TITLE:
Mineral Chemistry and Thermobarometry of the Upper Eocene Volcanic Rocks in NE Tafresh, Iran
AUTHORS:
Neda Baranpurian, Mohamad Hashem Emami, Mansor Vossoughi Abedini, Rahim Dabiri
KEYWORDS:
Volcanic, Mineral Chemistry, EPMA, Thermobarometry, NE Tafresh
JOURNAL NAME:
Open Journal of Geology,
Vol.4 No.12,
December
11,
2014
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.