Evolution of slab tearing-related high potassium volcanism: Petrogenetic findings from the Emirdağ and İscehisar volcanic units

Abstract

Volcanism that has been active since the early Miocene along a N-S trending line from Eskisehir to Isparta displays calc-alkaline and alkaline character and is closely associated with slab tearing processes. However, the geodynamic setting of these volcanic units between Afyon and Emirdag is still poorly known. In this study, petrological characteristics of the Emirdag and Iscehisar volcanic units have been investigated using petrography, whole-rock geochemistry and Sr-Nd isotopes. The Emirdag and Iscehisar volcanic units overlap the SeydileIgnimbrites. The Emirdag volcanic unit is trachyandesite and the Iscehisar volcanic unit is trachyte, basaltic trachyandesite and trachydacite in composition. The Emirdag volcanic unit displays calc-alkaline character, while the Iscehisar volcanic unit is alkaline but the rocks from both the units have shoshonite character defined by their high K 2 O contents. The Emirdag volcanic unit has 87 Sr/ 86 Sr ratios of 0.706790-0.706284 and 143 Nd/ 144 Nd ratios of 0.512472-0.512463, while these ratios in the Iscehisar volcanic unit are of 0.707650-0.706527 and 0.512464-0.512424, respectively. Data revealed by this study indicate that these volcanic units were affected by crustal contamination, fractional crystallization and magma mixing. Rising of asthenosphere in the region due to the extensional regime in the Early Miocene appears to have caused formation of volcanism that pass from calc-alkaline to alkaline in character. The Emirdag and Iscehisar volcanic units are the products of the volcanism that developed in the late stages of southward slab roll-back and in the extensional regime prior to the slab tearing event.