Implications of Jurassic chert identified in the Tokat Complex, northern Turkey

Abstract

The Tokat Complex is a strongly deformed tectono-sedimentary mixture of low-grade metamorphic rocks with abundant recrystallized limestone and relatively rare serpentinite and radiolarian chert in blocks of variable size. Samples from the radiolarian chert blocks, found in highly crushed zones, each of which corresponds to a thrust sheet within an imbricate thrust zone, have yielded a Tithonian fossil assemblage. They are interpreted as tectonic inclusions emplaced within the Tokat Complex after its main post-early Permian–pre-Liassic metamorphism, and were derived from the rifting and opening of a Neotethyan ocean. The presence of Tithonian blocks within low-grade metamorphic rocks of the Tokat Complex shows that Tethys ocean was in existence in this region by latest Jurassic time. We also suggest that the presence of ophiolitic slices imbricated with the Pontide basement, Tokat Complex, explains the swarm of North Anatolian Fault Zone (NAFZ) splays in this region where the NAFZ likely followed a major pre-existing crustal weakness.