Geochronology and geochemistry of the Cida complex in the Panxi district:Constraints on the duration of the Emeishan mantle plume
攀西茨达复式岩体年代学和地球化学:对峨眉山地幔柱活动时间的约束

The Cida complex is located in the Panxi rift, the western margin of Yangtze craton, SW China. The SiO2 contents for mafic rocks to felsic rocks range from 40.06% to 68.54% smoothly. The mafic rocks and felsic rocks are the dominant rock types, whilst the intermediate rocks are rare, mineralogically heterogeneous, and usually have mottled structure. The chondrite normalized REE patterns display a trend from slightly enriched to significantly enriched LREE relative to HREE for mafic rocks to felsic rocks. The primitive mantle normalized trace element diagrams of felsic rocks are characterized by positive anomalies of Rb, Th, K, La, Ce, Pb, Nd, Zr, Hf, Sm, and negative anomalies of Ba, Nb, Ta, Sr, P, Ti. All incompatible element anomalies except Ti and Pb are absent in mafic rocks. Except for negative Ti, Sr anomalies and positive Pb anomalies, the intermediate rocks are between the mafic rocks and felsic rocks for other incompatible elements. The field and petrographic observations suggest that intermediate rocks were likely formed by magma mixing. The felsic rocks characterized by metaluminous affinities and low SiO2 contents, imply that they are possibly resulted from partial melting of basaltic lower crust. In contrast, the mafic rocks with OIB geochemistry and high temperature signature indicate that the mafic magma was derived from a mantle plume source. The LA-MC-ICP-MS U-Pb zircon dating yields an average of age is 243±0.77Ma for the mafic rocks, and 240.5±0.76Ma for the felsic rocks, possibly representing the end age of the Emeishan large igneous province magmatism.