Abstract:

The forth unit of the Daguding Group in central Jiangxi Province consists of intermediate to basic volcanic rocks in the
Shengyuan basin and adjacent areas. Our systematic study of petrology and geochemistry of this unit identifies that these rocks belong to typical interplate shoshonitic volcanic rock series, which are characterized by high contents of total alkali and K2O, low contents of TiO2 and iron, and an enrichment of the LREE and LILE elements. The Rb-Sr isochron age of the shoshonite series is (138±8.8)Ma, with distinctively high initial Sr isotopic ratios; intermediate initial Nd isotopic ratios and enriched radiogenic Pb. In addition,the shoshonite series shows a remarkable Dupal anomaly (△7/4Pb=14~19.6 with an average value of 16; △8/4Pb=70.5~97 withan average value of 89.2; △Sr=121.5~161.8 with an average value of 136.3). The correlations of Sr-Nd, Sr-Pb, Nd-Pb and Pb-Pbisotopes imply a mixing source of the depleted mantle (DM) endmember and the lithosphere enriched mantle (LEM) endmember.According to the two-component (Sr-Nd) mixing equation, the source of the shoshonite series is composed of about 37% DM

Key words: shoshonite, petrology and geochemistry, Sr-Nd-Pb isotopes, lithosphere enriched mantle, central Jiangxi Province