International audiencePermian-Triassic and Late Cretaceous accretionary complexes, ascribed to the consumption of two distinct oceans, the Paleo- and Neo-Tethys, are exposed over extensive areas in the Eastern Mediterranean region. However, a separating continental ribbon, the so-called Cimmeride continent, between the Paleo- and Neo-Tethys during early Mesozoic time cannot be defined. Here we report a previously unknown Early Jurassic metamorphic oceanic accretionary complex and ophiolite from northeast Turkey, bounded by oceanic accretionary complexes of Permian-Triassic and Late Cretaceous age to the north and the south, respectively, without a continental domain in between. This special tectonic position and widespread coexistence of Permian-Triassic and Late Cretaceous accretionary complexes alongside the Izmir-Ankara-Erzincan suture imply that (1) the southern margin of Laurasia in the eastern Mediterranean region grew by episodic accretionary processes from late Paleozoic to end-Mesozoic time without involvement of a Cimmerian continental ribbon, and (2) the Paleo-Tethys and northern branch of the Neo-Tethys were not distinct oceans in the Eastern Mediterranean region

Two isolated metamorphic accretionary complexes of Jurassic age, the Refahiye and Kurtlutepe metamorphic rocks, crop out as tectonic slices within the coeval suprasubduction-zone ophiolite at the southern margin of the Eastern Pontides (NE Turkey), close to the İzmir-Ankara-Erzincan suture. The Refahiye metamorphic rocks are made up of greenschist, marble, serpentinite, phyllite and minor garnet amphibolite, garnet micaschist and metachert. The whole unit was metamorphosed under garnet-amphibolite-facies conditions and strongly retrogressed during exhumation. The Kurtlutepe metamorphic rocks consist of subgreenschist-facies metavolcanics, metavolcaniclastics, marble, calc-phyllite, and minor serpentinite and metachert. Metabasites in the Refahiye metamorphic rocks are represented by four distinct geochemical affinities: (i) cumulate “flavor,” (ii) alkaline oceanic island basalt (OIB), (iii) enriched mid-ocean ridge basalt (E-MORB) and (iv) tholeiitic island arc basalt (IAB). On the other hand, the Kurtlutepe metavolcanic rocks display only tholeiitic to calc-alkaline island arc geochemical affinities. The metabasic rocks with OIB affinities were interpreted as parts of the accreted oceanic islands, and those with E-MORB affinities as parts of accreted ridge segments close to oceanic islands and/or plume-distal mid-ocean ridges with a mantle previously metasomatized by plume components. The metabasic rocks with IAB affinities might have been derived from the overlying suprasubduction ophiolite and/or arc domain by a number of tectonic or sedimentary processes including tectonic slicing of accretionary complex and overlying fore-arc ophiolite, juxtaposition of the magmatic arc with subduction zone by strike slip faults, submarine gravity sliding and debris flows or subduction erosion. However, totally recrystallized nature of the metabasic rocks together with field relations does not allow any inference on the processes involved. The Kurtlutepe metavolcanic rocks might represent collided and accreted oceanic island arc with the subduction zone. Attempted subduction of an intraoceanic island arc may also explain the magmatic lull during Late Jurassic–Early Cretaceous in the Eastern Pontides.

Neo-Tetis Okyanusunun, Türkiye’nin kuzey kesiminde yitimi sonucunda İzmir-Ankara-Erzincan sütur zonu (IAESZ) gelişmiştir. Sutürlaşma sürecinin bitmesi sonrasında, IAESZ’nin her iki tarafı ve üzerinde gerilme ve magmatizma eş zamanlı olarak gelişmiştir. Bu dönem boyunca, Almus, Yıldızeli ve Yıldızdağ bölgelerinde yoğun magmatik aktivite gelişmiştir. Almus ve Yıldızeli bölgesindeki Orta Eosen magmatizması volkano-sedimentar birimler ile temsil edilmektedir. Buna karşın Yıldızdağ bölgesindeki gabroyik ve diyoritik kayalar magmatizmanın genel unsurlarıdır. Almus ve Yıldızeli bölgelerindeki volkano-sedimanter kayalar alt kesimlerinde sığ denizel sedimanter kayalar, orta ve üst kesimlerinde ise lav akıntıları ve volkanoklastik birimler ile temsil edilmektedir. Almus ve Yıldızeli bölgelerindeki eş zamanlı olarak gelişen magmatik birimlerin evrimini anlamak adına sekiz adet volkanosedimanter istif ölçülmüştür. Her iki bölgede, stratigrafiye bağlı olarak üç farklı volkanik dönem ayırtlanmıştır. İlk evre amfibollü bazaltik andezit, andezit ve dasitlerden oluşur. İkinci evre bazalt ve piroksenli bazaltik andezitler ve üçüncü evre ise trakit ve trakiandezit dayk ve stoklarından meydana gelmektedir. Bütün bölgelerden elde edilen arazi verisi sonucunda orta-Eosen magmatik birimlerinin eş zamanlı olarak çarpışma sonrası dönemde geliştiği ve magmatizmayı tetikleyen olayın bölgesel ölçekte bir delaminasyon veya litosferik ayrılma süreçleri ile kontrol edildiği görülmektedir.