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Abstract
Rizo, Asphordi and Hormoz formations which are part of the post tectonic activities of the Katangan Orogeny all have some volcanic rocks similar in lithology, age and petrology which have been the motive for this research. Igneous rocks of these formations are generaly made up of two typs, acidic volcanic rocks with the tendancy towards calc-alkalic composition and basic lava flow or doloritic dykes which are alkalic. These have reached the suite simultaneously with the acidic rocks or soon after them.
This contrast or bimodal (acidic-basic) magmatism in addition to petrological and geochemical facts is characteristic of an intercontinental rift similar to the east suite of the East African Rift or previous rifts like Rio grand Rift. Rift in these examples are in an embryonic stage and have never developed to the further stage of ocean building. Most probably the basic rocks have originated from the asthenosphere and partial melting of the upper mantle. While the resulting magma has been rising and settling in suitable depth the diffraction and crystalization has taken place and partial melting of the upper crust has occured so that the calc-alkalen acidic magma in the form of rhyolitic lava flow has reached the ground after some fierse pyroclastic activities. The scarsity of the basic rocks may be explained by their higher density than the very viscous acidic rocks which have been over them hence only dykes and small intrusions could form and the number of these has been increased after consolidation of the acidic mass.
We would like to express our gratitude to the Tehran University Research. Council for making it possible to carry on this research project by supporting it through Research Centre for Desert and Barren lands of Iran. We also deeply appreciate the help we received from Prof. Abdoraheem Hushmandzadeh for making the unpublished data from the Compiling and Publishing Office available to us.