ISOTOPE GEOCHEMICAL STUDIES OF THE DARONGSHAN PERALUMINOUS COMPOSITE BATHOLITH OF GRANITOIDS IN GUANGXI AUTONOMOUS REGION, CHINA
Huang Lin(Institute of Geochemistry, Academia. Sinica)
Rb-Sr and 40Ar-39Ar isotope chronological studies of the Darongshan peraluminous com-posite batholith of granitoids show that the Yunkaidashan migmatite has a final emplacement age of 370 Ma, Sr isotope homogenization in the batholith's source region took place at 310 Ma ago, and the ages of the Darongshan, Taima and Jiuzhou massifs are dated at 270, 258 and 228 Ma, respectively. Studies of the Sr and O isotope systematics demonstrate that the massifs have initial (87Sr/86Sr)o ratios greater than 0.7200 and σ18O values greater than 10‰, indicating that they are typical S-type granites derived from partial remelting of sedimentary rocks rharac-terized by similar chemical composition and poor fracdonation. The Darongshan and Jiuzhou massifs belong to the same system with an evolutionary relation, and the Taima massif was derived from another deeper source region. The composition of the Luodin migmatite is cha-racterized by two- end-member mixing. The consistency between the inclusion isochron and regional isochron ages provides evidence showing that the inclusions are mainly residual relics.