Objective The Muzidian granite complex is located in Northern Dabie Orogen, and its main lithology is porphyritic biotite monzogranite, porphyritic biotite hornblende monzogranite, fine−medium grain biotite monzogranite and fine grain biotite monzogranite. In order to discuss the material source, petrogenetic machanism, and geochemical dynamic background of the Muzidian granites, and even study the large−scale tectono−magmatic evolution during the Early Cretaceous in Dabie area,

Methods the Muzidian granite complex was chosen to test the Sr−Nd−Pb systematic isotopic geochemistry after the previous work.

Results The Muzidian granites have a low initial Sr ratio(⁸⁷Sr/⁸⁶Sr)_i=0.70670~0.70895, and ε_Nd(t) is also low, mainly concentrated in −23.16~−14.11. They have much old Nd model age (T_DM2=2.99~2.07 Ga) and low radioactive Pb isotopic composition (²⁰⁶Pb/²⁰⁴Pb)_i=17.0056~17.4476, (²⁰⁷Pb/²⁰⁴Pb)_i=15.4595~15.5996, (²⁰⁸Pb/²⁰⁴Pb)_i=37.7627~38.1417. The results tell us that the main rocks in the Muzidian granite complex are characterized for adakite, which is derived from the melting of the thickened basaltic lower crust. Only the Yuexingtang unit is characterized for arc magmatic rocks, which is also derived from the melting of the subducted lower crust, and carry more enriched mantle components.

Conclusions With the geochemical, chronological and zircon Hf isotopic studies, it is concluded that the Muzidian granite complex was derived from the lower crust of the northern margin of the Yangtze craton. And the composition of the granites may be similar to the Neoproterozoic TTG rocks. The delamination didn’t happen after the northern margin of the Yangtze subducted to the North China Craton, but partial melting happened at different parts of the subduction slab to form the Muzidian granite complex. This diagenesis may record the transition process from subduction collision to extension in Dabie area, and the transition time is most likely to be 131 Ma.