Age and geochemical features of dredged basalts from offshore SW Taiwan: The coincidence of intra-plate magmatism with the spreading South China Sea

This study reports age and geochemical analyses of basaltic rocks dredged from volcanic seamounts offshore SW Taiwan. ⁴⁰Ar/³⁹Ar dating results of these rocks show them to be of the early Miocene age of ~22 - 21 Ma. They are evolved alkali basalts that show OIB-type geochemical features similar to post-spreading seamount basalts (14 - 3.5 Ma) in the South China Sea (SCS) and Miocene intraplate basalts on the Penghu Islands (16 - 8 Ma) and NW Taiwan (23 - 9 Ma). Their Sr-Nd-Pb isotope data plot within the range of the SCS seamount basalts that show an EM2-like component in the mantle source. The age and overall geochemical characteristics of the dredged basalts are comparable to those of the Kungkuan basalts, NW Taiwan and Baolai basalts, SW Taiwan, suggesting an extensive alkali basaltic volcanism along the southeastern Eurasian continental margin during the early Miocene that resulted from regional lithospheric extension in association with seafloor spreading in the South China Sea.