Geochronological Data from the Southern Part (Niğde Area) of the Central Anatolian Massif

Year 1986, Volume: 105-106 Issue: 105-106, 92 - 106, 01.10.1986

M.cemal Göncüoğlu

Abstract

 In the Niğde massif, which forms the southern end of the Central Anatolian massif, three formations are exposed. These are, from bottom to top: 1. Gümüşler formation, composed mainly of metaclastics; 2. Kaleboynu formation, which is formed by the alternation of carbonates and elastics, 3. Aşıgediği formation, consisting of carbonates. Overlying this sequence, Niğde group, is an ophiolitic melange which has undergone deformation and metamorphism together with the underlain formations. It is assumed that the metamorphism of the sequence has transformed into low P-high T condition from the initial medium P-high T condition. The Niğde group is intruded by posttectonic Üçkapilı granodiorite which is concluded to have crystallized in lower Cenomanian (95±11 m.y.) according to the whole-rock Rb/Sr analyses. The initial Sr value (Sr=0.7104), which is obtained from the whole-rock isochrone, indicates that the granodiorite magma is generated either by the melting of the continental crust itself or by the extensive contamination of the continental crust. The cooling ages of granodiorite and gneisses acquired by Rb/Sr whole-rock mineral method and by K/Ar method are 77.8±1-2 m.y. and 76.5±1.1-m.y., respectively. These are the ages for granodiorite and gneisses to cool together down to 300±500C, which is the blocking temperature for micas whose isotope ratios have been measured. These data, obtained by geochronological methods are correlated with the other radiometric ages from the other parts of the Central Anatolian Massif and it is put forward that the main metamorphism and ophiolite emplacement have occurred pre-Cenomanian in the massif

Keywords

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