GEOCHRONOLOGICAL DATA FROM THE SOUTHERN PART (NİĞDE AREA) OF THE CENTRAL ANATOLIAN MASSIF

In the Nigde massif, which forms the southern end of the Central Anatolian massif, three formations are exposed. These are, from bottom to top: 1. Gumusler formation, composed mainly of metaclastics; 2. Kaleboynu formation, which is formed by the alternation of carbonates and elastics, 3. Asigedigi formation, consisting of carbonates. Overlying this sequence, Nigde 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 Nigde group is intruded by posttectonic Uc- kapih granodiorite which is concluded to have crystallized in lower Cenomanian (95±11 m.y.) according to the wholerock Rb/Sr analyses. The initial Sr value (Sr=0.7104), which is obtained from the wholerock isochrone, indi- cates 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 wholerock- 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 gran- odiorite and gneisses to cool together down to 300±50 0C, which is the blocking temperature for micas whose isotope ratios have been measured. These data, obtained by geochronologi cal methods are correlated with the other radiomet- ric 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.