Linear magnetic anomalies in the Shikoku Basin, northeastern Philippine Sea.

Abstract

A linear magnetic pattern, offset along fracture zones was found in the Shikoku Basin, which lies between the Izu-Bonin and northern Kyushu-Palau Ridges.This lineation, nearly parallel to the trend of the Kyushu-PalauRidge, seems to indicate that this basin originated from a type of seafloor spreading.A possible spreading center was suggested on the basis of symmetry of magnetic anomaly profiles and distribution of sediment cover in the basin. The anomaly profiles were tentatively correlated to the synthetic profile calculated from the reversal history of the earth's magnetic field during a period in Early to Middle Miocene, which gives a good fit of age to the result of the DSDP hole 297.

Magnetic Lineations in the Shikoku Basin

“…Prior to DSDP Leg 58 drilling, a number of different correlation schemes on the magnetic lineations from the Shikoku Basin were proposed by Tomoda et al (1975), Watts and Weissel (1975), Murauchi and Asanuma (1978) and Kobayashi and Nakata (1978). These agree with the DSDP results only in part (Table 1).…”

“…The addition of the MGS data to published data of Tomoda et al (1975) and Watts and Weissel (1975) has significantly improved the quality of magnetic correlation in the Shikoku Basin. With these additional data, I have been able to interpret the lineation pattern throughout the basin, except in its axial area.…”

Magnetic properties of pillow basalt from the Kinan seamount chain, the Shikoku Basin.

“…1). The Shikoku Basin is characterized by its linear magnetic anomalies similar to those observed in the normal ocean basins formed by sea-floor spreading (ToMODA et al, 1975;WATTS and WEI55EL, 1975;KOBAYASHI and ISEZAKI, 1976;NAKADA, 1977, 1978), although the magnetic lineations in the basin seem to be somewhat disturbed by the topography of seamounts. However, the topographic anomaly over this seamount is only a few hundred gammas (nT) in magnitude and is not so large as observed over seamounts in the Mid-Pacific Mountains (a few thousand gammas peak to peak).…”

Gravity in the junction between the Japanese and the Izu-Bonin Islands.

“…But, it is uncertain whether or not these gravity lows are also due to some kind of plate convergence. Among them, the negative zones at the east and west sides of the Kii Peninsula appear particularly interesting, because the area aligns with a possible spreading center of the Shikoku Basin (WATTS and WEISSEL, 1975;TOMODA et al, 1975), and the zones of gravity low may possibly be discussed in relation to the interaction between the southwestern Honshu and the Shikoku Basin.…”