Tectonic synthesis and implications of Japan Sea ODP drilling

Abstract

Legs 127 and 128 completed drilling of six sites in the Japan Sea. Analyses of new data, together with more detailed identification of magnetic anomaly lineations in the Japan Basin, have yielded a tectonic scenario for the evolution of the Japan Sea. The entire Japan Sea was extending from 32 Ma to 10 Ma, during which major opening associated with vigorous basin volcanism occurred about 28 to 18 Ma. The Japan Sea started its opening by crustal thinning within the proto-Japan arc. As thinning proceeded, breakup of the lithosphere was initiated at the major strike-slip fault forming the eastern margin of the juvenile sea, triggering seafloor spreading. Subsequent rifting and seafloor spreading process propagated southwestward during a period when the southern part of the Japan Sea was still undergoing crustal thinning, which ceased about 18 Ma and left oceanic crust in its wake. This crust now forms the eastern floor of the Japan Basin. -from Authors