40Ar/39Ar ages of seamount trachytes from the South China Sea and implications for the evolution of the northwestern sub-basin

• First Ar-Ar ages of rocks from the NW sub-basin of the South China Sea.
• The two samples yielded 23.80 ± 0.18 Ma and 23.29 ± 0.22 Ma.
• The expansion of the NW sub-basin began prior to 24 Ma.

A chronological study of seamount rocks in the South China Sea basin provides a great opportunity to understand the expansion and evolution history of the sea basin. In this paper, we analyzed the 40Ar/39Ar age of trachytic samples collected from the Shuangfeng seamounts in the northwestern sub-basin of the South China Sea. The two samples yielded plateau ages of 23.80 ± 0.18 and 23.29 ± 0.22 Ma, respectively, which indicate magmatic activity in late Oligocene which helpful constraints the expansion time of the northwest sub-basin. Previous studies suggested that the northwestern sub-basin and southwestern sub-basin have experienced a relatively consistent expansion in the NW–SE direction followed by a late expansion of the eastern sub-basin. We concluded that the expansion of the northwestern sub-basin began prior to ca. 24 Ma, which also implicated magmatic events of a late or stop expansion of the northwestern sub-basin combined with our results of 40Ar/39Ar age data and previous geophysical data.

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