The magnetic basement and geological structure of the southernOkinawa Trough and its vicinity

Fault structures of basement in the study area develop well. The large basement faults in EW, NEE and NE direcdons construct and control the principle frame of the regional geological structure on a grand scale. The faults in NS, NNW and NW directions are mostly tensile translational faults, which strongly cut apart, destroy and break the principle structure, form and control secondary differential regional tectonic movement and magmatism characteristics. The burial depth of magnetic basement in the edge rise zone of the East China Sea shelf is ordinarily 3-4 km. The basement comprises Pre-Miocene metamorphic rock and series of igneous rocks formed in different epoches. The crust belongs to continental crust, whose thickness is 24-28 km. The burial depth of magnetic basement in the southern Okinawa Trough basin is ordinarily 5-7 km. The basin can be divided into 4 secondary basins. The basement may mostly comprise basalt or part-metamorphic rock formed by trough tensile movement since Pre-Miocene, which may include old Pre-Tertiary stratigraphy close to continental slope foot. The crust belongs to suboceanic:rust, whose thickness is 15-20 km.