Relationships between the Sakarya Zone and the Ankara-Erzincan suture (central-northern Turkey): Geological and petrographic data from the Ankara-Çankiri, Çorum and Amasya areas

Abstract

The study was performed in central-northern Anatolia (from Ankara to Amasya) to investigate the relationships of the Sakarya Zone units and the Izmir-Ankara-Erzincan suture (IAES) melange. It reveals that all the Sakarya Zone units are metamorphic and three main tectonostratigraphic units have been distinguished for the first time: the BAA (metasiliciclastic rocks capped by metacarbonates and varicoloured phyllite), the BKC (poly-metamorphic garnet-bearing micaschist and metabasite with a well-preserved relict HP-LT amphibole in a low-amphibolitic to greenschist-facies framework) and the AMC (meta-arkose passing vertically to carbonate-phyllitic alternations and, then, to a thick succession of prevailing acidic to intermediate-basic metavolcanites and volcanic-rich metasediments). The BAA and AMC, whose metamorphic frameworks are of Cimmerian age, underlie the Mesozoic carbonate cover sequences (e.g. t2-3, j3-k1) that often show tectonic detachments and slicing. The piling up of the BAA above the HP-LT BKC can be correlated to the tectonic superposition of two similar units (i.e. the Cimmerian Çangaldaǧ Complex and the Alpine Middle-Upper Cretaceous Domuzdaǧ Complex, respectively) defined by previous authors in other sectors of the Central Pontides front. The ophiolitic melange generally underlies the Sakarya Zone, but locally (e.g. SE of Amasya) tectonically rests above the latter, probably owing to back-thrusting that occurred during the Tertiary syn-collisional shortenings and the later strike-slip tectonics. We hypothesize that, also in these areas, the Sakarya Zone-IAES consists of a complex tectonic stack of different units, belonging to different palaeogeographic domains and orogenic events (Cimmerian versus Alpine orogenies), but originated within a single long-lived (since Late Triassic to Paleocene/Eocene times), prograding subduction-accretion system in front of the Laurasian continent.