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Mafic microgranular enclaves and interaction between felsic and mafic magmas in the agacoren intrusive suite: Evidence from petrographic features and mineral chemistry

1996-01-01
Kadioglu, Yusuf Kagan
Güleç, Nilgün Türkan
The Agacoren Intrusive Suite is exposed as a large intrusive body over ∼500 km2 east of Lake Tuz in central Anatolia and consists of the Cokumkaya gabbro, the Agacoren granitoid, and young dikes. The Agacoren granitoid is the predominant lithology of the Agacoren Intrusive Suite, and is differentiated into several subunits ranging in composition from monzonite, through granite, to alkali feldspar granite. The Cokumkaya gabbro occurs as stocks enclosed in the Agacoren granitoid; individual bodies range in size from 10 m × 20 m to 7 km × 3 km. Young dikes cut both the Cokumkaya gabbro and the Agacoren granitoid, and are particularly abundant in the central part of the intrusive body. Centimeter- to meter-size mafic microgranular enclaves (MME) are enclosed in the Agacoren granitoid. The enclaves are diorite, quartz diorite, and monzodiorite in composition, and represent blobs of mafic magma injected into a felsic host magma. The MME have a mineral assemblage (plagioclase + amphibole + biotite ± quartz ± K-feldspar) almost identical to that of host granitoid, but with different mineral proportions. The characteristic petrographic features of the MME are the presence of acicular apatite, blade-shaped biotite, quartz ocelli, and K-feldspar poikilitically enclosing mafic minerals. Microprobe analyses performed on amphibole and plagioclase reveal similar mineral chemistries for both the MME and the host granitoid. The anorthite contents of the plagioclases show an increase from rim to core in both the MME and the host granitoid. The rims of the MME plagioclase have compositions ranging from An5 to An40, whereas those of the host granitoid vary from An0 to An42. The cores, on the other hand, range from An30 to An90 and An20 to An90 in the MME and the host, respectively. Amphiboles are essentially of ferro-hornblende composition in the MME, and of ferro- to magnesiohornblende composition in the host granitoid. The similarity in mineral compositions reflects chemical equilibrium attained through the magma-mixing process.