Constraints on the Time of the Evolution of the Japan Sea Floor Based on Radiometric Ages
1986 年 38 巻 5 号 p. 475-485
詳細
1986 年 38 巻 5 号 p. 475-485
Based on available radiometric ages on igneous rocks recovered from the Japan Sea area, the constraints on the time of the evolution of the Japan Sea floor are discussed. To evaluate the reliability of radiometric ages on submarine rocks, some general problems related to each dating method are also referred.
As far as volcanic rocks recovered from seamounts in typical oceanic regions such as the Yamato Basin and the Japan Basin are concerned, they show relatively young K-Ar ages of less than 20Ma. However, rocks recovered from the Yamato Bank area, which is regarded to be a remnant land mass, suggest the occurrence of definitely older volcanic activity more than 20Ma ago. In the southwestern part of the Japan Sea, which has a continental crust, granitic rocks of more than 100Ma together with Precambrian gneisses were recovered. Thus radiometric age data support a relatively young formation of the typical ocean floor in the Japan Sea area.
