The newly discovered Moshigou lower greenschist facies metamorphism basalts crop out in Xinyang town of Tianshui area at the conjuction of the Qinling－Qilian orogens．There are also a little bedded siliceous rocks and veined diabases cropping together with the meta-basalts．The narrow variations of SiO2 content and MgO content of the meta-basalts range from 47.32% to 50.18%，and 4.71% to 7.33%，respectively．The low Al2O3 content（12.33%~14.97%）and high TiO2 content（0.98%~1.98%，with an average of 1.44%）are close to those of MORB，similar to E-MORB．The ∑REE range from 46.52×10-6 to 113.21×10-6．LREE/HREE range from 2.00 to 4.01，δEu range from 0.86 to 1.09 and (La/Yb)N range from 1.18 to 3.59．The Moshigou meta-basalts belong to the tholeiitic series according to their geochemical charateristics．The abundance and variation of high field strength elements and ratios of associated elements suggest that Moshigou meta-basalts are E-type MORB，derived from weakly to strongly enriched mantle．The composition of the meta-basalts are mainly controlled by magma source，but hybridized by crust or subduction materials in a small degree during the upwelling of basaltic magma．The geochemistry characteristics indicate that the generation of Moshigou meta-basalt results from the late stage of the back-arc basin．LA-ICP-MS zircon U-Pb dating yields a 206Pb/238U weighted average age of（432.6±3.8）Ma，indicating that the meta-basalt should form in the Wenlock of the Middle Silurian. The formation of the back-arc basin represented by Moshigou meta-basalt is closely related to the northward subduction of Tianshui – Wushan Ocean in the Middle Silurian，which suggest a tectonic framework with the relatively integrated ocean-arc-basin system in the Early Paleozoic at the conjunction of the Qinling－Qilian orogens．