Geochemical characteristics of microgranular enclaves in Early Eocene adakitic andesites (Gümüşhane, NE Türkiye)

Abstract

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 microgranular enclaves. This study presents petrochemistry data of the enclaves and discusses petrological relationships with the host rock. The enclaves, with more basic composition compared to the parent rocks, are observed in ranging from a few to 20 cm in size. They are microlithic to porphyritic in texture and mainly composed of plagioclase, hornblende, clinopyroxene, orthoclase and opaques. Both petrographic and petrochemical characteristics indicate that they are of basaltic and basaltic andesite and may have derived from a sub-alkaline magma. Major and trace element variations indicate that fractional crystallization was effective, and plagioclase, pyroxene, hornblende, magnetite and apatite fractionation played an important role. Similar trace element distributions of enclaves and host rocks may indicate interaction processes while mixing of felsic and mafic magmas. Similarly, REE models of the rocks, indicated hornblende fractionation played an important role in their evolution, whereas plagioclase fractionation was less effective. Petrochemical data suggest that the parent magma of the enclaves was produced by the partial melting of oceanic basalts under amphibole-eclogite facies conditions during the initial stages of the extensional tectonic regime just after the complete closure of the northern Neotethys Ocean. © 2024, Hacettepe Universitesi Yerbilmleri. All rights reserved.