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

Abstract

The rock assemblages of the Princes’ Islands, which are located to the south of mainland İstanbul, are regarded as parts ofthe Lower Paleozoic quartz sandstones, although they were initially considered as volcanic rocks by Swan in 1868. They differ fromquartz 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 arecharacterized by strongly fractionated patterns with demonstrative negative Eu anomaly, whereby middle REE are not fractionatedrelative to the heavy REE. These geochemical features suggest a fractionating mineral assemblage of feldspar, apatite, and biotite withoutsignificant involvement of garnet. The Lutetian rhyolites of the Princes’ Islands are a part of the Middle Eocene magmatic associationsof the West Pontides, related to collision of the Menderes-Taurus block with the Pontides.