Double saloon door tectonics in the Japan Sea, Fossa Magna, and the Japanese Island Arc

Abstract

A number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the Japanese Arc. These include: i) a pair of terranes, SW and NE Honshu, which rotated in opposite directions from 22–21 Ma to 14–11 Ma; ii) rotated terranes which comprise a retro-arc fold/thrust belt attached to an accretionary wedge intruded by a magmatic arc; iii) contemporaneous backarc extension from 24 to 21 Ma which is brought to a halt by progressive collision of the Izu-Bonin and Japan Arcs from 15 to 5 Ma; iv) isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust, during backarc rifting; v) such isolation may be due to simultaneous rifting or to progressively seaward rifts, associated with ridge jumps towards the subduction zone; vi) opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30–26 Ma to 16–15 Ma; vii) concurrent development of a major arc-orthogonal rift, the Fossa Magna, from 23–18 Ma to 14 Ma, which was thereafter inverted from 15 Ma to the Recent; viii) a northeast propagating rift in the northern Japan Basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary. Driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest Pacific. Opposite rotational torques, leading to opposite terrane rotations, may be caused by rollback of a curved trench hingeline, or by the divergent slab sinking forces of the Pacific and Philippine Sea Plates.