Geochronology, Petrography, and Geochemistry of the Kazdag Metamorphic Rocks in The Biga Peninsula - NW Turkey


Çalık A. , Bozcu M.

2011 GSA Annual Meeting in Minneapolis, Minnesota, United States Of America, 9 - 12 October 2011, pp.76

  • Publication Type: Conference Paper / Summary Text
  • City: Minnesota
  • Country: United States Of America
  • Page Numbers: pp.76

Abstract

The Kazdag metamorphic rocks which form a structural and topographic dome of high-grade metamorphic rocks in the Kazdag mountain range in northwest Turkey are subdivided into two groups that are the Kazdag group and the Ayýdere Group in this study. The present study is concerned with the field aspects and petrographic features of these rocks with further focus on the whole-rock geochemistry, mineral chemistry, and Ar-Ar and Rb – Sr geochronology of the rocks of the Kazdag group. The Kazdag metamorphic rocks which form a structural and topographic dome of high-grade metamorphic rocks in the Kazdag mountain range in northwest Turkey are subdivided into two groups that are the Kazdag group and the Ayýdere Group in this study. The present study is concerned with the field aspects and petrographic features of these rocks with further focus on the whole-rock geochemistry, mineral chemistry, and Ar-Ar and Rb – Sr geochronology of the rocks of the Kazdag group.

The Kazdag group consists of gneisses with marble and amphibolite intercalations at the base upwards metaophiolitic rocks tectonically lay on the basement. Metaophiolitic rocks are mainly represented by metadunite, metapyroxenite, layered metagabbro and serpentinite. The mineral assemblage in the amphibolite consists of hornblende+ plagioclase+ quartz+ clinopyroxene± biotite ± garnet ± epidote, whereas the mineral assemblage in the metaophiolitic rocks is comprised by olivine (Fo) + serpentine + orthopyroxene ± amphibole; olivine (Fo) + serpentinite ± talc; orthopyroxene + garnet. These rocks underwent amphibolite – granulite facies metamorphism. Hornblende and plagioclase 40Ar/39Ar ages in amphibolites from the Kazdag group yield an age of 29.5 ± 4 Ma (late Oligocene) for the amphibolite – granulite facies metamorphic event. In additional to that, Rb – Sr dating ages in amphibolites of the basement of the Kazdag group present the age of 917±31 Ma indicating the age of the basement is the oldest age to get in this region. The Kazdag metaophiolite sequence tectonically overlain on the Precambrian basement in the Kazdag region.

Geochemical data reveal that the metaophiolitic rocks of the Kazdag group are sub alkaline in nature and display tholeiitic affinity. The Kazdag metamorphics are characterized by relatively high Zr/Y (1.23 – 5.95), Th/Ta (0.67 – 16.77), and Th/ Yb (0.103 – 3.852) ratios. They show marked negative Nb and Ti anomalies, implying subduction-related chemistry.REE patterns display enrichment of LREE fairly comparable with N- MORB. The Kazdag metaophiolitic rocks might be derived from a highly depleted mantle in an arc-related setting in the light of the trace and REE geochemistry.