Abstract
The main petrographic composition of the Ca Vịnh magmatic rocks are trondhjemit, tonalite, granodiorite and granite. The rocks belong to calc-alkaline magmatic series and display geochemical characteristics of adakitic type with high content of Sr (206-791 ppm) and light rare earth elements (La=17.65-30.09 ppm), but very low concentration of heavy rare earth elements (Y=11.59-18.08 ppm; Yb=0.87-1.61 ppm). They have high ratios of Sr/Y (15.51-51.01) and La/Yb (10.96-34.58). The initial Sr isotope and εNd values of Ca Vịnh granitoid are low, ranging from 0.700 to 0.702 and - 0.3 to -3.9, respectively. These characteristics are evidence for generation of magmatic melt through re-melting of the lower continental crust having mafic composition. This is supported by relative high magnesium values (Mg #=46.1-53.5). The emplacement age of the Ca Vịnh granitoid and its Sr-Nd isotopic composition are completely similar or closely to those of trondhjemit from the Kongling and the Kanding complexes forming during the Meso-Neoproterozoic time in the northern margin of the Yangtze plate.