Petrology of Eocene volcanic rocks from the Central Sakarya Zone (northwestern Anatolia, Turkey): new evidence from Ar-Ar and Sr-Nd isotope determinations

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• 作者：Gökhan Büyükkahraman
• 关键词：Ar/Ar dating ; Central Sakarya Zone ; Petrology ; Sr ; Nd isotopes
• 刊名：Arabian Journal of Geosciences
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：9
• 期：16
• 全文大小：2,885 KB
• 刊物类别：Earth and Environmental Science
• 出版者：Springer Berlin Heidelberg
• ISSN：1866-7538
• 卷排序：9

文摘

In this study, petrological characteristics of the Early-Middle Eocene Bozaniç volcanic rocks resulting from the closure of the Neotethys Ocean in the Central Sakarya region and geodynamic evolution of the Eocene magmatism in the region were investigated. Although previous researchers attained insightful findings about the geodynamic evolution of the region, the age of the post-collisional volcanism, petrological characteristics, and source of the magma remain uncertain. Therefore, volcanic rocks outcropping nearby Sarıcakaya-Mihalgazi (Eskişehir) are investigated in this study. For that purpose, geological map of the study area was drawn and mineralogical, petrographic, geochemical, and isotopic analyses were performed on rock samples collected from different locations. Bozaniç volcanic rocks outcropping as lavas and pyroclastics (agglomerate, lapillistone, and tuff) seem to be derived from four separate volcanic chimneys located in the study area and their composition are typically andesite. According to petrographic data, hypocrystalline porphyritic and microlitic porphyritic are the dominant textures of the rocks. Plagioclase, amphibole, clinopyroxene, and biotite are the main minerals, while sanidine, opaque minerals, chalcedony, calcite, and chlorite can also be observed in small amounts. Geochemically, they show calc-alkaline characteristics and contain medium-high K. Fractional crystallization is the most important process in the development of the rocks. Bozaniç volcanic rocks were derived from a lithospheric mantle source that developed in the active continental margin. According to 40Ar/39Ar age spectra of the samples, the ranges of 48.13 ± 0.15–48.78 ± 0.23 Ma plateau ages were obtained. (87Sr/86Sr)_i ratios of the rocks range between 0.705404 and 0.705502, while (143Nd/144Nd)_i ratios range between 0.512570 and 0.512581. Consequently, the age data obtained in this study show that the formation time of the first products of the post-collisional volcanism be as early as the Early Eocene and the presence of those is important in terms of the elucidation of geodynamic evolution of the region.