Abstract:

New found basalt crop is located near the Nanxi Town, Taihe County, south of Ji'an-Taihe Basin, middle Jiangxi Province. With brown-grey and dark green color, the fresh basalt has compacted texture and some blisters and amygdules. Microscope observation reveals that the rocks have intergranular textures,more than 60% basic plagioclases, filling with olivines and augites, less than 5% almond-shaped calcites, and weak corrosion. According to its geochemical features, the basalt belongs to alkalibasalt, produced by quick regional extension within a plate. Rb-Sr and Sm-Nd isotopic composition of the basalt are as follow:(⁸⁷Sr/⁸⁶Sr)_i =0.704 1-0.704 8 and ε_Nd(t)=+3.78-+4.38, indicating that the magma came from the deficit mantle and had not mixed with crust material. The zircon solution U-Pb geochronological data of(139±0.7)to(143±1.1)Ma for the alkali-basalt indicates that mantle-reached strike-slip faulting along northeast-striking Ganjiang Fault and Wuchuan-Sihui Fault was active from early period of Early Cretaceous under the extensional background of the area

Key words: alkali-basalt, deficit mantle, extension environment within a plate, early period of Early Cretaceous, Ganjiang Fault, Wuchuan-Sihui Fault, Ji'an-Taihe Basin