Sr-Nd-Pb isotopic characteristics of the granitoids in the Douling complexes, eastern Qinling, China and its geological significance

The granitic batholiths in Douling complexes of eastern Qinling, such as Gangou, Sanpinggou and Fengzishan intrusions, are characterized by large variation of SiO2, low alkaline, high Na2O and enriched in LREE and LILE as well as poor in HFSE and depleted in Nb, Sr, P and Ti, displaying peraluminous calc-alkaline I-type granitoids. In contrast, Tuwushan intrusion, as a small granitic body, is highly enriched in SiO2 and alkaline, with higher total REE and strong negative Eu anomaly as well as enrichment in Rb, Th, U and Pb and strong depletes in Sr, P and Ti, showing geochemical features of A2-type granite. Both of them have similar Nd-Pb isotopic composition, indicating that they were formed by partial melting from the same crustal materials. Whereas, the difference of geochemical characteristics between them was resulted from quite different processes during magma evolution. In addition, they have low radiogenic Pb isotopic composition similar to those of basement blocks in southern Qinling and Yangtze block but quite different to those of basement and granitoids in northern Qinling with the higher radiogenic Pb isotopic composition, suggesting that the granitic magmatism in southern Qinling should be closely related to the final formation of Yangtze block during mid-Neoproterozoic, lack of any genesis relationship with northern Qinling.