Abstract:

The mica granitic gneisses is an important rock type for Qushan complex from UHP belt in the southern Sulu terrane, which had suffered UHP metamorphism, but still had the petrological features of granite. The geochemical analysis data indicate that the mica granitic gneisses have the characteristics of A-type granitoid with high K₂O contents and TFeO/MgO ratios, and with low CaO contents, and high peraluminous coefficient. The mica granitic gneisses have the characteristics of the REE patterns with steeply fractionated and strongly negative Eu anomalies, the trace elements patterns with negative Ba, P, Ti and Sc anomalies, high Sr/Y, La/Yb, Rb/Sr, Rb/Ba ratios, and TiO₂＜0.2％，Y/Nb ＞1.2，and all of the samples plots in the Within Plate Field in the Rb vs (Yb+Ta) and Rb vs (Y+Nb) discrimination diagrams, which show that the mica granitic gneisses formed in non-orogenic environment but within plate related with rifting. The zircon SHRIMP U-Pb dating inferred that the time of magmatic emplacement was middle-late Upper Proterozoic ((722±32)Ma), it was resulted from the magmatic activity that was identical early emplaced feldspar granitic gneisses in Qushan complex and the metamorphic volcanics overlying on Qushan complex during Rodinia continent breakup and within plate rifting in Yangtz block.

Key words: Sulu terrane, Qushan complex, ultrahigh pressure metamorphic belt, mica granitic gneisses, zircon SHRIMP U-Pb dating