Petrology and geochemistry of tavshana volcanics located in the square (1: 100,000) of Astara, Iran

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Research Paper 01/01/2015
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Petrology and geochemistry of tavshana volcanics located in the square (1: 100,000) of Astara, Iran

Mostafa Baratiyan, Ebrahim Nazemi, Saeed Naeimi, Fatemeh Ghotb Tahriri
J. Bio. Env. Sci.6( 1), 743-750, January 2015.
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Tavshana volcanic rocks have a considerable outcrop to Eocene in the mountains of Talesh, West of Gilan Province in Iran. From petrographic point of view, they have the major composition of Trachyandesite with Mega porphyric tissue. Geochemically speaking, these rocks belong to Alkaline Potassium series and negative anomalies of Ti, Ta, Nb and positive anomalies of K and Pb are proof of contamination of these rocks with their continental crust. In diagrams identifying tectonic positions, Tavshana Trachyandesites are located within the rift basalts range in the continental plates. Studying the patterns of incompatible elements and comparing them with the values of continental Tholeiites indicates that primary magmas forming are similar to continental Tholeiites that have been contaminated by the rocks of upper continental crust. Eocene volcanism in this area is similar to that of inter-continental rifts so that our research shows that primary magma continental tholeiitic trachyandesite of the same region in which an inter-continental rift environment emanating from the upper continental crust rocks have been affected to some degree. We believe that the potassic feature is not of the characteristic of the origin zone but crustal contamination leads to rise in magma potassium and the formation of potassic series and false Shoshonites in the rocks of the region


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