NDLI: Geochronology of the Karadere basement (NW Turkey) and implications for the geological evolution of the Istanbul zone

Content Provider	Springer Nature Link
Author	Chen, F. Siebel, W. Satir, M. Terzioğlu, M. Saka, K.
Copyright Year	2001
Abstract	Earlier geological work in the Istanbul zone, western Pontide tectonic belt, has revealed the presence of extensive basement outcrops exposed underneath Palaeozoic and Mesozoic to Tertiary cover sequences. The basement of suspected Neoproterozoic age plays an important role in understanding the crustal accretion process in NW Turkey. We report the first results of a detailed Pb–Pb and U–Pb zircon study complemented by Nd–Sr whole rock and mineral data from basement rocks exposed in the Karadere valley, Safranbolu area. Five samples were selected for this study, comprising three metagranitoids and two metasediments. Zircon geochronology indicates that the metagranitoids were formed during Late Proterozoic pan-African magmatic events between 590 and 560 Ma. The rocks are of tonalitic and granitic composition and have low Nb/Y ratios and Ti contents, consistent with those of arc rocks. A continental arc setting is supported by their Sr and Nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis. The metasediments can clearly be distinguished from the metagranitoids by their higher 87Sr/86Sr ratios and lower εNd-values at 580 Ma, which supports the suggestion that the arc was underlain by mature continental crust. Zircons from the metasediments yield a range of Pb–Pb ages between 1,860 and 710 Ma. Thirty per cent of them fall between 890 and 710 Ma, possibly suggesting a derivation from Gondwana (Afro-Arabian) regions. A Sm–Nd garnet–whole rock analysis obtained on a metagranite gives an age of 559±8 Ma, which either reflects pre-metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high-temperature metamorphic event. Uplift and cooling of the basement is further constrained by Rb–Sr biotite ages of 548–545 Ma. These lower Cambrian mineral ages demonstrate that the Istanbul zone was not thermally reactivated during the Hercynian, Cimmerian or Alpine orogeny, in contrast to its neighbouring tectonic zones, confirming its role as a suspect terrane in the modern western Pontide tectonic belt.
Starting Page	469
Ending Page	481
Page Count	13
File Format	PDF
ISSN	14373254
Journal	International Journal of Earth Sciences
Volume Number	91
Issue Number	3
e-ISSN	14373262
Language	English
Publisher	Springer-Verlag
Publisher Date	2001-12-15
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Geology Geophysics/Geodesy
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences

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