古新世晚期由于太平洋板块洋脊俯冲，日本海(西部)第一次拉张。

Due to the subduction of Pacific Plate at late Palaeocene, the western part of Japan Sea was pulled-apart.

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海槽玄武岩构造环境属于过渡洋中脊玄武岩 （张性 ）与岛弧玄武岩 （压性 ）之间 ，代表的仍是海槽早期的岩浆活动。

The tectonic settings of the basalts are transitional between MORB (tensile) and IAB (compressive), still representing the earlier stage of magma activities in the Okinawa Trough.

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