The Almacik mafic-ultramafic complex: exhumed Sakarya subcrustal mantle adjacent to the Istanbul Zone, NW Turkey

Bozkurt, Erdin
Satir, Muharrem
Crowley, Quentin G.
Ottley, Christian J.
The Almacik Mountains in northwestern Turkey expose an upper-amphibolite-facies complex consisting of alternating ultramafic (harzburgitic and websteritic) and mafic (metagabbroic) rock types. In the eastern part of this complex are island arc meta-tholeiites and transitional to calc-alkaline metabasites that are chemically quite similar to those of the Permo-Triassic Cele mafic complex north of Bolu, and this suggests an equivalence. However, much of the section exposes structurally deeper and chemically different mafic and ultramafic rocks, which have no equivalent in the Cele mafic complex, and isotopic dating has suggested that these rocks also formed during the Permian period and underwent Triassic and Jurassic metamorphism. Furthermore, sparse inherited ages, unlike those from. Istanbul Zone granitoids, suggest a link with North African-derived Armorican-type basement (and hence the Sakarya Zone), rather than Amazonia-derived Avalonian basement. Alternating mafic and ultramafic rocks suggest structural repetition, supported by the exposure of discrete high-strain zones or poorly exposed shattered rock west of each outcrop of ultramafic rocks. The high grade of metamorphism, and the absence of either extrusive lavas or sheeted dyke rocks, suggests that the Almacik complex was not an ophiolite, but formed instead as subcontinental lower crust and subjacent mantle. Dominantly calc-alkaline geochemistry suggests that it formed the basement to an active continental margin bounding the north side of the Sakarya Continent, with S-dipping subduction of Palaeotethys. The Almacik complex was uplifted as a late result of compression against the southern margin of the. Istanbul Zone in the Jurassic period. Lack of coeval high-grade metamorphism in the. Istanbul Zone indicates that the latter was overthrust southwards over the Sakarya margin, and that there was therefore a change of subduction polarity in the Triassic period. The evidence further casts doubt on the existence of a Mesozoic Intra-Pontide Ocean in northwestern Turkey and suggests that the latest Permian magmatism, with subsequent Triassic and Jurassic metamorphism, was instead related to the closure of the Palaeotethyan Ocean.


Göncüoğlu, Mehmet Cemal; Sayıt, Kaan; Ottria, Giuseppe; Pandolfi, Luca; Ellero, Alessandro (2012-12-01)
The Ayli Dag ophiolites occur as an independent tectonic unit within the Intra-Pontide suture zone, central-northern Turkey. They crop out, together with the other units of the Intra-Pontide suture zone, at the top of the Late Cretaceous-Middle Paleocene foredeep sediments of the Sakarya Terrane. The Ayli Dag ophiolites sequence include in its lower part a mantle sequence consisting of not less than 2-3 km-thick peridotites, topped by 500-600 m-thick layered gabbros with alternating, dm- to m-thick layers o...
The Cele mafic complex: Evidence for Triassic collision between the Sakarya and Istanbul Zones, NW Turkey
Bozkurt, Erdin; Satir, Muharrem (2013-06-04)
The lowest structural levels of the Istanbul Zone are exposed in the Sunnice Massif, north of Bolu. They comprise the greenschist-facies Ediacaran calc-alkaline bimodal Yellice metavolcanics, which are intruded by the Dirgine granitoid. Amphibolite-facies mafic and subordinate ultramafic rocks of the Cele mafic complex, hitherto termed the Cele meta-ophiolite, include hornblende gneisses of island arc meta-tholeiitic and transitional to calc-alkaline metagabbroic compositions, and were previously thought to...
The upper Coniacian to upper Santonian drowned Arabian carbonate platform, the Mardin-Mazidag area, SE Turkey: Sedimentological, stratigraphic, and ichthyofaunal records
Yılmaz, İsmail Ömer; Hosgor, Izzet; Wagreich, Michael; Rebman, Katherine; Murray, Alison M. (2018-04-01)
A measured stratigraphic section including the upper Coniacian - upper Santonian interval in the Mardin-Mazidag area in Southeastern Turkey lies on the Arabian Platform and documents the drowning of the Arabian platform. The studied succession transgressively overlies the exposed carbonate platform and exhibits a relatively condensed sequence characterized by presence of fish remains, phosphate nodules, oncoids, phosphatic fragments, glauconites and planktonic foraminifera. Calcareous nanno-fossils attest a...
The Upper Cretaceous intrusive rocks with extensive crustal contribution in Hacimahmutusagi Area (Aksaray/Turkey)
Köksal, Serhat (Central Library of the Slovak Academy of Sciences, 2019-06-01)
The Hacimahmutusagi area (Aksaray/Turkey) is located in the western part of the Central Anatolian Crystalline Complex (CACC). Gneiss and marble compose the basement units, while intrusive rocks are gabbros and granitoids. The pegmatitic hornblende gabbros contain pegmatitic to fine-grained hornblendes, plagioclase, clinopyroxene, and accessory opaque minerals. The fine-grained gabbros, on the other hand, are composed of plagioclase, hornblende, and biotite as major components whereas the apatite and opaque ...
Geochemical and palaeontological characterization of a new K-Pg Boundary locality from the Northern branch of the Neo-Tethys: Mudurnu – Göynük Basin, NW Turkey
Açıkalın, Sanem; Vellekoop, Johan; Ocakoğlu, Faruk; Yılmaz, İsmail Ömer; Smit, Jan; Altıner, Sevinç; Goderis, Steven; Vonhof, Hubert; Speijer, Robert P.; Woelders, Lineke; Fornaciari, Eliana; Brinkhuis, Henk (Elsevier BV, 2015-1)
A Cretaceous-Paleogene (K-Pg) succession is studied in detail in the Mudurnu-Goynuk basin in northwestern Turkey. To characterize the K-Pg transition in this basin, two stratigraphic sections were measured and sampled at high resolution: the Okcular and the Goynuk North sections. These sections were analysed for siderophile trace elements, including Ir and other platinum group elements (PGE: Ru, Rh, Pd, Ir, Pt), bulk stable carbon isotopes, calcareous nannofossils, planktic foraminifera and organic-walled d...
Citation Formats
E. Bozkurt, M. Satir, Q. G. Crowley, and C. J. Ottley, “The Almacik mafic-ultramafic complex: exhumed Sakarya subcrustal mantle adjacent to the Istanbul Zone, NW Turkey,” GEOLOGICAL MAGAZINE, pp. 254–282, 2013, Accessed: 00, 2020. [Online]. Available: