Paleozoic sequence in the İstanbul Zone termed as depositional rocks of the Rheic ranges from
virtually uninterrupted terrestrial clastics to platform deposits with Ordovician to Carboniferous ages,
and occurs in İstanbul, Çamdağ, Düzce, Karadere areas. Basement of the Paleozoic is exposed in
the Armutlu peninsula, Karadere area, and the Sünnice Massif as highgrade
amphibolitefacies
quartzplagioclasebiotitehornblende
gneiss (Demirci paragneisses) and greenschistfacies
metavolcanic
associationlavas
and pyroclastics (Yellice metavolcanics;
1782±130 Ma), intruded by the
Dirgine granite (576565
Ma). Tectonically overlain terrestrial deposits of the Paleozoic are
represented by fluvial finecoarse
grained clastics (Kurtköy Formation; t>3000 m) that conformably
overlies lacustrine deposits (Kocatöngel Formation; t≈2000 m).
Depositional ages of the lacustrinefluvial
deposits are accepted as the earlymiddle
Ordovician
without any fossil data for two reasons: (a) the fluvial deposits are overlain by the beach deposits
(Aydos formation) which have an upper age of Darriwilian, and (b) in the Karadere area, the
basement made up of highgrade
metadeposits
is intruded by the granitic bodiesdykes
(590560
Ma) and is unconformably overlain by the fossiliferous strata of fluvial fine grained deposits
representing a fluvialbeach
setting that have an upper age of Tremadocian.
For this study, two folded dykes have been mapped in 1/1000 scale in the Sünnice Massif and its
surroundings. Geochemical data suggest both folded dykes have calcalkaline
magma with a
subduction signature. Fold axis of the dacite dykes crosscutting
the Dirgine granite is N740E with a
plunge of 760NE, and fold axis of the dioritic diabase dykes crosscutting
the Kurtköy formation is
N740E with a plunge of 810NE. UPb
dating of the zircons yield an age of 555.9±2.6 Ma for the
folded dacite dyke and 548.8±2.8 Ma for the folded dioritic diabase dyke. Field and analytical data
suggest that these folded dykes were folded after the host rocks had been intruded, and age of the
basal terrestrial deposits is older than previously suggested for the İstanbul Zone.