Tectonic Setting and petrology of collision-related Eocene volcanism around the Cankırı Basin, North Central Turkey

KESKİN M., GENÇ Ş. C., TÜYSÜZ O.

32nd International Geological Congress (ICG 2004), Florence, Italy, Italy, 1 - 04 August 2004, pp.1299

  • Publication Type: Conference Paper / Full Text
  • Country: Italy
  • Page Numbers: pp.1299
  • Istanbul University Affiliated: Yes

Abstract

 

The Cankiri basin, one of the main tectono-sedimentary entities of the North Central Anatolia Region, has a complex evolutionary history. It began as a fore-arc basin over a northward-subducting oceanic lithosphere during the Late Cretaceous, and gradually changed into a post-collisional one after the collision of Sakarya and Kirsehir micro-continents along Ankara-Erzincan suture zone between the Late Cretaceous and Eocene. The collision resulted in the thickening of the crust at the base of the basin by south-vergent thrusts. Rapid change in facies characteristics of the sediments (i.e. from marine to subaerial) in the basin indicates that collision was accompanied by the rapid uplift of the region. Volcanism started during the Middle to Late Eocene in and around the Cankiri basin right after the uplift. Volcanic activity created a volcanic belt, confined basically into the suture zone.

Petrographically, lavas of this belt are divided into two volcanic series: (1) PAm: (plg+amp±bio-phyric lavas) and, (2) POAM (plg+olv+cpx-phyric lavas). While the POAM lavas span a compositional range from basalts to andesites, the PAm lavas cover a broader range from basaltic-andesites to rhyolites. Lavas of both series are calc-alkaline in character. The PAm – POAM division is also apparent in trace element fractionation trends. We argue that these differences should have been created by differences in magma chamber processes, not by differences in source composition, because the trends diverge from the same basic end-member composition. Variation diagrams indicate that magma replenishment and mixing were important processes in the magma chamber evolution of these lavas. Our AFC modelings suggest that both PAm and POAM lavas have very significant contributions from the continental crust, with some PAm samples displaying almost crustal compositions. All lavas exhibit a selective enrichment in LILEs and LREEs over HFSEs relative to MORB. Such a subduction signature requires the presence of an active subduction but this contradicts with the tectono-sedimentary record of the Cankiri basin.

We suggest that the slab breakoff model is the most viable model for the Eocene volcanic units since it better explains (1) why the Eocene volcanism initiated right after the rapid uplift, (2) why it formed a volcanic belt confined into the suture zone, and (3) why it produced lavas with a distinct subduction signature and a significant contribution from the continental crust.