Development and Sedimentary Process of Basins in the Daito Ridges Area

Abstract

Some small basins have developed in the northern Philippine Sea along the northern and southern sides of the Daito Ridge (DR) : the Kita-Daito Basin (KDB) , Amami-Sankaku Basin (ASB) and Minami-Daito Basin (MDB) . From the interpretation of multichannel reflection seismic profiles crossing these basins, their noticeable differences of geological character can be recognized. There are several E-W trending normal faults in the main part of the KDB which suggest that this basin was formed by seafloor spreading. A seismic section crossing the OkiDaito Ridge (ODR) and DR presents a reflector, possibly indicating subduction of the slab containing the ODR. The subduction probably caused back-arc spreading of the KDB, which finally ceased upon the collision of both ridges. Based on the trace of characteristic reflectors in seismic sections and correlations with several drill holes, sediments are divided into Units I through V, ranging from Lower Eocene to Holocene. The Choju Seamounts occupy the middle part of the MDB, dividing the basin into the eastern main basin and the western small subbasin (MinamiDaito Nishi Sub Basin; MDNSB) . The seismic character of Unit II (≒ Middle to Upper Eocene) is noticeably different among the ASB, the main basin of MDB, and the MDNSB, indicating different sources of sediments. The thickness of Unit II in the ASB increases towards the KyushuPalau Ridge (KPR) , indicating that sediments were supplied by the KPR. Unit II in the main basin of MDB has no direct relationship with the KPR, and should have had another source, such as the DR or the ODR. The thickness of Unit II in the MDNSB increases towards the DR, suggesting an equivalent origin of the carbonate layer at the top of the DR.

Correlations Between Subduction of Linear Oceanic Features and Arc Volcanism Volume Around the Pacific Basin

“…The Amami Plateau and Daito Ridge were separated from a single volcanic arc by a back‐arc rifting and formation of the North Daito Basin from 50–40 Ma to 30–33 Ma (Deschamps & Lallemand, 2002; Okino, 2015). On the other hand, the Oki Daito Ridge was formed separately and moved closer to Daito Ridge from the far south (Higuchi et al., 2015).…”

“…The Amami Plateau and Daito Ridge were separated from a single volcanic arc by a back-arc rifting and formation of the North Daito Basin from 50-40 Ma to 30-33 Ma (Deschamps & Lallemand, 2002;Okino, 2015). On the other hand, the Oki Daito Ridge was formed separately and moved closer to Daito Ridge from the far south (Higuchi et al, 2015). Okamura et al (2017) investigated the effect of these ridge subductions to the forearc structure, and show that the Daito Ridge, the Amami Plateau and the Kyushu-Palau Ridge migrated north and west in the last 23 Ma, but did not discuss their effects on volcanism.…”