Geochemical and isotopic constraints on the genesis of the Late Palaeozoic Deliktas and Sivrikaya granites from the Kastamonu granitoid belt (Central Pontides, Turkey)

Abstract

The Late Palaeozoic Sivrikaya and Deliktas granitoids of the Kastamonu granitoid belt (KGB) are of sub-alkaline affi- nity, belong to the high-K calc-alkaline series and display features of transitional to S-type granites. Sivrikaya granitoid is host to biotite-hornblende granodiorite-tonalite and minor two-mica granites. The rocks are 303 - 300 Ma old, have low initial 87 Sr/ 86 Sr ratios (0.7041- 0.708), moderately low eNd(t) values (-1 to - 3.8) and young TDM model ages (0.75 to 1.08 Ga). All these charac- teristics, combined with low Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO + TiO2) and δ 18 O values of 10-11.6 ‰ point to dehydration melting of heterogeneous protoliths dominated by amphibolite and greywackes-type sources with mantle contribution. Chondrite-normalized REE patterns of the Sivrikaya rocks are characterized by concave-upward patterns suggesting that amphibole played a more significant role than garnet during magma segregation. The main portion of the Deliktas granitoid consists of peraluminous muscovite-rich monzogranite. Compared to Sivrikaya, rocks from this pluton have higher initial Sr ra- tios (0.7109 - 0.7185), older Nd model ages (1.2 to 2.2 Ga) and similar eNd(t) values ( - 2.0 to - 4.7). U - Pb zircon analyses give an age range of 295 - 275 Ma. The nearly constant δ 18 O values (~ 11.5 to 11.7‰) in conjunction with the chemical characteristics in- dicate a predominantly pelitic source similar to the basement, which consists of felsic high-grade granulite-facies metasedimen- tary rocks, of continental origin.