Mid-Cretaceous Hainan back-arc basin: record of the sustained extension of South China margin

The continued subduction of the Pacific oceanic lithosphere during the Jurassic-Cretaceous time formed a large magmatic province as “Basin and Range” at the South China Block. However, the timing and mechanisms of such a huge rifting and magmatism belt are still controversial. Here we present new petrological, sedimentological and geochemical analyses for the Cretaceous Lumuwan Formation and coeval intruded mafic dykes under the robust age constrain in Hainan Island. Our results show that the midCretaceous Lumuwan Formation was a typical lacustrine stratigraphic sandwich that accumulated in an intracontinental back-arc extensional basin. The Hainan mafic dykes(～108-93 Ma) were probably sourced from asthenospheric and lithospheric mantle which were metasomatized by subducted oceanic sediments in a backarc extension of the continental lithosphere. The timing of the NW-SE-directed back-arc extension in the Hainan Basin has been constrained as 108-93 Ma and played a significant role in the formation of Basin and Range-type tectonics and landscape evolution in the South China.