Mesozoic mafic dykes in the Jinqu basin, Gan-Hang tectonic belt, are predominant diabases. The K-Ar determined age data from 69.5Ma to 131.7Ma indicated that mafic dykes were all intruded during Cretaceous Period. The SiO2 contents range from 46.70 to 50.23 wt %, and K2O+Na2O from 4.01 to 7.82 wt %, belong to alkaline and sub-alkaline. The trace elements are characterized by enrichment in LREE and LILE (K, Rb, Ba), and depletion in HREE and HFSE (Ta, Nb, Ti). Magma sources came from relative depleted mantle to enrich mantle; with (87Sr/86Sr)i=0.70642～0.70869, (143Nd/144Nd)i=0.512244～0.512352, εNd(t)=-2.3～-5.9. Near the center of the tectonic belt, source magma leaned to depleted mantle and in the flanks leaned to enrichment mantle. The mafic dykes were mainly produced by partial melting with the fractional crystallization of olivine, clinopyroxenes, plagioclases and apatites. Mafic dykes from Anding in Jiangshan were related to the cumulation of plagioclases. The mafic dykes were derived from the partial delamination of lower crust and basalts magma’s underplating in Jinqu basin, Gan-Hang tectonic belt. Especially, reactivity of the deep fault played an important role in diagenesis of mafic dykes.