Tectonic mechanism and evolution of eastern China during the Early Cretaceous: a view from magmatism in the middle to Southern Tan-Lu fault zone

Mesozoic magmatic rocks are widely distributed in and around the Tan-Lu fault zone (TLF) and show great significance related to the destruction processes of the lithosphere and the evolution of magma sources. This study aims to decipher the petrogenesis of the Early Cretaceous magmatism along the TLF, in order to address the tectonic mechanism for the North China Craton (NCC) lithospheric destruction. This contribution combines investigations of geochemistry, SHRIMP zircon U-Pb ages and O-Hf isotopes of the intermediate to felsic rocks from middle-southern TLF with previous geochronological and geochemical characteristics of other rocks from the study area. Four different rocks are identified: high Mg# adakitic rocks (HMA), low Mg# adakitic rocks (LMA), normal intermediate-felsic rocks (NIF) and A-type granitoids. The emplacement time of the LMA rocks in the Dabie area (143 Ma) were earlier than in the Sulu area (130 Ma). The HMA rocks were formed at the same time (~135 Ma) in the above two areas but the magmatism lasted longer in Jiaodong area, which was near the subduction zone of the Paleo-pacific plate. The HMA rocks are concluded to be derived from the melting of a delaminated thickened lower crust and including reaction with overlying mantle. After 135 Ma, the magmatism in this area exhibited an eastward-younging trend, consistent with plate retreat in the Early Cretaceous. Plutons that were emplaced during 135–125 Ma have higher Ba/Th, Ba/La and Ce/Pb, suggesting magma source for these rocks was metasomatized by hydrous fluids from the subducted plate. At ~125 Ma, A-type granitoids began to be formed. The TLF acted as a favourable channel for transporting mantle material and fluids which made the lithosphere in this area more likely to be destroyed and thinned.