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A post-collision slab-breakoff model for the orgin of the Middle Eocene magmatic rocks of the Armutlu–Almacık belt, NW Turkey and its regional implications

By
Fatma Gülmez
Fatma Gülmez
1
Department of Geological Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
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Ş. Can Genç
Ş. Can Genç
1
Department of Geological Engineering, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey
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Mehmet Keskіn
Mehmet Keskіn
2
Department of Geological Engineering, Istanbul University, Faculty of Engineering, 34320 Avcılar, Istanbul, Turkey
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Okan Tüysüz
Okan Tüysüz
3
Istanbul Technical University, Eurasian Institute of Earth Sciences, 34469 Maslak, Istanbul, Turkey
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Published:
January 01, 2013

Abstract

Middle Eocene magmatic rocks (MEMR) (49.3±2 to 38.1±1.9 Ma) formed an east–west trending belt after continental collision and rest unconformably on pre-Middle Eocene units as a common cover. The origin and tectonic setting of MEMR are controversial as both arc and post-collisional settings are proposed. We present new geological and petrological data from the western part of the belt, between the Armutlu Peninsula and the Almacık Mountains. The MEMR are represented by basic to intermediate volcanic rocks, dykes and coeval granites. The lavas exhibit a continuous trend from basalt to dacite. The MEMR as a whole display low- to medium-K subalkaline (to rarely mildly alkaline) affinities and a calc-alkaline trend. On N-type Mid Ocean Ridge Basalt-normalized spidergrams these rocks display relative enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, but depletion in Ta and Nb. Geochemical data and Sr, Nd, Pb and δ18O isotope compositions, coupled with ɛNd(T) values, reveal that the MEMR magma was of hybrid type, with both depleted sub-continental lithospheric mantle and crustal components. We conclude that the MEMR was produced in a post-collisional setting, and we favour a slab-breakoff mechanism to explain this as it is consistent with the known Middle Eocene tectonic evolution of northwestern Turkey.

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Geological Society, London, Special Publications

Geological Development of Anatolia and the Easternmost Mediterranean Region

A. H. F. Robertson
A. H. F. Robertson
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O. Parlak
O. Parlak
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U. C. Ünlügenç
U. C. Ünlügenç
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Geological Society of London
Volume
372
ISBN electronic:
9781862396357
Publication date:
January 01, 2013

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