LAUSR

Abstract The eastern China region underwent an intense lithosphere thinning event during Mesozoic but the mechanism for this process remains controversial. Here we investigate the Early Cretaceous Guandian intrusive complex in southern segment of the Tancheng-Lujiang (Tan-Lu) fault zone, central-eastern China, to gain insights into lithospheric extension and thinning. We present zircon U Pb ages and Lu Hf isotope data, together with whole rock major and trace elements, and Sr Nd isotopes. The major rock types in this igneous complex are high-K calc-alkaline granodiorites, diorites and lamprophyre dikes. LA-ICP-MS zircon U Pb dating yielded emplacement ages of 128 ± 2 Ma, 131 ± 2 Ma and 130 ± 1 Ma, for lamprophyre dikes, diorites and granodiorites respectively. These ages coincide with the commencement of lithospheric extension and thinning in eastern China. The elemental and isotopic characteristics of the lamprophyre dikes suggest that they were derived from partial melting of amphibole-bearing lithospheric mantle that was metasomatized by subducted continental crust and slab-derived fluids. Petrographic evidence, as well as geochemical and Sr Nd isotope characters suggest that the dioritic and granodioritic magmas were likely derived through magma mixing between partial melts of ancient lower crust and enriched lithospheric mantle. In conjunction with the coeval regional magmatism, mineralization and tectonic setting, we correlate the genesis of Guandian complex with crust-mantle interaction, and the extensional tectonic regime is correlated to slab rollback of the Paleo-Pacific Plate.