Geochemical modelling of early Eocene adakitic magmatism in the Eastern Pontides, NE Anatolia: continental crust or subducted oceanic slab origin?

Karsli O., UYSAL İ., Dilek Y., AYDİN F., Kandemir R.

INTERNATIONAL GEOLOGY REVIEW, vol.55, no.16, pp.2083-2095, 2013 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 55 Issue: 16
  • Publication Date: 2013
  • Doi Number: 10.1080/01431161.2013.819958
  • Journal Name: INTERNATIONAL GEOLOGY REVIEW
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.2083-2095
  • Keywords: adakitic magmatism, partial melting of mafic lower crust, Eastern Pontides - NE Anatolia, slab break off, asthenospheric upwelling, TRONDHJEMITE-GRANODIORITE TTG, PB ISOTOPIC CHARACTERISTICS, THICKENED LOWER CRUST, I-TYPE GRANITOIDS, TECTONIC EVOLUTION, VOLCANIC-ROCKS, NEOTETHYAN CONVERGENCE, TURKEY IMPLICATIONS, MAGNESIAN ANDESITE, CENOZOIC VOLCANISM
  • Karadeniz Technical University Affiliated: Yes

Abstract

Early Eocene adakitic volcanic and granitoid rocks are widespread in the Eastern Pontides of NE Turkey, providing significant constraints for the early Cenozoic tectonomagmatic evolution of the region. These adakitic rock units exhibit relatively high Sr/Y and La/Yb ratios, but low Y and Yb values, similar to modern adakites generated by partial fusion of a subducted oceanic slab. They also have high K2O and low MgO contents, and show moderately enriched I-Sr and low E-Nd(t) isotopic signatures. Our trace element modelling suggests that these adakitic magmas were generated from partial melting at low pressures of a garnet-bearing amphibolitic source in the continental lower crust. This lower crustal melting resulted from slab break off-induced asthenospheric upwelling and related magmatic underplating beneath the Eastern Pontides. We interpret this melting event and the adakitic magmatic activity as a syn- to post-collisional process involving early Cenozoic collision of the Pontide and Anatolide-Tauride continental blocks. The geochemical and tectonic constraints presented here indicate that early Eocene adakitic magmatism in the Eastern Pontides did not result from partial fusion of a subducted oceanic slab, but instead represent continental-type adakite formation.