Tectonic setting and structural evolution of post-Late Cretaceous the Oltu-Balkaya basin (NE Turkey)

Abstract

The Oltu-Balkaya basin has started to open by the collision (soft-collision) between Pontide Arc and Anatolide-Tauride Platform since late Maastrihtian and was evolved as collisional foreland basins during Upper Maastrihtian and Eocene time. At this period, turbiditic continental deposits intercalated with carbonates, marine deltaic deposits and marine detritics are deposited, from bottom to top, respectively. Middle-Late Eocene shallow marin clastic deposits and high-K volcanics which may be attributed to post collisional magmatism lie on this basin fill characterizing the collisional phase. At the begining of Oligocene time, a molas consisting of continental clastics and shallow marine units with interlayeres of gypsum and high-K volcanics were deposited on a regional unconformity at the Oligocene-Late Miocene interval in the region which was a completely emergent land (hard-final collision) at the end of Eocene. After deposition of the sequence characterizing this period, the region has completely become a land in the Miocene time by compression. Normal faults with NW-SE striking and in the direction of NE -SW dipping are observed in Late Miocene-Early Pliocene units consisting of fluvial to lacustrine completely continental deposits and volcanics. A widespread andesitic and dasitic volcanism occured at this period reflecting an extensional tectonic regime. Late Pliocene-Quaternary semi-consolidated continental clastic deposits cover these units by ungular unconformity. The Oltu-Balkaya basin is characterized by dominant folding with approximately NE-SW trending axis and a thrust fault striking NE-SW, which dips about 40o northward. These structures as a whole represent NW-SW-directed compressional tectonic regime prevailed in the basin at least during Late OligoceneMiocene time. As for the Late Pliocene-Quaternary beds rest on an angular unconformity over the older units and this sequence which have not been folded represents Neotectonic period. As a result, the Oltu-Balkaya basin represents a superimposed basin which is syn-collisional in Upper Maastrictian-Middle Eocene, post-collisional in Middle Eocene-Early Pliocene and where the strike-slipe regime dominant since the Late Pliocene to present time (Neotectonic Period).