Abstract:Chemical components of Jiaonan granitic gneiss indicate that SiO2 and Al2O3 contents of the samples range from 68.4% to 78.2%and from 11.34% to 15.84%, respectively. TiO2, Fe2O3, FeO, MnO and MgO contents are obviously low; Fe203=0.69%～2.12%, FeO=0.18%～1.56% and MgO=0.05%～1.53%. Na2O, K2O contents of the rock are high and CaO is evidently low, with Na2O+K2O being 8.32%～10.33%, k2O 3.87%～5.24%, and CaO 0.19%～1.27%.The REEpatterns are characterized by obvious enrichment of light rare earth elements, clear deficiency of heavy rare earth elements, and medium-intense negative Eu anomalies. In the MORB normalized multi-element variation diagram, multi-element variations show the relative concentration of K, Rb, Ba and Th, evident depletionof Ti, Nb and Ta, and clear negative P anomalies. The protolith of granitic gneiss in Jiaonan belongs to A-type granite formed in volcanic arc tectonic surroundings under the action of tensional force. The source rock of A-type granite might have been derived from partial melting of the lower crust K-rich metabasalt formed in Neoproterozoic. It was formed at the temperature up to 1000℃,pressure from 0.8 GPa to 1.0 GPa, and partial melting degree lower than 10%. The formation of A-type gran-ite might have been related to the volcanic arc activity on the northeast margin of the Yangtze block in Neoproterozoic, which is supposed to be the reflection of the Neoprotorozoic Rodinia supercontinent breakup event in Sulu area.
