Mineral Chemistry and Thermobarometry of the Upper Eocene Volcanic Rocks in NE Tafresh, Iran

Neda Baranpurian,Mansor Vossoughi Abedini,Mohamad Hashem Emami,Rahim Dabiri

doi:10.4236/ojg.2014.412045

Abstract

Petrography and chemistry of minerals show that rocks of Upper Eocene in northeast of Tafresh are composed mostly of andesitic basalt, basaltic andesite and andesite volcanic rocks. Mineralogically these rocks are composed of phenocrystals of olivine, clinopyroxene and plagioclase and main texture of them is porphyry with cryptocrystalline or microcrystalline matrix. In addition, aphyric and pitted textures (amygdala) are also observed. According to the results of EPMA, phenocrystals of plagioclase in mentioned rocks include a range of anorthite to albite minerals. Alkali feldspars also contain a range of sodic to potassic minerals. Pyroxene crystals include hedenbergite, augite and hypersthene. Olivine minerals are often of the ferrohornblendite type. Based on thermobarometry it is estimated that to form clinopyroxene crystals of basaltic andesite rocks, temperature between 750°C to 1000°C is needed. Andesitic basalt rocks at higher temperature (1100°C) and andesite rocks at lower temperature (below 750°C) are formed. According to the distribution of aluminum in clinopyroxenes, these minerals at pressures less than 5 kbar and water content between 5% to 10% are crystallized. The mineral composition indicates that these rocks are formed in a tensional environment.

Highlights

Eocene volcanic occurrences are the most important volcanic demonstrations In Iran, because it has led to the creation of a volcanic arc which has a length of 1700 km and a width of 100 km [1] [2]
This volcanic arc which is known as the Urmia Dokhtar volcanic arc is widespread from northwest to southeast in Iran and is the most important volcanic zone of Iran [3]-[6]
One of the most complete volcanic sequences of the Urmia Dokhtar magmatic arc, with a thickness of over 3 km, is in the north and northeast Tafresh. Volcanic occurrences in this area have begun since Lutetian, so that these volcanic units are located on the Upper Cretaceous units [8]

Summary

Introduction

Eocene volcanic occurrences are the most important volcanic demonstrations In Iran, because it has led to the creation of a volcanic arc which has a length of 1700 km and a width of 100 km [1] [2]. One of the most complete volcanic sequences of the Urmia Dokhtar magmatic arc, with a thickness of over 3 km, is in the north and northeast Tafresh Volcanic occurrences in this area have begun since Lutetian, so that these volcanic units are located on the Upper Cretaceous units [8]. The purpose of this article is to identify and determine the structural formulas of minerals in the Upper Eocene volcanic rocks of NE part of Tafresh (Figure 1)

Objectives

Methods

Results

Conclusion