Abstract: The Xiong'er Group formed in 1.80-1.75 Ga of Paleo-Proterozoic and contains predominantly volcanic lavas with minor sedimentary rocks and volcanic clastic rocks (4.3% in thickness). It is the largest magmatism in scale after the formation of the crystalline basement of the North China Craton，which vary from 3 km to 7 km in thickness，and crops out over an area of 60 000 km2. The volcanic lavas are composed predomiantly of basaltic andesites and andesites, and minor dacitic-rhyolitic rocks. The volcanic lavas are lack of the rocks with SiO2 = 62% ±and therefore appear as a bimodal association. The mineral assemblage of mafic-intermediate lavas mainly contains pyroxene and plagioclase, and rarely with amphibole and bitotite. The rocks are characteristic of high Fe and K and low Al, Ca and Mg contents. All the volcanic rocks are enriched in large-ion lithophile elements (LILE, eg, Rb, Ba) and light REEs (LREE) and are depleted in high field strength elements (HFSE, e.g., Nb, Ta and Ti), suggesting an arc-related setting. The geochemical and isotopic compositions of the lavas indicate derivation from a mantle source previously contaminated by subducted material and minor crustal contamination during the upwelling of the magmas. The sedimentary rocks of the Xiong'er Group formed the Dagushi and Majiahe Formations. The rock assemblage and geochemisty of the sedimentary rocks indicate that the Xiong'er Group formed in a passive continental margin and it was mainly a marine facies when lava erupted. Therefore the paleogeographic environment of the Xiong'er Group evolved from continental facies to marine facies then to continental facies again. It is suggested that the Xiong'er Group was originated from a failed trident continental rift environment. The arc-like geochemisty resulted from an enriched subcontinental lithospheric mantle previously contaminated by subducted slab. The volcanic rocks of the Xiong'er Group is also widespread in the Baoji and Lvliang area and also appear as 1.75 Ga-old mafic dyke swarms, A-type granites, later anorthosite and rapakivi granites (1.75-1.70 Ga), and alkaline granitoids (~1.65 Ga). These intrusive rocks are assumed to have genetic link to the volcanic rocks of the Xiong'er Group. These intrusive rocks resulted from the breakup of the North China Craton, suggesting that the North China Craton was under an extention environment at~1.80 Ga. However, a detailed work is worthwhile to figure out whether a post-collision magmatism or a mantle plume that triggered the emplacement of the intrusive rocks.