Yamazaki, T., K. Okino, Y. Hasegawa, H. Saitake, and M. Ito

Geophysical mapping of Mariana Trough and West Philippine Basin: a preliminary report of Kairei KR9812 cruise

JAMSTEC Deep Sea Res.A15, 63-72, 1999

Abstract.

Bathymetric and geophysical (magnetic and gravity) mapping were conducted in the Mariana Trough between 1915N and 2220N and the West Philippine Basin aroung the central Basin Fault (CBF) during R/V Kairei KR9812 cruise. Spreading ridges in the mapped area of the Mariana Trough consists of five segments. The segment boundary show typical structure of slow-spreading ridges, those are nodal deeps and inside-corner highs, except for the northernmost boundary. It is estimated from magnetic anomalies that seafloor spreading between 19 and 20N started at 5 Ma or a little older, and the average spreading half-rate during the last 3.6 m.y. is about 1 cm/year. The centrl part of the CBF between 12750E and 131E can be divided into four segments bounded by N-S trending fracture zones. Extinct spreading centers of E-W trend with parallel minor ridges, noda deeps and inside-corner highs were cut by lineaments and depression of NW-SE trend, These features can be interpreted as the combination of the earlier N-S spreading and the late NE-SW extension, although the age and cause of the latter remain unclear.

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