Türkiye Jeoloji Bülteni

Geology, Petrography and Geochemistry of the Subduction Related Volcanic Rocks, West of Konya, Central Anatolia

Abstract: 1 he northwest of Konya is covered by Neogene volcanic breccias, agglomerates, tuffites, tuffs and lavasof andesite, dacite and basaltic andesite. The basaltic andesites contain about 7-10% of olivine, 3-5 % clinopyroxene, 5-10 % orthopyroxene, 60-70 % plagioclase and 5-10 % opaque minerals while the andesitic lavasinclude 50-60 % plagioclase, 10-15 % hornblende, 5% biotite, 2 %, clinopyroxene, 1 % sanidine, 1 % quartz and3 % opaque minerals. Main constituents in the dacitic rocks are plagioclase (35-40%), quartz (10-15 %), hornblende (15-20 %), biotite (10-12 %), opaque minerals (2-3%) and sanidine (3 %). The plagioclase in dacites andandesitic rocks have oscillatory zoning and sieve texture .The volcanic rocks range in composition from basaltic andesites to dacites with calc-alkaline character.Co-variation of major and trace element contents suggest fractional crystallization of hornblende, plagioclase,pyroxene and titaniferous magnetite. The plagioclase fractionation is confirmed by a slight development of negative Eu anomaly. High LREE/HREE and L1LE/ HFSE ratios show that the samples were possibly formed froma subduction-related magma at active continental margin. The strong fractionated and riched REE patterns of therocks indicate that the formation of these rocks may have involved continental crust.