The geothermobarometric of Uchbolaq trachyandesitic lavas, Research on the Early- Cenozoic volcanism in Tarom-Hashtjin magmatic zone

This study presents the results of mineral chemistry data of Early–Cenozoic volcanic rocks in the south of the Tarom-Hashtjin magmatic zone. The Uchbolaq lavas in the north of Zanjan are a part of Oligocene eruptions within Turkish- the Iranian plateau. Based on microprobe analysis of the andesite-trachyandesites’ samples of this area, show that these rocks are composed of, labradorite (An55-66), augite (Wo44 En44 Fs12), mg-hastangsite ((Na+K) A≥0.50 and Alvi<Fe3+), and mg-biotite (Fe2+/(Fe2++Mg)>0.3). Geothermometric calculations suggest that the range of crystallization temperatures for amphiboles is between 985 to 941 ºC, and biotite’s temperature ranges are between 770 to 758 ºC. Based on geobarometric calculations, amphiboles are indicated a pressure range between 5.3 to 6.5 kb, and biotite’s pressures are shown from 0.9 to1.9 kb. The results of the amphibole and biotite's mineral chemistry data suggest that these rocks are derived from a calk-alkaline magma with approximately high ƒO2, in a volcanic arc related to subduction zone and orogenic setting suites.