Middle Eocene high-K acidic volcanism in the Princes’ Islands (İstanbul) and its geodynamic implications

Fatih Şen

doi:10.3906/yer-1905-19

Abstract

The rock assemblages of the Princes? Islands, which are located to the south of mainland Istanbul, are regarded as parts of the Lower Paleozoic quartz sandstones, although they were initially considered as volcanic rocks by Swan in 1868. They differ from quartz sandstones by their vesicular texture and are devoid of any stratigraphic layering. Their mineral constituents are plagioclase (30%-35%), feldspar (35%-40%), and quartz (20%-25%), corresponding to rhyolite. The crystallization age of the rhyolites is 45.66 ± 0.84 Ma on the basis of the U-Pb zircon data. They show high-K calc-alkaline affinity. On primitive-normalized spider diagrams, negative anomalies of Ba, Nb, Sr, P, and Ti and positive anomalies of Pb are noteworthy. Their chondrite-normalized REE patterns are characterized by strongly fractionated patterns with demonstrative negative Eu anomaly, whereby middle REE are not fractionated relative to the heavy REE. These geochemical features suggest a fractionating mineral assemblage of feldspar, apatite, and biotite without significant involvement of garnet. The Lutetian rhyolites of the Princes' Islands are a part of the Middle Eocene magmatic associations of the West Pontides, related to collision of the Menderes-Taurus block with the Pontides.

Highlights

The Tethys Ocean, which began to subduct under Laurasia during the late Paleozoic-early Mesozoic (Topuz et al, 2018), was completely consumed during the Eocene along the İzmir-Ankara-Erzincan suture (İAES) (Şengör and Yılmaz, 1981)
It is stated that Eocene magmatism is not present in the western section of the İstanbul-Zonguldak Tectonic Unit (İZTU), except for the Armutlu-Almacık zone (e.g., Gülmez et al, 2013)
The rocks defined as Paleozoic quartz sandstones (e.g., Özgül, 2012) are, volcanic rocks as initially

Summary

Introduction

The Tethys Ocean, which began to subduct under Laurasia during the late Paleozoic-early Mesozoic (Topuz et al, 2018), was completely consumed during the Eocene along the İzmir-Ankara-Erzincan suture (İAES) (Şengör and Yılmaz, 1981). The models explaining the Eocene tectonic setting of the Pontides are a matter of debate. It is stated that Eocene magmatism is not present in the western section of the İstanbul-Zonguldak Tectonic Unit (İZTU), except for the Armutlu-Almacık zone (e.g., Gülmez et al, 2013). I present new U-Pb zircon age and geochemical data for volcanic rocks from the Princes’ Islands, located in western section of the İZTU, with the aim of shedding light on the Eocene geodynamic evolution

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Discussion

Conclusion