Erken eosen adakitik andezitler (Altinpinar, Torul) içerisindeki mafik mikrogranüler anklavlarin petrokimyasal karakteristikleri

The early Cenozoic magmatism in the Eastern Sakarya Zone (NE Turkey) provides significant insights into the regional tectonomagmatic evolution. Adakite-like intrusive/extrusive rocks have been widely observed from the Late Paleocene to the Plio-Quaternary period in the region. In the study area, Early Eocene adakitic andesites are observed in outcrop areas smaller than 10 km2 and they contain abundant mafic microgranular enclaves (MMEs). This study presents petrochemistry data of the MMEs and discusses petrological relationships with the host rock. The MMEs, with more basic composition compared to the parent rocks, are observed in ranging from a few to 30 cm in size. They are microlithic to porphyritic in texture and mainly composed of hornblende, plagioclase, clinopyroxene and opaques. Both petrographic and petrochemical characteristics indicate that the MMEs are of basalt and basaltic andesite and may have derived from a sub-alkaline magma. Major and trace element variations indicate that fractional crystallization was effective, and pyroxene, hornblende, plagioclase, magnetite and apatite fractionation played an important role. Both trace and REE patterns of the rocks show a similar distribution, suggesting that they may be derived from similar sources, and indicating hornblende fractionation played an important role in their evolution, whereas plagioclase fractionation was less effective. Tectonomagmatic characteristics of the rocks reveal that they were differentiated from the same origin and are similar to orogenic andesites. Petrochemical data suggest that the parent magma of the MMEs was produced by the partial melting of oceanic basalts under amphibole-eclogite facies conditions during the subduction of the northern Neotethyan oceanic slab.