Eocene granitoids of northern Turkey: Polybaric magmatism in an evolving arc-slab window system
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| Authors: | Eyuboglu, Y; Dudas, FO; Thorkelson, D; Zhu, DC; Liu, Z; Chatterjee, N; Yi, K; Santosh, M |
| Year: | 2017 |
| Journal: | Gondwana Res. 50: 311-345 Article Link (DOI) |
| Title: | Eocene granitoids of northern Turkey: Polybaric magmatism in an evolving arc-slab window system |
| Abstract: | The Eastern Pontides Orogenic Belt offers critical clues on the origin of Early Cenozoic continental arc magmatism in the Alpine-Himalayan system. Systematic geological, geochemical and chronological studies indicate that there are three subgroups among the Early Cenozoic intrusions in the Eastern Pontides Oro genic Belt - Late Paleocene-Early Eocene adakitic intermediate-felsic intrusions, Eocene mafic intrusions, and Eocene non-adakitic granitoid intrusions. Here we focus on the petrology and geodynamic setting of the Eocene non-adakitic granitoid intrusions that are well exposed in a belt between the Thanetian-Ypresian adakitic intrusions in the south and the Lutetian gabbroic intrusions in the north. We also present data on enclaves and surrounding Eocene volcanics. The studied intrusions can be grouped into two main categories, based on their field and petrographical characteristics: granodiorite and monzodiorite-dominated and syenite-dominated bodies. They can be further subdivided into four groups of differing K2O content: low-K2O (cevrepinar, Kaletas, Saricicek and Uzengili), mixed (Sorkunlu, Kozluk and Tamdere), and high-K2O (Dolek, Mesebasi, cakirbag, and Arslandede) rocks are granodioritic and monzodioritic, whereas shoshonitic (Kosedak, Meydanli and Bademli) bodies are syenitic. Zircon U-Pb age determinations reveal that these granitoids were emplaced into crustal rocks of the Eastern Pontides Orogenic Belt between 47 and 42 Ma, in Lutetian time, simultaneously with the gabbroic intrusions in the north. Mineral compositions and P-T calculations are consistent with the interpretation that crustal melting or magma storage started at mid-crustal depth (similar to 25 km), with a magma system that subsequently extended to shallow levels (<4 km). The studied granitoids, enclaves and volcanics exhibit geochemical signatures typical of subduction-related arc magmas, however, the shoshonitic intrusions are younger than most of the other Lutetian intrusions, and indicate a temporal change in arc magmatism. The Sr-Nd-Pb isotopic data indicate that the Lutetian rocks are mixtures of three or four end-member compositions. Considering all geological, geochemical and chronological data, we conclude that the Early Cenozoic magmatism was generated by slab window processes related to ridge subduction in a south-dipping subduction zone below the Eastern Pontides Oro genic Belt. (C) 2017 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. |
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