Geophysical mapping of Mariana Trough and West Philippine Basin: a preliminary report of Kairei KR9812 cruise
JAMSTEC Deep Sea Res.A15, 63-72, 1999
Bathymetric and geophysical (magnetic and gravity) mapping were conducted in the Mariana Trough between 19”15ÕN and 22”20ÕN 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 20”N 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 127”50ÕE and 131”E 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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