The Armutlu peninsula is a composite tectonic entity made up of sections of the Sakarya continent, the Rhodope-Pontide fragment and an ophiolite. These were assembled following a continental collision between Gondwanaland and Laurasia during the Late Cretaceous. The northern margin of the Sakarya continent underwent progressively increasing deformation prior to and during the advancing collision, due to continued convergence between the two continents. Initially, the leading edge of the continent subsided under the load of an approaching ophiolitic slab. Following this, a north-directed thrusting and folding occurred during the Turonian.
Progressive elimination and eventual closure of the ocean preceded the thrusting of northerly situated, collisiondashinduced, nappe packages over the leading edge of the Sakarya continent. The nappe-laden edge of the continental margin then collapsed and steadily subsided under the heavy load of the ophiolitic slab and the northern continental fragment. Consequently, the nappe packages and the ophiolite were collectively metamorphosed during the ConiaciandashSantonian interval. During the subsidence the main body of the Sakarya continent partially detached from its collapsed edge along a fault zone and thus suffered an independent but less severe deformation, which lasted until the uplift of the collapsed edge in the Campanian. From the late Campanian onward, throughout later orogenic stages, the metamorphic and nondashmetamorphic units amalgamated into a single tectonic entity, forming a basement for younger cover rocks.