Mineral Chemistry and Geochemistry of Volcanic Rocks in The North of Pasinler (Erzurum)

Abstract

In the north of Pasinler (Erzurum), Upper Miocene-Pliocene volcanic rocks crop out. These volcanites are composed of basaltic andesite, andesite, dacite, rhyolite lavas and rhyolitic pyroclastics. The rocks show porphyritic, microlitic porphyritic, hyalo-microlitic porphyritic, vitrophyric, glomeroporphyritic, pilotaxitic and hyalopilitic textures. The investigated volcanites contain plagioclase (An29-80), olivine (Fo65-82), clinopyroxene (augite), orthopyroxene (enstatite), amphibole (Mg#: 0.57-0.71), biotite (phlogopite: 0.44-0.47, annite: 0.33-0.37), sanidine, quartz and opaque mineral (titano-magnetite and ilmenite). The volcanic rocks are calc-alkaline in character and have medium to high-K contents. Major oxide and trace element variations point out open-system magmatic differentiation in the evolution of rocks. Geochemical data indicate an important role of fractionation of phenocryst phases in the rocks during differentiation process. However, it is considered that assimilation±magma mixing might have accompanied to the process. High LILE (K, Rb, Ba, Th) and relatively low HFSE (Nb, Ta, Hf, Zr) contents of the rocks indicate that these rocks derived from parental magmas carrying subduction signature.

Keywords

• Pasinler, Mineral chemistry, Geochemistry, Calc-alkaline volcanites.

Pasinler (Erzurum) Kuzeyindeki Volkanik Kayaçların Mineral Kimyası ve Jeokimyası

Öz

Pasinler (Erzurum) kuzeyinde Üst Miyosen-Pliyosen yaşlı volkanik kayaçlar yüzeylemektedir. Bu volkanitler bazaltik andezit, andezit, dasit, riyolit türü lav ve riyolitik piroklastiklerden oluşmaktadır. Kayaçlarda porfirik, mikrolitik porfirik, hyalo-mikrolitik porfirik, vitrofirik, glomeroporfirik, pilotaksitik ve hyalopilitik dokular gözlenmektedir. Kayaçlar plajiyoklas (An29-80), olivin (Fo65-82), klinopiroksen (ojit), ortopiroksen (enstatit), amfibol (Mg#: 0.57-0.71), biyotit (filogopit: 0.44-0.47, annit: 0.33-0.37), sanidin, kuvars ve opak mineral (titanomanyetit ve ilmenit) içermektedir. Kayaçlar kalkalkali karakterli olup, orta-yüksek potasyum içeriğine sahiptirler. Ana oksit ve iz element değişimleri kayaçların gelişimindeki açık sistem mağmatik diferensiyasyona işaret etmektedir. Jeokimyasal veriler kayaçlardaki fenokristal fazların fraksiyonlaşmasının diferansiyasyon sürecinde etkili olduğunu göstermektedir. Fakat buna asimilasyon±mağma karışımının da eşlik etmiş olabileceği düşünülmektedir. Kayaçların yüksek büyük iyon yarıçaplı element (K, Rb, Ba, Th) ve göreceli olarak düşük yüksek alan enerjili element (Nb, Ta, Hf, Zr) içerikleri kayaçların yitim izleri taşıyan bir ana mağmadan oluştuklarına işaret etmektedir.

Anahtar Kelimeler

• Pasinler, Mineral kimyası, Jeokimya, Kalkalkali volkanitler.

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