volcanic rocks of the Saveh quadrangle map comprise a significant proportion of the whole volcanic rocks present in the region. Most studies carried out on the acidic volcanics attribute the origin of these rocks to the partial melting of crustal rocks. Some geochemical characteristics of these volcanic rocks are not consistent with their derivation from crustal rocks. For instance, on oxides vs. silica diagrams, acidic rocks appear clearly in continuation of the basic-intermediate rocks and their formation can be related to the differentiation of basic-intermediate magmas by fractional crystallization. Ba and Sr vs. silica and CaO vs. (Na2O+K2O)/Al2O3 variation trends in the acidic rocks are not consistent with compositional evolution of an acidic partial melt. Furthermore, Saveh acidic rocks lack crustal xenoliths which could be considered as possible parental rock of the acidic magmas. Acidic partial melts obtained experimentally under crustal conditions also differ from acidic rocks from the study area. Geochemical characteristics of the acidic rocks from the region indicate that combined Assimilation Fractional Crystallization (AFC) process is more likely to be responsible for their generation than crustal partial melting.

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