Sr and Nd Isotopic Characteristics of Some S-, I- and A-type Granitoids from Central Anatolia

Authors: SERHAT KÖKSAL, M. CEMAL GÖNCÜOĞLU

Abstract: The petrogenesis of some Late Cretaceous S-, I- and A-type granitoids in the Aksaray and Kırşehir regions of Central Anatolia is investigated by means of whole-rock Sr and Nd isotope data with supplementary field, petrographic, and whole-rock geochemical studies. The S-type Central Anatolian granitoids (Sinandı and Namlıkışla) have calc-alkaline peraluminous characteristics and show LILE and LREE enrichment. The I-type Central Anatolian granitoids (Borucu, Terlemez, Hisarkaya, Baranadağ), on the other hand, are calc-alkaline (excepting the alkaline Baranadağ sample) and metaluminous or slightly peraluminous with LILE and LREE enriched patterns and variable Eu-anomalies. Additionally, the A-type Çamsarı granitoid is alkaline and metaluminous with the highest LREE contents. Isotope data from the I-type Central Anatolian granitoids (^{87}Sr/^{86}Sr_{(i)}: 0.7078-0.7109; \epsilonNd: -5.4 to -7.9), and the A-type Çamsarı granitoid (^{87}Sr/^{86}Sr_{(i)}: 0.7082; \epsilonNd: -7.1) are similar. The S-type Central Anatolian granitoids, on the other hand, have more radiogenic initial Sr isotopic ratios (^{87}Sr/^{86}Sr_{(i)}: 0.7128-0.7152) and lower eNd values (-9.1 to -9.7) than the I- and A-type granitoids from Central Anatolia. When combined with the available petrological and age data, the isotope data presented in this study support the suggestion of collisional S-type granitic associations, and younger post-collisional and subsequent extensional I- and A-type magmatism in Central Anatolia. Sr and Nd isotope data infer that the I- and A-type Central Anatolian granitoids have hybrid and heterogeneous sources, while in the A-type granitoids a mantle component is likely to be dominant. Moreover, the S-type Central Anatolian granitoids were possibly derived from crustal, or crustal-dominated sources. Furthermore, the increase of ^{87}Sr/^{86}Sr_{(i)} and decrease of \epsilonNd values observed from S-type granitoids to I- and A-type magmatic rocks is either related to distinct source characteristics or to isotopic mixing between mantle and crustal sources through time.

Keywords: Sr-Nd isotope geochemistry, Central Anatolia, granitoid

Full Text: PDF